The Halo 2 AI In 10 Minutes or

The Halo 2 AI In 10 Minutes or Less Damián Isla Bungie Studios

Halo • • • First person shooter for XBox Interesting sci-fi world Lots to do (combat, exploration, vehicles, weapons) Lots of decisions to make Slower-paced More strategic in nature?

The AI Single-player campaign only (no multiplayer) Character-based Enemies • • • Allies Large variety • Clear behavioral patterns for the player • to learn and exploit • 4 - 30 second lifespans Not terribly effective “Kid brothers” ~10 seconds or ~30 minutes

The “I” in “AI” • Perception and world-modeling – Each AI maintains mental world model – Internal mental object-state updated according to perceivability via the “senses” (e. g. , line of sight, sound events, etc. ) – Perception sharing (via explicit communication) • Behavior – – • Take cover when taking damage Uncover hidden enemies Use vehicles when appropriate Joint behaviors Skills – Use weapons appropriately – Drive vehicles – Navigate the environment Strongly agent-based approach “Strategy” controlled through scripting Behave

Behavior Decision-making: Behavior DAG (HFSM) Behavior: a program that takes temporary control of the actor in order to get something done. • Good – Intuitive – Modular – Scalable (more IS better) • Bad – Memory is hard – Debugging is hard – Never really that simple

An ethological interlude… Baerends, The Functional Organization of Behavior, 1976

What about Reasoning and Planning? • Spatial Reasoning – Firing point selection • Path-planning – A* – Dynamic obstacle interaction … but no concept-reasoning or action-planning

So in the end… • • Second-to-second decision-making Reactive in nature Closer to A-Life than classical AI Closer to animal than to human intelligence