Artificial Intelligence in Games(2022)[Dent][9781003305835]

310 Pages·2022·17.887 MB·English

by  Dr. Roberts

Artificial Intelligence
in Games
This book covers all the necessary topics that a professional game AI programmer
needs to know, from math and steering behaviours to terrain analysis, pathfinding,
and decision-making. Written to be easily accessible, each topic is accompanied by
an example game that allows the reader to add their own code to see the effects their
changes have.
Each chapter is split into two parts. The first part covers the necessary theory in a
friendly, conversational manner, using visual examples and fictional game scenarios
to give additional context. The second part is a coding tutorial in C# for the topic
at hand. Each chapter has its own example game available to download, written in
C# in the Unity Game Engine.
This book will be suitable for students and aspiring games programmers looking
to gain a grounding in game AI techniques.
Paul Roberts is a Lead AI Games Programmer who has worked for companies
such as Activision, Team17, Traveller’s Tales and Sumo Digital. Credits include
Call of Duty: Strike Team, Pitfall!, Worms Revolution and The Lego Movie: The
Video Game.

Artificial Intelligence
in Games
Paul Roberts
Illustrations by Nicholas Dent
First edition published 2023
by CRC Press
6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742
and by CRC Press
4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN
CRC Press is an imprint of Taylor & Francis Group, LLC
© 2023 Paul Roberts
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Library of Congress Cataloging‑in‑Publication Data
Names: Roberts, Paul (Game programmer), author. | Dent, Nicholas (Illustrator), illustrator.
Title: Artificial intelligence in games / Paul Roberts ; illustrated by Nicholas Dent.
Description: First edition. | Boca Raton : CRC Press, 2023. | Includes bibliographical
references and index. | Summary: “This book covers all the necessary topics that a
professional game AI programmer needs to know, from math and steering behaviours to
terrain analysis, pathfinding, decision making, and more. Written to be easily accessible,
each topic is accompanied by an example game, where the reader can add their own code to
see the effects their changes have. This book will be suitable for students and aspiring games
programmers looking to gain a grounding in game AI techniques”-- Provided by publisher.
Identifiers: LCCN 2022005391 | ISBN 9781032305950 (hardback) |
ISBN 9781032033228 (paperback) | ISBN 9781003305835 (ebook)
Subjects: LCSH: Computer games--Programming. | Computer games--Design. |
Video games--Design. | Artificial intelligence. Classification: LCC
QA76.76.C672 R6327 2023 | DDC 794.8/1526--dc23/eng/20220412 LC record
available at https://lccn.loc.gov/2022005391
ISBN: 9781032305950 (hbk)
ISBN: 9781032033228 (pbk)
ISBN: 9781003305835 (ebk)
DOI: 10.1201/9781003305835
Typeset in Times LT Std
by KnowledgeWorks Global Ltd.
Access the Support Material: https://www.routledge.com/9781032033228
Contents
Chapter 1 Introduction ..........................................................................................1
About the Author ..................................................................................1
Who Is this Book for? ..........................................................................1
How to Read this Book ........................................................................1
Accompanying Framework ..................................................................2
What Is Game AI? ................................................................................2
Game AI and Game Genres ..................................................................6
Chapter 2 Math .....................................................................................................9
What Is a Vector? ..................................................................................9
Dot Product ........................................................................................13
Rotation ..............................................................................................21
Math – Practical ................................................................................25
Project Overview ................................................................................25
Step-By-Step Guide ............................................................................25
Future Work ........................................................................................27
Chapter 3 Steering Behaviours ...........................................................................29
Steering Forces ...................................................................................29
Combining Behaviours .......................................................................48
Group Behaviours ...............................................................................50
Final Thoughts ....................................................................................54
Steering Behaviours – Practical ........................................................56
Project Overview ................................................................................56
Step-By-Step Guide ............................................................................57
Future Work ........................................................................................72
Chapter 4 Terrain Analysis .................................................................................73
Influence Maps ...................................................................................73
Heat Maps...........................................................................................77
Cell Granularity ..................................................................................81
Final Thoughts ....................................................................................82
Terrain Analysis – Practical ..............................................................83
Project Overview ................................................................................83
Step-By-Step Guide ............................................................................84
Future Work ........................................................................................90
v
vi Contents
Chapter 5 Pathfinding .........................................................................................91
Spatial Representation ........................................................................91
Pathfinding ..........................................................................................96
Final Thoughts ..................................................................................116
Pathfinding – Practical ....................................................................117
Project Overview ..............................................................................117
Step-By-Step Guide ..........................................................................118
Future Work ......................................................................................123
Chapter 6 Decision-Making ..............................................................................125
Finite State Machine .........................................................................125
Fuzzy State Machine ........................................................................128
Stack-Based FSM .............................................................................129
Behaviour Trees ................................................................................130
Final Thoughts ..................................................................................133
Decision-Making – Practical ...........................................................134
Project Overview ..............................................................................134
Step-By-Step Guide ..........................................................................134
Future Work ......................................................................................149
Chapter 7 Fuzzy Logic ......................................................................................151
Sets ...................................................................................................153
Fuzzy Sets ........................................................................................155
Fuzzy Rules ......................................................................................161
Defuzzification .................................................................................169
Final Thoughts ..................................................................................175
Fuzzy Logic – Practical ...................................................................176
Project Overview ..............................................................................176
Step-By-Step Guide ..........................................................................176
Future Work ......................................................................................194
Chapter 8 Chess AI ...........................................................................................195
Minimax Algorithm ..........................................................................196
Alphabeta Pruning ............................................................................201
Evaluation Functions ........................................................................208
Final Thoughts ..................................................................................217
Chess AI – Practical ........................................................................218
Project Overview ..............................................................................218
Contents vii
Step-By-Step Guide ..........................................................................219
Future Work ......................................................................................224
Chapter 9 Genetic Algorithms ..........................................................................227
Initial Population ..............................................................................230
Encoding ...........................................................................................230
Fitness ...............................................................................................232
Selection ...........................................................................................233
Crossover ..........................................................................................240
Mutation ...........................................................................................245
Final Thoughts ..................................................................................246
Genetic Algorithms – Practical .......................................................248
Project Overview ..............................................................................248
Step-By-Step Guide ..........................................................................249
Future Work ......................................................................................261
Chapter 10 Neural Networks ..............................................................................263
Biology .............................................................................................263
Single-Layer Perceptron ...................................................................264
Multi-Layer Perceptron ....................................................................270
Learning............................................................................................273
Game Example: Snake .....................................................................277
Final Thoughts ..................................................................................279
Neural Networks – Practical ............................................................281
Project Overview ..............................................................................281
Step-By-Step Guide ..........................................................................282
Future Work ......................................................................................297
Index ......................................................................................................................299

1 Introduction
ABOUT THE AUTHOR
My name is Paul Roberts and I am a Lead AI games programmer. I’ve worked on
a variety of big releases over the years including titles such as Call of Duty: Strike
Team, The Lego Movie: The Video Game and Worms Revolution and have developed
quite a few smaller mobile games too, including Power-Up, Pixel 8, Rituals and
Captain CupCake and Donut Disaster. I have worked at big studios like Activision,
Sumo Digital, Team17 and Traveller’s Tales and been an indie developer at my own
studio too – Playing with Giants. I also spent around six years leading the Computer
Games Programming undergraduate degrees and master’s degrees at a UK univer-
sity, where I was fortunate enough to rewrite all their game AI content and set our
students on the right path.
I have been programming since the ZX Spectrum days and am currently dabbling
in some assembly language programming for the Atari 2600 for fun. I also write
novels as a hobby; so if you are a fantasy fan, check out my novel, The Betrayer:
Prophecy of the Dragon Book One (Amazon, 2022).
WHO IS THIS BOOK FOR?
This book was written for anyone wishing to get a grounding in-game AI techniques.
I have pitched everything at an undergraduate level, but that does not mean that if
you are not currently studying that you cannot get anything from this book. Not at
all. I feel that anyone interested in game AI that has never approached the subject
before can work their way through this book and gain a lot. There are, however, cod-
ing tutorials in each chapter written in C#; so to get the most from these, it would be
beneficial if you could already code at a basic level.
HOW TO READ THIS BOOK
Each chapter is split into two parts. The first gives an overview of the topic in a
friendly conversational manner and there are a lot of visual examples and fictional
game scenarios to give some context to the area being covered. The second part of
each chapter has been written as a coding tutorial. It will guide you through how to
code the techniques the first half of the chapter covered. It is recommended that you
read both parts of a chapter in order, but if you already have an understanding of an
area and wish to jump right into the code, then skip straight to the second half of the
relevant chapter. Likewise, if you are not interested in coding the solutions and just
want to get an understanding of the different areas of game AI, feel free to just read
the first halves.
I have compiled the topics for this book in a way that each chapter builds upon the
last. If you choose to read the chapters in order, at the end of this book you should
DOI: 10.1201/9781003305835-1 1