Of Stack

Native js realizes the effect of commercial magnifying glass

  • 2021-07-10 18:29:05
  • OfStack

Implementation principle

Magnifying glass on big picture: Display area of small picture = size of big picture: size of small picture = offsetLeft of big picture: offsetLeft of small picture

Then only offsetLeft of large picture is unknown in the above formula, so offsetLeft of large picture = large picture size/small picture size * offsetLeft of small picture

There are detailed comments in the code

Complete code

Note: Replace the pictures to see the effect after copying to the local area 


<!DOCTYPE html>
<html lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>demo</title>
<style>
body,h1,h2,h3,h4,h5,h6,hr,p,blockquote,dl,dt,dd,ul,ol,li,pre,form,fieldset,legend,button,input,textarea,th,td{margin:0;padding:0;}
h1,h2,h3,h4,h5,h6{font-size:100%;}
address,cite,dfn,em,var{font-style:normal;}
code,kbd,pre,samp{font-family:courier new,courier,monospace;}
ul,ol{list-style:none;}
a{text-decoration:none;}
a:hover{text-decoration:none;}
sup{vertical-align:text-top;}
sub{vertical-align:text-bottom;}
legend{color:#000;}
fieldset,img{border:0;}
button,input,select,textarea{font-size:100%;}
table{border-collapse:collapse;border-spacing:0;}
.clear{clear: both;float: none;height: 0;overflow: hidden;}
#demo{display:block;width:400px;height:255px;margin:50px;position:relative;border:1px solid#ccc}
#small-box{position:relative;z-index:1}
#float-box{display:none;width:160px;height:120px;position:absolute;background:#ffffcc;border:1px solid#ccc;filter:alpha(opacity=50);opacity:0.5}
#mark{position:absolute;display:block;width:400px;height:255px;background-color:#fff;filter:alpha(opacity=0);opacity:0;z-index:10}
#big-box{display:none;position:absolute;top:0;left:460px;width:400px;height:300px;overflow:hidden;border:1px solid#ccc;z-index:1}
#big-box img{position:absolute;z-index:5}
</style>
</head>
<body>
<div id="demo">
  <div id="small-box">
    <div id="mark"></div>
    <div id="float-box"></div>
    <img src="images/small.jpg"/>
  </div>
  <div id="big-box">
    <img src="images/big.jpg"/>
  </div>
</div>
<script type="text/javascript">
  // Execute multiple function scenarios immediately after the page loads 
  function addloadEvent(func){
    var oldonload=window.onload;
    if(typeof window.onload !="function"){
      window.onload=func;
    }
    else{
      window.onload=function(){
        if(oldonload){
          oldonload(); 
        }
        func();
      }
    }
  }
  // Execute multiple functions immediately after the page loads. Scenario ends 
  addloadEvent(b);
  function b(){
   // Get Perimeter Container 
   var demo=document.getElementById("demo");
   // Get Small Picture Container 
   var s_Box=document.getElementById("small-box");
   // Get Large Picture Container 
   var b_Box=document.getElementById("big-box");
   // Get a large picture 
   var b_Image=b_Box.getElementsByTagName("img")[0];
   // Get magnifying glass 
   var f_Box=document.getElementById("float-box");
   // The top cover plate is used for mouse movement 
   var mark=document.getElementById("mark");
   // Move into magnifying glass and large picture container display 
   mark.onmouseover=function(){
   f_Box.style.display="block";
   b_Box.style.display="block";
   }
   // Remove magnifying glass and hide large picture container 
   mark.onmouseout=function(){
   f_Box.style.display="none";
   b_Box.style.display="none";
   }
   // Move event 
   mark.onmousemove=function(ev){
   // Get mouse coordinates window Compatible ie
   var e=ev||window.event;
   // Current mouse x Shaft - Container relative body Offset - Offset value of small container relative to parent container - Magnifying glass width 1 Half = Current position of magnifying glass 
   var left=e.clientX-demo.offsetLeft-s_Box.offsetLeft-f_Box.offsetWidth/2;
   // The formula is the same as above 
   var top=e.clientY-demo.offsetTop-s_Box.offsetTop-f_Box.offsetHeight/2;
   // Judge is displayed on the edge when the magnifying glass is moved out of the container 
   if(left<0){
    left=0;
   }else if(left>(s_Box.offsetWidth-f_Box.offsetWidth)){
    left=s_Box.offsetWidth-f_Box.offsetWidth;
   }
   if(top<0){
    top=0;
   }else if(top>(s_Box.offsetHeight-f_Box.offsetHeight)){
    top=s_Box.offsetHeight-f_Box.offsetHeight;
   }
   // Magnifier current position 
   f_Box.style.left=left+"px";
   f_Box.style.top=top+"px";
   // Acquisition ratio 
   var z=b_Image.offsetWidth/s_Box.offsetWidth;
   // Offset with magnifying glass * Proportion = The offset of a large picture is in the opposite direction, so it is negative 
   b_Image.style.left=-left*z+"px";
   b_Image.style.top=-top*z+"px";
   }
  }
</script>
</body>
</html>
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