using UnityEngine;
using UnityEngine.EventSystems;

public class DragUIMove : MonoBehaviour, IPointerDownHandler, IDragHandler, IPointerUpHandler,IEndDragHandler{
    public RectTransform canvas; 
    private RectTransform imgRect;
    Vector2 offset = new Vector3();
    private bool UICanMove = false; //判斷當前的拖拽是否可以讓整個UI移動，滑鼠在其他按鈕上時拖拽，避免造成錯誤。
    // Use this for initialization
    void Awake()
    {
        imgRect = GetComponent<RectTransform>();

    }

    public void OnPointerDown(PointerEventData eventData)
    {
        Vector2 mouseDown = eventData.position;
        Vector2 mouseUguiPos = new Vector2();
        bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDown, eventData.enterEventCamera, out mouseUguiPos);
        if (isRect)
        {
            offset = imgRect.anchoredPosition - mouseUguiPos;
            UICanMove = true;
        }
    }
    public void OnDrag(PointerEventData eventData)
    {
        if(UICanMove)
        {
            Vector2 mouseDrag = eventData.position;   
            Vector2 uguiPos = new Vector2();  
            bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDrag, eventData.enterEventCamera, out uguiPos);

            if (isRect)
            {
                imgRect.anchoredPosition = offset + uguiPos;
            }
        }
    }
    public void OnPointerUp(PointerEventData eventData)
    {
        offset = Vector2.zero;
        UICanMove = false;
    }
    public void OnEndDrag(PointerEventData eventData)
    {
        offset = Vector2.zero;
        UICanMove = false;
    }
}