godot-steering-ai-framework/project/src/Behaviors/GSTMatchOrientation.gd

# Calculates an angular acceleration to match an agent's orientation to that of
# its target. Attempts to make the agent arrive with zero remaining angular
# velocity.
class_name GSTMatchOrientation
extends GSTSteeringBehavior


# The target orientation for the behavior to try and match rotations to.
var target: GSTAgentLocation
# The amount of distance in radians for the behavior to consider itself close
# enough to be matching the target agent's rotation.
var alignment_tolerance: float
# The amount of distance in radians from the goal to start slowing down.
var deceleration_radius: float
# The amount of time to reach the target velocity
var time_to_reach: float = 0.1


func _init(agent: GSTSteeringAgent, target: GSTAgentLocation).(agent) -> void:
	self.target = target


func _match_orientation(acceleration: GSTTargetAcceleration, desired_orientation: float) -> GSTTargetAcceleration:
	var rotation := wrapf(desired_orientation - agent.orientation, -PI, PI)

	var rotation_size := abs(rotation)

	if rotation_size <= alignment_tolerance:
		acceleration.set_zero()
	else:
		var desired_rotation := agent.angular_speed_max

		if rotation_size <= deceleration_radius:
			desired_rotation *= rotation_size / deceleration_radius

		desired_rotation *= rotation / rotation_size

		acceleration.angular = (desired_rotation - agent.angular_velocity) / time_to_reach

		var limited_acceleration := abs(acceleration.angular)
		if limited_acceleration > agent.angular_acceleration_max:
			acceleration.angular *= agent.angular_acceleration_max / limited_acceleration

	acceleration.linear = Vector3.ZERO

	return acceleration


func _calculate_steering(acceleration: GSTTargetAcceleration) -> GSTTargetAcceleration:
	return _match_orientation(acceleration, target.orientation)