The Formal Approach to Computer Game Rule Development Automation

1
The Formal Approach to Computer Game Rule
Development Automation
Elena Pavlova Moscow Engineering-Physics Institute (National Nuclear Research University), PhD student 05.13.11
2
Agenda

• Game rule development automation problem
• Turn-based strategy game rule description
  language
• Formal game rule verification method
• Prototype rules development environment
• Summary

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Game rules

• Game rules include the definition of
• specific game world entities
• entity interaction rules
• the main goal of the game and secondary goals
• start conditions and winning conditions
• player state definition
• Rule examples
• A troop, moved to a map cell with an enemys
  town, must fight or run away
• Building a castle requires 3000 stones and 100
  bars of gold

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Game rules development
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Object

• The object of this paper is to develop an
  approach to game rule development allowing
• formal visual rule design
• automated rule verification
• rule-based code and data generation
• Game class specificity consideration

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Rules description language

• The language allows to describe
• specific game domain entities (entity data and
  behavior)
• entity behavior constraints
• entity relations
• the reaction of entities to another entity
  behavior

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Game rule example The town attack

• An army may attack a town if
• it is an enemys town
• army moves count is greater than 0 (the army
  still can make a move)
• When the army attacks the town, the army moves
  count is decreased by 1.
• The population of the town may defend it.
• The player who possesses the town should be
  informed about the attack.

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Rules model
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Rules in the language textual notation

• army Army,
• playerID 1,
• movepoints 5,
• attackCity ( city City )
• ((army.playerID ! city.playerID) and (
  army.movepoints gt 0 ))
• attackCityBody
• (army.movepoints army.movepoints - 1)
• player Player,
• playerID 1,
• cityAttackDetected ( city City )
• cityAttackDetectedPrecondition Body
  cityAttackDetectedPostCondition
• city City,
• playerID 1,
• autoDefend ()
• autoDefendPrecondition autoDefendBody
  autoDefendPostCondition
• AddReactor ( army.attackCity, city.autoDefend)

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Type System

• Static typing
• Type inference
• Language library includes
• simple types for behavior constraints
• types for turn-based strategy domain

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Object cloning

• The language is prototype-based

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Language semantics

• Denotational semantics
• ?? calculus for denotats
• Hoare Logic elements for methods preconditions
  and postconditions

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Rules model verification

• Rules model consistency static analysis
• Syntactic model consistency
• Semantic model consistency
• Static balance formal properties monitoring
• Superior side detection
• Invincible troops detection
• First turn superiority detection
• Dynamic balance - automated theorem proving
• Turn result superiority detection

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Consistency

• Syntactic consistency
• Semantic consistency

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Dynamic balance

• Dynamic balance ? Each turn the game is fair.
• The turn invariant is placed into appropriate
  methods (related to the end of turn event)
• Rule model described in the formal language
  designed is converted into the automatic theorem
  prover input format (ESC/Java)
• The theorem prover attempts to verify the model

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Summary

• The approach to game rule development was
  suggested. The approach allows
• formal visual rule design
• rule verification
• rule-based code and data generation
• game class specificity consideration

17
References

• TorqueEngineAdvanced http//www.garagegames.com/
  products/torque/tgea/features/
• FPS Creator http//www.darkgamestudio.com/
• NeoAxisEngine http//www.neoaxisgroup.com/descri
  ption.htm
• Offset Engine http//www.projectoffset.com/game.
  html
• Unreal Engine http//www.unrealtechnology.com/ht
  ml/technology/ue30.shtml
• C4 Engine http//www.terathon.com/c4engine/featu
  res.php
• Moreno-Ger P., Martinez-Ortiz I., Sierra J. L.,
  Fernandez-Manjon B. Language-Driven Development
  of Videogames The lte-Gamegt Experience //
  Entertainment Computing - ICEC 2006. Berlin
  Springer, 2006, pp 153-164
• Moreno-Ger P., Sierra J. L., Martinez-Ortiz I.,
  Fernandez-Manjon B. A documental approach to
  adventure game development // Science of Computer
  Programming. Volume 67 , Issue 1 (June 2007).
  Amsterdam, The Netherlands Elsevier
  North-Holland, Inc, 2007, pp 3-31
• Hu W. A Reusable Eduventure Game Framework //
  Transactions on Edutainment I . Berlin
  Springer, 2008, pp 74-85
• Furtado A. W. B., Santos A. L. M., Ramalho G. L.
  A Computer Games Software Factory and
• Edutainment Platform for Microsoft .NET // IET
  Software. Volume 1, Issue 6, December 2007.
  IEEE, 2007, pp 280 - 293
• Amory A. Game object model version II a
  theoretical framework for educational game
  development // Educational Technology Research
  and Development. Volume 55, Number 1 / February,
  2007 Boston Springer, 2007, pp 51 - 77
• Rollings A., Morris D. Game Architecture and
  Design. A New Edition. Indianapolis New Riders
  Publishing, 2004
• Wihlidal G. Game Engine Toolset Development.
  Boston, MA Thomson Course Technology PTR, 2006

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References 2

• Clarke E. M.,  Grumberg O., Peled D. A.   Model
  Checking. - The MIT Press, 1999
• V. V. Kulyamin, Software verification methods,
  Russian State Analytical-Review Articles Contest
  for Priority Concept Information-Telecommunicatio
  n Systems, 2008. (in Russian.).
• Baier Ch., Katoen J.-P., Larsen K. G. Principles
  of Model Checking. -  The MIT Press, 2008
• Mosses P. D. Fundamental Concepts and Formal
  Semantics of Programming Languages An
  Introductory Course. http//wiki.daimi.au.dk/dSp
  rogSem-01, 2002
• Abadi M., Cardelli L. A Theory of Objects. New
  York Springer, 1996
• Hoare C. An Axiomatic Basis of Computer
  Programming. Communications of the ACM, v.12.
  New York ACM Press, 1969
• A. V. Gavrilov, E. A. Pavlova, Functional
  interface analysis for formalization of complex
  information system design, Information
  Technologies, 9, pp. 9-15, 2008. (in Russian).
• E. A. Pavlova, Design of formal domain-specific
  language for computer game rules development for
  turn-based strategy game genre, Computer and
  Information Technology Reporter 4, April. 2009.
  (in Russian).

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Summary

• The approach to game rule development was
  suggested. The approach allows
• formal visual rule design
• rule verification
• rule-based code and data generation
• game class specificity consideration
• Elena.pav_at_gmail.com

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A type system is a tractable syntactic method
for proving the absence of certain program
behaviors by classifying phrases according to the
kinds of values they compute. Benjamin
Pierce Types and Programming Languages
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Object

• unit Unit,
• power 2,
• arrows_count 5,
• attackMethod ( unit_to_attack Unit, cell Cell
  )
• precondition methodBody postcondition

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Method

• attackMethod ( unit_to_attack Unit,
• cell Cell )
• ( arrows_count gt 0 ) and ( power gt 1)
• methodBody
• ( arrows_count arrows_count 1) and
• ( power power 2 )

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Reactor method

• AddReactor (unit.AttackMethod, army2.OnAttack)

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Reactors

• AddReactor ( unit.AttackMethod, map.UnitMoved)
• AddReactor ( unit.Attackmethod , army2.OnAttack)

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Static balance

• Superior side detection
• Invincible troops detection
• First turn superiority detection
• The game is played according to the rules
  defined. Players are represented by simple AI
  module.

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• Computer game is a game represented by a program
  for personal computer.
• Thus, we dont consider games for mobile devices,
  consoles, etc.