University of Alberta Quest Patterns for Story-Based Video Games by Marcus Alexander Trenton A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science Department of Computing Science © Marcus Alexander Trenton Fall 2009 Edmonton, Alberta Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission. Examining Committee Duane Szafron, Computing Science Jonathan Schaeffer, Computing Science Mike Carbonaro, Faculty of Education Abstract As video game designers focus on immersive interactive stories, the number of game object interactions grows exponentially. Most games use manually- programmed scripts to control object interactions, although automated techniques for generating scripts from high-level specifications are being introduced. For example, ScriptEase provides designers with generative patterns that inject commonly-occurring interactions into games. ScriptEase patterns generate scripts for the game Neverwinter Nights. A kind of generative pattern, the quest pattern, generates scripting code controlling the plot in story-based games. I present my additions to the quest pattern architecture (meta quest points and abandonable subquests), a catalogue of quest patterns, and the results of two studies measuring their effectiveness. These studies show that quest patterns are easy-to-use, substantially reduce plot scripting errors, and their catalogue is highly-reusable between games. These studies demonstrate ScriptEase generative quest patterns are a desirable alternative to manual plot scripting in commercial, story-based games. Table of Contents Chapter 1 - Introduction ....................................................................................... 1 1.1 - The Massive Video Game Industry ...................................................... 1 1.2 - Scripting in Video Games..................................................................... 3 1.3 - Expanding the Use of Video Games ..................................................... 8 1.4 - Thesis .................................................................................................... 9 Chapter 2 - Related Work .................................................................................. 12 2.1 - Computers as Authors ........................................................................ 12 2.2 - Tools to Assist Authors ...................................................................... 17 2.2.1 - Petri Nets ......................................................................................... 17 2.2.2 - Quests in Botfighters2 ..................................................................... 19 2.2.1 - Neverwinter Nights ......................................................................... 22 2.2.2 - Plot Wizard ..................................................................................... 25 2.2.3 - Lilac Soul‟s NWN Script Generator ................................................ 28 2.2.4 - Previous Version of Quests in ScriptEase ...................................... 30 2.3 - Contributions ...................................................................................... 33 Chapter 3 - ScriptEase and Quest Patterns ........................................................ 35 3.1 - ScriptEase ........................................................................................... 36 3.2 - Quest Patterns ..................................................................................... 40 3.2.1 - Quest Points .................................................................................... 40 3.2.2 - Options ............................................................................................ 42 3.2.3 - States of a Quest Point .................................................................... 44 3.2.4 - Meta Quest Points ........................................................................... 47 3.2.5 - Branching ........................................................................................ 50 3.2.6 - Subquests ........................................................................................ 52 3.2.7 - Quest completed Quest Points ........................................................ 55 3.2.8 - Commitment ................................................................................... 57 3.3 - Improvements and Limitations ........................................................... 63 3.4 - Implementation ................................................................................... 66 Chapter 4 - Quests in Commercial Video Games .............................................. 69 4.1 - Previous Studies and New Questions ................................................. 69 4.2 - Updating the Pattern Catalogue .......................................................... 71 4.3 - Metrics ................................................................................................ 78 4.4 - Results ................................................................................................ 85 4.5 - Conclusion .......................................................................................... 92 Chapter 5 - ScriptEase versus NWScript ........................................................... 94 5.1 - Method ................................................................................................ 95 5.2 - Results .............................................................................................. 100 5.3 - Conclusion ........................................................................................ 108 Chapter 6 - Future Work and Conclusions ...................................................... 110 6.1 - Summary ........................................................................................... 110 6.2 - Future Work ...................................................................................... 115 6.3 - Conclusions ...................................................................................... 116 Bibliography ....................................................................................................... 117 Appendices .......................................................................................................... 124 Appendix A - Quest Catalogue ..................................................................... 124 Appendix B - Participant Briefing ................................................................ 153 Appendix C - Consent Form ........................................................................ 154 Appendix D - Demographics Form .............................................................. 156 Appendix E - NWScript Tutorial ................................................................. 158 Appendix F - ScriptEase Tutorial ................................................................ 169 Appendix G - Quest Instructions .................................................................. 179 Appendix H - Quest Comparison ................................................................. 191 Appendix I - Overall Tool Comparison ...................................................... 193 List of Tables Table 4.1 – Quest catalogue inherited from Curtis Onuczko ................................ 73 Table 4.2 – The number of patterns in catalogue after analyzing each game ....... 73 Table 4.3 – Quest catalogue updated from my experience. Added patterns are bolded; the rest are from Table 4.1, with some renamings and deletions. ............ 74 Table 4.4 – Quest catalogue updated from Oblivion, relative to Table 4.3 .......... 75 Table 4.5 – Quest catalogue updated from KOTOR, relative to Table 4.4 .......... 76 Table 4.6 – Types of Adaptation ........................................................................... 83 Table 4.7 - Summary of metric scores .................................................................. 86 Table 4.8 – Quests in Oblivion and KOTOR ......................................................... 86 Table 4.9 – Quest points in Oblivion and KOTOR ............................................... 87 Table 4.10 – Meta quest points in Oblivion and KOTOR ..................................... 87 List of Figures Figure 1.1 – The plot diagram for The Three Little Pigs [38] ................................ 6 Figure 1.2 – A plot diagram for an interactive narrative ........................................ 6 Figure 2.1 – Petri net model of a quest to obtain a puppet [5] .............................. 19 Figure 2.2 – The quest events and their relationships in the Defeat Enemy for Money quest [42] ................................................................................................... 21 Figure 2.3 – Neverwinter Nights [32] ................................................................... 23 Figure 2.4 – The Aurora Toolset for Neverwinter Nights ....................................