Chapter 15: The AI System

The AI system is implemented using a behavior tree. A behavior tree is a model of the decision process of an agent in a game. It represents a set of decisions, which take the form of nodes in a tree structure. These nodes are of two types: leaf nodes (Action) and internal nodes (Selector and Sequence).

Leaf nodes represent actions, the basic building blocks of behavior. Each action returns a BehaviourTreeResult, which can be either Success, Failure, or Running.

Internal nodes, Selector and Sequence, each contain a vector of other nodes. They decide which of their child nodes will be processed and in what order. A Selector node will return immediately with a Success result as soon as one of its child nodes returns Success. On the other hand, a Sequence node will stop processing and return Failure as soon as one of its child nodes fails.

The tick method is called to process the behavior tree. It executes the action, selector, or sequence based on the node type, thus driving the AI's decision-making process.