Javascript implements 3D switching focus map_javascript skills

I made a small attempt to use mouse dragging with CSS3. The screenshot is as follows:

Friends who are familiar with the drag effect should be familiar with the method of dragging left and right after holding down the mouse.
What this small demo attempts is to apply relevant knowledge points in CSS3 to image display,
When dragging the picture, it will show a three-dimensional feeling~~

The direct code is as follows:

#list{ width:400px; height:440px; margin:30px auto 30px; position:relative;z-index:500;}
#list li{height:40px;width:400px; position:relative;cursor:pointer;-webkit-perspective:800px; }
#list li div{height:40px;width:400px; -webkit-transform-style:preserve-3d;-webkit-backface-visibility:hidden;position:relative;-webkit-transform:translateZ(-200px);-webkit-transform:50ms all linear;}
#list span{height:40px; width:400px; position:absolute;left:0;top:0; overflow:hidden;}
#list div span:nth-child(1){background:url(img/1.jpg) no-repeat; -webkit-transform:translateZ(200px);}
#list div span:nth-child(2){background:url(img/2.jpg) no-repeat;-webkit-transform-origin:right;-webkit-transform:translateZ(200px) rotateY(-90deg);
}
#list div span:nth-child(3){background:url(img/3.jpg) no-repeat;-webkit-transform-origin:right;-webkit-transform:translateZ(-200px);
}
#list div span:nth-child(4){background:url(img/4.jpg) no-repeat;-webkit-transform-origin:left;-webkit-transform:translateZ(200px) rotateY(90deg);
}
#list em{ width:400px;height:400px; position:absolute;left:0;background:#666;}
#list li em:nth-of-type(1){-webkit-transform-origin:top;-webkit-transform:translateZ(200px) rotateX(-90deg); top:0;}
#list li em:nth-of-type(2){-webkit-transform-origin:bottom;-webkit-transform:translateZ(200px) rotateX(90deg); bottom:0;}
#list li:nth-last-child(1){ z-index:10;}
#list li:nth-last-child(2){ z-index:20;}
#list li:nth-last-child(3){ z-index:30;}
#list li:nth-last-child(4){ z-index:40;}
#list li:nth-last-child(5){ z-index:50;}
#list li:nth-last-child(6){ z-index:60;}
#list li:nth-child(2) span{ background-position:0 -40px;}
#list li:nth-child(3) span{ background-position:0 -80px;}
#list li:nth-child(4) span{ background-position:0 -120px;}
#list li:nth-child(5) span{ background-position:0 -160px;}
#list li:nth-child(6) span{ background-position:0 -200px;}
#list li:nth-child(7) span{ background-position:0 -240px;}
#list li:nth-child(8) span{ background-position:0 -280px;}
#list li:nth-child(9) span{ background-position:0 -320px;}
#list li:nth-child(10) span{ background-position:0 -360px;}
#list li:nth-child(11) span{ background-position:0 -400px;}
#btns{ width:130px; margin:0 auto;}
#btns li{ width:20px;height:20px;background:#fff; font-size:14px; font-weight:bold; text-align:center; line-height:20px; float:left; color:#f60; margin:0 3px; cursor:pointer;}
#btns .active{ background:#f60;color:#fff;}

HTML

<ul id="list">
 <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
  <li>
   <div>
      <span></span>
      <span></span>
      <span></span>
      <span></span>
      <em></em>
      <em></em>
    </div>
  </li>
</ul>
<ol id="btns">
 <li class="active">1</li>
  <li>2</li>
  <li>3</li>
  <li>4</li>
</ol>

JAVASCRIPT

var oList=document.getElementById("list");
var oBtns=document.getElementById("btns");
tabPic(oList,oBtns);
function tabPic(obj,btns)
{
 var aLi=obj.getElementsByTagName("li");
 var aBtn=btns.getElementsByTagName("li");
 var oUl=document.getElementsByTagName('ul')[0];
 var iDis=aLi[0].offsetWidth;
 var iDeg=90;
 aBtn.iNow=0;
 for(var i=0;i<aBtn.length;i++)
 {
 oUl.title=aBtn[i].title='妙味课堂-www.miaov.com';
 aBtn[i].index=i;
 aBtn[i].onclick=function()
 {
  for(var i=0;i<aLi.length;i++)
  {
  starMove(aLi[i],-this.index*iDeg,aBtn);
  }
 };
 }
 for(var i=0;i<aLi.length;i++)
 { 
 aLi[i].index=i;
 aLi[i].iDeg=0;
 aLi[i].off=false;
 aLi[i].onmousedown=function(ev)
 {
  if(this.off)
  {
  return;
  }
  var ev=event||ev;
  var iNowX=ev.clientX;
  var iNowDeg=0;
  var oThis=this;
  var iLength=0;
  var iMin=0;
  var iMax=0;
  document.onmousemove=function(ev)
  {
  if(Math.abs(iNowDeg)>=80)
  {
   return;
  }
  var ev=event||ev;
  iNowDeg+=(ev.clientX-iNowX)/iDis*(iDeg-30);
  iLength=Math.abs(parseInt(iNowDeg/9));
  iMin=oThis.index-iLength>0&#63;oThis.index-iLength:0;
  iMax=oThis.index+iLength<aLi.length&#63;oThis.index+iLength:aLi.length-1; 
  for(var i=iMin;i<=iMax;i++)
  {
   aLi[i].iDeg+=(ev.clientX-iNowX)/iDis*(iDeg-30);
   setDeg(aLi[i]);
  }
  iNowX=ev.clientX;  
  }
  document.onmouseup=function()
  {
  var iEnd=0;
  document.onmouseup=document.onmousemove=null;
  if( Math.abs(iNowDeg)>iDeg/4)
  {
   iEnd=iNowDeg>0&#63;90-iNowDeg:-(90-Math.abs(iNowDeg));
  }
  else
  {
   iEnd=-iNowDeg;
  }  
  iEnd=Math.round(iEnd+oThis.iDeg);
  for(var i=0;i<aLi.length;i++)
  {
   starMove(aLi[i],iEnd,aBtn);
  }
  }
  return false;
 };
 }
}
function starMove(obj,iTarget,aBtn)
{
 if(obj.timer)
 {
 clearInterval(obj.timer);
 }
 obj.off=true;
 var iSpeed=0;
 var iNow= iTarget>=0&#63; Math.abs((aBtn.length-iTarget/90)%aBtn.length): Math.abs((iTarget/90) % aBtn.length);
 if(iNow!=aBtn.iNow)
 {
 aBtn[aBtn.iNow].className="";
 aBtn.iNow=iNow;
 aBtn[aBtn.iNow].className="active";
 }
 obj.timer=setInterval(
 function()
 {
  iSpeed+=(iTarget-obj.iDeg)/12;
  iSpeed*=0.86;
  if(Math.abs(obj.iDeg-iTarget)<0.5 && Math.abs(iSpeed)<0.5)
  {
  clearInterval(obj.timer);
  obj.iDeg=iTarget;
  obj.off=false;
  }
  else
  { 
  obj.iDeg+=iSpeed;
  }
  setDeg(obj);
 },24
 );
}
function setDeg(obj)
{
 var oDiv=obj.children[0];
 with(oDiv.style)
 {
 WebkitTransform="translateZ(-200px) rotateY("+obj.iDeg+"deg)";
 }
}

This effect is just a trial. If you need it, you can leave a message below and send the source code directly.