html5 canvas从圆开始

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>html5 canvas从圆开始</title>
<script src="js/modernizr.js"></script>
</head>
 
<body>
 
 
<script type="text/javascript">
window.addEventListener('load',eventWindowLoaded,false);
function eventWindowLoaded(){
    canvasApp();
}
function canvasSupport(){
    return Modernizr.canvas;
}
function canvasApp(){
    if(!canvasSupport()){
        return;
    }else{
        var theCanvas = document.getElementById('canvas')
        var context = theCanvas.getContext("2d")
 
    }
    drawScreen();
    function drawScreen(){
        //颜色粉色，线宽10,
         context.beginPath();
         context.strokeStyle="pink";
         context.lineWidth=10;
         context.arc(100,100,20,(Math.PI/180)*0,(Math.PI/180)*360,false);
         //100,100圆心的位置
         //20半径
         //开始喝结束的弧度制从0-360
         //1弧度 =  π/180°弧度不是角度哦
         //true和false对象弧线方向
         context.stroke();
         context.closePath();
          
         context.beginPath();
         context.arc(200,100,20,(Math.PI/180)*0,(Math.PI/180)*90,false);
         context.stroke();
         context.closePath();
          
         context.beginPath();
         context.arc(300,100,20,(Math.PI/180)*0,(Math.PI/180)*90,true);
         context.stroke();
         context.closePath();
          
   }
}
 
 
</script>
<canvas id="canvas" width="500" height="500">
你的浏览器无法使用canvas
如有疑问加QQ：1035417613;小白童鞋；你的支持是我最大的快乐！！
</canvas>
</body>
</html>