game-ai-patterns

Game AI Patterns

Behavior Tree Node Types

Composite Nodes

# Sequence: all children must succeed (AND)
# Returns FAILURE on first child failure, SUCCESS if all succeed
class_name BTSequence extends BTComposite
func _tick(delta: float) -> Status:
    for child in children:
        var status := child.tick(delta)
        if status != Status.SUCCESS:
            return status  # FAILURE or RUNNING propagates up
    return Status.SUCCESS

# Selector: first child to succeed wins (OR)
# Returns SUCCESS on first child success, FAILURE if all fail
class_name BTSelector extends BTComposite
func _tick(delta: float) -> Status:
    for child in children:
        var status := child.tick(delta)
        if status != Status.FAILURE:
            return status  # SUCCESS or RUNNING propagates up
    return Status.FAILURE

# Parallel: runs all children simultaneously
# succeeds when N children succeed (default: all)
class_name BTParallel extends BTComposite
@export var success_threshold: int = -1  # -1 = all children
func _tick(delta: float) -> Status:
    var success_count := 0
    var threshold := success_threshold if success_threshold > 0 else children.size()
    for child in children:
        var status := child.tick(delta)
        if status == Status.SUCCESS:
            success_count += 1
    return Status.SUCCESS if success_count >= threshold else Status.RUNNING

Decorator Nodes

# Inverter: flips SUCCESS <-> FAILURE
class_name BTInverter extends BTDecorator
func _tick(delta: float) -> Status:
    match child.tick(delta):
        Status.SUCCESS: return Status.FAILURE
        Status.FAILURE: return Status.SUCCESS
        _: return Status.RUNNING

# Cooldown: prevents child from running more than once per interval
class_name BTCooldown extends BTDecorator
@export var cooldown_time: float = 2.0
var _last_success_time: float = -INF
func _tick(delta: float) -> Status:
    if Time.get_ticks_msec() / 1000.0 - _last_success_time < cooldown_time:
        return Status.FAILURE
    var status := child.tick(delta)
    if status == Status.SUCCESS:
        _last_success_time = Time.get_ticks_msec() / 1000.0
    return status