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In your responses to enterprise users, prioritize clarity, trustworthiness, and appropriate formality.
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File: 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf
Page: 2
Context: Copyright © 2019-2024 Daniele Penazzo
2D Game Development: From Zero T
o Hero (python edition, version 0.7.10-r4) is distributed under the terms of the
Creative Commons Attribution-NonCommercial-ShareAlike International 4.0 license.
If you want to view a copy of the license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/ or check the
LICENSE file in the book repository.
The PDF and EPub releases of this book can be found at the following address:
• https://therealpenaz91.itch.io/2dgd-f0th (Official Itch.io Page)
This book’s source code can be found in the following official repositories:
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NO AI TRAINING: any use of this publication to train generative artificial intelligence (AI) technologies to generate
text is expressly prohibited.
Please avoid printing this book: this work is being periodically updated and changed as new things get added
and remade, thus printing it does not make sense. Printing this book would be a waste of resources, so please think
well before printing.
This work shall be attributed to Daniele Penazzo and the ”2D Game Development: From Zero T
o Hero” community,
to see a full list of the contributors, please check the CONTRIBUTORS file in the repository, or head to the Contributors
section in this book.
####################
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Context: 4.9.1
Some basics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
CONTENTS
V
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o Hero
4.9.2
What happens when we have more than one big-O? . . . . . . . . . . . . . . . . . . . . . 76
4.9.3
A problem with asymptotic complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.9.4
What do we do with recursive algorithms? . . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.9.5
How do big-O estimates compare to each other?
. . . . . . . . . . . . . . . . . . . . . . 77
4.10
Simplifying your conditionals with Karnaugh Maps . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.10.1
“Don’t care”s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
4.10.2
A more complex map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
4.10.3
Guided Exercise
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
4.11
Object Oriented Programming
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.11.1
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.11.2
Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
4.11.3
Abstraction and Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.11.4
Inheritance and Polymorphism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.11.5
Mixins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.11.6
The Diamond Problem
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.11.7
Composition
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
4.11.8
Composition vs. Inheritance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.11.9
“Composition over Inheritance” design . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
4.11.10
Coupling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.11.11
The DRY Principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.11.12
SOLID Principles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.12
Designing entities as data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
4.13
Reading UML diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.13.1
Use Case Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
4.13.1.1
Actors
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
4.13.1.2
Use Cases
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
4.13.1.3
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.13.1.4
Sub-Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.13.2
Class Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.13.2.1
Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
4.13.2.2
Interfaces
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
4.13.2.3
Relationships between entities of the class diagram . . . . . . . . . . . . . . . . . 97
4.13.2.4
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
4.13.3
Activity Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
4.13.3.1
Start and End Nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
4.13.3.2
Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
4.13.3.3
Decisions (Conditionals) and loops . . . . . . . . . . . . . . . . . . . . . . . . . .101
4.13.3.4
Synchronization
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
4.13.3.5
Swimlanes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103
4.13.3.6
Signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
CONTENTS
VI
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4.13.3.7
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
4.13.3.8
A note on activity diagrams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
4.13.4
Sequence Diagrams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
4.13.4.1
Lifelines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
4.13.4.2
Messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
4.13.4.3
Object Instantiation and Destruction . . . . . . . . . . . . . . . . . . . . . . . . .107
4.13.4.4
Grouping and loops
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
4.13.4.5
Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
4.13.5
Other diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
4.14
Generic Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
4.15
Data Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
4.15.1
Graphs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
4.15.2
Trees
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
4.15.2.1
Depth-first Search
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .113
4.15.2.2
Breadth-first search
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117
4.15.3
Dynamic Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
4.15.3.1
Performance Analysis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119
4.15.4
Linked Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
4.15.4.1
Performance Analysis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
4.15.5
Doubly-Linked Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
4.15.6
Hash T
ables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
4.15.7
Binary Search Trees (BST)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
4.15.8
Heaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126
4.15.9
Stacks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
4.15.10
Queues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
4.15.11
Circular Queues
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
4.16
The principle of locality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129
4.17
Treating multidimensional structures like one-dimensional ones . . . . . . . . . . . . . . . . . . .130
4.18
Data Redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .131
4.19
Introduction to Multi-T
asking
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
4.19.1
Multi-Threading vs Multi-Processing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .134
4.19.2
Coroutines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134
4.20
Introduction to Multi-Threading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
4.20.1
What is Multi-Threading
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
4.20.2
Why Multi-Threading? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .135
4.20.3
Thread Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
4.20.3.1
Race conditions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
4.20.3.2
Critical Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
4.20.4
Ensuring determinism
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
4.20.4.1
Immutable Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
CONTENTS
VII
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4.20.4.2
Mutex
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
4.20.4.3
Atomic Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
5
A Game Design Dictionary
142
5.1
Platforms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
5.1.1
Arcade
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
5.1.2
Console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
5.1.3
Personal Computer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
5.1.4
Mobile
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
5.1.5
Web . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
5.2
Input Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146
5.2.1
Mouse and Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146
5.2.2
Gamepad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .146
5.2.3
T
ouch Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147
5.2.4
Dedicated Hardware
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147
5.2.5
Other Input Devices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .147
5.3
Game Genres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
5.3.1
Shooters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
5.3.2
Strategy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
5.3.3
Platformer
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .148
5.3.4
RPG . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
5.3.5
MMO
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
5.3.6
Simulation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
5.3.7
Rhythm Games . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149
5.3.8
Visual novels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
5.3.9
Puzzle games . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
5.4
Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
5.4.1
Emergent Gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150
6
Project Management Basics and tips
153
6.1
The figures of game design and development
. . . . . . . . . . . . . . . . . . . . . . . . . . . .153
6.1.1
Producer/Project Manager
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .153
6.1.2
Game Designer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
6.1.3
Writer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154
6.1.4
Developer
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .155
6.1.5
Visual Artist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
6.1.6
Sound Artist
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
6.1.7
Marketing/Public Relations Manager
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
6.1.8
T
ester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
6.2
Some general tips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
6.2.1
Be careful of feature creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
CONTENTS
VIII
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6.2.2
On project duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .158
6.2.3
Brainstorming: the good, the bad and the ugly
. . . . . . . . . . . . . . . . . . . . . . .159
6.2.4
On Sequels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159
6.3
Common Errors and Pitfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
6.3.1
Losing motivation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
6.3.2
The “Side Project” pitfall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
6.3.3
Making a game “in isolation” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
6.3.4
(Mis)Handling Criticism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
6.3.4.1
Misusing of the Digital Millennium Copyright Act
. . . . . . . . . . . . . . . . . .161
6.3.5
Not letting others test your game
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
6.3.6
Being perfectionist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
6.3.7
Using the wrong engine
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
6.4
Software Life Cycle Models
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
6.4.1
Iteration versus Increment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164
6.4.2
Waterfall Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
6.4.3
Incremental Model
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
6.4.4
Evolutionary Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
6.4.5
Agile Software Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
6.4.5.1
User Stories
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
6.4.5.2
Scrum
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167
6.4.5.3
Kanban . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168
6.4.5.4
ScrumBan
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168
6.4.6
Lean Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169
6.4.7
Where to go from here . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169
6.5
Version Control
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169
6.6
Metrics and dashboards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
6.6.1
SLOC
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
6.6.2
Cyclomatic Complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
6.6.2.1
How cyclomatic complexity is calculated
. . . . . . . . . . . . . . . . . . . . . .171
6.6.3
Code Coverage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
6.6.4
Code Smells
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
6.6.5
Coding Style infractions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
6.6.6
Depth of Inheritance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
6.6.7
Number of methods / fields / variables . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
6.6.8
Number of parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
6.6.9
Other metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .174
7
Writing a Game Design Document
176
7.1
What is a Game Design Document
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
7.2
Possible sections of a Game Design Document . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
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7.2.1
Project Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .176
7.2.2
Characters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177
7.2.3
Storyline
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177
7.2.3.1
The theme
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177
7.2.3.2
Progression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
7.2.4
Levels and Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
7.2.5
Gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
7.2.5.1
Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .178
7.2.5.2
Game Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179
7.2.5.3
Skills
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .179
7.2.5.4
Items/Powerups
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .180
7.2.5.5
Difficulty Management and Progression
. . . . . . . . . . . . . . . . . . . . . . .180
7.2.5.6
Losing Conditions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
7.2.6
Graphic Style and Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
7.2.7
Sound and Music . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .181
7.2.8
User Interface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182
7.2.9
Game Controls
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .182
7.2.10
Accessibility Options
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183
7.2.11
T
ools
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183
7.2.12
Marketing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183
7.2.12.1
T
arget Audience
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184
7.2.12.2
Available Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184
7.2.12.3
Monetization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184
7.2.12.4
Internationalization and Localization . . . . . . . . . . . . . . . . . . . . . . . . .185
7.2.13
Other/Random Ideas
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185
7.3
Where to go from here
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185
8
The Game Loop
188
8.1
The Input-Update-Draw Abstraction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188
8.2
Input
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189
8.2.1
Events vs Real Time Input
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .189
8.3
Timing your loop
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190
8.3.1
What is a time step . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190
8.3.2
Fixed Time Steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190
8.3.3
Variable Time Steps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .190
8.3.4
Semi-fixed Time Steps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .191
8.3.5
Frame Limiting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .192
8.3.6
Frame Skipping/Dropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193
8.3.7
Multi-threaded Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .193
8.4
Issues and possible solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
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8.4.1
Frame/Screen T
earing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
8.5
Drawing to screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
8.5.1
Clearing the screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195
9
Collision Detection and Reaction
197
9.1
Why Collision Detection is done in multiple passes . . . . . . . . . . . . . . . . . . . . . . . . . .197
9.2
Narrow-Phase Collision Detection: did it really collide? . . . . . . . . . . . . . . . . . . . . . . . .197
9.2.1
Collision Between T
wo Points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .198
9.2.2
Collision Between A Point and a Circle . . . . . . . . . . . . . . . . . . . . . . . . . . . .199
9.2.3
Collision Between T
wo Circles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .202
9.2.4
Collision Between T
wo Axis-Aligned Rectangles (AABB)
. . . . . . . . . . . . . . . . . . .204
9.2.5
Line/Point Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207
9.2.6
Line/Circle Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .210
9.2.7
Point/Rectangle Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214
9.2.8
Point/Triangle Collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215
9.2.9
Circle/Rectangle Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .216
9.2.10
Line/Line Collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .218
9.2.11
Line/Rectangle Collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221
9.2.12
Point/Polygon Collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221
9.2.12.1
Jordan Curve Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222
9.2.12.2
Thinking outside the box: polygon triangulation . . . . . . . . . . . . . . . . . . .224
9.2.12.3
Bounding Boxes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225
9.2.12.4
Point/Polygon collision detection using triangulation . . . . . . . . . . . . . . . . .227
9.2.13
Circle/Polygon Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .230
9.2.14
Line/Polygon Collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .232
9.2.15
Polygon/Polygon Collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .233
9.2.16
Non-convex polygons collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .234
9.2.16.1
Polygon triangulation: the return
. . . . . . . . . . . . . . . . . . . . . . . . . .235
9.2.17
Pixel-Perfect collision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236
9.3
Broad-phase collision detection: is a collision even possible?
. . . . . . . . . . . . . . . . . . . .238
9.3.1
The Brute Force Method
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .239
9.3.2
Building Quad Trees
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .240
9.3.2.1
A more precise definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .241
9.3.2.2
Querying quad trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .242
9.3.3
Building AABB-Trees
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .242
9.3.3.1
Querying AABB-trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .243
9.3.4
Collision groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245
9.4
Other Collision Detection Methods
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246
9.4.1
Calculating the position of tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246
9.4.2
The “Tile + Offset” Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .249
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9.5
Collision Reaction/Correction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .250
9.5.1
HitBoxes vs HurtBoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .250
9.5.2
Collision Reaction Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .251
9.5.2.1
A naive approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .251
9.5.2.2
Shallow-axis based reaction method . . . . . . . . . . . . . . . . . . . . . . . . .253
9.5.2.3
Interleaving single-axis movement and collision detection
. . . . . . . . . . . . .255
9.5.2.4
The “Snapshot” Method
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .256
9.5.3
When two moving items collide
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .257
9.6
Common Issues with time-stepping Collision Detection
. . . . . . . . . . . . . . . . . . . . . . .258
9.6.1
The “Bullet Through Paper” problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . .258
9.6.2
Precision Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259
9.6.3
One-way obstacles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259
9.7
Separating Axis Theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .260
9.7.1
Why only convex polygons?
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .261
9.7.2
How it works
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .261
9.7.2.1
Finding the axes to analyze
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .262
9.7.2.2
Projecting the shapes into the axes and exiting the algorithm . . . . . . . . . . . .263
9.7.2.3
From arbitrary axes to “x and y” . . . . . . . . . . . . . . . . . . . . . . . . . . .264
9.8
Ray Casting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .265
9.8.1
What is Ray Casting? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .265
9.8.2
Other uses for ray casting: Pseudo-3D environments
. . . . . . . . . . . . . . . . . . . .266
10
Scene Trees
267
10.1
What is a scene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .267
10.2
Scene trees and their functionalities
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .267
10.2.1
How scene trees can make drawing entities easier
. . . . . . . . . . . . . . . . . . . . .267
10.3
Implementing a scene tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .268
11
Cameras
269
11.1
Screen Space vs. Game Space
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .269
11.2
Cameras and projections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .270
11.3
Most used camera transitions and types
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
11.3.1
Static Camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
11.3.2
Grid Camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
11.3.3
Position-Tracking Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
11.3.3.1
Horizontal-Tracking Camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
11.3.3.2
Full-Tracking Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272
11.3.4
Camera Trap
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272
11.3.5
Look-Ahead Camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273
11.3.6
Hybrid Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .274
11.4
Clamping your camera position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .274
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Game Design Tips
276
12.1
T
utorials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276
12.1.1
Do not pad tutorials
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276
12.1.2
Integrate tutorials in the lore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276
12.1.3
Let the player explore the controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .276
12.2
Consolidating and refreshing the game mechanics . . . . . . . . . . . . . . . . . . . . . . . . . .277
12.2.1
Remind the player about the mechanics they learned . . . . . . . . . . . . . . . . . . . .277
12.2.2
Introduce new ways to use old mechanics . . . . . . . . . . . . . . . . . . . . . . . . . .277
12.3
Rewarding the player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .277
12.3.1
Reward the player for their “lateral thinking”
. . . . . . . . . . . . . . . . . . . . . . . .277
12.3.2
Reward the player for their tenacity
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .278
12.3.3
Reward the player for exploring
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279
12.3.4
Reward the player for not immediately following the given direction
. . . . . . . . . . . .279
12.3.5
Reward the player for not trusting you entirely
. . . . . . . . . . . . . . . . . . . . . . .279
12.3.6
Reward Backtracking (but don’t make it mandatory!)
. . . . . . . . . . . . . . . . . . . .280
12.3.7
The “lives” system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .280
12.3.7.1
1-UPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .281
12.3.7.2
Other approaches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .281
12.4
Loading Screens
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282
12.4.1
What to put in a loading screen
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282
12.4.2
Letting the player “exit” the loading screen
. . . . . . . . . . . . . . . . . . . . . . . . .282
12.4.3
Avoiding a loading screen altogether . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283
12.5
Designing the story and gameplay flow
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283
12.5.1
Linear Gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .283
12.5.2
Branching gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .284
12.5.3
Parallel gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285
12.5.4
Threaded gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285
12.5.5
Episodic gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .286
12.5.6
Adding parallel paths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .286
12.5.7
Looping Gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .287
12.5.7.1
Soft-reset mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .287
12.6
Some game genres and their characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288
12.6.1
Roguelikes and Rogue-lites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288
12.6.1.1
Use of pseudo-randomness and procedural generation
. . . . . . . . . . . . . . .288
12.6.1.2
Permadeath
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288
12.6.1.3
T
urn-based Gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289
12.6.1.4
Lack of mode-based gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . .289
12.6.1.5
Multiple ways to accomplish (or fail!) a task . . . . . . . . . . . . . . . . . . . . .289
12.6.1.6
Resource Management is key
. . . . . . . . . . . . . . . . . . . . . . . . . . . .289
12.6.1.7
Peace was never an option . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289
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12.6.1.8
Dealing with the unknown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289
12.7
Tips and Tricks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .290
12.7.1
General Purpose
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .290
12.7.1.1
Make that last Health Point count
. . . . . . . . . . . . . . . . . . . . . . . . . .290
12.7.1.2
Avoiding a decision can be a decision itself
. . . . . . . . . . . . . . . . . . . . .290
12.7.1.3
T
elegraphing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .291
12.7.1.4
Minigames
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .291
12.7.1.5
When unlockables are involved, be balanced
. . . . . . . . . . . . . . . . . . . .292
12.7.2
Shooters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292
12.7.2.1
Make the bullets stand out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292
12.7.3
RPGs
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293
12.7.3.1
Grinding and farming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293
12.7.3.2
Leveling Curves
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .294
12.7.3.3
“Mastering” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295
12.8
Perceived Fairness
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .296
12.8.1
You don’t need precise collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . .296
12.8.2
Immediate dangers should be well visible . . . . . . . . . . . . . . . . . . . . . . . . . .297
12.9
Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .298
12.9.1
You cannot use the “Red Cross” in games
. . . . . . . . . . . . . . . . . . . . . . . . . .299
12.9.2
Auto-saving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299
12.9.3
Feedback is important
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299
13
Creating your assets
302
13.1
Assumptions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
13.2
Graphics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
13.2.1
Some computer graphics basics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
13.2.1.1
The “color wheel”
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
13.2.1.2
Color representations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .303
13.2.1.3
Primary, Secondary and T
ertiary colors
. . . . . . . . . . . . . . . . . . . . . . .305
13.2.1.4
Analogous Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305
13.2.1.5
Complementary Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305
13.2.1.6
Color Depth
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .306
13.2.1.7
Direct Color vs. Indexed Color
. . . . . . . . . . . . . . . . . . . . . . . . . . . .309
13.2.1.8
Lossless Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309
13.2.1.9
Lossy Formats
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309
13.2.1.10 Transparency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .310
13.2.1.11 T
exture Filtering
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .310
13.2.2
General Tips
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .311
13.2.2.1
Practice, Practice, Practice… . . . . . . . . . . . . . . . . . . . . . . . . . . . . .311
13.2.2.2
References are your friends
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .311
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13.2.2.3
Don’t compare your style to others’ . . . . . . . . . . . . . . . . . . . . . . . . .311
13.2.2.4
Study other styles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .311
13.2.2.5
Learn to deconstruct objects into shapes
. . . . . . . . . . . . . . . . . . . . . .312
13.2.3
Sprite sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .312
13.2.3.1
Sprite Sheet Gotchas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313
13.2.4
Virtual Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .314
13.2.5
Using limited color palettes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315
13.2.5.1
Dithering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315
13.2.5.2
Palette Swapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
13.2.6
Layering and graphics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
13.2.6.1
Detail attracts attention
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
13.2.6.2
Use saturation to separate layers further
. . . . . . . . . . . . . . . . . . . . . .318
13.2.6.3
Movement is yet another distraction . . . . . . . . . . . . . . . . . . . . . . . . .318
13.2.6.4
Use contrast to your advantage
. . . . . . . . . . . . . . . . . . . . . . . . . . .318
13.2.6.5
Find exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .319
13.2.6.6
Summarizing Layering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .319
13.2.7
Pixel Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321
13.2.7.1
What pixel art is and what it is not . . . . . . . . . . . . . . . . . . . . . . . . . .321
13.2.7.2
T
ools
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .321
13.2.7.3
Layers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322
13.2.7.4
Sub-pixel animation with palette cycling . . . . . . . . . . . . . . . . . . . . . . .322
13.2.8
Normal Mapping
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .322
13.2.8.1
A simple example
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .323
13.2.9
Tips and Tricks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .325
13.2.9.1
Tiles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .325
13.2.9.2
Sprites and icons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .327
13.3
Sounds And Music . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
13.3.1
Some audio basics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
13.3.1.1
Sample Rate
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
13.3.1.2
Bit Depth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329
13.3.1.3
Lossless Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .330
13.3.1.4
Lossy Formats
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .330
13.3.1.5
Clipping
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .330
13.3.2
Sound Synthesis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .331
13.3.2.1
AM Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .331
13.3.2.2
FM Synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .332
13.3.2.3
FM Synthesis vs Sample-based music
. . . . . . . . . . . . . . . . . . . . . . . .332
13.3.3
Basic Wave Forms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333
13.3.3.1
Sine Wave
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .333
13.3.3.2
Square Wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334
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13.4
Fonts
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .348
13.4.1
Font Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .348
13.4.1.1
Serif and Sans-Serif fonts
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
13.4.1.2
Proportional and Monospaced fonts
. . . . . . . . . . . . . . . . . . . . . . . . .349
13.4.2
Using textures to make text
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .350
13.4.3
Using Fonts to make text . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .351
13.5
Shaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
13.5.1
What are shaders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
13.5.2
Shader Programming Languages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352
13.5.3
The GLSL Programming Language
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353
13.5.3.1
The data types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353
13.5.4
Some GLSL Shaders examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .354
14
Design Patterns
356
14.1
Creational Design Patterns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .356
14.1.1
Singleton Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .356
14.1.2
Dependency Injection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .358
14.1.3
Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .360
14.2
Structural Design Patterns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .360
14.2.1
Flyweight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .361
14.2.2
Component/Composite Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .362
14.2.3
Decorator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .364
14.2.4
Adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .365
14.2.4.1
Object Adapter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .365
14.2.4.2
Class Adapter
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
14.2.5
Facade
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
14.2.6
Proxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368
14.3
Behavioural Design Patterns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .369
14.3.1
Command Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .370
14.3.2
Observer Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .371
14.3.3
Strategy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372
14.3.4
Chain of Responsibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .374
14.3.5
Visitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .375
14.4
Architectural Design Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .375
14.4.1
Service Locator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .375
15
Useful Containers and Classes
376
15.1
Resource Manager
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .376
15.2
Animator
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .376
15.3
Finite State Machine
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377
15.4
Menu Stack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .379
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15.5
Particle Systems
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .380
15.5.1
Particles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .380
15.5.2
Emitters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .383
15.5.3
Force Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .384
15.6
Timers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .385
15.6.1
Accounting for “leftover time”
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .387
15.6.1.1
A naive solution
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .387
15.6.1.2
A different approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .388
15.7
Inbetweening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390
15.7.1
Bouncing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .392
15.8
Chaining
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .392
16
Artificial Intelligence in Videogames
393
16.1
Path Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393
16.1.1
Representing our world . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393
16.1.1.1
2D Grids
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .393
16.1.1.2
Path nodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394
16.1.1.3
Navigation meshes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .394
16.1.2
Heuristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .397
16.1.2.1
Manhattan Distance heuristic
. . . . . . . . . . . . . . . . . . . . . . . . . . . .397
16.1.2.2
Euclidean Distance heuristic . . . . . . . . . . . . . . . . . . . . . . . . . . . . .398
16.1.3
Algorithms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .399
16.1.3.1
A simple “Wandering” Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . .399
16.1.3.2
A slightly better “Wandering” algorithm . . . . . . . . . . . . . . . . . . . . . . .403
16.1.3.3
The Greedy “Best First” Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . .404
16.1.3.4
The Dijkstra Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .406
16.1.3.5
The A* Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407
16.2
Finite state machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .408
16.3
Decision Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409
16.4
Behaviour Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .410
16.5
Tips and tricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .410
16.5.1
“Jump when the player shoots” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .410
16.5.2
Distance-based patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .411
16.5.2.1
“Ranged pattern” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .412
16.5.2.2
“Melee pattern” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .413
17
Other Useful Algorithms
414
17.1
World Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .414
17.1.1
Midpoint Displacement Algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .414
17.1.2
Diamond-Square Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .416
17.1.3
Maze Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .419
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17.1.3.1
Randomized Depth-First Search (Recursive Backtracker)
. . . . . . . . . . . . . .419
17.1.3.2
Randomized Kruskal’s Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . .425
17.1.3.3
Recursive Division Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . .427
17.1.3.4
Binary Tree Algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .430
17.1.3.5
Eller’s Algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .432
17.2
Dungeon Generation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .434
17.3
Noise Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .434
17.3.1
Randomized Noise (Static) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .434
17.3.2
Perlin Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .435
17.4
Animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .435
17.4.1
Skeleton animation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .435
18
Procedural Content Generation
436
18.1
What is procedural generation (and what it isn’t) . . . . . . . . . . . . . . . . . . . . . . . . . . .436
18.2
Advantages and disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437
18.2.1
Advantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437
18.2.1.1
Less disk space needed
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .437
18.2.1.2
Larger games can be created with less effort
. . . . . . . . . . . . . . . . . . . .438
18.2.1.3
Lower budgets needed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438
18.2.1.4
More variety and replayability . . . . . . . . . . . . . . . . . . . . . . . . . . . .438
18.2.2
Disadvantages
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438
18.2.2.1
Requires more powerful hardware . . . . . . . . . . . . . . . . . . . . . . . . . .438
18.2.2.2
Less Quality Control
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .438
18.2.2.3
Worlds can feel repetitive or “lacking artistic direction” . . . . . . . . . . . . . . .438
18.2.2.4
You may generate something unusable
. . . . . . . . . . . . . . . . . . . . . . .439
18.2.2.5
Story and set game events are harder to script
. . . . . . . . . . . . . . . . . . .439
18.3
Where it can be used . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .439
18.4
Procedural Generation and Difficulty Management . . . . . . . . . . . . . . . . . . . . . . . . . .440
18.4.1
Static difficulty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440
18.4.2
Adaptive Difficulty
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440
18.4.2.1
Rubberbanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .440
18.4.3
Static vs. Adaptive Difficulty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .441
19
Developing Game Mechanics
442
19.1
General Purpose
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .442
19.1.1
I-Frames
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .442
19.1.2
Tilemaps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443
19.1.2.1
Rectangular Tilemaps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .443
19.1.2.2
Hexagonal Tilemaps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
19.1.2.3
Isometric Tilemaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .446
19.1.3
Scrolling Backgrounds and Parallax Scrolling . . . . . . . . . . . . . . . . . . . . . . . . .447
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Find other chances to clear some bullets . . . . . . . . . . . . . . . . . . . . . . . . . . .472
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19.5.6
T
urn enemy bullets into collectibles at the end of a boss fight . . . . . . . . . . . . . . . .472
19.5.7
The “Chain Meter”
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .472
19.5.8
Managing the player’s death . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .473
19.5.9
The Enemy AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .473
19.5.10
Be fair to the player, but also to the computer . . . . . . . . . . . . . . . . . . . . . . . .473
19.5.11
Inertia
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .474
19.5.12
Some examples
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .474
19.6
Match-x Games . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .474
19.6.1
Managing and drawing the grid
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .474
19.6.2
Finding and removing Matches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .475
19.6.2.1
Why don’t we delete the matches immediately? . . . . . . . . . . . . . . . . . . .477
19.6.3
Replacing the removed tiles and applying gravity . . . . . . . . . . . . . . . . . . . . . .477
19.7
Cutscenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .479
19.7.1
Videos
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .479
19.7.2
Scripted Cutscenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .479
20
Balancing Your Game
481
20.1
Do not annoy the player
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .481
20.2
Favour the player when possible
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .481
20.3
Difficulty curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .482
20.3.1
Simple Lines
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .482
20.3.2
Flat Line
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .482
20.3.2.1
Linear Increase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483
20.3.2.2
Logarithmic Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483
20.3.2.3
Exponential Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .484
20.3.3
Wave patterns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .485
20.3.3.1
Linearly Increasing wave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .485
20.3.3.2
Logarithmically Increasing wave . . . . . . . . . . . . . . . . . . . . . . . . . . .485
20.3.4
Interval Patterns
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .486
20.3.4.1
Simple Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .486
20.3.4.2
Widening Interval
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .487
20.3.4.3
Widening Interval with Logarithmic trend
. . . . . . . . . . . . . . . . . . . . . .488
20.3.5
This is not everything
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .488
20.3.5.1
Sawtooth pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .488
20.3.5.2
What not to do . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .489
20.3.5.3
Beyond difficulty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .490
20.4
Economy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .490
20.4.1
Supply and Demand
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .490
20.4.2
Money sources and sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491
20.4.3
Inflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .492
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20.4.4
Deflation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .492
20.5
A primer on Cheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .492
20.5.1
Information-based cheating
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .493
20.5.2
Mechanics-based cheating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .493
20.5.3
Man-in-the-middle
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .493
20.5.4
Low-level exploits
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .493
20.6
How cheating influences gameplay and enjoyability . . . . . . . . . . . . . . . . . . . . . . . . .494
20.6.1
Single Player
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .494
20.6.2
Multiplayer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .494
20.6.2.1
P2P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .494
20.6.2.2
Dedicated Servers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .496
20.7
Cheating protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .497
20.7.1
Debug Mode vs Release Mode
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .498
20.8
Some common exploits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .498
20.8.1
Integer Under/Overflow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .498
20.8.1.1
How the attack works
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .499
20.8.2
Repeat attacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .499
21
Accessibility in video games
501
21.1
What accessibility is and what it is not . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .501
21.2
UI and HUD Scaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .501
21.3
Subtitles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .501
21.4
Mappable Buttons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .501
21.5
Button T
oggling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.6
Dyslexia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.6.1
T
ext Spacing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.6.2
Fonts
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.7
“Slow Mode” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.8
Colorblind mode
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .502
21.9
No Flashing Lights
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503
21.10
No motion blur
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503
21.11
Reduced Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503
21.12
Assisted Gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503
21.13
Controller Support
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .503
21.14
Some special cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .504
22
Testing your game
505
22.1
When to test
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .505
22.1.1
T
esting “as an afterthought” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .505
22.1.2
T
est-Driven Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .505
22.1.3
The “Design to test” approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .505
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22.1.4
You won’t be able to test EVERYTHING . . . . . . . . . . . . . . . . . . . . . . . . . . . .505
22.2
Mocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .506
22.3
T
ypes of testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .506
22.3.1
Automated T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .506
22.3.2
Manual T
esting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .507
22.4
Unit T
esting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .507
22.5
Integration T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .508
22.6
Regression T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .508
22.7
Playtesting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .508
22.7.1
In-House T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .508
22.7.2
Closed Beta T
esting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509
22.7.3
Open Beta T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509
22.7.4
A/B T
esting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .509
23
Profiling and Optimization
510
23.1
Profiling your game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .510
23.1.1
Does your application really need profiling? . . . . . . . . . . . . . . . . . . . . . . . . .510
23.1.1.1
Does your FPS counter roam around a certain “special” value? . . . . . . . . . . .510
23.1.1.2
Is the animation of your game stuttering but the FPS counter is fine? . . . . . . . .510
23.1.2
First investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .510
23.1.2.1
Is your game using 100% of the CPU? . . . . . . . . . . . . . . . . . . . . . . . .510
23.1.2.2
Is your game overloading your GPU?
. . . . . . . . . . . . . . . . . . . . . . . .511
23.1.2.3
Is your game eating up more and more RAM as it’s running?
. . . . . . . . . . . .511
23.2
Optimizing your game
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .512
23.2.1
Working with references vs. returning values
. . . . . . . . . . . . . . . . . . . . . . . .512
23.2.2
Optimizing Drawing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .513
23.2.2.1
Off-screen objects
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .513
23.2.3
Reduce the calls to the Engine Routines . . . . . . . . . . . . . . . . . . . . . . . . . . .513
23.2.4
Entity Cleanup and Memory leaks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .514
23.2.5
Using analyzers to detect Memory Leaks
. . . . . . . . . . . . . . . . . . . . . . . . . .515
23.2.5.1
Static Scanners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .515
23.2.5.2
Dynamic testing tools
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .515
23.2.6
Resource Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .515
23.2.7
Lookup T
ables
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .517
23.2.8
Memoization
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .517
23.2.9
Approximations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .520
23.2.10
Eager vs. Lazy Evaluation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .520
23.2.10.1 Eager approach
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .521
23.2.10.2 Lazy approach
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .521
23.2.11
Detach your updating from drawing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .522
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23.2.12
Be mindful of how you query your data structures . . . . . . . . . . . . . . . . . . . . . .522
23.3
Tips and tricks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .522
23.3.1
Be mindful of your “updates”
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .522
23.3.2
Use the right data structures for the job . . . . . . . . . . . . . . . . . . . . . . . . . . .523
23.3.3
Dirty Bit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .523
23.3.4
Far-Away entities (Dirty Rectangles)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .524
23.3.5
T
weening is better than animating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .525
23.3.6
Remove dead code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .525
23.4
Non-Optimizations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .525
23.4.1
“Switches are faster than IFs”
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .526
23.4.2
Blindly Applying Optimizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .527
24
Marketing your game
530
24.1
An Important Note: Keep your feet on the ground
. . . . . . . . . . . . . . . . . . . . . . . . . .530
24.2
The importance of being consumer-friendly
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .530
24.3
Pricing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .531
24.3.1
Penetrating the market with a low price
. . . . . . . . . . . . . . . . . . . . . . . . . . .531
24.3.2
Giving off a “premium” vibe with a higher price . . . . . . . . . . . . . . . . . . . . . . .531
24.3.3
The magic of “9” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .532
24.3.4
Launch Prices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .532
24.3.5
Bundling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .532
24.3.6
Nothing beats the price of “Free” (Kinda)
. . . . . . . . . . . . . . . . . . . . . . . . . .533
24.4
Managing Hype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533
24.5
Downloadable Content
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .533
24.5.1
DLC: what to avoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .534
24.5.2
DLC: what to do
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .534
24.6
Digital Rights Management (DRM)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .534
24.6.1
How DRM can break a game down the line . . . . . . . . . . . . . . . . . . . . . . . . . .536
24.7
Free-to-Play Economies and LootBoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .536
24.7.1
Microtransactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .536
24.7.1.1
The human and social consequences of Lootboxes
. . . . . . . . . . . . . . . . .536
24.7.2
Free-to-Play gaming and Mobile Games
. . . . . . . . . . . . . . . . . . . . . . . . . . .537
24.8
Assets and asset Flips . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .538
24.9
Crowdfunding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .538
24.9.1
Communication Is Key
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .539
24.9.2
Do not betray your backers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .539
24.9.3
Don’t be greedy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .539
24.9.4
Stay on the “safe side” of planning
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .540
24.9.5
Keep your promises, or exceed them . . . . . . . . . . . . . . . . . . . . . . . . . . . . .540
24.9.6
A striking case: Mighty No. 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .540
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24.10
Engagement vs Fun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .541
24.11
Streamers and Content Creators
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .542
24.11.1
The game developers’ side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .542
24.11.2
The Streamers’ side
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .542
24.11.3
Other entities and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .543
25
Keeping your players engaged
544
25.1
Communities
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .544
25.1.1
Forums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .544
25.1.2
Wikis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .544
25.1.3
Update Previews
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .544
25.1.4
Speedrunning
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .545
25.1.5
Streaming
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .546
25.2
Replayability
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .546
25.2.1
Modding
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .546
25.2.2
Fan games
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .547
25.2.3
Mutators
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .547
25.2.4
Randomizing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .548
25.2.5
New Game+
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .548
25.2.6
Transmogrification
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .548
26
When the time for retirement comes
550
26.1
Remonetization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .550
26.2
Free release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .551
26.3
Open Sourcing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .551
26.3.1
When “Open Sourcing” is not enough
. . . . . . . . . . . . . . . . . . . . . . . . . . . .552
26.4
Hybrid Approaches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .552
26.5
What not to do
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .552
27
Dissecting games: three study cases
555
27.1
A bad game: Hoshi wo miru hito
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .555
27.1.1
Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .555
27.1.2
Balance Issues
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .555
27.1.2.1
You can’t beat starter enemies . . . . . . . . . . . . . . . . . . . . . . . . . . . .555
27.1.2.2
The Damage Sponge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .555
27.1.2.3
You can’t run away from battles, but enemies can . . . . . . . . . . . . . . . . . .556
27.1.2.4
Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .556
27.1.3
Bad design choices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .556
27.1.3.1
You get dropped in the middle of nowhere . . . . . . . . . . . . . . . . . . . . . .556
27.1.3.2
The starting town is invisible . . . . . . . . . . . . . . . . . . . . . . . . . . . . .557
27.1.3.3
The Jump Ability
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .557
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27.1.3.4
Items are invisible
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .557
27.1.3.5
Item management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .557
27.1.3.6
Buying Weapons makes you weaker . . . . . . . . . . . . . . . . . . . . . . . . .557
27.1.3.7
Enemy Abilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.3.8
You can soft lock yourself
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.4
Confusing Choices
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.4.1
Starting level for characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.4.2
Slow overworld movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.4.3
Exiting a dungeon or a town . . . . . . . . . . . . . . . . . . . . . . . . . . . . .558
27.1.4.4
The Health Points UI
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559
27.1.5
Inconveniencing the player . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559
27.1.5.1
The battle menu order . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559
27.1.5.2
Every menu is a committal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559
27.1.5.3
Password saves
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .559
27.1.5.4
Each character has their own money stash
. . . . . . . . . . . . . . . . . . . . .560
27.1.6
Bugs and glitches
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .560
27.1.6.1
Moonwalking and save warping
. . . . . . . . . . . . . . . . . . . . . . . . . . .560
27.1.6.2
The final maze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .560
27.1.6.3
The endings
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .561
27.1.7
Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .561
27.2
The first good game - VVVVVV: Slim story and essential gameplay
. . . . . . . . . . . . . . . . .561
27.2.1
A Slim story that holds up great
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .561
27.2.2
Essential gameplay: easy to learn, hard to master . . . . . . . . . . . . . . . . . . . . . .562
27.2.3
Diversified challenges
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .562
27.2.4
Graphics
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .562
27.2.5
Amazing soundtrack
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563
27.2.6
Accessibility Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563
27.2.7
Post-endgame Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563
27.2.8
User-generated content
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .563
27.2.9
“Speedrunnability” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .564
27.2.10
Characters are memorable, even if you don’t see them a lot
. . . . . . . . . . . . . . . .564
27.2.11
Conclusion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .564
27.3
Another good game - Undertale: A masterclass in storytelling . . . . . . . . . . . . . . . . . . . .564
27.3.1
The power of choice
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .564
27.3.2
The game doesn’t take itself very seriously (sometimes)
. . . . . . . . . . . . . . . . . .564
27.3.3
All the major characters are very memorable
. . . . . . . . . . . . . . . . . . . . . . . .565
27.3.4
The game continuously surprises the player . . . . . . . . . . . . . . . . . . . . . . . . .565
27.3.5
Player choices influence the game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .565
27.3.6
Great (and extensive!!) soundtrack
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .566
27.3.7
Conclusion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .566
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o Hero
28
Project Ideas
567
28.1
Tic-T
ac-T
oe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .567
28.1.1
Basic Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .567
28.1.2
Advanced Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .568
28.1.3
Master Level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .568
28.2
Space Invaders
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .568
28.2.1
Basic Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .569
28.2.2
Advanced Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .570
28.2.3
Master level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .570
28.3
Breakout
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .571
28.3.1
Basic Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .571
28.3.2
Advanced Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .571
28.3.3
Master Level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .572
28.4
Shooter Arena . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .573
28.4.1
Basic Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .573
28.4.2
Advanced level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .574
28.4.3
Master Level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .574
29
Game Jams
576
29.1
Have Fun
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .576
29.2
Stay Healthy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .576
29.3
Stick to what you know . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .576
29.4
Hacking is better than planning (But still plan ahead!) . . . . . . . . . . . . . . . . . . . . . . . .576
29.5
Graphics? Sounds? Music? FOCUS! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .577
29.6
Find creativity in limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .577
29.7
Involve Your Friends!
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .578
29.8
Write a Post-Mortem (and read some too!) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .578
29.9
Most common pitfalls in Game Jams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .578
30
Where To Go From Here
580
30.1
Collections of different topics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .580
30.1.1
Books . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .580
30.1.2
Videos
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .580
30.1.3
Multiple formats
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .580
30.2
Pixel Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.2.1
Multiple Formats
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.3
Sound Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.3.1
Multiple Formats
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.4
Game Design
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.4.1
Books . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
30.5
Game Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .581
CONTENTS
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• Pseudocode Edition: This is the standard edition, using a C-like syntax that tries to be as readable as
possible and abstracts itself from any kind of engine.
• Python Edition: Python is considered one of the easiest language to start coding on. Many tend to complain
about its performance, but its similarity to Godot Engine’s GDScript and its flexibility make it a good candidate
for starters.
• C++ Edition: C++ is probably the most used language in game development (along with C#) but it can be
really difficult to manage. It has no garbage collection, forcing you to manage the memory manually, and
pointers can prove to be a difficult concept for many.
• JavaScript Edition: Javascript is the de-facto “internet language” and its influence is spreading to desktop
applications and video games too. Many games now can be played on the browser thanks to it and the HTML5
canvas elements. This is a language that can be very forgiving and frustrating at the same time.
• Lua Edition: Lua is one of the most spread scripting languages in the world of video games. Since it has a very
small interpreter, it can be added to a lot of code bases without weighing them down much. It is not a proper
object-oriented language, but it has very strong metaprogramming capabilities (where you can “program the
programming language”). There are also some libraries that allow for classes and object-oriented concepts
to fit in Lua.
2.3
Structure of this Book
This book is structured in many chapters, here you will find a small description of each and every one of them.
• Foreword: You didn’t skip it, right?
• Introduction: Here we present the structure of the book and the reasons why it came to exist. You are
reading it now, hold tight, you’re almost there!
• The Maths Behind Game Development: Here we will learn the basic maths that are behind any game, like
vectors, matrices and screen coordinates.
• Some Computer Science Fundamentals: Here we will learn (or revise) some known computer science
fundamentals (and some less-known too!) and rules that will help us managing the development of our game.
• A game design dictionary: Here we will introduce some basic concepts that will help us in understanding
game design: platforms, input devices and genres.
• Project Management Basics and Tips: Project management is hard! Here we will take a look at some
common pitfalls and tips that will help us deliver our own project and deliver it in time.
• Writing a Game Design Document: In this section we will take a look at one of the first documents that
comes to exist when we want to make a game, and how to write one,
• The Game Loop: Here we will learn the basics of the “game loop”, the very base of any video game.
• Collision Detection and Reaction: In this section we will talk about one of the most complex and compu-
tationally expensive operations in a video game: collision detection.
• Scene Trees: Here we will briefly talk about probably the most important structure in games and game
engines: the scene tree.
• Cameras: In this section we will talk about the different types of cameras you can implement in a 2D game,
with in-depth analysis and explanation.
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• Game Design Tips: In this chapter we will talk about level design and how to walk your player through the
learning and reinforcement of game mechanics, dipping our toes into the huge topic that is game design.
• Creating your own assets: Small or solo game developers may need to create their own assets, in this
section we will take a look at how to create our own graphics, sounds and music.
• Design Patterns: A head-first dive into the software engineering side of game development, in this section
we will check many software design patterns used in many games.
• Useful Containers and Classes: A series of useful classes and containers used to make your game more
maintainable and better performing.
• Artificial Intelligence in Video games: In this section we will talk about algorithms that will help you coding
your enemy AI, as well as anything that must have a “semblance of intelligence” in your video game.
• Other Useful Algorithms: In this section we will see some algorithms that are commonly used in game,
including path finding, world generation and more.
• Procedural Content Generation: In this chapters we will see the difference between procedural and random
content generation and how procedural generation can apply to more things than we think.
• Developing Game Mechanics: Here we will dive into the game development’s darkest and dirtiest secrets,
how games fool us into strong emotions but also how some of the most used mechanics are implemented.
• Balancing Your Game: A very idealistic vision on game balance, in this chapter we will take a look inside
the player’s mind and look at how something that may seem “a nice challenge” to us can translate into a
“terrible balance issue” to our players.
• Accessibility in video games: Here we will learn the concept of “accessibility” and see what options we
can give to our players to make our game more accessible (as well as more enjoyable to use).
• Testing your game: This section is all about hunting bugs, without a can of bug spray. A deep dive into the
world of testing, both automated and manual.
• Profiling and Optimization: When things don’t go right, like the game is stuttering or too slow, we have to
rely on profiling and optimization. In this section we will learn tips and tricks and procedures to see how to
make our games perform better.
• Marketing Your Game: Here we will take a look at mistakes the industry has done when marketing and
maintaining their own products, from the point of view of a small indie developer. We will also check some of
the more controversial topics like loot boxes, micro transactions and season passes.
• Keeping your players engaged: a lot of a game’s power comes from its community, in this section we will
take a look at some suggestion you can implement in your game (and out-of-game too) to further engage your
loyal fans.
• Dissecting Games: A small section dedicated to dissecting the characteristics of one (very) bad game, and
two (very) good games, to give us more perspective on what makes a good game “good” and what instead
makes a bad one.
• Project Ideas: In this section we take a look at some projects you can try and make by yourself, each project
is divided into 3 levels and each level will list the skills you need to master in order to be able to take on such
level.
• Game Jams: A small section dedicated on Game Jams and how to participate to one without losing your mind
in the process, and still deliver a prototype.
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• Where to go from here: We’re at the home stretch, you learned a lot so far, here you will find pointers to
other resources that may be useful to learn even more.
• Glossary: Any world that has a g symbol will find a definition here.
• Engines and Frameworks: A collection of frameworks and engines you can choose from to begin your game
development.
• Tools: Some software and tool kits you can use to create your own resources, maps and overall make your
development process easier and more manageable.
• Premade Assets and resources: In this appendix we will find links to many websites and resource for
graphics, sounds, music or learning.
• Contributors: Last but not least, the names of the people who contributed in making this book.
Have a nice stay and let’s go!
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4.11.3
Abstraction and Interfaces
Abstraction is a fundamental point in O.O.P
., and it is usually taken care of via so-called Interfaces.
Interfaces are the front-end that an object offers to other objects so they can interact.
As an example: the interface to your PC is given by Keyboard, Mouse and Screen - you don’t need to know how
the single electron travels through the circuits to be able to use a computer; same goes for a class that offers a
well-abstracted interface.
Being able to abstract a concept, removing the necessity to know the internal workings of the code that is used,
is fundamental to be able to write solid and maintainable code, because implementations change, but interfaces
rarely do.
Making classes work together with interfaces allows you to modify and optimize your code without having each edit
snowball into a flurry of compiler (or interpreter) errors. For instance: a rectangle class exposes in its interface a
method getArea() - you don’t need to know how to calculate the area, you just call that method and know it will return
the area of the rectangle.
The concept of keeping the internal workings of a class is called Information Hiding.
4.11.4
Inheritance and Polymorphism
One of the biggest aspects of O.O.P
. is inheritance: you can create other classes based on a so-called “base class”,
allowing for extensibility of your software.
You can create a “Person” class, with a name, surname and age as fields, and by inheriting from the “Person” class
you can create a “Student” class, which has all the fields from Person, plus the “clubs” and “grade” fields.
This allows to create a “tree of classes” that represents part of your software.
From inheritance, O.O.P
. presents a concept called Polymorphism (From “Poly” - Many, “Morph” - Shape), where
you can use the base class to represent the entire class tree, allowing for substitution.
In our “Person-Student” example, you could use a pointer to either a Person or a Student for the sake of getting their
first name.
In some languages it is possible for an object to inherit from multiple other objects, this is called “Multiple Inheritance”
4.11.5
Mixins
Mixins are classes that contain certain methods that are made to be used by other classes. We can see mixins as
some kind of interface with methods already implemented.
Mixins encourage the reuse of code (since the common functionalities get separated into their own classes), allowing
for some interesting mechanisms and enforcing the Dependency Inversion principle.
Many times, Mixins are described as “included” rather than “inherited”, due to their nature.
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Interfaces
Implementations
Objects
Updatable
update();
Visible
draw();
Collidable
collide();
VisibleObject
draw();
InvisibleObject
draw();
CollidableObject
collide();
NonCollidableObject
collide();
MovableObject
update();
ImmovableObject
update();
PlayableCharacter
visiblecomponent: Visible;
collidablecomponent: Collidable;
movablecomponent: Updatable;
update();
draw();
collide();
Building
visiblecomponent: Visible;
collidablecomponent: Collidable;
movablecomponent: Updatable;
update();
draw();
collide();
The fields will contain the following instances:
- visiblecomponent: VisibleObject
- collidablecomponent: CollidableObject
- movablecomponent: ImmovableObject
The fields will contain the following instances:
- visiblecomponent: VisibleObject
- collidablecomponent: CollidableObject
- movablecomponent: MovableObject
Figure 51: How components make things a bit simpler
4.11.10
Coupling
Coupling is a term used to define the phenomenon where an edit to some part of a software snowballs into a bunch
of edits in parts of the software that depend on the modified part, and the part that depend on the previously edited
dependency, etc…
The parts involved are defined as “coupled” because, even though they are separated, their maintenance very much
behaves like they were a single entity. This also means that the elements that are coupled are harder to reuse, since
they are so tightly related that they end up serving each other and nothing else.
Introducing unnecessary coupling in our software will come back to bite us in the future, affecting maintainability in
a very negative way, since any edit we make (for instance, to fix a bug) can potentially lead to the need to edit the
rest of the software (or game) we are writing.
Reducing coupling is done by reducing interdependence, coordination and information flow between elements of a
program.
Examples of coupling include:
• A module uses code of another module (this breaks the principle of information hiding[g]);
• Many modules access the same global data;
• A module controls the flow of another module (like passing a parameter that decides “what to do”);
• Subclassing.
This means that it’s in our best interest to reduce code coupling as much as possible, following the good principles
of “nutshell programming” and following the SOLID principles, shown next.
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Note!
We may be tempted to try and “remove coupling completely”, but that’s usually a
wasted effort. We want to reduce coupling as much as possible and instead improve
“cohesion”. Sometimes coupling is unavoidable (as in case of subclassing). Balance is
the key.
4.11.11
The DRY Principle
DRY is a mnemonic acronym that stands for “Don’t Repeat Yourself” and condenses in itself the principle of reducing
repetition inside a software, replacing it with abstractions and by normalizing data.
This allows for each piece of code (and knowledge, since the DRY principle applies to documentation too) to be
unambiguous, centralizing its responsibilities and avoiding repetition.
Violations of the DRY principle are called “WET” (Write Everything Twice) solutions, which base themselves on
repetition and give higher chances of mistakes and inconsistency.
4.11.12
SOLID Principles
SOLID is a mnemonic acronym that condenses five principles of good design, to make code and software that is
understandable, flexible and maintainable.
• Single Responsibility: Each class should have a single responsibility, it should take care of one part of
the software specification and each change to said specification should affect only said class. This means
you should avoid the so-called “God Classes”, classes that take care of too much, know too much about the
system and in a nutshell: have too much responsibility in your software.
• Open-closed Principle: Each software entity should be open to extension, but closed for modification. This
means that each class (for instance) should be extensible, either via inheritance or composition, but it should
not be possible to modify the class’s code. This is practically enforcing Information Hiding.
• Liskov Substitution Principle: Objects in a program should be replaceable with instances of their subtypes
and the correctness of the program should not be affected. This is the base of inheritance and polimorphism,
if by substituting a base class with one of its children (which should have a Child-is-a-Base relationship, for
instance “Circle is a shape”) the program is not correct anymore, either something is wrong with the program,
or the classes should not be in a “IS-A” relationship.
• Interface Segregation: Classes should provide many specific interfaces instead of one general-purpose
interface, this means that no client should depend on methods that it doesn’t use. This makes the software
easier to refactor and maintain, and reduces coupling.
• Dependency Inversion: Software components should depend on abstractions and not concretions. This is
another staple of nutshell programming and O.O.P
. - Each class should make use of some other class’s interface,
not its inner workings. This allows for maintainability and easier update and change of code, without having
the changes snowball into an Armageddon of errors.
[This section is a work in progress and it will be completed as soon as possible]
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6
"spritesheet ": "./ skelly.png",
7
"animations ":{
8
"walking ":{
9
"start_sprite ": 4,
10
"frame_no ": 4,
11
"duration ": 0.2
12
},
13
"attacking ":{
14
"start_sprite ": 9,
15
"frame_no ": 2,
16
"duration ": 0.1
17
}
18
}
19
}
20 }
With more complex building algorithms, it is possible to change behaviors and much more with just a configuration
file, and this gives itself well to rogue-like games, which random selection of enemies can benefit from an extension
of the enemy pool. In fact, it’s really easy to configure a new type of enemy and have it work inside the game without
recompiling anything.
This allows for more readable code and a higher extensibility.
4.13
Reading UML diagrams
UML (Universal Modeling Language) is a set of graphical tools that allow a team to better organize and plan a software
product. Diagrams are drawn in such a way to give the reader an overall assessment of the situation described while
being easy to read and understand.
In this chapter we will take a look at 4 diagrams used in UML:
• Use Case Diagrams
• Class Diagrams
• Activity Diagrams
• Sequence Diagrams
4.13.1
Use Case Diagrams
Use Case Diagrams are usually used in software engineering to gather requirements for the software that will come
to exist. In the world of game development, use case diagrams can prove useful to have an “outside view” of our
game, and understand how an user can interact with our game.
Here is an example of a use case diagram for a game:
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| | GameMenu
Start The Game Remember to clear the menu stack!
Open the Options Menu
Open the Credits Screen
Exit to Desktop |
| -------- | -------- |
Player
Figure 52: Example of a use case diagram
4.13.1.1
Actors
Actors are any entity that can interface with our system (in this case, our game) without being part of it. Actors can
both be human, machines or even other systems.
Actors are represented with a stick figure and can inherit from each other: this will create an “IS-A” relationship
between actors.
Authenticated User
Free User
Power User
Ultimate User
Figure 53: Example of an actor hierarchy
In the previous example, we can see that a “Free User” is an “Authenticated User”, as well as a “Power User” (which
could be a paying user) is itself an “Authenticated User” while an “Ultimate User” (which could be a higher tier
of paying user) is a “Power User” (thus has all the “Power User” capabilities, plus some unique) and by transitive
property an “Authenticated User”.
As seen, inheritance between actors is represented with a solid line with a hollow closed arrow. Such arrow points
towards the “super-type” or “parent” from which the subject (or “sub-type”, or “child”) inherits.
This representation will come back in the UML language for other diagrams too.
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4.13.1.2
Use Cases
Use cases represent the functionalities that our system offers, and the relationships between them.
Use cases are represented with an ellipse with the name of the use case inside. Choosing the right name for a use
case is extremely important, since they will represent the functionality that will be developed in our game.
Start The Game
Figure 54: Example of a use case
4.13.1.2.1
Inheritance
As with many other elements used in UML, use cases can inherit from each other. Inheritance (also called “General-
ization”) is represented with a closed hollow arrow that points towards the parent use case.
Website
Search
Search By Name
Search By Category
Search By Tag
Player
Figure 55: Example of a use case hierarchy
4.13.1.2.2
Extensions
Use case extensions specify how and when optional behavior takes place.
Extended use cases are meaningful
on their own and are independent from the extending use case, while the extending use case define the optional
behavior that may not have much sense by itself.
Extensions are represented via a dashed line with an open arrow on the end, labeled with the <> keyword,
pointing towards the extending use case.
| User | System
«extend»
Login Help on Login |
| -------- | -------- |
Figure 56: Example of a use case extension
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4.13.1.2.3
Inclusions
Inclusions specify how the behavior of the included use case is inserted in the behavior of the including use case.
Inclusions are usually used to simplify large use cases by splitting them or extract common behaviors of two or more
use cases.
In this situation, the including use case is not complete by itself.
Inclusions are represented via a dashed line with an open arrow on the end, labeled with the <> pointing
towards the included use case.
System
Deposit
Withdraw
Customer Authentication
User
«include»
«include»
Figure 57: Example of a use case inclusion
4.13.1.3
Notes
In use case diagrams, as well as in many other UML diagrams, notes are used to jot down conditions, comments and
everything useful to better understanding the diagram that cannot be conveyed through a well definite structure
inside of UML.
Notes are shaped like a sheet of paper with a folded corner and are usually connected to the diagram with a dashed
line. Each note can be connected to more than one piece of the diagram.
You can see a note at the beginning of this chapter, in the use case diagram explanation.
4.13.1.4
Sub-Use Cases
Use cases can be further detailed by creating sub-use cases, like the following example.
Checkout
Checkout
Payment
Help
Customer
Clerk
«include»
«extends»
Figure 58: Example of a sub-use case
4.13.2
Class Diagrams
4.13.2.1
Classes
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its departments will cease to exist. Conversely, a teacher may have some students under their wing, but when a
teacher remains without students they won’t magically disappear: the teacher’s life cycle is independent from their
students’.
4.13.2.3.5
Dependency
The dependency relationship is the one that gives us the least amount of coupling, it represents a “supplier-client”
relationships, where the supplier supplies its functions (methods) to the client. The association is represented in a
dashed line with an open arrow that points towards the supplier.
This means that the client class requires, needs or depends on the supplier.
There are many categories of dependency, like < or <> that explain further the type of dependency
exists between the supplier and the client.
An example could be between a “Car Factory” and a class “Car”: the “CarFactory” class depends on the “Car” class,
and such dependency is an instantiation dependency.
CarFactory
Car
Figure 67: Example of dependency in UML class diagrams
4.13.2.4
Notes
As with Use Case diagrams, class diagrams can make use of notes too, and the graphical language used to represent
them is exactly the same one used in the Use Case Diagrams.
4.13.3
Activity Diagrams
Activity diagrams are the more powerful version of flow charts: they represent the flux of an activity in detail, allowing
to have a better understanding of a process or algorithm.
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Take Shopping cart
Take Item
Put Item in Shopping Cart
Delete Item name from Shopping list
More Items in Shopping List?
yes
Go to checkout
Pay
no
Figure 68: Example of an activity diagram
4.13.3.1
Start and End Nodes
Each diagram begins what a “start node”, represented with a filled black circle, and they end with an “end node”
which is represented with a filled black circle inside of a hollow circle.
Figure 69: Example of activity diagrams start and end nodes
4.13.3.2
Actions
Each action taken by the software is represented in the diagram via a rounded rectangle, a very short description of
the action is written inside the rounded rectangle space.
Delete Item name from Shopping list
Figure 70: Example of Action in activity diagrams
4.13.3.3
Decisions (Conditionals) and loops
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Read cell
cell is even
yes
Double the cell value
Triple the cell value
Write cell value to console
yes
There are more cells in the row
yes
There are more rows in table
Figure 73: Example of how nested loops and conditions are performed
Note!
Sometimes loops can make use of empty diamonds (called “merges”) to make the
diagram clearer.
4.13.3.4
Synchronization
Synchronization (or parallel processing) is represented in activity diagrams by using filled black bars that enclose
the concurrent processes: the bars are called “synchronization points” or “forks” and “joins”
Take Order
Send Order confirmation
Process Order
Figure 74: Example of concurrent processes in activity diagrams
In the previous example, the activities “Send Order Confirmation” and “Process Order” are processed in parallel,
independently from each other, the first activity that finishes will wait until the other activity finishes before entering
the end node.
4.13.3.5
Swimlanes
Swimlanes are a way to organize and group related activities in columns. For instance a shopping activity diagram
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can have the “Customer”, “Order”, “Accounting” and “Shipping” swimlanes, each of which contains activities related
to their own categories.
| Customer
Place Order
Receive Confirmation
Receive Order
Pay Bill | Order
Take Order | Accounting
Process Order
Record Shipping Close Order |
Figure 75: Example of swimlanes in activity diagrams
4.13.3.6
Signals
Signals are used to represent how activities can be influenced or modified from outside the system. There are two
symbols used to represent signals.
The “Sent Signal” symbol is represented with a convex pentagon (which reminds an arrow going away from our
system), while the “Received Signal” is represented by a concave pentagon (which reminds a “slot” where the “sent
signal” symbol can connect to).
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Search product
Put product in basket
Place Order
Deliverer rings
Confirm Receipt
Accept Order
Take products from store
Deliver Products
Customer
Store
Figure 76: Example of signals in activity diagrams
4.13.3.7
Notes
As with Use Case and Class diagrams, Activity Diagrams can make use of notes, in the same way as the other two
diagrams we presented in this book do.
Make sure the shopping cart works well!
Take Shopping cart
Take Item
Put Item in Shopping Cart
Delete Item name from Shopping list
More Items in Shopping List?
yes
Go to checkout
Pay
no
Figure 77: Example of a note inside of an activity diagram
4.13.3.8
A note on activity diagrams
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The components of activity diagrams shown here are just a small part of the used components, but they should be
enough to get you started designing and reading most of the activity diagrams that exist.
4.13.4
Sequence Diagrams
Sequence diagrams are used to represents how objects (called “participants”) interact with each other and such
interactions are represented in a time sequence.
4.13.4.1
Lifelines
The central concept of sequence diagrams are lifelines: the represent the time a participant is “alive” and when it
is doing something.
WebServer
WebServer
Request
Response
Figure 78: Example of a sequence diagram lifeline
The time flows from top to bottom, a dashed line represents the participant exists (for instance an object is instan-
tiated in memory), while the rectangle that replaces the dotted line represents the participant being “active” (for
instance one of the object’s functions is called).
4.13.4.1.1
Participants
The participants don’t have to be actual classes, since sequence diagrams represent interactions at a “higher level”
than mere code-bound planning.
Some UML drawing software allows for custom shapes for each participant, like the following:
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Sometimes it may be useful to represent the instantiation and destruction of objects in a sequence diagram. UML
provides such facilities via the <>, <> and <> keywords, as well as a symbol for the de-
struction of an object.
Class_1
Class_1
Class_2
<>
Class_2
doStuff()
result
<>
Figure 81: Object instantiation and destruction in a sequence diagram
4.13.4.4
Grouping and loops
From time to time, we may need to represent a series of messages being sent in parallel, a loop, or just group some
messages to represent them in a clearer manner. This is where grouping comes of use: it has a representation based
on “boxes”, like the following:
User
User
Monte_Carlo_Calculator
Monte_Carlo_Calculator
Input_Generator
Input_Generator
compute()
| loop [1 | 0000 times]
generate_input() result |
result
Figure 82: A loop grouping in a sequence diagram
4.13.4.5
Notes
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Like all UML diagrams, it is possible to use notes to add some comments that may be useful for the interpretation
of our diagrams, like follows.
Class_1
Class_1
Class_2
Class_2
doStuff()
result
This is a note.
Figure 83: Example of notes in a sequence diagram
4.13.5
Other diagrams
UML is composed by a ton of diagrams that can be used to communicate with your teammates and organize your
work, among them we find:
• Component Diagrams;
• Communication Diagrams;
• Composite Structure Diagrams;
• Deployment Diagrams;
• Package Diagrams;
• Profile Diagrams;
• State Diagrams;
• Timing Diagrams.
In this chapter we just saw the ones that will help you the most when reading the rest of this book, as well as
effectively planning any project you have in mind.
4.14
Generic Programming
Sometimes it may be necessary (mostly in the case of containers) to have the same kind of code to work on different
data types, which means that we need to abstract types into variables and be able to code accounting for such
types.
Generic Programming is a blanket-term that defines a style of computer programming where algorithms are
written in terms of “to be specified later” data types, this usually applies to languages that make use of static
typing[g].
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| 7 | |
| -------- | -------- |
Figure 110: Singly-Linked List has no redundancy
Our “pointer” is pointing the node containing the number “5”, and now we want to know the value of the node that
precedes it. T
o do that we need to start from the head, saving in a temporary variable our nodes, until we find the
node pointed by our “pointer”.
Listing 31: Finding the previous element in a singly linked list
1
def get_previous_node(lst , current_node):
2
pointer = lst.head
3
previous = None
4
while (pointer != current_node):
| 5 | |
| -------- | -------- |
previous = pointer
6
pointer = pointer.next
| 7 | |
| -------- | -------- |
return previous
This operation has O(n) complexity, which is not great. If we wanted to print a list in reverse with such technique,
the situation would be even worse.
Doubly-linked lists are another example of data redundancy. We are saving the content of the “previous” node, so
that we can do a simple lookup with complexity O(1) and easily (and efficiently) do our “reverse printing”.
| 7 | |
| -------- | -------- |
| 9 | |
| -------- | -------- |
| | 5 |
| -------- | -------- |
Figure 111: A doubly linked list is an example of redundancy
4.1| | 9 |
| -------- | -------- |
Introduction to Multi-Tasking
When it comes to humans, we are used to have everything at our disposal immediately, but when it comes to
computers, each processing unit (CPU) is usually able to perform only one task at a time.
T
o allow for multi-tasking (doing many activities at once), the CPU switches between tasks at high speeds, giving
us the illusion that many things are happening at once. There are many methods to ensure multi-tasking without
process starvation[g], the most used is pre-emption[g] where there are forced context switches between processes,
to avoid one hogging the CPU.
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more. Let’s try to make sense of this.
First of all, coroutines are computer programs can run in multitasking (so it can run separated from our main game
loop) which are used in non-preemptive multitasking. Differently from the preemptive style defined in the glossary,
in non preemptive multitasking the operating system never forces a context switch, but it’s the coroutine’s job to
yield the control over to another function.
Instead of “fighting for resources”, coroutines politely free the processor and give control of it to something else
(could be the caller or another coroutine), this form of multitasking is often called cooperative multitasking.
A particularly interesting point of coroutines is the fact that their execution can be “suspended” and “resumed”
without losing its internal state. Coroutines are used in more advanced engines (using the Actor Model) and in some
particular situations. You may never need to use a single coroutine, or you may need to use them every day, so it’s
worth knowing at least what they are.
4.20
Introduction to Multi-Threading
When it comes to games and software, we usually think of it as a single line of execution, branching to (not really)
infinite possibilities; but when it comes to games, we may need to dip our toes into the world of multi-threaded
applications.
4.20.1
What is Multi-Threading
Multi-Threading means that multiple threads exist in the context of a single process, each thread has an independent
line of execution but all the threads share the process resources.
In a game, we have the “Game Process”, which can contain different threads, like:
• World Update Thread
• Rendering Thread
• Loading Thread
• …
Multi-Threading is also useful when we want to perform concurrent execution of activities.
4.20.2
Why Multi-Threading?
Many people think of Multi-Threading as “parallel execution” of tasks that leads to faster performance. That is not
always the case. Sometimes Multi-Threading is used to simplify data sharing between flows of execution, other
times threads guarantee lower latency, other times again we may need threads to get things working at all.
For instance let’s take a loading screen: in a single-threaded application, we are endlessly looping in the input-
update-draw cycle, but what if the “update” part of the cycle is used to load resources from a slow storage media
like a Hard Disk or even worse, an optical disk drive?
The update function will keep running until all the resources are loaded, the game loop is stuck and no drawing will
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be executed until the loading has finished. The game is essentially hung, frozen and your operating system may
even ask you to terminate it. In this case we need the main game loop to keep going, while something else takes
care of loading the resources.
4.20.3
Thread Safety
Threads and concurrent execution are powerful tools in our “programmer’s toolbox”, but as with all powers, it has
its own drawbacks.
4.20.3.1
Race conditions
Imagine a simple situation like the following: we have two threads and one shared variable.
Thread 1
Result
Copy of
Variable
Variable
1
Result
Copy of
Variable
Thread 2
Figure 114: T
wo threads and a shared variable
Both threads are very simple in their execution: they read the value of our variable, add 1 and then write the result
in the same variable.
This seems simple enough for us humans, but there is a situation that can be really harmful: let’s see, in the following
example each thread will be executed only once. So the final result, given the example, should be “3”.
First of all, let’s say Thread 1 starts its execution and reads the variable value.
Thread 1
Result
Copy of
Variable
Variable
1
Result
Copy of
Variable
Thread 2
Read
Figure 115: Thread 1 reads the variable
Now, while Thread 1 is calculating the result, Thread 2 (which is totally unrelated to Thread 1) starts its execution
and reads the variable.
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Thread 1
Result
Copy of
Variable
Variable
1
Result
Copy of
Variable
Thread 2
Read
1
...
Figure 116: While Thread 1 is working, Thread 2 reads the variable
Now Thread 1 is finishing its calculation and writes the result into the variable.
Thread 1
Result
Copy of
Variable
Variable
1
Result
Copy of
Variable
Thread 2
1
...
2
1
Write
Result
Figure 117: Thread 1 writes the variable
After That, Thread 2 finishes its calculation too, and writes the result into the variable too.
Thread 1
Result
Copy of
Variable
Variable
Result
Copy of
Variable
Thread 2
1
2
1
Write
Result
2
2
Terminated
Figure 118: Thread 2 writes the variable
Something is not right, the result should be “3”, but it’s “2” instead.
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Thread 1
Result
Copy of
Variable
Variable
Result
Copy of
Variable
Thread 2
1
2
1
2
2
Terminated
Terminated
Figure 119: Both Threads T
erminated
We just experienced what is called a “race condition”: there is no real order in accessing the shared variable, so
things get messy and the result is not deterministic. We don’t have any guarantee that the result will be right all
the time (or wrong all the time either).
4.20.3.2
Critical Regions
Critical Regions (sometimes called “Critical Sections”) are those pieces of code where a shared resource is used, and
as such it can lead to erroneous or unexpected behaviors. Such sections must be protected from concurrent access,
which means only one process or thread can access them at one given time.
4.20.4
Ensuring determinism
Let’s take a look at how to implement multi-threading in a safe way, allowing our game to perform better without
non-deterministic behaviors. There are other implementation approaches (like thread-local storage and re-entrancy)
but we will take a look at the most common here.
4.20.4.1
Immutable Objects
The easiest way to implement thread-safety is to make the shared data immutable. This way the data can only
be read (and not changed) and we completely remove the risk of having it changed by another thread. This is an
approach used in many languages (like Python and Java) when it comes to strings. In those languages strings are
immutable, and “mutable operations” only return a new string instead of modifying the existent one.
4.20.4.2
Mutex
Mutex (Short for mutual exclusion) means that the access to the shared data is serialized in a way that only one
thread can read or write to such data at any given time. Mutual exclusion can be achieved via algorithms (be careful
of out of order execution[g]), via hardware or using “software mutex devices” like:
• Locks (known also as mutexes)
• Semaphores
• Monitors
• Readers-Writer locks
• Recursive Locks
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3
3
Figure 126: How mutex works (7/8)
Now both threads finished their jobs and the result inside the variable is correct.
3
3
Figure 127: How mutex works (8/8)
4.20.4.3
Atomic Operations
[This section is a work in progress and it will be completed as soon as possible]
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important!).
6.1.2
Game Designer
The game designer takes care of the game concept, usually (but not only!) working with really specific software,
usually provided by the programmers in the team (like specific level editors).
They design balanced game mechanics, manage the learning curve and take care of level design too.
Under the “Game Designer” term you can find different roles, among them:
• Level Designer;
• World Builder;
• Narrative Designer;
• Quest/Mission Designer.
A good game designer must know mathematics, some scripting and be able to use planning tools (again, our friendly
Kanban Board comes into play) as well as diagram drawing tools.
6.1.3
Writer
Writers are the ones who can help you give your game its own story, but also help with things that are outside the
mere game itself.
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• developing and executing marketing campaigns;
• creating press releases and other promotional materials;
• managing social media accounts;
• working with journalists and influencers to publicize the game;
• publicizing the game on dedicated trade shows.
6.1.8
Tester
Probably the most important job in a game development team, testing needs people with high attention to detail,
as well as the ability to handle stress well.
T
esters are able to find, describe and help you reproduce bugs and misbehaviors of your game.
6.2
Some general tips
6.2.1
Be careful of feature creep
The “it would be cool to…” trap, formally called “feature creep”, is a huge problem in all projects that involve any
amount of passion in them.
Saying “it would be cool to do : let’s implement it!” can spiral out of control and make us
implement new features forever, keeping us from taking care of the basics that make a good game (or make a game
at all).
Try to stick to the basics first, and then eventually expand when your game is already released, if it’s worth it: first
make it work, then make it work well and only in the end make it elegant.
6.2.2
On project duration
When it comes to project management, it’s always tough to gauge the project duration, so it can prove useful to
remember the following phrase:
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“If you think a project would last a month, you should add a month of time for unforeseen events. After that,
you should add another month for events that you really cannot foresee.”
This means that projects will last at least 3 times the time you foresee.
That may seem a lot like an exaggeration, but unforeseen events happen and they can have a huge impact on the
release of your game. It’s better to err on the side of caution and even delay the release if something goes wrong.
Shigeru Miyamoto said the following:
A delayed game is eventually good, a bad game is bad forever.
so maybe being “abundant” with your time estimates is not that wrong.
6.2.3
Brainstorming: the good, the bad and the ugly
Brainstorming is an activity that involves the design team writing down all the ideas they possibly can (without
caring about their quality yet).
This is a productive activity to perform at the beginning of the game development and design process, but it can be
a huge source of feature creep if done further down the line.
After the initial phase of brainstorming, the team analyzes the ideas and discards the impossible ones, followed by
the ones that are not “as good as they sounded at first”. The remaining ideas can come together to either form a
concept of a video game or some secondary component of it.
In short: brainstorming is a great activity for innovation, but since it’s essentially “throwing stuff at a wall and see
what sticks”.
This activity can sometimes be either unproductive or “excessively productive”: in both cases we end up with nothing
of use in our hands.
6.2.4
On Sequels
In case your game becomes a hit, you will probably think about making a sequel: this is not inherently a bad thing,
but you need to remember some things.
When developing a sequel, you will have to live up to your previous game, as well as the expectations of the players,
and this becomes more and more difficult as the “successful sequels” go on.
Not only a sequel must be “as good or better” than its predecessor, but also it should add something to the original
game, as well as the established lore (if there is any).
Your time and resource management must be top-notch to be able to “bring more with less”, since your need for
resources cannot skyrocket without a very good reason.
Also don’t get caught in the some kind of “sequel disease” where you end up making a sequel just to “milk the
intellectual property”: you will end up ruining the whole series: it may end up being hated by the ones who played
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the first games, and new players will be discouraged by a series that either overstays its welcome, or has one or
more low-quality sequels.
6.3
Common Errors and Pitfalls
When you are making a new game, it’s easy to feel lost and “out of your comfort zone”, and that’s okay! It’s also
easy to fall into traps and pitfalls that can ruin your experience, here we take a look at the most common ones.
6.3.1
Losing motivation
Sometimes it can happen to lose motivation, usually due to having “too much ambition”: make sure you can develop
the kind of game you want to make, for instance leave multiplayer out of the question (multiplayer games are really
hard and network code can be a real pain to work on). It will just suck up development time, and it isn’t that much
of an important feature anyway (and it can still be implemented later, like it happened in Stardew Valley).
Like in music, many people prefer “mediocrity” to “something great”, so don’t force yourself to innovate: do things
well enough and if the innovative idea comes, welcome it.
If you get tired, take a break, you’re your own boss, and no one is behind you zapping you with a cattle prod: just
focus on making a good overall product and things will go well.
6.3.2
The “Side Project” pitfall
It happens: you have a ton of ideas for games of all kinds, and probably you’ll start thinking:
What’s bad about a small “side project”? I want to change things up a bit…
You will end up having lots of “started projects” and nothing finished, your energy will deplete, things will become
confusing and you won’t know what game you’re working on anymore.
Instead, make a small concept for the new mechanic and try to implement it in your current game, you may find a
new mix that hasn’t been tried before, making your game that much more unique.
6.3.3
Making a game “in isolation”
While making a game you will need to gather some public for it, as well as create some hype around it: making a
game on your own without involving the public is a mistake that deprives you of a huge source of suggestions and
(constructive) criticism (as well as satisfaction, when you manage to get some people interested in your game).
Make your game public, on platforms like itch.io or IndieDB, get feedback and encouragement. Create trailers towards
the end of development, put them on YouTube or Vimeo and if you want to go all out, get in touch with the press (locally
first) and create hype around your product.
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6.3.4
(Mis)Handling Criticism
Among all the other things that are happening, we also need to handle feedback from our “potential players”, and
this requires quite the mental effort, since we can’t make it “automatic”.
Not all criticism can be classified as “trolling”, and forging our game without listening to any feedback will only mean
that such game won’t be liked by as many people as we would like, maybe for a very simple problem that could
have been solved if only we listened to them.
At the same time, not all criticism is “useful” either, not classifying criticism as “trolling” does not mean that trolling
doesn’t exist, some people will take pride in ruining other people’s mood, either by being annoying and uselessly
critic, or by finding issues that don’t actually exist.
The question you should ask yourself is simple:
Is this criticism I’m receiving constructive? Can it make my game better?
If the answer is no, then you may want to ignore such criticism, but if it is constructive, maybe you want to keep it
in consideration.
6.3.4.1
Misusing of the Digital Millennium Copyright Act
This is what could be considered the apex of mishandling criticism: the usage of DMCA takedowns to quash criticism
towards your game.
Note!
What follows is not legal advice. I am not a lawyer.
If you want to know more (as in quantity and quality of information), contact your
favorite lawyer.
Sadly, mostly in the YouT
ube ecosystem, DMCA takedowns are often used as a means to suppress criticism and
make video-reviews disappear from the Internet. Useless to say that this is potentially illegal as well as definitely
despicable.
T
akedowns according to the DMCA are a tool at your disposal to deal with copyright infringements by people who
steal part (or the entirety of) your work, allowing (in the case of YouT
ube at the very least) to make the allegedly
infringing material. This should be used carefully and just after at the very least contacting the alleged infringer
privately, also because there is an exception to the copyright rule.
6.3.4.1.1
The Fair Use Doctrine
The so-called “Fair Use” is a limited exception to the copyright law that targets purposes of review, criticism, parody,
commentary, and news reporting, for instance.
The test for “Fair use” has four factors (according to 17 U.S.C. §107):
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1. The Purpose and character of the use: if someone can demonstrate that their use advances knowledge
or the progress of arts through the addition of something new, it’s probably fair use. This usually is defined
by the question “is the work transformative enough?”
2. The nature of the copyrighted work: For instance, facts and ideas are not protected by copyright, but
only their particular expression or fixation is protected. Essentially you can’t really sue someone for making
a game very similar to yours (For instance making a 2D sidescrolling, run’n’gun platformer).
3. The amount and substantiality of the portion used in relation to the work as a whole: If someone
uses a small part (compared to the whole) of the work, and if that part is not really substantial, then it’s
probably fair use.
4. The effect on the potential market for the copyrighted work: this defines if the widespread presence
of the “allegedly infringing use” can hinder on the copyright owner’s ability to exploit (earn from) their original
work.
There can also be some additional factors that may be considered, but these four factors above are usually enough
to decide over the presence (or absence) of fair use.
6.3.4.1.2
The “Review Case”
Let’s take a simple example: a video-review on our brand new video game, that takes some small pieces of gameplay
(totaling about 5 minutes), on video and comments on the gameplay, sound and graphics. A very common scenario
with (I hope) an unsurprising turnout.
Let’s take a look at the first point: the purpose is criticism, the review brings something new to the table (essentially
it is transformative): someone’s impression and comments about the commercial work.
Second point: the game is an interactive medium, while the review is non-interactive by nature, the mean of trans-
mission is different.
Third point: considering the average duration of 8 to 10 hours of a video game, 5 minutes of footage amounts for
around 0.8% to 1% of the total experience, that’s a laughable amount compared to the total experience.
Fourth Point: this is the one many people may get wrong. A review can have a huge effect on the market of a
copyrighted work (a bad score from a big reviewer can result in huge losses), but that’s not really how the test
works. The fourth test can usually be answered by the following questions:
What’s the probability that someone would buy (or enjoy for free) the work from the alleged infringer, instead
than from me (the copyright owner)?
This is called “being a direct market substitute” for the original work. The other question is:
Is there a potential harm (other than market substitution) that can exist?
This usually is related to licensing markets.
And here lies the final nail on the coffin: there is no direct market
substitution and courts recognize that certain kinds of market don’t negate fair use, and reviews are among those
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• Rigid rules are not good;
• A working software is more important than a comprehensive documentation;
• Seek collaboration with the stakeholder instead of trying to negotiate with them;
• Responding to change is better than following a plan
• Interactions and individuals are more important than processes and tools.
Obviously not everything that shines is actually gold, there are many detractors of the Agile model, bringing on the
table some criticism that should be noted:
• The agile way of working entails a really high degree of discipline from the team: the line between “flexibility”
and “complete lack of rules” is a thin one;
• Software without documentation is a liability more than an asset: commenting code is not enough - you need
to know (and let others know) the reason behind a certain choice;
• Without a plan, you can’t estimate risks and measure how the project is coming along;
• Responding to change can be good, but you need to be aware of costs and benefits such change and your
response entail.
6.4.5.1
User Stories
Agile models are based on “User Stories”, which are documents that describe the problem at hand.
Such documents are written by talking with the stakeholder/customer, listening to them, actively participating in
the discussion with them, proposing solutions and improvements actively.
A User Story also defines how we want to check that the software we are producing actually satisfies our customer.
6.4.5.2
Scrum
The term “scrum” is taken from the sport of American Football, where you have an action that is seemingly product
of chaos but that instead hides a strategy, rules and organization.
Let’s see some Scrum terminology:
• Product Backlog: This is essentially a “todo list” that keeps requirements and features our product must
have;
• Sprint: Iteration, where we choose what to do to create a so-called “useful increment” to our product. Each
Sprint lasts around 2 to 4 weeks and at the end of each sprint you obtain a version of your software that can
be potentially sold to the consumer;
• Sprint Backlog: Essentially another “todo list” that keeps the set of user stories that will be used for the
next sprint.
As seen from the terminology, the Scrum method is based on well-defined iterations (Sprints) and each sprint is
composed by the following phases:
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• Sprint Planning: You gather the product backlog and eventually the previous sprint backlogs and decide
what to implement in the upcoming sprint;
• Daily Scrum: A daily stand-up meeting that lasts around 15 minutes where a check on the daily progress is
done;
• Sprint Review: After the sprint is completed, we have the verification and validation of the products of the
sprint (both software and documents);
• Sprint Retrospective: A quality control on the sprint itself is done, allowing for continuous improvement
over the way of working.
6.4.5.2.1
Criticisms to the Scrum approach
The Scrum approach can quickly become chaotic if User Stories and Backlogs are not well kept and clear. Also, no
matter how short it can be, the Daily Scrum is still an invasive practice that interrupts the workflow and requires
everyone to be present and ready.
6.4.5.3
Kanban
Kanban is an Agile Development approach taken by the scheduling system used for lean and just-in-time manufac-
turing implemented at T
oyota.
The base of Kanban is the “Kanban Board” (sometimes shortened as “Kanboard”), where plates (also called “cards”
or “tickets”) are moved through swimlanes that can represent:
• The status of the card (T
o Do, Doing, T
esting, Done)
• The Kind of Work (Frontend, Backend, Database, …)
• The team that is taking care of the work
The board helps with organization and gives a high-level view of the work status.
Backlog
In Progress
Testing
Done
Blocked
Fix Bug #1234
Implement New Bugs
Fix Bug #159
Antigravity Engines
World Domination
Figure 139: Example of a Kanban Board
6.4.5.4
ScrumBan
ScrumBan is a hybrid approach between Scrum and Kanban, mixing the Daily Scrum and Sprint Approach with the
Kanban Board.
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This approach is usually used during migration from a Scrum-Based approach to a purely Kanban-based approach.
6.4.6
Lean Development
Lean development tries to bring the principles of lean manufacturing into software development. The basis of lean
development is divided in 7 principles:
• Remove Waste: “waste” can be partial work, useless features, waiting, defects, work changing hands…
• Amplify Learning: coding is seen as a learning process and different ideas should be tested on the field,
giving great importance to the learning process;
• Decide late: the later you take decisions, the more assumptions and predictions are replaced with facts, Also
strong commitments should happen as late as possible, as they will make the system less flexible;
• Deliver early: technology evolves rapidly, and the one that survives is the fastest. If you can deliver your
product free from defects as soon as possible you will get feedback quickly, and get to the next iteration
sooner;
• Empower the team: managers are taught to listen to the developers, as well as provide suggestions;
• Build integrity in: the components of the system should work well together and give a cohesive experience,
giving the customer and impression of integrity;
• Optimize the whole: optimization is done by splitting big tasks into smaller ones which helps finding and
eliminating the cause of defects.
6.4.7
Where to go from here
Obviously the models presented are not set in stone, but are “best practices” that have been proven to help with
project management, and not even all of them.
Nothing stops you from taking elements of a model and implement them into another model. For example you could
use an Evolutionary Model with a Kanban board used to manage the single increment.
6.5
Version Control
When it comes to managing any resource that is important to the development process of a software, it is vitally
important that a version control system is put in place to manage such resources.
Code is not the only thing that we may want to keep under versioning, but also documentation can be subject to it.
Version Control Systems (VCS) allow you to keep track of edits in your code and documents, know (and blame) users
for certain changes and eventually revert such changes when necessary. They also help saving on bandwidth by
uploading only the differences between commits and make your development environment more robust (for instance,
by decentralizing the code repositories).
The most used Version Control system used in coding is Git, it’s decentralized and works extremely well for tracking
text-based files, like code or documentation, but thanks to the LFS extension it is possible for it to handle large files
efficiently.
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First of all, we need to convert it into the corresponding flow diagram, which usually means eliminating the start
nodes and merge nodes used by UML. The result should look something like the following:
a=input()
a == 0
b='zero'
a % 2 == 0
return b
b='even'
b='odd'
Figure 142: Flow diagram of the program we’ll calculate the cyclomatic complexity of
Now we need to count 3 things:
• The number of “nodes”: that is the number of boxes and diamonds in our flow diagram. In our case it is 7.
• The number of “edges”: that is the number of arrows that connect the nodes in our flow diagram. In our case
it is 8.
• The number of “exit points”: usually that is the number of stop nodes in our UML diagram, in our flow diagram
it’s the number of return statements. In our case it is 1.
Now we need to apply the following formula: C = E −N + 2 · P .
This formula can be explained as follows:
Cyclomatic Complexity = Edges −Nodes + 2 · Exit Points
In our case we have: C = 8 −7 + 2 · 1 = 3
Usually a complexity lower than 15 is considered OK, but also the lower the better.
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6.6.3
Code Coverage
When you have a test suite, you may already be thinking about a metric that tells you how much of your code is
tested. Well, here it is: the code coverage metric tells you what percentage of your code base has been run when
executing a test suite.
That is both the useful and damaging part of this metric: code coverage doesn’t tell you how well your code is
tested, just how much code was executed, so it’s easy to incur into what I like to call “incidental coverage”: the
code coverage presents a higher value, when the code is merely “executed” and not thoroughly “tested”.
Code coverage is split in many “sub-sets”, like:
• Statement Coverage: how many statements of the program are executed;
• Branch Coverage: defines which branches (as in portions of the if/else and “switch” statements) are exe-
cuted;
• Function Coverage: how many functions or subroutines are called.
This is also why it’s better to prepare unit tests first, and delay the integration tests for a while.
T
o know more about those terms, head to the testing section.
6.6.4
Code Smells
Code Smells is a blanket term representing all the common (and thus known) mistakes done in a certain programming
language, as well as bad practices that can be fixed more or less easily.
Some of these smells can be automatically detected by static analysis programs (sometimes called Linters), others
may require dynamic execution, but all code smells should be solved at their root, since they usually entail a deeper
problem.
Among code smells we find:
• Duplicated Code;
• Uncontrolled Side Effects;
• Mutating Variables;
• God Objects;
• Long Methods;
• Excessively long (and thus complex) lines of code.
6.6.5
Coding Style infractions
When you are collaborating with someone, it is absolutely vital to enforce a coding style, so that everyone in the
team is able to look at everyone else’s code without having to put too much effort into it.
Coding style can be enforced via static analysis tools, when properly configured.
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Counting (automatically) the number of coding style infractions can help you estimate how much effort working on
the code is necessary, thus you would be able to foresee slowdowns in the development process.
6.6.6
Depth of Inheritance
Some people say that inheritance is evil and should be avoided, some other say it’s good. As with all things, in
medio stat virtus (virtue stands in the middle), sometimes inheritance is better left where it is, other times its usage
is necessary for things to make sense.
The depth of inheritance metric tells us how deep the inheritance hierarchy is, thus this metric will tell the us the
strength of one of the possible dependency types. The deeper the inheritance, the more dependencies we have,
which means that we have more classes that, if edited, will change the behavior of the “children classes”.
It’s better having a short inheritance depth, (although it’s not necessarily wrong) having a longer chain of dependen-
cies might mean we have a structural problem, where some classes are “too generic” and at the top of the hierarchy
we have some kind of “universal object”.
6.6.7
Number of methods / fields / variables
Let’s talk numbers: having too many methods or fields in a class can be an indicator of a so-called “god object”:
an object that has too many responsibilities under its wing (does too many things), this is a breach of the single
responsibility principle and should be avoided.
We can fix this by splitting the class into smaller classes, each with its own single responsibility.
A high number of local variables instead may point to a complexity issue: your algorithm may be more complex than
needed, or needs to be split into different functions.
6.6.8
Number of parameters
This metric is specific for functions, when a function has a lot of parameters, it’s harder to call and harder to under-
stand. Functions should have no more than 5 parameters in most cases, more and it will be complex.
Some automated tools in your IDE may be able to warn you in case methods and functions have too many parame-
ters.
T
o solve this issue, you may need to review the function (maybe it has too many responsibilities?) or pass a so-called
“complex structure” to it (thus merging all the parameters into one).
6.6.9
Other metrics
The metrics listed above are not the only ones available to you, some IDEs have aggregated metrics (like the “main-
tainability index” in Visual Studio), while there may be other metrics you want to measure, some follow:
• Lead Time: Time elapsed between the start and end of a process (may be a ticket, or a task);
• MTBF: (Mean Time Before Failure) represents the mean time before the software crashes;
• Crash Rate: The number of times a software crashes, over the number of times it’s used.
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7
Writing a Game Design Document
If you don’t know where you are going. How can you expect to get there?
Basil S. Walsh
One of the most discussed things in the world of Game Development is the so-called “GDD” or “Game Design
Document”. Some say it’s a thing of the past, others swear by it, others are not really swayed by its existence.
Being an important piece of any software development process, in this book we will talk about the GDD in a more
flexible way.
7.1
What is a Game Design Document
The Game Design Document is a Body Of Knowledge that contains everything that is your game, and it can take
many forms, such as:
• A formal design document;
• A Wiki[g];
• A Kanboard[g];
• A collection of various files, including spreadsheets.
The most important thing about the GDD is that it contains all the details about your game in a centralized and
possibly easy-to-access place.
It is not a technical document, but mostly a design document, technical matters should be moved to a dedicated
“T
echnical Design Document”.
7.2
Possible sections of a Game Design Document
Each game can have its own attributes, so each Game Design Document can be different, here we will present some
of the most common sections you can include in your own Game Design Document.
7.2.1
Project Description
This section is used to give the reader a quick description of the game, its genre (RPG, FPS, Puzzle,…), the type of
demographic it covers (casual, hardcore, …). Additional information that is believed to be important to have a basic
understanding of the game can be put here.
This section should not be longer than a couple paragraphs.
A possible excerpt of a description could be the following:
This game design document describes the details for a 2D side scrolling platformer game where the player
makes use of mechanics based on using arrows as platforms to get to the end of the level.
The game will feature a story based on the central America ancient culture (Mayan, Aztec, …).
The name is not defined yet but the candidate names are:
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7.2.2
Characters
If your game involves a story, you need to introduce your characters first, so that everything that follows will be
clear.
A possible excerpt of a characters list can be the following:
Ohm is the main character, part of the group called “The Resistance” and fights for restoring the electrical
order in the circuit world.
Fad is the main side character, last survivor and heir of the whole knowledge of “The Capacitance” group.
Its main job is giving technical assistance to Ohm.
Gen. E. Rator is the main antagonist, general of “The Reactance” movement, which wants to conquer the
circuit world.
This can be a nice place where to put some character artwork.
If your game does not include a story, you can just avoid inserting this section altogether.
7.2.3
Storyline
After introducing the characters, it’s time to talk about the events that will happen in the game.
An example of story excerpt can be the one below:
It has been 500 mega-ticks that the evil Rator and the reactance has come to power, bringing a new era of
darkness into the circuit world.
After countless antics by the evil reactance members, part of the circuit world’s population united into what
is called “The Resistance”.
Strong of thousands of members and the collaboration of the Capacitance, the resistance launched an attack
against the evil reactance empire, but the empire stroke back with a carpet surcharge attack, decimating
the resistance and leaving only few survivors that will be tasked to rebuild the resistance and free the world
from the reactance’s evil influence.
This is when a small child, and their parents were found. The child’s name, Ohm, sounded prophetic of a
better future of the resistance.
And this is where our story begins.
As with the Characters section, if your game does not include a story, you can just skip this section.
7.2.3.1
The theme
When people read the design document, it is fundamental that the game’s theme is quickly understood: it can be
a comedy-based story, or a game about hardships and fighting for a better future, or maybe it is a purely fantastic
game based on ancient history…
Here is a quick example:
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This is a game about fighting for a better future, dealing with hardships and the deep sadness you face when
you are living in a world on the brink of ruin.
This game should still underline the happiness of small victories, and give a sense of “coziness” in such small
things, even though the world can feel cold.
If you feel that this section is not relevant for your game, you can skip it.
7.2.3.2
Progression
After defining the story, you should take care of describing how the story progresses as the player furthers their
experience in a high-level fashion.
An example:
The game starts with an intro where the ruined city is shown to the player and the protagonist receives their
magic staff that will accompany them through the game.
The first levels are a basic tutorial on movement, where the shaman teaches the player the basic movement
patterns as well as the first mechanic: staff boosting. Combat mechanics are taught as well.
After the tutorial has been completed, the player advances to the first real game area: The stone jungle.
…
7.2.4
Levels and Environments
In this section we will define how levels are constructed and what mechanics they will entail, in detail.
We can see a possible example here:
The First Level (T
utorial) is based in a medieval-like (but adapted to the center-America theme) training camp,
outside, where the player needs to learn jumping, movement and fight straw puppets. At the end of the basic
fighting and movement training, the player is introduced to staff boosting which is used to first jump to a
ledge that is too high for a normal jump, and then the mechanic is used to boost towards an area too far
forward to reach without boosting.
…
Some level artwork can be included in this section, to further define how the levels will look and feel.
7.2.5
Gameplay
This section will be used to describe your gameplay. This section can become really long, but do not fear, as you
can split it in meaningful sections to help with organization and searching.
7.2.5.1
Goals
Why is the player playing your game?
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This question should be answered in this section. Here you insert the goals of your game, both long and short term.
An example could be the following:
Long T
erm Goal: Stop the great circuit world war
Optional Long T
erm Goal: Restore the circuit world to its former glory.
Short T
erm Goals:
• Find the key to the exit
• Neutralize Enemies
• Get to the next level
7.2.5.2
Game Mechanics
In this section, you describe the core game mechanics that characterize the game, extensively. There are countless
resource on how to describe game mechanics, but we’ll try to add an example here below.
The game will play in the style of the well-known match-3 games. Each match of 3 items will add some points
to the score, and new items will “fall” from a randomly chosen direction every time.
Every time an “L
” or a “T” match is performed, a special item of a random color will be generated, when a
match including this item is made, all the items in the same row and column will be deleted and bonuses will
be awarded.
Every time a match with 4 items in a row is performed, a special item of a random color will be generated,
when a match including such item is made, all items in a 3x3 grid centered on the item will be deleted and
bonuses will be awarded.
Every time a match with 5 items in a row is performed, a special uncolored item will be generated, this can
be used as a “wildcard” for any kind of match.
In case the 5-item special is matched with any other special item, the whole game board will be wiped and
a bonus will be awarded.
…
7.2.5.3
Skills
Here you will describe the skills that are needed by the users in order to be able to play (and master) your game.
This will be useful to assess your game design and eventually find if there are some requirements that are too high
for your target audience; for instance asking a small child to do advanced resource management could be a problem.
This will also help deciding what the best hardware to use your game on could be, for instance if your game requires
precise inputs for platforming then touch screens may not be the best option.
Here’s an example of such section:
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The user will need the following skills to be able to play the game effectively:
• Pressing Keyboard Buttons or Joypad Buttons
• Puzzle Solving (for the “good ending” overarching puzzle)
• Timing inputs well (for the sections with many obstacles)
…
7.2.5.4
Items/Powerups
After describing the basic game mechanics and the skills the user needs to master to be able to play the game
effectively, you can use this section to describe the items and powerups that can be used to alter the core gameplay.
For example:
The player can touch a globular light powerup to gain invincibility, every enemy that will touch the player
will get automatically killed. The powerup duration is 15 seconds.
Red (incendiary) arrows can be collected through the levels, they can get shot and as soon as they touch the
ground or an enemy, the burst into flames, similarly to a match.
…
In this section you describe all items that can be either found or bought from an in-game store or also items derived
from micro-transactions. In-game currency acquisition should be mentioned here too, but further detailed in the
monetization section.
7.2.5.5
Difficulty Management and Progression
This section can be used to manage how the game gets harder and how the player can react to it. This will expand
on game mechanics like leveling and gear.
This section is by its own nature quite subjective, but describing how the game progresses helps a lot during the
tighter parts of development.
Below a possible example of this section:
The game will become harder by presenting tougher enemies, with more armor, Health Points and attack. T
o
overcome this difficulty shift, the player will have to create defense strategy and improve their dodging, as
well as leveling up their statistics and buy better gear from the towns’ shops.
In the later levels, enemies will start dodging too, and will also be faster. The player will need to improve
their own speed statistic to avoid being left behind or “kited” by fast enemies.
As the game progresses, the player will need to acquire heavy weapons to deal with bigger bosses, as well
as some more efficient ranged weapons to counteract ranged enemies.
…
This section is good if you want to talk about unlocking new missions/maps/levels too.
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7.2.5.6
Losing Conditions
Many times we focus so much on how the player will get to the end of the game that we absolutely forget how the
player can not get to the end of the game.
Losing conditions must be listed and have the same importance of the winning conditions, since they add to the
challenge of the game itself.
A possible example of how a “losing conditions” section could be written is the following:
The game can be lost in the following ways:
• Losing all the lives and not “continuing” (Game Over)
• Not finding all the Crystal Oscillators (Bad Ending)
An interesting idea could be having an “endings” section inside your game, where all endings (both good, bad and
neutral) are listed, encouraging the player to pull themselves out from the “losing condition” that is a bad ending.
7.2.6
Graphic Style and Art
Here we describe the ideas on how the game will look like. Describing the graphic style and medium.
Here is a possible example of the game:
This is a 2D side scroller with a dark theme, the graphics should look gloomy and very reminiscing of a circuit
board.
The graphical medium should be medium-resolution pixel art, allowing the player’s imagination to “fill in” the
graphics and allowing to maintain a “classic” and “arcade” feeling.
…
7.2.7
Sound and Music
Sadly, in way too many games, music and sound is an afterthought. A good soundtrack and sound effect can really
improve the immersion, even in the simplest of games.
In this section we can describe in detail everything about Music and Sound Effects, and if the section becomes hard
to manage, splitting it in different sub-sections could help organization.
Music should be based on the glitch-hop style, to complement the electronic theme. 8 or 16-bit style sounds
inside the score are preferable to modern high-quality samples.
Sound effects should appeal to the 8 or 16-bit era.
Lots of sound effects should be used to give the user positive feedback when using a lever to open a new
part of the level, and Extra Lives/1UP should have a jingle that overrides the main music.
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7.2.8
User Interface
In this section we will describe everything that concerns the User Interface: menus, HUD, inventories and everything
that will contribute to build the user experience that is not strictly tied to the gameplay.
This is especially important in games that make heavy use of menus, like turn-based strategy games or survival
games where inventory management can be fundamental.
Let’s see an example of how this section can be written:
The game will feature a cyberpunk-style main menu, looking a lot like an old green-phosphor terminal but
with a touch of futurism involved. The game logo should be visible on the left side, after a careful conversion
into pixel-art. On the right, we see a list of buttons that remind old terminal-based GUIs. On the bottom of
the screen, there should be an animated terminal input, for added effect.
Every time a menu item is highlighted or hovered by the mouse, the terminal input will animate and write a
command that will tie to the selected menu voice, such as:
• Continue Game: ./initiate_mission.bin -r
• Start Game: ./initiate_mission.bin --new
• Options: rlkernel_comm.bin --show_settings
• Exit: systemcontrol.bin --shutdown
The HUD display should remind a terminal, but in a more portable fashion, to better go with the “portability”
of a wrist-based device.
It’s a good idea to add some mock designs of the menu in this section too.
7.2.9
Game Controls
In this section you insert everything that concerns the way the game controls, eventually including special periph-
erals that may be used.
This will help you focusing on better implementing the input system and limit your choices to what is feasible and
useful for your project, instead of just going by instinct.
Below, a possible way to write such section
The game will control mainly via mouse and keyboard, using the mouse to aim the weapon and shoot and
keyboard for moving the character.
Alternatively, it’s possible to connect a twin-stick gamepad, where the right stick moves the weapon crosshair,
while the left stick is used to move the character, one of the back triggers of the gamepad can be configured
to shoot.
If the gamepad is used, there will be a form of aim assistance can be enabled to make the game more
accessible to gamepad users.
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7.2.10
Accessibility Options
Here you can add all the options that are used to allow more people to access your game, in more ways than you
think.
Below, we can see an example of many accessibility options in a possible game.
The game will include a “colorblind mode”, allowing the colors to be colorblind-friendly: such mode will
include 3 options: Deuteranopia, Tritanopia and Monochromacy.
Additionally, the game will include an option to disable flashing lights, making the game a bit more friendly
for people with photosensitivity.
The game will support “aim assistance”, making the crosshair snap onto the enemy found within a certain
distance from the crosshair.
In order to assist people who have issues with the tough platforming and reaction times involved, we will
include the possibility to play the game at 75%, 50% and 25% speed.
7.2.11
Tools
This section is very useful for team coordination, as having the same toolkit prevents most of the “works for me”
situations, where the game works well for a tester/developer while it either crashes or doesn’t work correctly for
others.
This section is very useful in case we want to include new people in our team and quickly integrate them into the
project.
In this section we should describe our toolkit, possibly with version numbers included (which help reducing incom-
patibilities), as well as libraries and frameworks. The section should follow the trace below:
The tools and frameworks used to develop the game are the following:
Pixel Art Drawing: Aseprite 1.2.13
IDE: Eclipse 2019-09
Music Composition: Linux Multimedia Studio (LMMS) 1.2.1
Map and level design: Tiled 1.3.1
Framework: SFML 2.5.1
Version Control: Git 2.24.0 and GitLab
7.2.12
Marketing
This section allows you to decide how to market the game and have a better long-term plan on how to market your
game to your players.
Carefully selecting and writing down your target platforms and audience allows you to avoid going off topic when it
comes to your game.
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7.2.12.1
Target Audience
Knowing who is your target audience helps you better suit the game towards the audience that you are actually
targeting.
Here is an example of this section:
The target audience is the following:
Age: 15 years and older
Gender: Everyone
T
arget players: Hardcore 2D platformer fans
7.2.12.2
Available Platforms
Here you describe the launch platforms, as well as the platforms that will come into the picture after the game
launched. This will help long term organization.
Here is an example of how this section could look:
Initially the game will be released on the following platforms:
• PC
• Playstation 4
After launch, we will work on the following ports:
• Nintendo Switch
• XBox 360
After working on all the ports, we may consider porting the game to mobile platforms like:
• Android 9.0 +
• iOS 11.0 +
…
7.2.12.3
Monetization
In this optional section you can define your plans for the ways you will approach releasing the game as well as
additional monetization strategies for your game.
For example:
The game will not feature in-game purchases.
Monetization efforts will be focused on selling the game itself at a full “indie price” and further monetization
will take place via substantial Downloadable Content Expansions (DLC)
The eventual mobile versions will be given away for free, with advertisements integrated between levels. It
is possible for the user to buy a low-price paid version to avoid seeing the advertisements.
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7.2.12.4
Internationalization and Localization
Internationalization and Localization are a matter that can make or break your game, when it comes to marketing
your game in foreign countries.
Due to political and cultural reasons, for instance you shouldn’t use flags to identify languages. People from territories
inside a certain country may not be well accepting of seeing their language represented by the flag of their political
adversaries.
Another example could be the following: if your main character is represented by a cup of coffee, your game could
be banned somewhere as a “drug advertisement”.
This brings home the difference between “Internationalization” and “Localization”:
Internationalization Making something accessible across different countries without major changes to its content
Localization Making something accessible across different countries, considering the target country’s culture.
We can see a possible example of this section below:
The game will initially be distributed in the following languages:
• English
• Italian
After the first release, there will be an update to include:
• Spanish
• German
• French
7.2.13
Other/Random Ideas
This is another optional section where you can use as a “idea bin”, where you can put everything that you’re not
sure will ever make its way in the game. This will help keeping your ideas on paper, so you won’t ever forget them.
We can see a small example here:
Some random ideas:
• User-made levels
• Achievements
• Multiplayer Cooperative Mode
• Multiplayer Competitive Mode
7.3
Where to go from here
This chapter represents only a guideline on what a Game Design Document can be, feel free to remove any sections
that don’t apply to your current project as well as adding new ones that are pertinent to it.
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A Game Design Document is a Body of Knowledge that will accompany you throughout the whole game development
process and it will be the most helpful if you are comfortable with it and it is shaped to serve you.
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P
Figure 183: Querying an AABB-tree (2/3)
We do the “left (red) child” test, we’re colliding with the relative bounding box, now we can do a narrow-phase
collision detection with the leaves of this node (and in the meantime we also excluded 5).
P
Figure 184: Querying an AABB-tree (3/3)
[This section is a work in progress and it will be completed as soon as possible]
9.3.4
Collision groups
[This section is a work in progress and it will be completed as soon as possible]
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Figure 208: Example of a ship attack formation
The situation here is more complex than it seems: this “troop” has a “captain” leading two other ships, who are
following at a fixed distance and angle: so if the captain moves, the “soldier ships” move, if the leader rotates, the
“soldier ships” will rotate accordingly.
Figure 209: What happens when the ship attack formation rotates
This can quickly get messy, since we’ll have to rotate the leader according to the screen, then rotate the “soldier
ships” according to the leader first, and then to the screen.
Scene trees can be used to make things easier, each node will rotate in relation to its parent.
10.3
Implementing a scene tree
[This section is a work in progress and it will be completed as soon as possible]
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being able to distinguish platforms from the background.
So a golden rule could be:
Use high detail in the foreground, gameplay-heavy elements - use less detail in the backgrounds
A good idea to make the background a bit less detailed is using blurring, which allows to keep the overall aesthetic
but makes it look “less interesting” than what’s in the foreground.
This doesn’t mean the background should be devoid of detail, just don’t overdo it.
13.2.6.2
Use saturation to separate layers further
Bright colors attract attention as much as detail does, so a good idea is making each background layer more “muted”
(color-wise) than the ones in foreground.
The main technique to make backgrounds more muted is lowering saturation, blending the colors with grey: this will
make the background less distracting to the player.
So another rule can be written as:
Layers farther away should have lower color saturation than the layers closer to the camera
13.2.6.3
Movement is yet another distraction
As detail and saturation are due to attract attention from the player, movement is another one of those “eye-catchers”
that can make the gameplay more chaotic and difficult for the player.
Small amounts of movement are OK, but fully-fledged animations in the background will prove distracting.
Let’s take note of rule number 3 then:
Try to avoid movement in the background
13.2.6.4
Use contrast to your advantage
Complementary colors tend to attract a lot of attention in the points of intersection of their hues.
If backgrounds feature complementary colors, it may distract the player from the main gameplay.
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Figure 255: Which spaceship is easier to spot at a glance?
Our rule number four should then be:
Keep backgrounds low-contrast to avoid distracting players
Also the opposite rule may apply:
Keep the main gameplay elements contrasting, so to attract the attention towards them
An orange-robed character will be easier to follow on a blue-ish background, for instance.
13.2.6.5
Find exceptions
Nothing is ever set in stone, and no rules should keep you from playing a bit outside the box and fiddling with some
exceptions to a couple rules.
13.2.6.6
Summarizing Layering
Let’s take the following image:
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Figure 256: How contrast and detail can help distinguishing foreground and background 6
You can notice that the grass in the foreground has a lot more hues of gold and brown, the trees and the grass are
darker and more saturated compared to the background, which is more “muted”.
If we were to break down the image into its main layers, from furthest to nearest, we would obtain something like
this:
Figure 257: Breaking down the image allows us to see the differences between the layers 7
From left to right we have:
• the background: our sky box, there is very little detail here, just enough to blend the color bands together
to make a cohesive piece;
• the farthest layer: the trees have very few hues in their bark and leaves, little detail is added, just enough
to make out lights and shadows;
• light rays: this semi-transparent layer is extremely simple, but being so light and monochromatic it adds
variety to make the image interesting without distracting from the foreground too much;
6Image by Roe61 (https://linktr.ee/Roe61) used with explicit permission
7Image by Roe61 (https://linktr.ee/Roe61) used with explicit permission
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Each row of a channel contains instructions for the tracker to execute, in the form of notes, instruments and com-
mands (or effects).
Figure 293: How each tracker channel is divided
Notes are written in the usual “Letter Notation” that you see in many music environments, while instruments are
enumerated, then there are commands: commands can instruct the tracker to apply a temporary effect on the note,
like portamento or vibrato.
In the previous example, there is a “vibrato” command going on, starting with the 48C: 4 is the “vibrato command”,
8 is the vibrato speed and C (hex for “12”) is the vibrato depth.
The vibrato continues with a V0 E41 command pair, where V0 changes the vibrato depth to 0 (the speed is the same
defined in the previous command), while E41 is a “vibrato control command” (E4) which changes the waveform of the
vibrato to 1 which is “ramp down”.
The next command does more or less the same thing, besides changing the vibrato waveform to “square”.
The E40 command resets the vibrato waveform to the default “sine wave”.
[This section is a work in progress and it will be completed as soon as possible]
13.3.10.2
Samples
Samples are the basis of a music tracker: they are essentially wave forms which can be sped up or slowed down
to create different notes. Without any sample, you wouldn’t have any instrument, which in turn would mean you’d
have no sound at all.
Usually samples come in the form of small digital sound files, most trackers allow the sample to be looped (wholly
or in part) to simulate a “sustain” effect.
[This section is a work in progress and it will be completed as soon as possible]
13.3.10.3
Instruments
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If multiple threads are involved in using a lazy-loading singleton, you may need to take care of preventing race
conditions[g] that could result in multiple instances of the singleton being created.
Many critics consider the singleton to be an “anti-pattern”, mostly because it is really overused and adds a possibly
unwanted “global state” (see it as a global variable, but in an object-oriented sense) into the application.
Before applying the singleton pattern, ask yourself the following questions:
• Do I really need to ensure that only one instance of this object is present in the whole program?
• Would the presence of more than one instance of this object be detrimental to the functionality of this program?
How?
• Does the instance of this object need to be accessible from everywhere in the program?
T
able 52: Summary table for the Singleton Pattern
Pattern Name
Singleton
When to Use it
In all situations that strictly require one instance of an object, accessible globally.
Advantages
Allows the class to control its own instantiation, allows for easier access to the sole
instance of a class.
Disadvantages
Introduces some restrictions that may be unnecessary, introduces a global state into
the application.
14.1.2
Dependency Injection
Dependency Injection is a very simple concept that is really hard to explain. It is essentially used to avoid having
classes build instances of services (which may be other classes or functions) inside of themselves and instead
receiving such services from outside.
Let’s make a concrete example. You have a class that takes care of everything concerning a file upload: from getting
it from the internet, to logging to saving it to the hard disk.
A first implementation would look something like the following:
Read HTTP
Input Stream
Save to
Local File
Log to
Console
Figure 306: A naive implementation of a local file upload system
What would happen if, instead of a hard disk you need to transfer the files to an external service like S3, or maybe it
just needs to be saved into memory for further processing? You would probably need to duplicate the class to allow
for these new “services”.
Read HTTP
Input Stream
Save to
S3 Bucket
Log to
Console
Figure 307: A naive implementation of a file upload system on S3
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A better solution for reuse would be having the “file saving service” separated from the entire “file upload” class,
and instead having this service “injected” onto the “file upload” class. This can happen via setter functions, via
constructors, builders, factories or even interface injection (where it’s the dependency interface that provides a
method to inject the dependency).
Read HTTP
Input Stream
Save to
S3 Bucket
Log to
Console
Log to
File
Save to
Local File
Saving
Interface
Logging
Interface
Figure 308: Using Interfaces and DI to build a flexible file upload
Since now the “file upload” class doesn’t depend on how or where the file is saved, you can also substitute such
“file saving service” with a mock during tests.
UploadSystem
saveFunction: function;
readStream();
saveFromHttp(stream: HttpStream);
saveFromHttp() uses both readStream()
and calls the saveFunction variable
as a function (it is a function reference)
SaveSystem
save(file:File);
S3SaveSystem
save(file: File);
LocalSaveSystem
save(file: File);
UploadSystemBuilder
build_system(type: str);
if type == "S3" then
create UploadSystem and assign S3SaveSystem
to its saveFunction
else if type == "Local" then
create UploadSystem and assign LocalSaveSystem
to its saveFunction
end if
«uses»
«instantiates»
Figure 309: Possible class structure for a DI file upload
Dependency injection can be divided in two main categories:
• Setter injection: In this case, an object has specific set() methods that allow you to set the dependency after
the object has been constructed. This allows also for changing the dependency on the fly (useful to change
the effect of a weapon, for instance);
• Constructor injection: In this case, the injection happens in the class’s constructor. The injected function-
ality is decided before the object that needs the dependency is constructed.
[This section is a work in progress and it will be completed as soon as possible]
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T
able 53: Summary table for the Dependency Injection Pattern
Pattern Name
Dependency Injection
When to Use it
In all situations that require a degree of configurability or where the behaviour of the
code needs to be changed without direct editing.
Advantages
Decreased coupling, reusability, maintainability, flexibility, less boilerplate code, allows
for concurrent development of services, allows for easier unit testing.
Disadvantages
Behaviour and construction are separated, which may make tracing code harder. May
hinder IDE automation if implemented using reflection or dynamic programming.
14.1.3
Prototype
Sometimes, in our game, we need to decide which objects to create at runtime, as well as instantiate dynamically
loaded classes. In these cases the prototype pattern comes to the rescue: we define a “prototype” that allows to
create classes by cloning itself.
There is the UML diagram for the pattern:
Prototype
clone()
ConcretePrototype
clone()
Client
doStuff()
calls "prototype.clone()"
the clone() method returns
a copy of the class
«import»
Figure 310: Diagram of the Prototype Pattern
T
able 54: Summary table for the Prototype design pattern
Pattern Name
Prototype
When to Use it
When you need to either decide the objects to create at runtime or instantiate
dynamically loaded classes.
Advantages
Decoupling, added flexibility.
Disadvantages
May become overused, depending on the situation can be difficult to implement.
[This section is a work in progress and it will be completed as soon as possible]
14.2
Structural Design Patterns
Structural patterns is a category of design patterns that deals with the relationships between entities, with the
objective of simplifying the realization of such relationships.
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When to Use it
When you need to add or remove functionalities from a class dynamically. Very useful
for applying memoization techniques.
Advantages
Decoupling, added flexibility.
Disadvantages
Usage of interfaces or abstract classes can seem a bit daunting at the beginning, it may
cause an explosion in number of classes.
[This section is a work in progress and it will be completed as soon as possible]
14.2.4
Adapter
Let’s face it, not everything is straight out compatible with everything else.
It happens with power plugs, why
wouldn’t it happen in a world as varied as software development?
Sometimes we need an adapter, and that’s exactly what this design pattern is: provide a layer of compatibility
between two incompatible interfaces.
The adapter design pattern can be implemented in two ways, but first let’s check the summary table.
T
able 58: Summary table for the Adapter design pattern
Pattern Name
Adapter
When to Use it
When you need to provide a layer of compatibility between two incompatible interfaces
or you need to provide an “alternative interface” to a class.
Advantages
Decoupling, added flexibility, better compatibility, code reuse.
Disadvantages
Needing many adapters may mean there is a deeper structural problem with your
program.
14.2.4.1
Object Adapter
The “object adapter” is the version where the adaptor delegates the task to the adaptee at runtime. T
o do so, it has
an instance of the adaptee class as its class field.
Client
adaptor: Target
doStuff()
Target
compatibleMethod()
Adaptor
adaptee: Adaptee
compatibleMethod()
The adapter "wraps"
the adaptee
Adaptee
incompatibleMethod()
Figure 314: Diagram of the Object Adapter Pattern
[This section is a work in progress and it will be completed as soon as possible]
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14.2.4.2
Class Adapter
The “class adapter” version instead inherits the adaptee class at compile-time. Since the adaptor inherits from the
adaptee class, the adaptee’s methods can be called directly, without needing to refer to a class field.
Client
adaptor: Adaptor
doStuff()
Target
compatibleMethod()
Adaptor
compatibleMethod()
The adapter subclasses
the adaptee and realizes
the target interface
Adaptee
incompatibleMethod()
Figure 315: Diagram of the Class Adapter Pattern
[This section is a work in progress and it will be completed as soon as possible]
14.2.5
Facade
There are times where you have a very complex library, with a very complex interface, that is extremely complex to
interact with. The Facade pattern hides such complexity behind a simple-to-use interface that works by delegation.
| Client
Facade
void doComplexThing()
Package1 Package2
Class2 Class1 Class3
void doSecondThing() void doFirstThing() void doLastThing() | |
| -------- | -------- |
| Package1 | Package2 |
| Class2 Class1
void doSecondThing() void doFirstThing() | Class3
void doLastThing() |
Figure 316: Diagram of the Facade Pattern
This pattern should be used with extreme care and only when necessary, since adding “levels of indirection” will
make the code more complex and harder to maintain.
T
able 59: Summary table for the Facade design pattern
Pattern Name
Facade
When to Use it
When you need to present a simple interface for a complex system or you want to
reduce the dependencies on a subsystem.
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of such algorithm.
| Strategy
Client
algorithm()
ConcreteStrategy1 ConcreteStrategy2 ConcreteStrategy3
algorithm() algorithm() algorithm() | |
| -------- | -------- |
| ConcreteStrategy1 | ConcreteStrategy3 |
| algorithm() | algorithm() |
Figure 320: The UML diagram of the strategy pattern
Listing 82: Code for a strategy pattern
1
class Strategy:
2
# This class defines the strategy interface the client will refer to
3
4
def algorithm(self):
5
# This algorithm will be implemented by the subclasses
6
raise
NotImplementedError("You should implement this")
7
8
9
class
ConcreteStrategy1(Strategy):
10
def algorithm ():
11
# Real implementation of the algorithm
12
# DO STUFF
13
pass
14
15
16
class
ConcreteStrategy2(Strategy):
17
def algorithm ():
18
# Real implementation of the algorithm
19
# DO STUFF SLIGHTLY DIFFERENTLY
20
pass
21
22
23 # Example Usage
24
def main():
25
to_execute = None
26
i f
condition:
27
to_execute = ConcreteStrategy1 ()
28
else:
29
to_execute = ConcreteStrategy2 ()
30
to_execute.algorithm ()
# This will execute 1 or 2 depending on "condition"
T
able 63: Summary table for the Strategy Pattern
Pattern Name
Strategy
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self.next = new_handler
19
return self.next;
# Allows for chaining .add_handler ().add_handler ()...
T
able 64: Summary table for the Chain of Responsibility Pattern
Pattern Name
Chain of Responsibility
When to Use it
When you need to implement flexible if…else if…else statements that change on
runtime. When you want to decouple a sender from a receiver.
Advantages
Decoupling, added flexibility.
Disadvantages
Some overhead is added by the objects and late binding, could lead to proliferation of
similar-looking handlers/receivers.
14.3.5
Visitor
[This section is a work in progress and it will be completed as soon as possible]
14.4
Architectural Design Patterns
Architectural patterns are a category of design patterns that provide reusable solutions to recurring problems in
creating software systems and structures. They can address problems like minimizing a defined risk or dealing with
performance limitations, for instance.
14.4.1
Service Locator
The service locator pattern is very useful when you need to manage connections between objects, usually at runtime:
instead of hard-coding each reference of each service, you have a “central hub” that you can ask such connections
to.
This allows you to swap out (or modify) individual parts of your program without affecting the rest of your software,
which can prove useful for testing.
[This section is a work in progress and it will be completed as soon as possible]
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15
Useful Containers and Classes
Eliminate effects between unrelated things. Design components that are
self-contained, independent, and have a single, well-defined purpose.
Anonymous
In this chapter we will introduce some useful data containers and classes that could help you solve some issues or
increase your game’s maintainability and flexibility.
15.1
Resource Manager
A useful container is the “resource manager”, which can be used to store and manage textures, fonts, sounds and
music easily and efficiently.
A resource manager is usually implemented via generic programming, which helps writing DRY code, and uses
search-efficient containers like hash tables, since we can take care of loading and deletion during loading screens.
First of all, we need to know how we want to identify our resource; there are many possibilities:
• An Enum: this is usually implemented at a language-level as an “integer with a name”, it’s light but every
time we add a new resource to our game, we will need to update the enum too;
• The file path: this is an approach used to make things “more transparent”, but every time a resource changes
place, we will need to update the code that refers to such resource too;
• A mnemonic name:
this allows us to use a special string to get a certain resource (for instance
skeleton_spritesheet), and every time our resource folder changes, we will just need to update our load-
ing routines (similarly to the Enum solution).
Secondarily, we need to make sure that the container is thread-safe (see more about multi-threading in the multi-
threading section), since we will probably need to implement a threaded loading screen (see how to do it here) to
avoid our game locking up during resource loading.
[This section is a work in progress and it will be completed as soon as possible]
15.2
Animator
This can be a really useful component to encapsulate everything that concerns animation into a simple and reusable
package.
The animation component will just be updated (like the other components) and it will automatically update the frame
of animation according to an internal timer, usually by updating the coordinates of the rectangle that defines which
piece of a sprite sheet is drawn.
[This section is a work in progress and it will be completed as soon as possible]
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4
# We scroll each column of the board
5
for column
in matrix:
6
for tile
in column:
7
i f
tile
i s
None:
8
new_tile = Tile.random ()
9
new_tile.y = - 64
# A value that is out of the board
10
matrix[column ][tile] = new_tile
11
12
# Add this tile to the falling tiles mapping
13
falling_tiles[new_tile] = tile.y
14
return falling_tiles
After creating the tiles and tweening them in place, it will be necessary to check for more matches that have been
created from the falling tiles (and eventually notify some kind of “combo system” to apply a “score multiplier system”
or even an achievement system using the Observer Pattern).
[This section is a work in progress and it will be completed as soon as possible]
19.7
Cutscenes
When you want to advance your storyline, a great tool is surely the undervalued cutscene. The game temporarily
limits its interactivity and becomes more “movie-like”, making the storyline go forward. Cutscenes can be scripted
or just true video files; in this chapter we will analyze the difference between the two, advantages and disadvantages
of both and how to implement each one, from a high-level perspective.
19.7.1
Videos
The easiest way to implement cutscenes in most engines and frameworks, is to use videos. Many frameworks have
native support for reproducing multimedia files with just a few lines of code, which makes this the preferred choice
when it comes to the code.
The bad thing is that videos are a “static” format.
They have their own resolution, their own compression and
characteristics, this means that when a video is presented at a higher resolution that is own native one, we’re bound
to have artifacts due to upscaling.
[This section is a work in progress and it will be completed as soon as possible]
19.7.2
Scripted Cutscenes
[This section is a work in progress and it will be completed as soon as possible]
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The only thing you can do is think first and try later: this book can give you some suggestions, but nothing should be
taken at face value. Remember the context your game is working in and do not treat all platforms like they’re
the same: WebGL is different than Console which is different than Mobile.
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27.1.6.3
The endings
This game, very ambitiously I shall say, features multiple endings. T
owards the end you have to take a very hard
decision:
• Join your enemy and leave humanity and live peacefully
• Leave the disputed territory and let the enemy live in peace
• Fight to gain control over the disputed territory
This can result in four different endings, which is really ambitious for a NES/Famicom game. If only the final boss
fight was implemented…
If you choose to fight, you will automatically lose the battle and the game will end with a “bad ending”.
27.1.7
Conclusions
“Hoshi wo miru hito” is a product of its situation, rumors state that this game was programmed by only one person,
and rushed beyond belief so it could compete with Dragon Quest in some way. For the sake of fairness, I will assume
that this game was made by a team.
The game has interesting ideas for its time: a cyberpunk theme, Extra-sensory powers, the character sprites “grow
up” as they gain levels, the enemy sprites are artistically well-done, … but the execution is littered with problems,
obstacles to the player, bad design decisions and bugs.
It seems that the developers were not familiar with the NES/Famicom architecture, game designers weren’t really
familiar with game design concepts and play testers were completely nonexistent.
Even though this game has earned the status of “legendary bad game” (not a literal translation of “Densetsu no
Kusoge”), “Hoshi wo miru hito” has gained a cult following that is really devoted, to the point that a hacker took upon
themselves the daunting task of patching the game and redraw the graphics, as well as rebalancing the weapons
and fix the walking speed.
There is even a “remake” called “STARGAZER” for windows.
27.2
The first good game - VVVVVV: Slim story and essential gameplay
VVVVVV is a 2D platformer created by T
erry Cavanagh that features essential gameplay mechanics, a slim story that
gives the player a reason to explore the game world and get to the end, as well as a satisfying level of challenge.
Let’s see what makes this a good game.
27.2.1
A Slim story that holds up great
VVVVVV’s story is as essential as it gets: you’re in a space ship, you run into some trouble and try to teleport out of
the ship. Now you and your crew are scattered in a new dimension. Your mission is to rescue your crew and explore
the new dimension you’re in.
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27.2.5
Amazing soundtrack
The soundtrack in VVVVVV is definitely one of the game’s highlights: the chiptune-style songs that characterize
every zone are catchy and so memorable that you will find yourself humming the tunes from time to time.
Each tune fits the zone it’s used in, and kind of “tells a story” of its own: from “Passion for exploring” (the overworld
theme) to “Predestined Fate” (used in intermissions and, in a remixed fashion, in the finale).
27.2.6
Accessibility Settings
VVVVVV is as accessible as it gets: there are a ton of accessibility features crammed in such a small game. Let’s
take a look at them.
• Invulnerability in case the challenge is too much, or you don’t want to feel challenged all the time. This also
helps people who want to enjoy the game, but can’t due to mobility problems;
• Slowdown mode some people with mobility issues or slower reflexes may benefit from playing the game at
75, 50 or even 25% speed;
• No screen flashing or shaking some people with photosensitivity may have huge issues with the flashing
and screen shaking, there are options to disable these effects and make the game much safer for those people.
It also helps if flashing and screen shaking just annoy you or simply give you headaches;
• No animated backgrounds this may help with visual clarity or if the movement in the background gives
you issues, like headaches.
27.2.7
Post-endgame Modes
After finishing the game, VVVVVV still offers some challenges. If you haven’t collected all the trinkets, that is a good
start, since they’re hard to get and will reveal a secret back at the ship.
VVVVVV offers other game modes too, after you finish the main story:
• Time trials: you can replay any level, but you have to finish it under a certain time limit.
• Flip mode: the whole game is flipped vertically;
• No death mode: the entire game must be played without dying, you cannot save, there are no checkpoints
and your companions in intermissions cannot die either;
• Intermissions mode: replay all completed intermissions, you can choose your companion too.
27.2.8
User-generated content
If the main story didn’t satisfy you enough, VVVVVV features a level editor. The game already includes some selected
user levels you can play, each with its own story and mechanics.
This also means that you can access the level editor yourself and create your own adventure from scratch, featuring
the mechanics and characters of the original game.
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27.2.9
“Speedrunnability”
Being an exceptionally difficult game, as well as the simple controls, the game has attracted an active and passionate
speedrun community. The first playthroughs can take up to a couple hours, but an average speedrun can take less
than 20 minutes!
The barrier of entry (usually for “glitchless” speedruns) is very low: you just need to go fast and die as little as
possible. There aren’t too many tricks to be learned, and those are usually quite simple, with very few exceptions.
27.2.10
Characters are memorable, even if you don’t see them a lot
Even though the characters are not a continuous presence in the game, each of them is memorable: they all have
very different colors, and different characters.
For instance: Vermillion is adventurous and always excited about exploring, after rescuing him, you will find him
here and there in the overworld, sometimes even in the zones where other crew mates are stuck.
Victoria is a bit of a crybaby, very emotional and gets depressed very easily, she’s always feeling blue (and blue is
her color too) and sniffles a lot when talking.
Verdigris is technical, being the ship’s technician (you will find him working on the ship’s antenna after rescue).
Professor Vitellary is analytical and curious (if you bring him into an intermission, he will express marvel at what’s
happening).
27.2.11
Conclusion
VVVVVV is a small game (as I said, it can be completed in less than 20 minutes if you’re quick), but it gives a lot of
options for everyone. Lots of accessibility, replayability and “speedrunnability”. Custom levels and the level editor
are the cherry on top of a game that is feature-complete and fun to play.
27.3
Another good game - Undertale: A masterclass in storytelling
Undertale is an RPG game created by T
oby Fox that features some unique mechanics and masterful story telling.
We’ll take a deeper dive into the game immediately!
27.3.1
The power of choice
The game features a huge innovation in the field of RPGs: you can run the entire game without killing anything. In
fact you are encouraged from the beginning to do so.
This innovation is not forced onto you though, you can play it as any other RPG out there (but you will miss a lot of
the game, more on that later).
27.3.2
The game doesn’t take itself very seriously (sometimes)
Undertale is a very unique game that doesn’t take itself very seriously, there are 4th wall breaks, bad puns, jokes,
worse puns and more. This gives the game a very lighthearted tone. That is if you’re doing a “pacifist run”.
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The game becomes more somber the more you lean into a “neutral” or even “genocide” run.
This gives the game a lot of layers and depth, making each “type of playthrough” a different experience.
27.3.3
All the major characters are very memorable
Each major character is extremely memorable, and will be etched into your memory for the entire game (and prob-
ably part of your life too), I can recall practically all of them on the top of my head:
• T
oriel, a gentle and motherly monster that loves puns and jokes;
• Sans, a skeleton that loves bad puns and “knows shortcuts” to every place in the game, somewhat lazy (that
is explained in a lot more detail in genocide runs);
• Papyrus, Sans’s brother. Hates bad puns, loves spaghetti and wants to enter the royal guard. Has high self-
esteem;
• Undyne, a brave, brash muscle-for-brains fish girl that has actually a very kind heart;
• Alphys, a pessimist doctor with very low self-esteem, even though she’s essentially a genius. Somewhat a
nerd too;
• Mettaton, the robot that wants to become a TV superstar,
• Muffet, the leader of the spider bakery,
• Asgore, the “final boss” that you have to face. Regretful of his actions and past;
• Flowey, a yellow flower that can’t have feelings (this is explained well in the pacifist run).
27.3.4
The game continuously surprises the player
The game is able to surprise the player continuously. At a certain point the player realizes that the game is playing
by different rules than expected: the game (as a piece of software) and the world become blurred when Asgore
breaks the “mercy” option in a pacifist run.
From that point on, the player realizes that the UI, saving, loading are all characteristics of the world itself, and not
of the game: each playthrough is treated like a timeline, and each reset is a new timeline (although some characters
may have memories from previous playthroughs).
It feels like the world inside the game actually exists.
27.3.5
Player choices influence the game
Each run can be a bit different than any previous run, but they can all be classified into 4 categories.
• Neutral runs these are the runs that entail killing some enemies, but not everyone. The ending of this kind
of runs is not satisfactory, and the game loses its meaning. The game will suggest (via its characters) to try
a different approach;
• Pacifist runs these runs entail not killing anyone, this will bring an extended playthrough and ending, ex-
plaining a lot more about the world (and the “meta” nature of the game);
• Genocide runs these runs entail killing everything, even the “random encounters”, this will bring a different
ending and will permanently change the game, even in successive runs (unless you physically delete your
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save file from the game folder).
• Partial/Aborted Genocide these runs entail killing everything, besides one of the main characters. This will
bring the player a different ending each time, but none of them will be “good”.
27.3.6
Great (and extensive!!) soundtrack
The soundtrack features over 100 (a hundred!!) tracks, each of them is unique in itself and memorable. Each zone
has its own fitting theme, as does each boss (so much so that many of them have different themes for normal and
genocide).
It’s hard to describe the soundtrack here, so I suggest you to try the game or at least listen to some of the most
famous tracks.
27.3.7
Conclusion
I tried to keep this analysis vague so not to ruin the game too much to the people who didn’t play it. The pacifist
story is extremely well-written and ties extremely well with the genocide one, together giving two sides of the same
world.
The fact that such world is working with the mechanics of a video game is a surprise to the player, who will be a bit
confused at the beginning but will soon understand things that may have felt weird before.
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• Planting and growing plants
• Personal Growth (getting experience in life)
• Eating, Surviving and Growing to adult
Many times you’ll find a hidden meaning behind a theme that could give you something really unique and eventually
an edge over the other participants in the Game Jam.
29.7
Involve Your Friends!
A Game Jam doesn’t have to be a quest for “lone wolves”, you can involve your friends in the experience, even if
they’re not coders or game developers: talk about your ideas, get new points of view, suggestions and help.
Game Jams can be a really strong bonding experience for friends and colleagues.
29.8
Write a Post-Mortem (and read some too!)
One of the most useful things you can do after a Game Jam, both for yourself and others, is writing a so-called
“Post-Mortem” of your game, where you state your experience with the Game Jam itself, what went right, what went
wrong and what you would do differently in a following event.
A Post-Mortem is a reflection on what happened and how to make yourself and your work better while leaving a
document that allows other people to learn from your mistakes and learn from a “more experienced you”.
Obviously a smart move would be reading a bunch of Post-Mortems yourself, so to learn more about Game Jams and
avoid some common pitfalls of such an experience.
An interesting take on Post-Mortems could be making a time-lapse video of your work, there are applications ready to
use that will take screenshots at regular intervals of your desktop and your webcam (with a nice picture-in-picture) if
enabled. At the end of everything, the program will take care of composing a time-lapse video for you. It’s interesting
to see a weekend go fast forward and say “oh, I remember that”.
29.9
Most common pitfalls in Game Jams
T
o conclude this section, we’ll see some of the most common problems in game jams:
• Bite more than you can chew: Aiming too high and being victims of “feature creep” is a real problem,
the only solution is staying focused and keep everything as simple as possible and be really choosy on the
features to add to the game: take time to refine what you have, instead of adding features;
• Limitations related to tools: If your tools have issues importing a certain asset or you are not able to create
your art for the game then you’re in real trouble. You can’t afford to waste time troubleshooting something
that is not even related to your game. You need to be prepared when the jam starts, test your tools and gather
a toolbox you can rely on, something that will guarantee you stability and productivity.
• Packaging: This is a hard one - sometimes the people who want to try your game won’t be able to play it,
either because of installer issues or missing DDLs. Make sure to package your game with everything needed
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and eventually to link to the possible missing components (like the Visual C++ Redist from Microsoft). The
easier it is for the evaluators to try your game, the better.
• Running out of time or motivation: plan well and be optimistic, you can do it!
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O
Oscillator An oscillator is a device (usually hardware) used to create an alternating current. Oscillators can be used
in audio synthesis to create pitches.
Out of order execution Paradigm used in high performance CPUs to reduce the wasted instruction cycles. The
instructions are performed in an order given by the availability of the input data and execution units instead
than the original order defined by the programmer.
P
Pre-emption See preemptive multitasking
Preemptive multitasking A multitasking environment where the operating system forcibly initiates context
switches (saves the state and interrupts temporarily) between running processes, regardless whether their
job is finished or not.
Process Starvation See starvation
R
Race Condition A condition where two or more threads are competing for a resource (variable, screen buffer, …)
and the order that the threads happen to take hold of such resource changes the result.
REPL Short for “Read-Eval-Print Loop”, sometimes called “language shell”. It’s a simple computer program that
presents a prompt where the user can write code in real time, line by line, and see each piece being executed
immediately.
Rootkit Usually associated with malware, a rootkit is a software that manages to get access to reserved areas of
an operating system, usually to hide its own, or other softwares’ presence.
S
Side Effect In computer science a function is said to have a “side effect” when it changes variables outside its local
environment, this can happen in languages which use call by reference[g] evaluation strategies.
Single Point of Failure This usually defines a part of a system that, if it fails, will stop the entire system from
working. This is often used to indicate objects that have too many responsibilities.
Soft Locking This is usually referred as an anomalous situation where a game is not “frozen” and still working
correctly, but the player is unable to continue playing. An example of soft-locking would be the player getting
trapped inside level geometry, unable to move: the game is not frozen (the level can be restarted), but the
player cannot finish the level.
Stack Overflow A stack overflow is a situation where too much data is pushed into a data structure called a “stack”.
One of the most common cases of “stack overflow” happens during recursion: when a function is called all
the current work variables are saved and pushed into a stack data structure in memory, along with a “return
address” that will allow us to come back to this point of the program. When a recursion is too deep (the
recursive function calls itself too many times), the call stack gets filled up and it’s not able to continue the
execution, leading to an aborted operation.
A
GLOSSARY
585
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1
Some rules that would help us calculating logarithms
. . . . . . . . . . . . . . . . . . . . . . . . . 12
2
Some simple derivation rules (k is any constant number and e is Euler’s number) . . . . . . . . . . . 14
3
Some derivation rules for combined functions (a and b are constants) . . . . . . . . . . . . . . . . . 14
4
Conversion between degrees and Radians
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
5
Some reflection formulas for trigonometry
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
6
Some Shift Formulas for Trigonometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
7
Some addition and difference identities in trigonometry
. . . . . . . . . . . . . . . . . . . . . . . . 32
8
Some double-angle formulae used in trigonometry . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
9
Counting the possible outcomes of two coin tosses . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
10
Comparison between decimal and binary representations
. . . . . . . . . . . . . . . . . . . . . . . 49
11
Comparison between decimal and octal representations . . . . . . . . . . . . . . . . . . . . . . . . 49
12
Comparison between decimal and hexadecimal representations . . . . . . . . . . . . . . . . . . . . 50
23
The first truth table we’ll simplify with Karnaugh Maps
. . . . . . . . . . . . . . . . . . . . . . . . . 79
24
Truth table with a “don’t care” value
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
27
A simple adjacency list for our reference image . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111
28
How to read an adjacency matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111
29
Performance table for Dynamic Arrays
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
30
Summary T
able for Dynamic Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120
31
Performance table for Linked Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
32
Summary T
able for Linked Lists
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122
33
Performance table for Doubly-Linked Lists
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
34
Summary T
able for Linked Lists
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
35
Performance table for Hash T
ables
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124
36
Summary T
able for Hash T
ables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .124
37
Performance table for Binary Search Trees
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
38
Summary T
able for Binary Search Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126
39
Performance table for Heaps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126
40
Summary T
able for Heaps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126
42
Summary of linear gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .284
48
An example of exponential level curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .294
49
An example of “level-based” experience rewards . . . . . . . . . . . . . . . . . . . . . . . . . . . .295
52
Summary table for the Singleton Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .358
53
Summary table for the Dependency Injection Pattern . . . . . . . . . . . . . . . . . . . . . . . . . .360
54
Summary table for the Prototype design pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . .360
55
Summary table for the Flyweight Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .362
56
Summary table for the Component/Composite design pattern
. . . . . . . . . . . . . . . . . . . . .364
57
Summary table for the Decorator design pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . .364
58
Summary table for the Adapter design pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .365
I
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Summary table for the Facade design pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
61
Summary table for the Command Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .370
62
Summary table for the Observer Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372
63
Summary table for the Strategy Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373
64
Summary table for the Chain of Responsibility Pattern
. . . . . . . . . . . . . . . . . . . . . . . . .375
List of Figures
1
Example of a Cartesian plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2
Image of a vector
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3
Graphical representation of a sum of vectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4
Example of a vector multiplied by a value of 3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5
Example of a vector multiplied by a value of 0.5
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
6
Example of a vector multiplied by a value of -2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Example of a convex shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8
Example of a concave shape
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9
Example of a self-intersecting polygon
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10
Projecting the point P onto the line r
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11
Projecting a line onto the axes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
12
Unit Circle definition of sine and cosine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
13
Graphical plotting of the angle of a vector
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
14
Image of a coordinate plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
15
Image of a screen coordinate plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
16
Reference image for transformation matrices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
17
Stretching along the x and y axes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
18
The result of applying a rotation matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
19
Shearing along the x and y axes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
20
Running the probability_20 example shows the probability floating around 20% . . . . . . . . . . . . 44
21
Running the probability_le_13 example shows the probability floating around 13%
. . . . . . . . . . 45
22
Intuitive representation of our prize pool
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
23
How we can pack wall information with a 4-bit integer
. . . . . . . . . . . . . . . . . . . . . . . . . 57
24
Example of a compiler output (G++)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
25
Python’s REPL Shell
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
26
Results of the simple float precision test
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
27
Python 2 has the same issues with precision as C++ . . . . . . . . . . . . . . . . . . . . . . . . . . 67
28
Python 3 doesn’t fare much better when it comes to precision . . . . . . . . . . . . . . . . . . . . . 67
29
Running a random number generator with the same seed will always output the same numbers
. . . 70
30
Using the system time as RNG seed guarantees a degree of randomness
. . . . . . . . . . . . . . . 71
31
O(n) growth rate, compared to O(n²)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
32
When coefficients have important values, asymptotic complexity may trick us . . . . . . . . . . . . . 77
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Big-O Estimates, plotted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
34
How O(2n) overpowers lower complexities
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
35
Karnaugh Map for A XOR B
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
36
Karnaugh Map where the elements of the two “rectangles” have been marked green and red . . . . . 79
37
Karnaugh Map with a “don’t care” value
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
38
Karnaugh Map where we pretend the “don’t care” value is equal to 1
. . . . . . . . . . . . . . . . . 80
39
First Rectangle in the Karnaugh map
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
40
Second Rectangle in the Karnaugh map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
41
A more complex Karnaugh map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
42
First rectangle of the more complex Karnaugh map . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
43
Second rectangle of the more complex Karnaugh map . . . . . . . . . . . . . . . . . . . . . . . . . 82
44
Guided Exercise: Karnaugh Map (1/4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
45
Guided Exercise: Karnaugh Map (2/4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
46
Guided Exercise: Karnaugh Map (3/4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
47
Guided Exercise: Karnaugh Map (4/4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
48
Example of a diamond problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
49
How an object may look using inheritance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
50
How inheritance can get complicated quickly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
51
How components make things a bit simpler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
52
Example of a use case diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
53
Example of an actor hierarchy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
54
Example of a use case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
55
Example of a use case hierarchy
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
56
Example of a use case extension
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
57
Example of a use case inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
58
Example of a sub-use case
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
59
Example of classes in UML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
60
Defining an interface in UML
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
61
Interface Realization in UML . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
62
Relationships between classes in an UML Diagram
. . . . . . . . . . . . . . . . . . . . . . . . . . . 98
63
Example of inheritance in UML class diagrams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
64
Example of interface realization in UML class diagram
. . . . . . . . . . . . . . . . . . . . . . . . . 98
65
Example of association in UML class diagrams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
66
Example of aggregation and composition in UML class diagrams . . . . . . . . . . . . . . . . . . . . 99
67
Example of dependency in UML class diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
68
Example of an activity diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
69
Example of activity diagrams start and end nodes
. . . . . . . . . . . . . . . . . . . . . . . . . . .101
70
Example of Action in activity diagrams
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
71
Example of decision, using hexagons to represent the condition . . . . . . . . . . . . . . . . . . . .102
72
Example of loops, using guards to represent the condition . . . . . . . . . . . . . . . . . . . . . . .102
LIST OF FIGURES
III
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Example of how nested loops and conditions are performed
. . . . . . . . . . . . . . . . . . . . . .103
74
Example of concurrent processes in activity diagrams
. . . . . . . . . . . . . . . . . . . . . . . . .103
75
Example of swimlanes in activity diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
76
Example of signals in activity diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
77
Example of a note inside of an activity diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
78
Example of a sequence diagram lifeline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106
79
Some alternative shapes for participants
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
80
Messages in a sequence diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107
81
Object instantiation and destruction in a sequence diagram
. . . . . . . . . . . . . . . . . . . . . .108
82
A loop grouping in a sequence diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
83
Example of notes in a sequence diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109
84
Graphical representation of a simple graph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110
85
Example of a tree structure
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
86
Order in which the nodes are visited during DFS
. . . . . . . . . . . . . . . . . . . . . . . . . . . .114
87
Example tree that will be traversed by DFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114
88
Order in which the nodes are visited during BFS
. . . . . . . . . . . . . . . . . . . . . . . . . . . .117
89
Dynamic Arrays Reference Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118
90
Adding an element at the beginning of a Dynamic Array
. . . . . . . . . . . . . . . . . . . . . . . .119
91
Adding an element at the end of a Dynamic Array
. . . . . . . . . . . . . . . . . . . . . . . . . . .119
92
Adding an element at an arbitrary position of a Dynamic Array . . . . . . . . . . . . . . . . . . . . .120
93
Linked List Reference Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
94
Double-Ended Linked List Reference Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .121
95
Inserting a new node at the beginning of a linked list . . . . . . . . . . . . . . . . . . . . . . . . . .121
96
Inserting a new node at the end of a (double-ended) linked list . . . . . . . . . . . . . . . . . . . . .122
97
Inserting a new node at an arbitrary position in a (double-ended) linked list . . . . . . . . . . . . . .122
98
Doubly Linked List Reference Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .123
99
Hash T
able Reference Image (Hash T
able with Buckets) . . . . . . . . . . . . . . . . . . . . . . . . .124
100
Binary Search Tree Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125
101
Heap Reference Image (Min-Heap)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .126
102
How a stack works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
103
Array and linked list implementations of a stack
. . . . . . . . . . . . . . . . . . . . . . . . . . . .127
104
How a queue works
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .128
105
Array and linked list implementation of a queue
. . . . . . . . . . . . . . . . . . . . . . . . . . . .128
106
How a circular queue works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .129
107
Array and linked list implementation of a circular queue
. . . . . . . . . . . . . . . . . . . . . . . .129
108
The “easy way” of dealing with frames
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130
109
A sample sprite sheet with the same frames as before . . . . . . . . . . . . . . . . . . . . . . . . .130
110
Singly-Linked List has no redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
111
A doubly linked list is an example of redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
112
In a multi-processing environment, each CPU takes care of a task
. . . . . . . . . . . . . . . . . . .134
LIST OF FIGURES
IV
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In multi-threading, the CPU uses I/O wait time to take care of another task
. . . . . . . . . . . . . .134
114
T
wo threads and a shared variable
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
115
Thread 1 reads the variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .136
116
While Thread 1 is working, Thread 2 reads the variable . . . . . . . . . . . . . . . . . . . . . . . . .137
117
Thread 1 writes the variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
118
Thread 2 writes the variable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .137
119
Both Threads T
erminated
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .138
120
How mutex works (1/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139
121
How mutex works (2/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139
122
How mutex works (3/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .139
123
How mutex works (4/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140
124
How mutex works (5/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140
125
How mutex works (6/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .140
126
How mutex works (7/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
127
How mutex works (8/8)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141
128
How an arcade machine usually looks like
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142
129
A portable console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .143
130
A personal computer
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144
131
How many abstraction layers are used just for a game to be able to play sounds
. . . . . . . . . . .144
132
A smartphone
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .145
133
Fully fledged games can run in your browser nowadays
. . . . . . . . . . . . . . . . . . . . . . . .145
134
How to approach improvements on your game . . . . . . . . . . . . . . . . . . . . . . . . . . . . .163
135
Diagram of the waterfall life cycle model
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
136
Diagram of the incremental life cycle model
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .165
137
High-level diagram of the evolutionary life cycle model . . . . . . . . . . . . . . . . . . . . . . . . .166
138
Diagram of the evolutionary life cycle model
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166
139
Example of a Kanban Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .168
140
An example screen from Git, a version control system
. . . . . . . . . . . . . . . . . . . . . . . . .170
141
UML of the program which we’ll calculate the cyclomatic complexity of
. . . . . . . . . . . . . . . .171
142
Flow diagram of the program we’ll calculate the cyclomatic complexity of . . . . . . . . . . . . . . .172
143
UML Diagram of the input-update-draw abstraction . . . . . . . . . . . . . . . . . . . . . . . . . . .188
144
An example of screen tearing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194
145
A small example of the “painter’s algorithm” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .195
146
How not clearing the screen can create glitches
. . . . . . . . . . . . . . . . . . . . . . . . . . . .196
147
Another type of glitch created by not clearing the screen . . . . . . . . . . . . . . . . . . . . . . . .196
148
Reference image for Point-Circle Collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . .199
149
Reference image for Circle-Circle collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . .202
150
Example used in the AABB collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205
151
T
op-Bottom Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205
152
T
op-Bottom Check is not enough
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205
LIST OF FIGURES
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An example of a left-right check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .206
154
Example of the triangle inequality theorem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208
155
Example of a degenerate triangle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .208
156
Point/Triangle Collision Detection: division into sub-triangles . . . . . . . . . . . . . . . . . . . . . .215
157
Example image for line/line collision
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .219
158
Example of a Jordan Curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222
159
A simple case where a point is outside the polygon . . . . . . . . . . . . . . . . . . . . . . . . . . .223
160
A simple case where a point is inside the polygon
. . . . . . . . . . . . . . . . . . . . . . . . . . .223
161
How a non-convex polygon makes everything harder . . . . . . . . . . . . . . . . . . . . . . . . . .224
162
Decomposing a polygon into triangles
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224
163
Example of a polygon with its bounding box
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225
164
Example image used for circle/polygon collision detection
. . . . . . . . . . . . . . . . . . . . . . .230
165
An edge case of the circle/polygon check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .231
166
Example image used for line/polygon collision detection . . . . . . . . . . . . . . . . . . . . . . . .232
167
Example image used for polygon/polygon collision detection . . . . . . . . . . . . . . . . . . . . . .233
168
How a non-convex polygon still makes everything harder
. . . . . . . . . . . . . . . . . . . . . . .234
169
Counting how many times we hit the perimeter gives us the result . . . . . . . . . . . . . . . . . . .235
170
Issues with vertices make everything even harder
. . . . . . . . . . . . . . . . . . . . . . . . . . .235
171
Triangulating a non-convex polygon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .236
172
T
wo Bitmasks that will be used to explain pixel-perfect collision
. . . . . . . . . . . . . . . . . . . .236
173
T
wo Bitmasks colliding, the ‘AND’ operations returning true are highlighted in white . . . . . . . . . .237
174
Example for collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .239
175
Graphical example of a quad tree, overlaid on the reference image
. . . . . . . . . . . . . . . . . .240
176
A quad tree
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .240
177
Quad trees as spacial acceleration structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .241
178
Redundancy in quad-tree pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .242
179
How an AABB-tree would process our example image
. . . . . . . . . . . . . . . . . . . . . . . . .243
180
How a possible AABB-tree structure would look like . . . . . . . . . . . . . . . . . . . . . . . . . . .243
181
Example of a search in an AABB-Tree
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .244
182
Querying an AABB-tree (1/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .244
183
Querying an AABB-tree (2/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245
184
Querying an AABB-tree (3/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .245
185
Example tile-based level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246
186
Tile-based example: falling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .246
187
Example tile-based level with a bigger object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .249
188
Tile-based example with a bigger object: falling
. . . . . . . . . . . . . . . . . . . . . . . . . . . .249
189
Example of a hitbox (red) and a hurtbox (blue) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .251
190
Images used as a reference for collision reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . .251
191
How the naive method reacts to collisions against a wall . . . . . . . . . . . . . . . . . . . . . . . .252
192
How the naive method reacts to collisions against the ground
. . . . . . . . . . . . . . . . . . . . .253
LIST OF FIGURES
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Example of shallow-axis based reaction on a horizontal plane
. . . . . . . . . . . . . . . . . . . . .253
194
Example of shallow-axis based reaction on a vertical plane . . . . . . . . . . . . . . . . . . . . . . .254
195
How the the interleaving method reacts to collisions on a horizontal plane . . . . . . . . . . . . . . .255
196
Example of the “Bullet through paper” problem
. . . . . . . . . . . . . . . . . . . . . . . . . . . .259
197
How velocity changing direction can teleport you . . . . . . . . . . . . . . . . . . . . . . . . . . . .260
198
Example of how you can draw a line between two convex non-colliding polygons
. . . . . . . . . . .260
199
Why the SAT doesn’t work with concave polygons
. . . . . . . . . . . . . . . . . . . . . . . . . . .261
200
How the SAT algorithm works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262
201
Finding the axes for the SAT (1/2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263
202
Finding the axes for the SAT (2/2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263
203
Projecting the polygons onto the axes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .264
204
Projecting our projections onto the x and y axes
. . . . . . . . . . . . . . . . . . . . . . . . . . . .265
205
How Ray Casting Works: Gun (1/2)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266
206
How Ray Casting Works: Gun (2/2)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266
207
How a scene tree looks (specifically in Godot)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .267
208
Example of a ship attack formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .268
209
What happens when the ship attack formation rotates
. . . . . . . . . . . . . . . . . . . . . . . . .268
210
Reference Image for Screen Space and Game Space . . . . . . . . . . . . . . . . . . . . . . . . . .269
211
How a person sees things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .270
212
How videogame cameras see things
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .271
213
Example of an horizontally-tracking camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272
214
Example of a full-tracking camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .272
215
Example of camera trap-based system
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273
216
Example of look-ahead camera
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .273
217
How the camera may end up showing off-map areas . . . . . . . . . . . . . . . . . . . . . . . . . .274
218
Example of how to induce lateral thinking with environmental damage
. . . . . . . . . . . . . . . .278
219
Example of how to induce lateral thinking by “breaking the fourth wall” . . . . . . . . . . . . . . . .278
220
Example of secret-in-secret
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .279
221
Example Scheme of linear gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .284
222
Example Scheme of branching gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .284
223
Example Scheme of parallel gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285
224
Example Scheme of threaded gameplay
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285
225
Example Scheme of episodic gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .286
226
Example Scheme of looping gameplay with a overarching story
. . . . . . . . . . . . . . . . . . . .287
227
Example of a telegraphed screen-filling attack in a shooter . . . . . . . . . . . . . . . . . . . . . . .291
228
A pixel perfect detection would trigger in this case . . . . . . . . . . . . . . . . . . . . . . . . . . .296
229
A smaller hitbox may save the player some frustration . . . . . . . . . . . . . . . . . . . . . . . . .297
230
A bomb spawned behind a chest, drawn in a realistic order . . . . . . . . . . . . . . . . . . . . . . .297
231
Moving the bomb in front of the chest may ruin immersion . . . . . . . . . . . . . . . . . . . . . . .298
232
Highlighting the hidden part of a danger can be useful . . . . . . . . . . . . . . . . . . . . . . . . .298
LIST OF FIGURES
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Making objects transparent is a solution too
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .298
234
The “color wheel” for screens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302
235
An example of an RGB picker
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .303
236
A simplified “slice” of an HSV representation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .304
237
More slices of the HSV representation show how value changes
. . . . . . . . . . . . . . . . . . . .304
238
The color star shows how complementary colors are on opposite sides
. . . . . . . . . . . . . . . .306
239
Reference image that we will for bit depth comparison . . . . . . . . . . . . . . . . . . . . . . . . .307
240
Reference image, quickly converted to 1-bit color depth
. . . . . . . . . . . . . . . . . . . . . . . .307
241
Reference image, converted to 2-bit color depth in CGA style
. . . . . . . . . . . . . . . . . . . . .307
242
Reference image, converted to a 4-bit color depth in EGA style
. . . . . . . . . . . . . . . . . . . .308
243
Reference image, converted to an 8-bit color depth
. . . . . . . . . . . . . . . . . . . . . . . . . .308
244
Indexed transparency takes a color and “marks it” as transparent . . . . . . . . . . . . . . . . . . .310
245
Example sprite that gets padded to match hardware constraints . . . . . . . . . . . . . . . . . . . .312
246
Example spritesheet that gets padded to match hardware constraints . . . . . . . . . . . . . . . . .313
247
T
wo platforms in a spritesheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .313
248
T
wo platforms in a spritesheet after heavy compression
. . . . . . . . . . . . . . . . . . . . . . . .314
249
Windowed Game Example - A 640x480 game in a 1920x1080 Window . . . . . . . . . . . . . . . . .314
250
Fullscreen Game Example - Recalculating items positions according to the window size . . . . . . . .315
251
Fullscreen Game Example - Virtual Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315
252
Dithering example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .316
253
Dithering T
able Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .316
254
Some more dithering examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317
255
Which spaceship is easier to spot at a glance?
. . . . . . . . . . . . . . . . . . . . . . . . . . . . .319
256
How contrast and detail can help distinguishing foreground and background
. . . . . . . . . . . . .320
257
Breaking down the image allows us to see the differences between the layers
. . . . . . . . . . . .320
258
A diagram to show how each section affects our perception of a layer . . . . . . . . . . . . . . . . .321
259
A texture (on the left), with a possible normal map (on the right) . . . . . . . . . . . . . . . . . . . .323
260
Aseprite’s normal mapping color picker (both in its normal and discrete versions) . . . . . . . . . . .323
261
A box that will be used to show how normal maps influence light . . . . . . . . . . . . . . . . . . . .324
262
How the lack of normal mapping makes lighting look artificial
. . . . . . . . . . . . . . . . . . . . .324
263
How normal mapping changes lighting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .324
264
A more detailed normal map results in better lighting
. . . . . . . . . . . . . . . . . . . . . . . . .324
265
Example of tile “alternatives” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .325
266
Tile “Rotation Trick” (1/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .325
267
Tile “Rotation Trick” (2/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .326
268
Tile “Rotation Trick” (3/3)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .326
269
Example of black and transparent tileset used in “inside rooms” . . . . . . . . . . . . . . . . . . . .327
270
Example of incomplete “inside room” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .327
271
Example of “inside room” with the black/transparent overlay
. . . . . . . . . . . . . . . . . . . . .327
272
How color can completely change an object
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328
LIST OF FIGURES
VIII
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Graphical Representation of Sample Rate (44.1KHz)
. . . . . . . . . . . . . . . . . . . . . . . . . .329
274
Graphical Representation of Sample Rate (8KHz) . . . . . . . . . . . . . . . . . . . . . . . . . . . .329
275
Example of audio clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .331
276
Example of AM Synthesis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .332
277
Example of FM Synthesis
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .332
278
How a sine wave looks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334
279
How a square wave looks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334
280
How a triangle wave looks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334
281
How a sawtooth wave looks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335
282
How a noise wave looks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335
283
Representation of an ADSR Envelope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335
284
Attack on ADSR Envelope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .336
285
Decay on ADSR Envelope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .336
286
Sustain on ADSR Envelope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .337
287
Release on ADSR Envelope
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .337
288
A freeze frame of a C64 song, you can see the instruments changing
. . . . . . . . . . . . . . . . .340
289
Example of a piano roll in LMMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344
290
Example of a piano roll in FamiStudio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344
291
A screen from MilkyTracker
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .345
292
Simple overview of a tracker
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .345
293
How each tracker channel is divided
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .346
294
A single bar in our basic rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .347
295
A basic four on the floor rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .347
296
Four on the floor with off-beat hi-hats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .348
297
A simple rock beat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .348
298
Example of a serif font (DejaVu Serif) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
299
Example of a sans-serif font (DejaVu Sans)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
300
Example of a proportional font (DejaVu Serif) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
301
Example of a monospaced font (Inconsolata) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349
302
A simple spritesheet for rendering text using textures
. . . . . . . . . . . . . . . . . . . . . . . . .350
303
Indexing our spritesheet for rendering
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .350
304
Godot’s “Visual Shader” Editor
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .353
305
The UML diagram for a singleton pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .357
306
A naive implementation of a local file upload system . . . . . . . . . . . . . . . . . . . . . . . . . .358
307
A naive implementation of a file upload system on S3
. . . . . . . . . . . . . . . . . . . . . . . . .358
308
Using Interfaces and DI to build a flexible file upload . . . . . . . . . . . . . . . . . . . . . . . . . .359
309
Possible class structure for a DI file upload
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .359
310
Diagram of the Prototype Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .360
311
UML Diagram of the Flyweight pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .361
312
Diagram of the Component Design Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .362
LIST OF FIGURES
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Diagram of the Decorator Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .364
314
Diagram of the Object Adapter Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .365
315
Diagram of the Class Adapter Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
316
Diagram of the Facade Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366
317
Diagram of the Proxy Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368
318
UML diagram for the Command Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .370
319
The UML diagram of the observer pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .371
320
The UML diagram of the strategy pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .373
321
UML Diagram of the Chain of Responsibility Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . .374
322
Diagram of a character’s state machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377
323
Diagram of a menu system’s state machine
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .377
324
Example of a simple menu stack
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .380
325
Some examples of particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .380
326
Map we will create a navigation mesh on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .395
327
Dividing the map into many convex polygons and labelling them
. . . . . . . . . . . . . . . . . . .396
328
Creating the graph
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .396
329
The final data structure
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .397
330
Example of Manhattan distance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .397
331
Example of Euclidean Distance
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .398
332
Pathfinding Algorithms Reference Image
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .399
333
Pathfinding Algorithms Heuristics Reference Image . . . . . . . . . . . . . . . . . . . . . . . . . . .399
334
Simple wandering algorithm 1/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .400
335
Simple wandering algorithm 2/2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .400
336
This maze breaks our wandering algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .401
337
The path taken by the greedy “Best First” algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . .406
338
The path taken by the Dijkstra Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .407
339
Finite state machine representing an enemy AI . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409
340
Example of a decision tree
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .409
341
Example of a behaviour tree . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .410
342
How the Midpoint Displacement Algorithm Works (1/4) . . . . . . . . . . . . . . . . . . . . . . . . .414
343
How the Midpoint Displacement Algorithm Works (2/4) . . . . . . . . . . . . . . . . . . . . . . . . .414
344
How the Midpoint Displacement Algorithm Works (3/4) . . . . . . . . . . . . . . . . . . . . . . . . .415
345
How the Midpoint Displacement Algorithm Works (4/4) . . . . . . . . . . . . . . . . . . . . . . . . .415
346
How the diamond-square algorithm works (1/5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .417
347
How the diamond-square algorithm works (2/5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .417
348
How the diamond-square algorithm works (3/5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .418
349
How the diamond-square algorithm works (4/5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .418
350
How the diamond-square algorithm works (5/5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .419
351
How the recursive backtracker algorithm works (1) . . . . . . . . . . . . . . . . . . . . . . . . . . .420
352
How the recursive backtracker algorithm works (2) . . . . . . . . . . . . . . . . . . . . . . . . . . .420
LIST OF FIGURES
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How the recursive backtracker algorithm works (3) . . . . . . . . . . . . . . . . . . . . . . . . . . .420
354
How the recursive backtracker algorithm works (4) . . . . . . . . . . . . . . . . . . . . . . . . . . .421
355
How the Randomized Kruskal’s Algorithm Works (1/6)
. . . . . . . . . . . . . . . . . . . . . . . . .425
356
How the Randomized Kruskal’s Algorithm Works (2/6)
. . . . . . . . . . . . . . . . . . . . . . . . .425
357
How the Randomized Kruskal’s Algorithm Works (3/6)
. . . . . . . . . . . . . . . . . . . . . . . . .426
358
How the Randomized Kruskal’s Algorithm Works (4/6)
. . . . . . . . . . . . . . . . . . . . . . . . .426
359
How the Randomized Kruskal’s Algorithm Works (5/6)
. . . . . . . . . . . . . . . . . . . . . . . . .426
360
How the Randomized Kruskal’s Algorithm Works (6/6)
. . . . . . . . . . . . . . . . . . . . . . . . .427
361
How the Recursive Division Algorithm Works (1/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .427
362
How the Recursive Division Algorithm Works (2/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .428
363
How the Recursive Division Algorithm Works (3/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .428
364
How the Recursive Division Algorithm Works (4/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .428
365
How the Recursive Division Algorithm Works (5/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .429
366
How the Recursive Division Algorithm Works (6/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .429
367
The bias of Recursive Division Algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .430
368
How the Binary Tree Maze generation works (1/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .430
369
How the Binary Tree Maze generation works (2/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .431
370
How the Binary Tree Maze generation works (3/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .431
371
How the Binary Tree Maze generation works (4/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .431
372
How the Binary Tree Maze generation works (5/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .432
373
How the Binary Tree Maze generation works (6/6)
. . . . . . . . . . . . . . . . . . . . . . . . . . .432
374
How Eller’s Maze Generation Algorithm Works (1/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .432
375
How Eller’s Maze Generation Algorithm Works (2/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
376
How Eller’s Maze Generation Algorithm Works (3/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
377
How Eller’s Maze Generation Algorithm Works (4/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
378
How Eller’s Maze Generation Algorithm Works (5/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
379
How Eller’s Maze Generation Algorithm Works (6/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
380
How Eller’s Maze Generation Algorithm Works (7/7)
. . . . . . . . . . . . . . . . . . . . . . . . . .433
381
Example of Random Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .434
382
Example of a tileset and a tilemap drawn with it
. . . . . . . . . . . . . . . . . . . . . . . . . . . .443
383
Simple structure of a hexmap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
384
The outer circle or an hexagon
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .444
385
The size of an hexagon, calculated
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .445
386
Making a hexmap
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .446
387
A simple isometric tiles and a tilemap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .446
388
Demonstration of an image with loop points
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .447
389
How we can split our game into layers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .449
390
Rough UML diagram of a multi-threaded loading screen
. . . . . . . . . . . . . . . . . . . . . . . .452
391
Example chart of how movement without inertia looks . . . . . . . . . . . . . . . . . . . . . . . . .453
392
Example chart of how movement without inertia looks: reversing directions . . . . . . . . . . . . . .453
LIST OF FIGURES
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Example chart of how movement with inertia looks . . . . . . . . . . . . . . . . . . . . . . . . . . .454
394
Example of character running . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .454
395
Applying an acceleration to a character running
. . . . . . . . . . . . . . . . . . . . . . . . . . . .455
396
Applying an acceleration frame by frame leads to the feeling of inertia
. . . . . . . . . . . . . . . .455
397
What would be a good collision response for this situation? . . . . . . . . . . . . . . . . . . . . . . .457
398
Corner correction makes for a more fluid experience . . . . . . . . . . . . . . . . . . . . . . . . . .457
399
Plotting a physics-accurate jump
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .459
400
Plotting a jump with enhanced gravity
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .460
401
Plotting a jump with multiple gravity changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .461
402
Example of how jump buffering would work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .462
403
Example of how coyote time would work
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .463
404
Example of how timed jumps would work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .464
405
A simple example of fake height in RPG
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .465
406
How few collisions may “sell” the effect of height
. . . . . . . . . . . . . . . . . . . . . . . . . . .466
407
A more complex example of fake height
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .466
408
Even with complex tilemaps, the texture sells the height effect
. . . . . . . . . . . . . . . . . . . .466
409
Reference image for video lag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .467
410
Reference image for audio lag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .468
411
Plotting amplitude against time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .469
412
Plotting frequency domain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .469
413
Example of how to better “highlight” bullets
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .470
414
An example of a Bullet Hell ship hitbox
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .471
415
Example of a matrix, saved as “array of arrays”
. . . . . . . . . . . . . . . . . . . . . . . . . . . .474
416
What happens when deleting a match immediately . . . . . . . . . . . . . . . . . . . . . . . . . . .477
417
A Flat line difficulty curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .482
418
A linearly increasing difficulty curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .483
419
As the player learns to predict, the difficulty curve changes from our design . . . . . . . . . . . . . .483
420
A Logarithmic difficulty curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .484
421
An exponential difficulty curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .484
422
A linearly increasing wavy difficulty curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .485
423
A Logarithmically increasing wavy difficulty curve
. . . . . . . . . . . . . . . . . . . . . . . . . . .486
424
A simple wavy difficulty interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .487
425
A widening and wavy difficulty interval
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .487
426
A widening wavy difficulty interval with a logarithmic trend
. . . . . . . . . . . . . . . . . . . . . .488
427
A sawtooth difficulty curve
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .489
428
Difficulty spikes are not good
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .489
429
A simplified vision of supply and demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .491
430
Example of a P2P connection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .495
431
T
wo cheaters meet in P2P . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .495
432
What would happen if one of the Peers had the authoritative game state
. . . . . . . . . . . . . . .496
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Example of a dedicated server
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .496
434
T
wo cheaters vs. Dedicated server
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .497
435
How the effort put in automated testing can give good returns . . . . . . . . . . . . . . . . . . . . .507
436
Using Valgrind’s Callgrind tool and Kcachegrind we can see what is bogging down our game . . . . .511
437
Not putting off-screen objects in the drawing queue can be a good optimization . . . . . . . . . . . .513
438
An example screen from LLVM’s scan-build
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .515
439
A screenshot from Valgrind, looks like we have a memory leak here
. . . . . . . . . . . . . . . . . .515
440
A screenshot from Godot’s profiler
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .515
441
A resource pool instantiates objects and “keeps them” ready when needed
. . . . . . . . . . . . . .516
442
Pulling an object from a resource pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .516
443
Returning an object from a resource pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .517
444
How a lookup table works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .517
445
How a simple memoization pattern works . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .518
446
How a more complex memoization pattern works . . . . . . . . . . . . . . . . . . . . . . . . . . . .519
447
Time taken by the IF code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .527
448
Time taken by the Switch code
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .527
449
How first impressions leave a mark, even when it comes to price
. . . . . . . . . . . . . . . . . . .532
450
What a simple “speedrun mode” may look like . . . . . . . . . . . . . . . . . . . . . . . . . . . . .545
451
What a mode advanced “speedrun mode” may look like
. . . . . . . . . . . . . . . . . . . . . . . .546
452
Example picture of Tic-T
ac-T
oe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .567
453
Example of a “Space Invaders”-style game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .569
454
Example picture of a breakout-style game
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .571
455
Biased Bouncing for breakout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .573
456
Possible Shooter Arena Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .573
List of Code Listings
1
Example code listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3
2
1 (out of 5) will be extracted with about 20% probability
. . . . . . . . . . . . . . . . . . . . . . . . . 43
3
A number less or equal than 13 (out of 100) has 13% probability of appearing . . . . . . . . . . . . . . 45
4
How to implement a tiered prize pool selector
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
5
A possible implementation of a luck stat
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6
Counting from n to 0 using a loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
7
Counting from n to 0 using recursion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
8
Counting from 0 to n using head recursion
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
9
A simple float precision test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
10
A simple random number generation program
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
11
A random number generation program that uses system time as seed . . . . . . . . . . . . . . . . . . 70
12
Example of an O(1) algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
13
Example of an O(log(n)) algorithm (Binary Search)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
LIST OF CODE LISTINGS
XIII
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Context: 2D Game Development: From Zero T
o Hero
14
Example of an O(n) algorithm (printing of a list)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
15
Example of an O(n²) algorithm (bubble sort)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
16
A simple O(1) algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
17
A simple o(n) algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
18
The bubble sort algorithm, an O(n²) algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
19
A more complex algorithm to estimate
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
20
An example of inheritance: Shapes
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
21
An example of inheritance: A coffee machine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
22
Example of an entity declared as YAML data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
23
Example of an entity declared as JSON data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
24
A possible implementation of a tree class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
25
Pre-order traversal of a tree using DFS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
26
In-order traversal of a tree using DFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
27
Post-order traversal of a tree using DFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
28
Traversal of a tree using BFS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
29
Counting the elements in a list
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
30
Counting the elements in a list with data redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
31
Finding the previous element in a singly linked list
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
32
Game Loop example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
33
Game loop with fixed timesteps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
34
Game loop with variable time steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
35
Game loop with Semi-Fixed time steps
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
36
Game loop with Frame Limiting
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
37
Point to point collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
38
Shortened version of a point to point collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . 198
39
Point to point collision detection with epsilon values
. . . . . . . . . . . . . . . . . . . . . . . . . . . 199
40
Point to circle collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
41
Shorter version of a point to circle collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
42
Circle to Circle Collision Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
43
Shorter Version of a Circle to Circle Collision Detection . . . . . . . . . . . . . . . . . . . . . . . . . . 203
44
Axis-Aligned Bounding Box Collision Detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
45
Line to Point Collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
46
Partial Implementation of a Line to Circle Collision Detection . . . . . . . . . . . . . . . . . . . . . . . 210
47
Line to circle collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
48
Point/Rectangle collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
49
Point/Triangle Collision Detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
50
Point/Triangle Collision Detection with epsilon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
51
Rectangle to Circle Collision Detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
52
Implementation of the line/line collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
53
Implementation of the line/rectangle collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . 221
LIST OF CODE LISTINGS
XIV
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Context: 2D Game Development: From Zero T
o Hero
54
How to find the bounding box of a polygon
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
55
A (not so) simple polygon class
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
56
Polygon vs Point collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
57
Polygon vs Circle collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
58
Polygon vs Line collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
59
Polygon vs Polygon collision detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
60
Example of a possibile implementation of pixel perfect collision detection . . . . . . . . . . . . . . . . 237
61
Brute Force Method of collision search
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
62
Converting player coordinates into tile coordinates . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
63
Tile-based collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
64
Tile + Offset collision detection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250
65
Code for the naive collision reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
66
Possible implementation for a shallow axis collision reaction . . . . . . . . . . . . . . . . . . . . . . . 254
67
Code for interleaving movement and collision reaction . . . . . . . . . . . . . . . . . . . . . . . . . . 255
68
Example of the ”snapshot” collision reaction method . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
69
Code for the collision reaction between moving objects . . . . . . . . . . . . . . . . . . . . . . . . . . 257
70
How FM music may be saved on an old console . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
71
Example of swappable sound effects
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
72
A simple algorithm to create a text using a texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
73
Simple GLSL Fragment shader . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
74
Example of a singleton pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
75
Example of a singleton pattern with lazy loading
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
76
Code for a flyweight pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
77
Example Implementation Of the Component Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . 363
78
Example Implementation Of the Facade Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
79
Example Implementation Of the Proxy Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
80
Example code for the Command Pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 370
81
Code for an observer pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
82
Code for a strategy pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
83
Code for a chain of responsibility pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
84
A simple finite state machine
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
85
An example of usage of a FSM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
86
A simple particle class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
87
A more complex particle class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 381
88
A simple particle emitter class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383
89
A more complex (and complete) particle emitter class
. . . . . . . . . . . . . . . . . . . . . . . . . . 384
90
A particle with mass and force application
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
91
A simple timer class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
92
A naive approach to account for leftover time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
93
A possible solution to account for leftover time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
LIST OF CODE LISTINGS
XV
####################
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Context: 2D Game Development: From Zero T
o Hero
94
Another possible solution to account for leftover time
. . . . . . . . . . . . . . . . . . . . . . . . . . 389
95
Linear T
weening . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
96
Example of a simple easing function
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
97
Ease-in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
98
Ease-out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
99
Ease-in-out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
100 Clamping values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
101 A bouncy tween function
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
102 Possible representation of a 2D grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
103 Example code calculating the Manhattan distance on a 2D grid
. . . . . . . . . . . . . . . . . . . . . 398
104 Example code calculating the Euclidean distance on a 2D grid . . . . . . . . . . . . . . . . . . . . . . 398
105 Implementation of a simple wandering algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
106 Implementation of a better wandering algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
107 The node structure used in the greedy ”Best First” algorithm . . . . . . . . . . . . . . . . . . . . . . . 404
108 The greedy ”Best First” algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
109 The node structure used in the Dijkstra Algorithm
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
110 The Dijkstra Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406
111 The A* Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
112 Example code for ”jump when player shoots” AI pattern
. . . . . . . . . . . . . . . . . . . . . . . . . 411
113 Example code for a ”ranged” AI pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
114 Example code for a ”melee” AI pattern
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 413
115 Example implementation of the midpoint displacement algorithm
. . . . . . . . . . . . . . . . . . . . 415
116 Example implementation of recursive backtracker maze generation . . . . . . . . . . . . . . . . . . . 421
117 Example implementation of recursive backtracker with an explicit stack . . . . . . . . . . . . . . . . . 423
118 Example implementation of randomized noise
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
119 Example procedural weapon creation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
120 Example Randomized weapon creation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
121 Example of I-Frames Implementation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
122 Example of an infinitely scrolling background implementation
. . . . . . . . . . . . . . . . . . . . . . 447
123 Example of parallax scrolling implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
124 Code for simulating inertia
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
125 Possible implementation of a simple corner correction
. . . . . . . . . . . . . . . . . . . . . . . . . . 458
126 Code for applying gravity to an object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
127 Code for jump with enhanced gravity while falling
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
128 Code for jump with more gravity while falling and less when peaking
. . . . . . . . . . . . . . . . . . 461
129 Code for jumping without buffering
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
130 Jump buffering example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
131 Coyote time code example
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
132 Example code of how timed jumps work
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
133 Finding horizontal matches in a match-3 game
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
LIST OF CODE LISTINGS
XVI
####################
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Page: 652
Context: 134 Finding vertical matches in a match-3 game
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
135 Eliminating matches and preparing the tween table
. . . . . . . . . . . . . . . . . . . . . . . . . . . 477
136 Creating new tiles and preparing another tween table
. . . . . . . . . . . . . . . . . . . . . . . . . . 478
137 Double Engine Movement Call . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 513
138 Single Engine Movement Call
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 514
139 An example of memoization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
140 An eager object
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
141 A lazy object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 521
142 Example on how to optimize entities with a dirty bit
. . . . . . . . . . . . . . . . . . . . . . . . . . . 524
143 IFs vs Switch - IF Statements
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
144 IFs vs Switch - Switch Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 526
##########
"""QUERY: Please summarize the whole context. It is important that you include a summary for each file. All files should be included, so please make sure to go through the entire context"""
Consider the chat history for relevant information. If query is already asked in the history double check the correctness of your answer and maybe correct your previous mistake. If you find information separated by a | in the context, it is a table formatted in Markdown - the whole context is formatted as md structure.
Final Files Sources: 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 2, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 7, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 8, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 9, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 10, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 11, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 12, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - Page 13, 2D%20Game%20Development%20From%20Zero%20To%20Hero%20-%20Daniele%20Penazzo%20HTML%2C%20PDF%2C%20EBPUB%2C.pdf - 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