Embracing Emergent Behavior with Goal-Based AI Kevin Dillkad@bluefang.com

Blue Fang GamesTo create compelling, emotionally engaging games, focused on the animal kingdom, that set the benchmark for broad-based family entertainment.

The PlanMotivationKohan 2 DemoCommon AI TechniquesGoal-based AIBoxy-dog DemoQuestions

The PlanWhat I Want:Cunning OpponentsResponsive AlliesReplayabilityOrganic Credibility Emotional AppealCompelling PerformancesOr, more generally:Situational AwarenessEmergent Behavior

Motivation, cont.Declarative AI (vs. Procedural AI)Wikipedia: A program is declarative if it describes what something is like, rather than how to create it.Developers role: not to tell the AI what to do, but to tell the AI how to decide for itself.

Techniques Scripted AIAI Follows a script, much like a movieScript specifies exactly what will happen, when it will happen, where it will happenAdvantages:Gives designers explicit control Easy to writeEasy to balanceDisadvantagesRepetitive and predictable

Techniques State MachinesA state is defined for every high-level action the AI can takeTransitions are defined to move from one state to another stateEach state has custom code to control the character while in that state

First Person Shooter ExampleGet AmmoGet HealthRun AwaySearch For EnemyAttackEnemy FoundEnemy LostLow on AmmoLow on HealthGot Away, Low on HealthGot HealthGot AmmoGot Away, Low on Ammo

Techniques State MachinesAdvantages:Easy to conceptualizeEasy to implementMiddleware tools existDisadvantages:Complexity scales poorly as AI growsRampant duplication of codeCan only do one thing at a time

Techniques Goal Based AIA goal is defined for every high-level action that the AI can takeEach goal is assigned a priority:Base priority (evaluate current situation)Allocate resourcesOptimize resources and calculate final priorityHighest priority goal(s) are executed

Goal TypesSome common RTS goals:Attack Construct BuildingDefend Repair BuildingExplore Upgrade BuildingRecruit Unit Sell BuildingRecover Health Give Resources To AllyResearch

Techniques Goal Based AIAdvantagesFlexible and powerfulComplexity scales fairly well as AI growsCan execute more than one goal at a timeEmergent behaviorDisadvantages:Priority calculations (Bucket of Floats)Emergent behavior

Goal Selection BasicsWWHD (What Would a Human Do?)Write down a list of the factors you would consider if you were playing the gameSome common tricks:Bonuses Repeat PenaltiesMultipliers One-Time BonusesExponents Actor CategoriesFuzzy Factors Templates

Example: Attack GoalBase priority:Actor value for the most desirable building or unit in the area (taking into account enemys economy if appropriate)Travel DistanceIntervening targets (attack goals only)

Attack Goal, cont.Priority Curve:Target CV ratioMin CV to assignLow CV exponent Max advantageMax multiplier Other considerationsCombined armsWall strengthAdjusting builder CV* CV = Combat Value

Loose EndsGoal CommitmentIF: you cant afford something nowBUT: you will be able to soonTHEN: dont perform lower priority goals that use the same resourceGoal InertiaBonus to keep doing what youre doingLocked GoalsDisable all other goals until current goal is complete

Jack the Terrier