<template>
  <div>
    <div class="move" @mouseover="over()" @mouseout="out()" @mousemove="move($event)">
      <div id="small">  //小圖片以及遮罩層容器
        <div id="float"></div>  //遮罩層
        <img :src="item" id="smallimg">  //需要放大的圖片
      </div>
    </div>
    <div id="big">
      <img :src="item">    //放大以后的圖片
    </div>
  </div>
</template>

<script>
  var float,smallimg,big,bigImg,small,float_maxJL_t,float_maxJL_l,bigImg_maxJL_t,bigImg_maxJL_l;

  export default{
    props: {
      item: {
        type: String
      }
    },
    data() {
     return{
     }
    }, 

    mounted(){
      float = document.getElementById("float"); //左側(cè)遮罩層
      smallimg = document.getElementById("smallimg"); //左邊的小圖
      big = document.getElementById("big"); //右側(cè)可視區(qū)域
      bigImg = big.getElementsByTagName("img")[0]; //右側(cè)大圖
      small = document.getElementById("small");// 左側(cè)的容器

      //得到右側(cè)可視區(qū)的寬高
      var bigW = big.clientWidth;
      var bigH = big.clientHeight;

      //右側(cè)大圖的寬高
      var bigImgW = bigImg.offsetWidth;
      var bigImgH = bigImg.offsetHeight;

      //左側(cè)的小圖的寬高
      var smallImgW = smallimg.offsetWidth;
      var smallImgH = smallimg.offsetHeight;

      //左側(cè)遮罩層的寬高
      float.style.width =  bigW/bigImgW * smallImgW + "px";   //175
      float.style.height = bigH/bigImgH * smallImgH/3*2 + "px";     

      //遮罩層運動的最大距離
      float_maxJL_l = small.clientWidth -float.offsetWidth-10;
      float_maxJL_t = small.clientHeight - float.offsetHeight-5;

      //右側(cè)圖片運動的最大距離
      bigImg_maxJL_l = bigImg.clientWidth - big.offsetWidth;
      bigImg_maxJL_t = bigImg.clientHeight - big.offsetHeight;

      big.style.display = "none";
      float.style.visibility ="hidden"; //鼠標未移入左側(cè)區(qū)域使遮罩層以及右側(cè)大圖均不可見
    },

    methods: {
    //鼠標移入左側(cè)區(qū)域使遮罩層以及右側(cè)大圖可見
      over: function () {
        float.style.visibility ="visible";
        big.style.visibility ="visible";
        big.style.display = "block";
      }, 

      //鼠標移出左側(cè)區(qū)域使遮罩層以及右側(cè)大圖不可見
      out: function () {
        float.style.visibility ="hidden";
        big.style.display = "none";
      }, 

      //鼠標移動時遮罩層隨鼠標的移動而移動
      move: function (ev) {
        var l = ev.clientX  - small.offsetLeft - float.offsetWidth/2;
        var t = ev.clientY  - small.offsetTop - float.offsetHeight/2;

        if( l < 0 ) l = 0;     // 超出左邊界賦值為0
        if( t < 0 ) t = 0;     // 超出上邊界賦值為0

        if( l > float_maxJL_l ) l = float_maxJL_l;  //限制其運動范圍在容器之內(nèi)
        if( t > float_maxJL_t ) t = float_maxJL_t;

        //求出來一個比例
        var scaleL = l/float_maxJL_l;
        var scaleT = t/float_maxJL_t;

         //遮罩層運動位置
        float.style.left = l + "px";
        float.style.top = t + "px"; 

         //右側(cè)大圖運動位置
        bigImg.style.left = -scaleL * bigImg_maxJL_l + "px";
        bigImg.style.top = -scaleT * bigImg_maxJL_t + "px";
      },
    },
  }
</script>

//css樣式
<style lang="scss" rel="stylesheet/scss" scoped>
  @import 'src/assets/scss/variable.scss';
  #float {
    width: 120px;
    height: 120px;
    position: absolute;     //必須
    background: $primary;
    border: 1px solid #ccc;
    opacity: 0.5;
    cursor:move ;
  }
  #big {
    position: absolute;  //必須
    top: 260px;
    left: 37.6%;
    width: 350px;
    height: 500px;
    overflow: hidden;
    border: 1px solid #ccc;
    background: #ffffff;
    z-index: 1;
    visibility: hidden;
  }
  #small {
    position: relative;  //必須
    z-index: 1;
    img{
      width:340px;
      height:320px;
    }
  }
  #big img {
    position: absolute;   //必須
    z-index: 5;
    width:700px;
    height:700px;
  }
</style>

move = function (ev){
        var scroll =  this.getClientHeight(); //得到當(dāng)前界面移動的位置

        var l = ev.clientX  - small.offsetLeft - float.offsetWidth/2;
        var t = ev.clientY  - small.offsetTop - float.offsetHeight/2;

        t=t+scroll;  //遮罩層移動的高度應(yīng)該相應(yīng)的加上界面滾動的高度

        if( l < 0 ) l = 0;
        if( t < 0 ) t = 0; 

        if( l > float_maxJL_l ) l = float_maxJL_l;
        if( t > float_maxJL_t ) t = float_maxJL_t;

        var scaleL = l/float_maxJL_l;
        var scaleT = t/float_maxJL_t;

        float.style.left = l + "px";
        float.style.top = t + "px";

        bigImg.style.left = -scaleL * bigImg_maxJL_l + "px";
        bigImg.style.top = -scaleT * bigImg_maxJL_t + "px";
},
//獲取界面滾動的高度的方法
getClientHeight: function(){
    var scrollTop=0;
    if(document.documentElement&&document.documentElement.scrollTop)
    {
      scrollTop=document.documentElement.scrollTop;
    }
    else if(document.body)
    {
      scrollTop=document.body.scrollTop;
    }
    return scrollTop;
}