A Naive Behavior Tree Plugin

Compile a behavior tree script, and turn it into a PackedScene file which contains a behavior tree.

简体中文

Introduction

The code of BTNode part in this project is literally a copy of this project: https://github.com/libgdx/gdx-ai/wiki/Behavior-Trees.

The compiler part is designed by myself, so it might have a lot of bugs. XD

More tests need to be done, so that it can actually be used in a real project.

The BTS is refer to Behavior Tree Script.

Syntex

line = [[indent] [guardableTask] [comment]]
guardableTask = [guard [...]] task
guard = '(' task ')'
task = name [param:value [...]] | subtreeRef

Behavior Tree Nodes

BTNode

All behavior tree nodes inherit from this node.

BehaviorTree

It stores the root node, and the agent storing your custom game object which can be used in BTNode like this: tree.agent.

BTAction

Refer to an action. Your custom node should inherit from this node.

Example:

tool
extends BTAction

export(String) var msg:String

#----- Methods -----
func execute():
  print(msg)
  return SUCCEEDED

You need to override execute() function in order to implement your custom function.

In this function, you can use tree to access the Behavior Tree itself, tree.agent to access your custom game object.

Return SUCCEEDED to indicate the action is done, FAILED is fail, RUNNING is running.

You can also use yield to wait for a signal in this function, which is considered a 'running' status.

An example implemented a timer using yield:

tool
extends BTAction

export(float) var wait:float = 1

#----- Methods -----
func execute():
  print('wait for 1 sec')
  yield(get_tree().create_timer(wait), "timeout")
  print('wait for 2 sec')
  yield(get_tree().create_timer(2), "timeout")
  print('wait for 3 sec')
  yield(get_tree().create_timer(3), "timeout")
  print('done.')
  return SUCCEEDED

More Example

# Comment
import alias: "path/to/your/custom/behavior/tree/node.gd" # Import custom node
import dead?: "path/to/your/custom/behavior/tree/node.gd" # Yes, you can use '?' as an ID or alias name.

subtree name: xxx # Define a subtree, the first node is root, use indent to indicate the relation of parent or child node.
 parrallel orchestrator: JOIN # the left of ':' is parameter，the right is an expression that eval at complie time
  alias
  alias

tree # A bts file can only contain at least one tree. Same as the subtree.
 sequence
  $xxx # Refer to a subtree
  (dead?) alias # use 'dead?' as a guard.

#
# The behavior tree of a dog.
#

import bark:"res://dog/bt/BarkTask.gd"
import care:"res://dog/bt/CareTask.gd"
import mark:"res://dog/bt/MarkTask.gd"
import walk:"res://dog/bt/WalkTask.gd"

subtree name: caretree
 parallel
  care times:  3 
  alwaysFail
   'res://dog/bt/RestTask' # Use a path to a gdscript directly.

tree
 selector 
  $caretree # use '$' to refer to a subtree
  sequence
   bark times: randi_range(1, 3) # use a buit-in function that return a random integer between 1 and 3.
   walk
   "res://dog/bt/BarkTask"

Built-in nodes in BTS

# Actions
fail # Always fail
success # Always success
timer wait: 1.0 # Wait for 1 sec.

# Composites
dynamic_guard_selector # Choose a child to run at a time by guard check that succeeded.
parallel policy: SEQUENCE/SELECTOR orchestrator: RESUME/JOIN # Run all children at a time with the policy and orchestrator applied.
selector # Choose a child to run in order.
random_selector
sequence # Run children one by one in order.
random_sequence

# Decorators - wrap the result of a child.
always_fail
always_succeed
invert
random success_posibility: 0.5 # Has a chance of 0.5 to run the child.
repeat times: 1 # Repeat the child for 1 time.
until_fail # Run child until it fail.
until_success # Run child until it scceeded.

License

MIT