Behavior Trees for Computer Games

Abstract

Although a Finite State Machine (FSM) is easy to implement the behaviors of None-Player Characters (NPC) in computer games, it is difficult to maintain and control the behaviors with increasing the number of states. Alternatively, Behavior Tree (BT), which is a tree of hierarchical nodes to control the ow of decision making, is widely used in computer games to address the scalability issues. This paper reviews the structure and semantics of BTs in computer games. Different techniques to automatically learn and build BTs as well as strengths and weaknesses of these techniques are discussed. This paper provides a taxonomy of BT features and shows to what extent these features are taken into account in computer games. Finally, the paper shows how BTs are used in practice in the gaming industry.