Behavior trees and state machines with LimboAI

LimboAI addon overview
We'll be using LimboAI for behavior trees and state machines
LimboAI docs | LimboAI on GitHub
 
LimboAI includes a demo project. It is highly recommended that you download it and check it out. When you run it, it has a nice little tutorial that walks you through the basics: https://github.com/limbonaut/limboai/tree/master/demo 
In its classes and nodes, LimboAI uses the following prefixes:
BT: Behavior Tree
Nodes/classes that start with this have to do with parts of behavior trees
As an example, the 
BTPlayer node "plays" a behavior tree every frame and inside of that tree you have 
BTSequence, 
BTSelector, etc
BB: BlackBoard
The blackboard is a shared place for agents to write values to.
These values can be read and written by any task in the tree.
LimboHSM: Hierarchical State Machine
HSMs have 
LimboStates inside of them.
LimboHSM is itself a 
LimboState, and 
BTState can put states inside of behavior trees
Behavior trees
Read the intro to behavior trees here
Accessing LimboAI behavior tree editor
When installed, LimboAI adds a button to the top of the Godot editor, alongside the 2D/3D/Script buttons
When you click on a 
BTPlayer node, it has a 
BehaviorTree attached to it. When clicking that, it will automatically switch over to the LimboAI tab.
Building blocks: sequences and selectors
The main building blocks of a behavior tree are:
BTSequence: Think of these like an AND operator on the child tasks.
As long as a task return 
SUCCESS, the next one will be executed.
BTSelector: Think of these like an OR operator on the child tasks.
On the first task that returns 
SUCCESS, it will stop executing.
Writing custom tasks
Read the documentation on writing custom tasks.
Custom tasks go inside of 
ai/tasks in the project.
At the time of writing, we have:
follow_path: Follows a 
Path3D node (i.e. for preset patrol paths)
generate_navigation_path / 
follow_navigation_path: Using a 
NavigationAgent3D, generate and follow a path to a 
target in the blackboard
follow_navigation_path will follow the path until it gets close enough to the 
target, it will return 
RUNNING until it gets there
distance_based_cooldown: Takes in a 
Curve2D and uses that to do a cooldown based on how close the agent is to the 
target
Useful for generating navigation paths more frequently the closer you are to the 
target, and less frequently the further you are
in_shape_and_visible: Returns 
SUCCESS if there's a target in a 
ShapeCast3D that is visible (hit by a raycast, in "front" of the agent)
This also sets the 
target when it is visible
State machines
https://limboai.readthedocs.io/en/stable/hierarchical-state-machines/create-hsm.html