using UnityEngine;
using UnityEngine.EventSystems;
using System.Collections;
using System;

//給空間添加監(jiān)聽事件要實(shí)現(xiàn)的一些接口
public class MyDrag : MonoBehaviour, IPointerDownHandler, IDragHandler, IPointerUpHandler, 
 IEndDragHandler, IPointerEnterHandler, IPointerExitHandler {

 public RectTransform canvas;   //得到canvas的ugui坐標(biāo)
 private RectTransform imgRect;  //得到圖片的ugui坐標(biāo)
 Vector2 offset = new Vector3(); //用來得到鼠標(biāo)和圖片的差值
 Vector3 imgReduceScale = new Vector3(0.8f, 0.8f, 1); //設(shè)置圖片縮放
 Vector3 imgNormalScale = new Vector3(1, 1, 1); //正常大小

 // Use this for initialization
 void Start () {
  imgRect = GetComponent<RectTransform>();

 }

 //當(dāng)鼠標(biāo)按下時(shí)調(diào)用 接口對(duì)應(yīng) IPointerDownHandler
 public void OnPointerDown(PointerEventData eventData)
 {
  Vector2 mouseDown = eventData.position; //記錄鼠標(biāo)按下時(shí)的屏幕坐標(biāo)
  Vector2 mouseUguiPos = new Vector2(); //定義一個(gè)接收返回的ugui坐標(biāo)
  //RectTransformUtility.ScreenPointToLocalPointInRectangle()：把屏幕坐標(biāo)轉(zhuǎn)化成ugui坐標(biāo)
  //canvas：坐標(biāo)要轉(zhuǎn)換到哪一個(gè)物體上，這里img父類是Canvas，我們就用Canvas
  //eventData.enterEventCamera：這個(gè)事件是由哪個(gè)攝像機(jī)執(zhí)行的
  //out mouseUguiPos：返回轉(zhuǎn)換后的ugui坐標(biāo)
  //isRect：方法返回一個(gè)bool值，判斷鼠標(biāo)按下的點(diǎn)是否在要轉(zhuǎn)換的物體上
  bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDown, eventData.enterEventCamera, out mouseUguiPos);
  if (isRect) //如果在
  {
   //計(jì)算圖片中心和鼠標(biāo)點(diǎn)的差值
   offset = imgRect.anchoredPosition - mouseUguiPos;
  }
 }

 //當(dāng)鼠標(biāo)拖動(dòng)時(shí)調(diào)用 對(duì)應(yīng)接口 IDragHandler
 public void OnDrag(PointerEventData eventData)
 {
  Vector2 mouseDrag = eventData.position; //當(dāng)鼠標(biāo)拖動(dòng)時(shí)的屏幕坐標(biāo)
  Vector2 uguiPos = new Vector2(); //用來接收轉(zhuǎn)換后的拖動(dòng)坐標(biāo)
  //和上面類似
  bool isRect = RectTransformUtility.ScreenPointToLocalPointInRectangle(canvas, mouseDrag, eventData.enterEventCamera, out uguiPos);

  if (isRect)
  {
   //設(shè)置圖片的ugui坐標(biāo)與鼠標(biāo)的ugui坐標(biāo)保持不變
   imgRect.anchoredPosition = offset + uguiPos;
  }
 }

 //當(dāng)鼠標(biāo)抬起時(shí)調(diào)用 對(duì)應(yīng)接口 IPointerUpHandler
 public void OnPointerUp(PointerEventData eventData)
 {
  offset = Vector2.zero;
 }

 //當(dāng)鼠標(biāo)結(jié)束拖動(dòng)時(shí)調(diào)用 對(duì)應(yīng)接口 IEndDragHandler
 public void OnEndDrag(PointerEventData eventData)
 {
  offset = Vector2.zero;
 }

 //當(dāng)鼠標(biāo)進(jìn)入圖片時(shí)調(diào)用 對(duì)應(yīng)接口 IPointerEnterHandler
 public void OnPointerEnter(PointerEventData eventData)
 {
  imgRect.localScale = imgReduceScale; //縮小圖片
 }

 //當(dāng)鼠標(biāo)退出圖片時(shí)調(diào)用 對(duì)應(yīng)接口 IPointerExitHandler
 public void OnPointerExit(PointerEventData eventData)
 {
  imgRect.localScale = imgNormalScale; //回復(fù)圖片
 }
}