The Halo 2 AI In 10 Minutes or Less

Damin IslaBungie Studios

HaloFirst person shooter for XBoxInteresting sci-fi worldLots to do (combat, exploration, vehicles, weapons)Lots of decisions to makeSlower-paced More strategic in nature?

The AIAlliesNot terribly effectiveKid brothers~10 seconds or ~30 minutesEnemiesLarge varietyClear behavioral patterns for the player to learn and exploit4 - 30 second lifespansSingle-player campaign only (no multiplayer)Character-based

The I in AIPerception and world-modelingEach AI maintains mental world modelInternal mental object-state updated according to perceivability via the senses (e.g., line of sight, sound events, etc.)Perception sharing (via explicit communication)BehaviorTake cover when taking damageUncover hidden enemiesUse vehicles when appropriateJoint behaviorsSkillsUse weapons appropriatelyDrive vehiclesNavigate the environment

Strongly agent-based approach

Strategy controlled through scriptingBehave

Sense

Plan

Act

BehaviorDecision-making: Behavior DAG (HFSM)

Behavior: a program that takes temporary control of the actor in order to get something done.

GoodIntuitiveModularScalable (more IS better)

BadMemory is hardDebugging is hardNever really that simple

Root

Self-preservation

Engage

Search

Charge

Fight

Guard

Grenade

Cover

Presearch

Uncover

Guard

Grenade

Vehicle

Investigate

Suppressing fire

Grenade

Postcombat

Shoot corpse

Check corpse

Idle

Guard

Moving, aiming, shooting, animation

Perception and World Modeling

Object states, events

Orders

An ethological interludeBaerends, The Functional Organization of Behavior, 1976

Root

Self-preservation

Engage

Search

Charge

Fight

Guard

Grenade

Cover

Presearch

Uncover

Guard

Grenade

Vehicle

Investigate

Suppressing fire

Grenade

Postcombat

Shoot corpse

Check corpse

Idle

Guard

What about Reasoning and Planning?Spatial ReasoningFiring point selection

Path-planningA*Dynamic obstacle interaction

but no concept-reasoning or action-planning

So in the endSecond-to-second decision-makingReactive in natureCloser to A-Life than classical AICloser to animal than to human intelligence