html5 canvas arcTo()

<!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="red";
                 context.lineWidth=4;
         context.lineTo(100,200);
         context.arcTo(350,350,100,100,20);
         context.stroke();
         context.closePath();
          
         //以下为了给个直观的感觉，画的参考线
         context.beginPath();
         context.strokeStyle="#ddd";
         context.lineWidth=2;
         context.moveTo(0,350);
         context.lineTo(350,350);
         context.stroke();
         context.closePath();
           
         context.beginPath();
         context.moveTo(350,0);
         context.lineTo(350,350);
         context.stroke();
         context.closePath();
          
         context.beginPath();
         context.moveTo(100,0);
         context.lineTo(100,100);
         context.stroke();
         context.closePath();
          
          
         context.beginPath();
         context.moveTo(0,100);
         context.lineTo(100,100);
         context.stroke();
         context.closePath();
          
          
         context.beginPath();
         context.moveTo(350,350);
         context.lineTo(100,200);
         context.stroke();
         context.closePath();
          
          
         context.beginPath();
         context.moveTo(100,100);
         context.lineTo(350,350);
         context.stroke();
         context.closePath();
   }
}
 
 
</script>
<canvas id="canvas" width="500" height="500">
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</canvas>
</body>
</html>