The Game Maker’s
Apprentice
Game Development for Beginners

Jacob Habgood
Mark Overmars

The Game Maker’s Apprentice: Game Development for Beginners
Copyright © 2006 by Jacob Habgood and Mark Overmars
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Maker. However, redistribution of the original games or their resources is prohibited and the authors
retain full copyright of all the original game concepts and the intellectual property associated with them.
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To halcyon days
with a frog,
a parrot,
and a talented bunch of gremlins.

Contents at a Glance
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv
About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
About the Illustrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx

PART 1

■■■

■CHAPTER 1
■CHAPTER 2

PART 2

PART 3

Action Games

More Actions: A Galaxy of Possibilities . . . . . . . . . . . . . . . . . . . . . . . . . 41
Target the Player: It’s Fun Being Squished . . . . . . . . . . . . . . . . . . . . . 65
Game Design: Interactive Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . 85

■■■

■CHAPTER 6
■CHAPTER 7
■CHAPTER 8

iv

Welcome to Game Maker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Your First Game: Devilishly Easy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

■■■

■CHAPTER 3
■CHAPTER 4
■CHAPTER 5

Getting Started

Level Design

Inheriting Events: Mother of Pearl . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
Maze Games: More Cute Things in Peril . . . . . . . . . . . . . . . . . . . . . . . 127
Game Design: Levels and Features . . . . . . . . . . . . . . . . . . . . . . . . . . . 149

PART 4

■■■

Multiplayer Games

■CHAPTER 9 Cooperative Games: Flying Planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
■CHAPTER 10 Competitive Games: Playing Fair with Tanks . . . . . . . . . . . . . . . . . . 191
■CHAPTER 11 Game Design: Balance in Multiplayer Games . . . . . . . . . . . . . . . . . . 211

PART 5
■CHAPTER
■CHAPTER
■CHAPTER
■CHAPTER

■■■
12
13
14
15

Enemies and Intelligence

GML: Become a Programmer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Clever Computers: Playing Tic-Tac-Toe . . . . . . . . . . . . . . . . . . . . . . . . 245
Intelligent Behavior: Animating the Dead . . . . . . . . . . . . . . . . . . . . . . 259
Final Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291

■BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
■INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

v

Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv
About the Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvi
About the Technical Reviewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii
About the Illustrator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx

PART 1

■■■

■CHAPTER 1

Getting Started

Welcome to Game Maker

...................................3

Installing the Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Registration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
The Global User Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Running a Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
How to Get More Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
What’s Next? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

■CHAPTER 2

Your First Game: Devilishly Easy

...........................9

Designing the Game: Evil Clutches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Sprites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
The Boss Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Events and Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
The Dragon Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Rooms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Save and Run . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Instances and Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Demons, Baby Dragons, and Fireballs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
The Fireball Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
The Demon Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Summoning Demons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
The Baby Dragon Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

vii

viii

■CONTENTS

Backgrounds and Sounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
A Background Image . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
Background Music . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Sound Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

PART 2

■■■

■CHAPTER 3

Action Games

More Actions: A Galaxy of Possibilities

. . . . . . . . . . . . . . . . . . . 41

Designing the Game: Galactic Mail . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
Sprites and Sounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
Moons and Asteroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Flying Around . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Winning and Losing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
An Explosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Scores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
Finishing Touches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
A Title Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
Winning the Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Adding Some Visual Variety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Help Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

■CHAPTER 4

Target the Player: It’s Fun Being Squished

. . . . . . . . . . . . . . . 65

Designing the Game: Lazarus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
An Animated Character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
A Test Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Falling Boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Finishing Touches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
No Way Out! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
Adding a Goal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Starting a Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
Sounds, Backgrounds, and Help . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

■CONTENTS

■CHAPTER 5

Game Design: Interactive Challenges

. . . . . . . . . . . . . . . . . . . . . 85

What Makes a Good Game? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
Game Mechanics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
Interactive Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Game Genres . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Difficulty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Rewards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Subgoals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Interactivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Choices and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Control Overload! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Unfair Punishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
Audio Feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

PART 3

■■■

■CHAPTER 6

Level Design

Inheriting Events: Mother of Pearl

. . . . . . . . . . . . . . . . . . . . . . . 101

Designing the Game: Super Rainbow Reef . . . . . . . . . . . . . . . . . . . . . . . . 101
A Game Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
The Front-End . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
The Completion Screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
Bouncing Starfish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
Biglegs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
Parent Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
Lives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Normal Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Solid Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Special Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Polishing the Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Sound Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Saving Games and Quitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
A Slower Start . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Creating the Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126

ix

x

■CONTENTS

■CHAPTER 7

Maze Games: More Cute Things in Peril

. . . . . . . . . . . . . . . . . 127

Designing the Game: Koalabr8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
The Basic Maze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128
The Game Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
A Moving Character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Save the Koala . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Creating Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
Tiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
Adding Additional Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
Locks and Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
A Detonator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Finishing the Game . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148

■CHAPTER 8

Game Design: Levels and Features

. . . . . . . . . . . . . . . . . . . . . . 149

Selecting Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Pie in the Sky . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
Do You Have That in Blue? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
Starting an Arms Race . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
One-Trick Ponies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
Emerging with More Than You Expected . . . . . . . . . . . . . . . . . . . . . 153
Designing Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
The Game Maker’s Apprentice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
Learning Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
Difficulty Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
Saving the Day . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Applying It All . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160
Emerging Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Training Missions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Dividing Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163

■CONTENTS

PART 4

■■■

■CHAPTER 9

Multiplayer Games

Cooperative Games: Flying Planes

. . . . . . . . . . . . . . . . . . . . . . . 169

Designing the Game: Wingman Sam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Variables and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
The Illusion of Motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Flying Planes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
Enemies and Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
Dealing with Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
Time Lines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
More Enemies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184
End Boss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
Finishing Touches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189

■CHAPTER 10 Competitive Games: Playing Fair with Tanks . . . . . . . . . . . . 191
Designing the Game: Tank War . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Playing with Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Firing Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195
Secondary Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210

■CHAPTER 11 Game Design: Balance in Multiplayer Games . . . . . . . . . . . 211
Competition and Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Independent Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
Dependent Competition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
Independent Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Dependent Cooperation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Mix and Match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
Balanced Beginnings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
Equivalent Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
Balancing Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214

xi

xii

■CONTENTS

Balanced Choice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Weighting Choices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Cyclic Relationships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218
Balanced Computer Opponents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Artificial Stupidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221

PART 5

■■■

Enemies and Intelligence

■CHAPTER 12 GML: Become a Programmer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225
Hello World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226
Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
Conditional Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
Repeating Things . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
Dealing with Other Instances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
Scripts As Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
Debugging Programs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244

■CHAPTER 13 Clever Computers: Playing Tic-Tac-Toe . . . . . . . . . . . . . . . . . . 245
Designing the Game: Tic-Tac-Toe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
The Playing Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Let the Computer Play . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
A Clever Computer Opponent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
Adaptive Gameplay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
Congratulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257

■CHAPTER 14 Intelligent Behavior: Animating the Dead . . . . . . . . . . . . . . . 259
Designing the Game: Pyramid Panic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
The Basic Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
Creating the Maze and the Explorer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263
Expanding Our Horizons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
Reactive Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Time for Treasure! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

■CONTENTS

Movable Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
Rule-Based Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
Walking Around . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273
Moving Toward the Explorer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
Dealing with States . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277
Scarabs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
Let There Be Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
Looking to the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

■CHAPTER 15 Final Words . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Creating Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Artwork: The GIMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
Music: Anvil Studio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
Sound Effects: Audacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
The Game Maker Community . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
Note to Teachers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
Good Luck . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

■BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297
■INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299

xiii

Foreword
W

ay back when Mario was still a mere twinkling in Miyamoto’s eye, I was the proud owner
of a state-of-the-art Commodore 64 microcomputer. It came with a game development system called “The Quill,” which allowed anyone to create their own text-based adventure games.
It may have been incredibly crude, but it suddenly put at my fingertips the thrill of entertaining my nearest and dearest by devising “interactive challenges” of my own. Unfortunately, I
knew little about game design, and rather than easing my players into a new and alien world, I
treated them as opponents that had to be defeated before they could reach the end. Their spirits crushed, they left, never to return . . .
It took me years of playing a variety of good (and bad) games to eventually learn how to
treat the player to the game-playing experience that their investment of time and money
deserved. It took just hours of reading this book to wish I’d had its invaluable guidelines and
the accompanying Game Maker tool to help me take my own first steps into game development all those years ago.
Two decades later, I now work for Real Time Worlds as the producer of Crackdown, an
imminent Xbox 360 title developed exclusively for Microsoft. Crackdown is the result of over
three years of development from a team that’s now nearly 70 strong in Dundee (Scotland),
with many more contributors across North America and Eastern Europe. This game has cost
millions of pounds to create, and already consists of over two and half million lines of programming code! Blood, sweat, and tears have been poured into this title to provide cutting-edge
graphics technology, stunning art assets, and dramatic surround sound. We’ve spent days
(and nights) wrestling with new technologies to provide the player with a “playground” and
“toy set” that was previously only the stuff of dreams.
Nonetheless, once you strip away the gloss, Crackdown boils down to a handful of gameplay linchpins, or what we term the “pillars of play.” Take it from me that when charged with
building such a grand gaming monument, it is vitally important to have absolute faith in the
basic foundations! I was therefore very pleased to see that this book encourages you to identify these pillars (or game mechanics) and discover how a system of simple rules can combine
in unique and compelling ways to create a spellbinding experience.
As you progress through the book you’ll build a series of excellent games that you might
never have even dreamed you could be capable of creating right now. The instructions are
clear and concise, but also encourage you to experiment with your own designs. For example,
your version of the captivating and original Koalabr8 game (Chapter 7) will almost certainly be
a unique piece of software. The crazy devices you invent, and the way you lay out your levels,
will certainly differ from mine. Watch out for Lazarus too (Chapter 4)—it may interest you to
know that this eponymous hero first appeared in Jacob’s student portfolio, and was partly
responsible for securing his first programming job in the industry!

xiv

■FOREWORD

Mark and Jacob have brought together decades of game development expertise in this
book. As well as being a professor of computing, and the creator of Game Maker, Mark first cut
his game-programming teeth creating versions of games like Super Breakout for the Atari ST.
Jacob has a string of titles to his name, and his in-depth knowledge of “the craft” consistently
yields outstanding results. Never more so was this the case than when I had the pleasure of
working with him on the team that created the PlayStation hit Hogs of War (also mentioned in
this book). Where Jacob differs from his peers is in his mastery of all four of the fundamental
game development disciplines: programming, sound, art, and, of course, design. Now, thanks
to Mark’s Game Maker software, you can find out what it feels like in their world!
One of the key messages I hope you’ll take away from this book is that there’s a world of
difference between having a great idea for a game and being a great game designer. The initial
idea is simply the seed from which the game grows, or the stone from which the pillars are
hewn. The role of a designer is to fully realize the vision: conceiving and continually refining
the various supporting mechanisms to make them mesh like the components of a Swiss timepiece. As is repeatedly stated in these pages, there is no correct solution to game design—only
a great idea, well executed and injected with personal flair and enthusiasm. Even if you’re
struggling to pin down that idea right now, I’m sure you will have wrestled it onto the screen
and into the hands of friends and family before finishing the final chapter of The Game
Maker’s Apprentice.
Good luck!
Phil Wilson
Producer, Real Time Worlds

Crackdown

xv

About the Authors
■JACOB HABGOOD is 30 years old and has been writing computer games since he was 10. He
wanted to be a psychologist when he grew up, but somehow he ended up with a computer
science degree and went into the games industry instead. He worked as a professional game
developer for seven years, programming console games for Gremlin Interactive and Infogrames/Atari in the north of England. During this time he contributed to a range of successful
titles and led the programming teams on Micro Machines (PlayStation 2, Xbox, and Nintendo
GameCube) and Hogs of War (PlayStation).
Jacob is now a doctoral student at the University of Nottingham, researching the educational potential of computer games. As part of this research, Jacob runs clubs and workshops teaching children and teenagers how to make their own computer games and provides
free teaching resources through his website: gamelearning.net. All being well, this work will
soon earn him a Ph.D. from Nottingham’s Department of Psychology so that he can finally
consider himself grown up.

■MARK OVERMARS is a full professor in computer science at Utrecht University in the
Netherlands. There he heads the research center for Advanced Gaming and Simulation
(www.gameresearch.nl) in which researchers from different disciplines collaborate on all
aspects of gaming and simulation. One of Mark’s prime research domains is computer games.
He is also one of the founders of the Utrecht Platform for Game Education and Research
(www.upgear.nl), a collaboration of different game-related educational programs in the
Netherlands. For many years he has taught courses on computer game design at Utrecht
University, and has given lectures on game design to many types of people (high school kids,
teachers, researchers, and politicians). Mark is the author of a number of popular software
packages, in particular, the Game Maker software package used as the development tool in
this book.

xvi

About the Technical Reviewer
■SEAN DAVIES is 28 years old and has been fascinated by computer games from an early age. He
grew up fairly certain that he would become a novelist—or possibly a rock star, but eventually
came to a number of important realizations:
1. He’s probably never going to be a rock star.
2. Game programming is quite cool, though.
3. Badgers are just really big weasels (the exchange rate is approximately 20 weasels to
the badger if you’re interested).
4. Any attempts to construct a serious calculus of the family Mustelidae are probably best
kept to yourself—people think you’re strange (see above).
Having made these startling realizations at such an early stage, the rest of his career path
was pretty much decided. After graduating with a degree in computer science, he joined Infogrames in Sheffield, UK, and has worked in the games industry ever since. When Infogrames
Sheffield closed its doors in 2002, he joined Sumo Digital, where he still is today. Sean is currently Xbox platform lead on Outrun 2006: Coast to Coast, which Sumo is developing for
SEGA, and is looking forward to working on some next-generation console programming in
the near future. He currently has no intention at all of ever becoming properly grown up.

Outrun 2006: Coast to Coast
xvii

About the Illustrator
T

he first things Kev Crossley remembers drawing as a child were some Daleks and the
Incredible Hulk, and he knew from that point on that he would grow up to be one or the other.
When Kev was five, his dad brought home the videogame Pong, and Kev has been trying to
come to grips with it ever since. Nonetheless, he has managed to get through a couple of Zelda
games and has spent many a happy hour blasting the head off one of this book’s authors with
a Rail Gun.
Kev spent some time in a university, but eventually realized that an art degree was not
going to give him access to Time Lords or gamma rays, so he decided to work in a bakery
instead. Eventually he got sick of eating coconut macaroons and biscuits and applied for a
job making videogames for a little green monster. For the next third of his life, he had a great
time producing graphics and animation for over 20 titles—some of which were quite good.
These days Kev is a concept artist at Core Design in Derby, UK, where he has occasionally
been known to hang out with women obsessed with tombs. He has also done copious
amounts of freelance illustration and writing for publishers all over the world, including a
series of instructional drawing books and sequential work for Rebellion’s sci-fi comic 2000AD.
His one regret is that he can’t ride a skateboard, because a cross between the Daleks and
Tony Hawk would be unstoppable.

xviii

Acknowledgments
B

y rights, this book really shouldn’t exist, because it’s required far too much effort from far
too many people to make it a profitable endeavor. Nonetheless, it does exist, and as a result
there are a lot of people who need to receive our heartfelt thanks in helping us to realize this
labor of love.
First and foremost, we need to thank all those people closest to the individuals directly
involved in bringing this book into existence. Their influence may not be obvious to the
reader, but projects like this could never happen without the support and understanding of
the wives, girlfriends, and families of all the people involved in this book. In particular, Jacob
would like to thank Jenny, Fiona, Michelle, and Amelia, all of whose names should adorn the
credits of many a videogame for the sacrifices that they regularly make to indulge the creative
passions of their loved ones.
The next biggest thanks should go to Matty Splatt, who has shied away from a full billing
in the “About the” sections but did a fantastic job of bringing Koalabr8 and Pyramid Panic to
life with his comical and beautifully polished graphics. We would also like to give a special
thanks to Ari Feldman for allowing us to use and modify his game sprites for the Wingman
Sam game.
More thanks go to Jenny and Marguerite Habgood
for their grammatical critiques, and the following people
for all their comments and input into the project: Sarah
Peacock, Judy Robertson, John Sear, and Phil Wilson.
Additional thanks goes to all the staff and students at
Sheffield West City Learning Centre, who suffered the
book’s instruction in its earliest form.
Quick thanks also to everyone who enthusiastically
play-tested the games in the book, including Gail
Clipson, Fiona Crossley, Katie Fraser, Giulia Gelmini,
Jasmin Habgood, Martijn Overmars, Ronald Overmars,
and Stuart Reeves.
Finally, we would like to thank everyone at Apress
for their support, and for sticking with us even after it
became plainly obvious that both authors were far too
busy to write a book!

xix

Introduction
W

ho wouldn’t want to make computer games? It’s creative, rewarding, and these days even
pretty darn cool too. You can make them to share with your school friends, your work colleagues, your grandchildren, or even the entire gaming world. This book is not specifically for
the young or old, but anyone who loves computer games and wants to have a go at making
them for themselves. We’ve all painted a picture, written a story, and made a wobbly piece of
pottery at some point in our lives, so it’s now time to embrace the art form of the future and
try making computer games too.
This book provides a collection of engaging tutorials that introduce you to the Game
Maker tool and teach you how to use it. The first four parts of the book take you step by step
through seven different projects using Game Maker’s simple drag-and-drop programming system. By the time you’ve finished making Evil Clutches, Galactic Mail, Lazarus, Super Rainbow
Reef, Koalabr8, Wingman Sam, and Tank War, you’ll have a well-rounded experience of making
games with Game Maker. Parts 2, 3, and 4 also end with game design chapters that encourage
you to stand back from your creations and consider how principles of game design can be
used to make them more fun. Moreover, we don’t just talk about it, but we provide new versions of the games with improved features so that you can experience for yourself how solid
game design can lead to good gameplay.
Game Maker provides a simple environment that allows complete beginners to quickly start
building games, using an icon-based system of events and actions (see Figure 1). This drag-anddrop programming technique provides an easy way to learn about game development and
allows you to create complete games without going near a traditional programming language.

xx

Figure 1. Game Maker’s simple drag-and-drop system uses iconic events and actions to program
computer games.

■INTRODUCTION

However, once you become more experienced, traditional languages can provide a more
powerful way to program games. Consequently, Game Maker also provides the Game Maker
Language (GML), which underpins Game Maker and makes it such a powerful tool (see
Figure 2). The last part of the book uses several simple examples to introduce you to GML,
before we demonstrate how you can use it to create artificial intelligence for undead creatures
in the Pyramid Panic game.

Figure 2. Game Maker Language (GML) provides extra power for advanced users.
The example games in this book have been brought to life with graphics and illustrations
by real games industry artists. Furthermore, you can use all the professional resources provided on the CD in your own Game Maker projects with the blessing of the publisher and
authors. We only ask that you share your creations with the online Game Maker community
so that we can see what you have created with them. We want you to enjoy the creative journey
ahead and hope that it will help you to share in our passion and enthusiasm for creating
computer games!

xxi