bt.gd

A (simple) script and text based behaviour tree for Godot.

Either create the tree directly:

_bt = BT.create() \
	.parallel() \
		.repeat() \
			.sequence() \
				.do(set_next_pos) \
				.do(walk_to_next_pos.bind(walk_speed)) \
				.wait(func() -> float: return randf_range(0.0, 1.0)) \
			.end() \
		.repeat() \
			.sequence() \
				.do(change_color) \
				.wait(0.75) \
			.end()

Or feed a text

 var text := "
 parallel
 	repeat
 		sequence
 			set_next_pos
 			walk_to_next_pos {0.5 * walk_speed}
			wait $wait_time
	repeat
		sequence
			change_color
			wait 0.75"
_bt = BT.create(self, text)

To actually run the behaviour tree, call _bt.tick() whenever you want it to update - for realtime games this is usually every frame, but for turn-based games this could be on each turn. Behaviour trees created via text also support variables from the target as arguments. If you want these to be updated even after the tree's initialisation, give them a $ prefix (this is probably expensive performance-wise, so only use this for testing purposes).

You can also use expressions by using curly braces, for example like this: {0.5 * _speed}. The expression will be evaluated at initialisation if you don't prefix it with $.

Text-based behaviour trees also support the node tree. If it's at the root, it creates a tree. If you use tree '<name>' inside a tree, it will insert this tree. You can only insert trees defined beforehand, preventing circular insertion. For non-text-based trees, use the insert_tree() method.

Composite nodes (more than 0 children):

• sequence
• selector
• parallel
• race
• randomizer
• if_else

Decorator nodes (1 child):

• ignore
• invert
• override
• repeat
• retry

Other nodes (0 children):

• nothing
• fail
• success
• log
• wait
• do/prep_do/check

do is the tree node that allows using your own custom behaviours. Your behaviour function should return BT.Status.Success, BT.Status.Fail or BT.Status.Running, or a bool. If the function is void or returns null, the status is set to Success; in all other cases the internal status is not changed. There's BT.Status.Nothing, which means the result does not change the execution of the parent decorator or composite node.

You can also create your own custom nodes by inheriting from the BT.N class. The do and check nodes both use the NAction class.

• Originally a port of https://github.com/ratkingsminion/simple-behaviour-tree
• Inspired by fluid BT: https://github.com/ashblue/fluid-behavior-tree
• Also by PandaBT: http://www.pandabt.com/documentation/2.0.0
• About behaviour trees: https://www.gamedeveloper.com/programming/behavior-trees-for-ai-how-they-work