放大镜

前提：两张图（200x200 , 450x450）

<style>
  .myDiv{position: relative;width: 200px;height: 200px;}
  .float_lay{width: 50px;height: 50px;border:1px solid #3c9;background: rgba(255,255,255,.6);
    position: absolute;top:0;left: 0;cursor: pointer; }
  .smallBox{position: relative;width:200px;height: 200px;}
  .smallBox img{height: 100%;}
  .largeBox{position: absolute;top:0;left:320px;border:4px solid #ff5454;overflow: hidden;
    width: 250px;height:250px;}
</style>
<div class="myDiv">
  <div class="smallBox">
    <div class="float_lay"></div>
    <img class="smallImg" src="../public/images/small.png" alt=""/>
  </div>
  <div class="largeBox">
    <img class="largeImg" src="../public/images/big.png" alt=""/>
  </div>
</div>
<script>
  $(function () {
    $smallBox.on('mousemove',function (e) {//火狐没有event，所以需要传
       var divPos=$('.myDiv').offset();//获取图片距离页面边距
       var x=e.clientX;
       var y=e.clientY;
       var picLeft=x-divPos.left-25;
       var picTop=y-divPos.top-25;
       var seePic=$('.largeBox').width();
       var largePic=$('.largeBox img').width();
       var percentL;
       var percentT;
       if(picLeft<0){
         picLeft=0;
       }else if(picLeft>150){
         picLeft=150;
       }
       if(picTop<0){
         picTop=0;
       }else if(picTop>150){
         picTop=150;
       }
       $('.float_lay').css({top:picTop+'px',left:picLeft+'px'});
       percentL=-picLeft/150*(largePic-seePic);
       percentT=-picTop/150*(largePic-seePic);
       $('.largeBox img').css({marginTop:percentT+'px',marginLeft:percentL+'px'});
    });
  });
</script>