Mimicking Human Player Strategies in Fighting Games Using Game Artificial Intelligence Techniques By Simardeep Singh Saini A Doctoral Thesis Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University March 2014 © By Simardeep Singh Saini 2014 1 Abstract Fighting videogames (also known as fighting games) are ever growing in popularity and accessibility. The isolated console experiences of 20th century gaming has been replaced by online gaming services that allow gamers to play from almost anywhere in the world with one another. This gives rise to competitive gaming on a global scale enabling them to experience fresh play styles and challenges by playing someone new. Fighting games can typically be played either as a single player experience, or against another human player, whether it is via a network or a traditional multiplayer experience. However, there are two issues with these approaches. First, the single player offering in many fighting games is regarded as being simplistic in design, making the moves by the computer predictable. Secondly, while playing against other human players can be more varied and challenging, this may not always be achievable due to the logistics involved in setting up such a bout. Game Artificial Intelligence could provide a solution to both of these issues, allowing a human player’s strategy to be learned and then mimicked by the AI fighter. In this thesis, game AI techniques have been researched to provide a means of mimicking human player strategies in strategic fighting games with multiple parameters. Various techniques and their current usages are surveyed, informing the design of two separate solutions to this problem. The first solution relies solely on leveraging k nearest neighbour classification to identify which move should be executed based on the in-game parameters, resulting in decisions being made at the operational level and being fed from the bottom-up to the strategic level. The second solution utilises a number of existing Artificial Intelligence techniques, including data driven finite state machines, hierarchical clustering and k nearest neighbour classification, in an architecture that makes decisions at the strategic level and feeds them from the top-down to the operational level, resulting in the execution of moves. This design is underpinned by a novel algorithm to aid the mimicking process, which is used to identify patterns and strategies within data collated during bouts between two human players. Both solutions are evaluated quantitatively and qualitatively. A conclusion summarising the findings, as well as future work, is provided. The conclusions highlight the fact that both solutions are proficient in mimicking human strategies, but each has its own strengths depending on the type of strategy played out by the human. More structured, methodical strategies are better mimicked by the data driven finite state machine hybrid architecture, whereas the k nearest neighbour approach is better suited to tactical approaches, or even random ‘button bashing’ that does not always conform to a pre- defined strategy. Keywords: Fighting Games, Artificial Intelligence, Finite State Machine, Machine Learning, Game AI, Strategies and Tactics, Mimicking 2 Acknowledgements I would like to thank my supervisors Professor Paul Chung and Dr Christian Dawson for their continued support, guidance and mentoring during my research. I would also like to extend my gratitude to Dr Daniel Reidenbach, whose feedback has been of utmost importance in shaping this Thesis. I am eternally grateful to my mother and father, my brother Amardeep, and my sister-in-law Sarbjit, for believing in me and telling me to never give up. The completion of this work would not have been possible without their undying support, encouragement and patience. I am indebted to those managers I have worked for over the years who have supported my studies by offering time off work to pursue my research. This has made a big difference and I am grateful for all they have done. Last, but certainly not least, I would like to thank my friends and family all over the world who have helped me along the way, and whose understanding and patience has been paramount to progressing the doctorate. Many thanks to Jag and Ricky in particular for their constant backing and encouragement over the years. Above all, I would like to thank God Almighty, without whom this achievement would simply not be possible. 3 To My Parents 4 Table of Contents Abstract ................................................................................................................................................... 2 Acknowledgements ................................................................................................................................. 3 Table of Contents .................................................................................................................................... 5 List of Figures .......................................................................................................................................... 8 List of Tables ........................................................................................................................................... 9 Part I – Introduction and Background ................................................................................................... 10 Chapter 1 – Overview ........................................................................................................................... 11 1.1 Introduction ................................................................................................................................ 11 1.2 Motivation ................................................................................................................................... 11 1.3 Research Aims and Objectives .................................................................................................... 12 1.4 Contribution of the Thesis .......................................................................................................... 12 1.5 Structure of the Thesis ................................................................................................................ 14 Chapter 2 – Anatomy of a Fighting Game ............................................................................................. 15 2.1 Introduction ................................................................................................................................ 15 2.2 What is a Fighting Game? ........................................................................................................... 15 2.3 A Brief History of Fighting Games ............................................................................................... 17 2.4 Chapter Summary ....................................................................................................................... 22 Chapter 3 - Strategies and Tactics......................................................................................................... 23 3.1 Introduction ................................................................................................................................ 23 3.2 Strategies and Tactics in Martial Arts ......................................................................................... 23 3.3 Martial Arts Movies ..................................................................................................................... 26 3.4 Strategies and Tactics in Videogames ......................................................................................... 28 3.5 Chapter Summary ....................................................................................................................... 30 Chapter 4 – AI Techniques applied to Fighting Games ......................................................................... 31 4.1 Introduction ................................................................................................................................ 31 4.2 The role of AI in Videogames ...................................................................................................... 31 4.3 Game AI Techniques ................................................................................................................... 33 4.4 Application of Game AI Techniques ............................................................................................ 42 4.5 Fighting Games ........................................................................................................................... 54 4.5 Chapter Summary ....................................................................................................................... 64 Part II – Analysis, Design and Development ......................................................................................... 71 5 Chapter 5 – Proof of Concept Game ..................................................................................................... 72 5.1 Introduction ................................................................................................................................ 72 5.2 Design .......................................................................................................................................... 72 5.3 Implementation .........................................................................................................................