两种模式：

1.Screen Space-Overlay

public void OnDrag(PointerEventData eventData){
        Vector2 targetDir = eventData.position - new Vector2(transform.position.x, transform.position.y); // 目标坐标与当前坐标差的向量　　 float ang = Vector2.Angle(Vector3.right, targetDir); // 返回当前坐标与目标坐标的角度    if (eventData.position.y 

2.Screen Space-Camera

public void OnDrag(PointerEventData eventData)    {
            Camera camera = GameObject.Find("Main Camera").GetComponent
     
      ();        Vector3 screenPos = camera.WorldToScreenPoint(transform.position);//世界坐标转屏幕坐标        Vector2 targetDir = eventData.position - new Vector2(screenPos.x, screenPos.y);// 目标坐标与当前坐标差的向量float ang = Vector2.Angle(Vector3.right, targetDir); // 返回当前坐标与目标坐标的角度        if (eventData.position.y < screenPos.y)        {            ang = 360 - ang;        }        transform.localEulerAngles = new Vector3(0, 0, ang);           }