JavaScript与HTML5 Canvas绘制圆环的实现代码

<!DOCTYPE html>
<html>
<head>
 <title> </title>
 <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
</head>
<body>
 <fieldset>
 <canvas id="myCanvas" width="400px" height="400px" >Your browser does not support the HTML5 canvas tag.</canvas>
</fieldset>
<script type="text/javascript">
  function yuanhuan(ctx,data,option){
   var cood=option.cood;
   var radius=option.radius;
   var lastpos=pos=0;
    for(var i=0;i<data.length;i++){
     ctx.beginPath(); 
     ctx.moveTo(cood.x,cood.y); 
     ctx.fillStyle = data[i].bgcolor; 
     pos=lastpos+Math.PI*2*data[i].value/100;
     ctx.arc(cood.x,cood.y,radius,lastpos,pos,false); 
     ctx.fill(); 
     lastpos=pos;
    }
    ctx.beginPath(); 
    ctx.fillStyle ="white"; 
    radius*=0.5;
    ctx.arc(cood.x,cood.y,radius,0,Math.PI*2 ,false); 
    ctx.fill(); 
   }
var data=[
    {bgcolor:'yellowgreen',value:30},
    {bgcolor:'green',value:30},
    {bgcolor:'yellow',value:40}
   ];
 var canvas = document.getElementById("myCanvas"); 
    var ctx = canvas.getContext("2d"); 
   yuanhuan(ctx,data,{cood:{x:200,y:200},radius:150})
</script>
</body>
</html>