【GDScript】检测在手机上的触摸按下、拖拽、抬手

如何在godot 里面 检测 手机触摸事件，在Godot 3.2.4版本下使用下面代码

var touch_pos = Vector2.ZERO	# 触摸位置
var lift_up_pos = Vector2.ZERO	# 抬手位置
func _input(event: InputEvent) -> void:
	# 触摸按下
	if event is InputEventScreenTouch:
		touch_pos = event.position
	
	# 拖拽
	elif event is InputEventScreenDrag:
		lift_up_pos = event.position
	
	# 触摸抬起
	elif event is InputEventMouseButton:
		if touch_pos.distance_to(lift_up_pos) > 10:
			printt(touch_pos.distance_to(lift_up_pos), 
				lift_up_pos, touch_pos
			)
		lift_up_pos = event.position
		touch_pos = event.position