Why is my player only being carried by a platform when they are already moving?

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:bust_in_silhouette: Asked By AlbeyAmakiir

My (3D) Kinematic First-Person player character can stand on a Kinematic moving platform that is translated and rotated horizontally using an AnimationPlayer. When the character has movement from inputs (including when inputs have been released, but deceleration hasn’t finished yet), the character is carried along with the moving platform. But when the character is standing still, the platform slides out from under them; they don’t move horizontally with it and will fall when it goes away. I can’t seem to find why this is or how to fix it?

The input/movement code is based on the FPS tutorial here: http://docs.godotengine.org/en/latest/tutorials/3d/fps_tutorial/index.html

However, the code is very similar to the code for the Kinematic Character 3D example from the templates, and that manages to move the “cubio” character on a horizontal platform without any explicit checks.

My code is below:

func process_movement(delta):
	var camera_transform = camera.get_global_transform()
	
	var axis_movement = Vector2()
	axis_movement.y = Input.get_action_strength("move_forward") - Input.get_action_strength("move_backward")
	axis_movement.x = Input.get_action_strength("move_strafe_right") - Input.get_action_strength("move_strafe_left")
	axis_movement = axis_movement.normalized()
	
	var h_velocity = ongoing_velocity
	h_velocity.y = 0
	
	var target_h_velocity = Vector3()
	var acceleration
	
	target_h_velocity += -camera_transform.basis.z.normalized() * axis_movement.y
	target_h_velocity += camera_transform.basis.x.normalized() * axis_movement.x
	target_h_velocity = target_h_velocity.normalized() * MAX_WALK_SPEED
	
	if axis_movement.length() > 0:
		acceleration = WALK_ACCELERATION
	else:
		acceleration = WALK_DECELERATION
	
	h_velocity = h_velocity.linear_interpolate(target_h_velocity, acceleration * delta)
	
	if is_on_floor():
		if Input.is_action_just_pressed("move_jump"):
			ongoing_velocity.y = JUMP_SPEED
	
	ongoing_velocity.y += delta * GRAVITY
	ongoing_velocity.x = h_velocity.x
	ongoing_velocity.z = h_velocity.z
	
	ongoing_velocity = move_and_slide(ongoing_velocity, Vector3(0, 1, 0), 0.05, 4, deg2rad(MAX_SLOPE_ANGLE))
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:bust_in_silhouette: Reply From: AlbeyAmakiir

In the line: move_and_slide(ongoing_velocity, Vector3(0, 1, 0), 0.05, 4, deg2rad(MAX_SLOPE_ANGLE)), stop_on_slope has been set to a non-zero (true) value. The FPS tutorial here includes this mistake, which is probably why your code has this. This supposedly only matters for slopes, but it also seems to matter for moving platforms. From the docs:

If the body is standing on a slope and the horizontal speed (relative to the floor’s speed) goes below slope_stop_min_velocity, the body will stop completely.

Setting the value to false made it work.