Combat Evolved: The Encounter Design of Halo 3

It's time we return to the Halo franchise with Bungie's 2007 release Halo 3. One of the earliest entries in AI and Games was an overview of the behaviour tree AI in Halo 2 and how it accommodated for a variety of combat situations. This time around we're looking at how new combat systems were built atop this framework to better control and manage the AI characters seen in Halo 3's large-scale encounters. Behaviour Tree's adopt a trickle-down approach to decision making where a tree comprised of all possible behaviours for a given character is constructed with conditions that dictate when to execute them. Based upon the current circumstances within the game, a particular sub-section of the tree will then be executed. This was ideal given the range of circumstances both ally and enemy AI characters could find themselves in, from Halo's variation in combat arena size to the ability for characters to jump in and out of vehicles at any time.