Behaviour tree
Also said as BT, Selector and sequence
AI written as a tree of tests and actions, walked from the top. A selector tries its children until one works; a sequence runs them until one fails. So the top is the most urgent.
Adding a behaviour means adding one branch, with no arrows to rewire. Designers can read it, and an enemy reacts to changes straight away because it asks the questions again.
Say it
“Add a branch above Patrol: if the guard heard a noise, walk there and look around for two seconds. Do not touch anything else.”
Where you’ve seen it
Damian Isla's GDC 2005 talk on Halo 2 described its AI as a tree-like graph of about 50 behaviours chosen by priority. It remains one of the best-known accounts of the approach.
Not to be confused with utility ai
A behaviour tree has a fixed order of priorities written by a person. Utility AI gives each option a score from the current situation, and takes the highest.