# Behavior Trees

Behavior trees are less formal than finite state machines, they are more of a software engineering tool that expands on finite state machines.

They are setup like a tree, the root node is the highest level goal and you traverse leafs.

Many game engines have replaced state machines with behavior tree implementations.

Ex: pyTrees.

# Sequence Nodes

A sequence node has multiple sequential leaf nodes. You walk the sequence, and if one leaf node fails the whole sequence node goes to a failed state. If they all succeed the sequence node succeeds.

# Selector Nodes

Executes leaves from left to right until the first one succeeds - try different things in decreasing priority.

# Parallel Node

Execute tasks in parallel, only succeed if all children succeed.

# Decorators

Nodes with special behavior that apply to any child or children, such as "repeat".

# Blackboards

• Shared memory
• Controlled read and write behavior

# Real-time Execution Model

• Introduce new state RUNNING
• Return to last RUNNING state after each tick
• We can now implement real-time reactive behaviors

# Advantages

• Forces engineers to consider failures early in the process
• Composability (because SUCCESS, FAILURE, and RUNNING gives a high level general interface for all nodes)