UNITY UItookit中panel元素的拖拽

using UnityEngine;
using UnityEngine.UIElements;

public class DragUI : MonoBehaviour
{
VisualElement m_VisualElement;
private float ScreenRatio;
private Vector2 pos;
bool CanMove = false;
private Vector2 Diff;
void Start()
{
UIDocument document = GetComponent<UIDocument>();
var root = document.rootVisualElement;
m_VisualElement = root.Q<VisualElement>();
m_VisualElement.RegisterCallback<PointerDownEvent>(OnPointerDown);
m_VisualElement.RegisterCallback<PointerMoveEvent>(OnPointerMove);
m_VisualElement.RegisterCallback<PointerUpEvent>(OnPointerUp);
}

private void Update()
{

pos = RuntimePanelUtils.ScreenToPanel(m_VisualElement.panel, new Vector2(Input.mousePosition.x, Screen.height - Input.mousePosition.y));
}


private void OnPointerDown(Poi