查看效果：http://keleyi.com/keleyi/phtml/html5/7.htm
完整代码：
<!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>
<title>用html5的canvas画布绘制贝塞尔曲线-柯乐义</title>
</head>
<body>
<div>
<a href="http://keleyi.com/a/bjac/j77m9131.htm" target="_blank">原文</a></div> <canvas id="keleyi_com" height="300" width="400"></canvas>
<script type="text/javascript">
function draw(id)
{
var canvas=document.getElementById(id);
if(canvas==null)
return false;
var context=canvas.getContext('2d');
context.fillStyle="#eeeeff";
context.fillRect(0,0,400,300);
var n=0;
var dx=150;
var dy=150;
var s=100;
context.beginPath();
context.globalCompositeOperation='and';
context.fillStyle='rgb(100,255,100)';
context.strokeStyle='rgb(0,0,100)';
var x=Math.sin(0);
var y=Math.cos(0);
var dig=Math.PI/15*11;
for(var i=0;i<30;i++)
{
var x=Math.sin(i*dig);
var y=Math.cos(i*dig);
context.bezierCurveTo(dx+x*s,dy+y*s-100,dx+x*s+100,dy+y*s,dx+x*s,dy+y*s);
}
context.closePath();
context.fill();
context.stroke();
} draw("keleyi_com");
</script>
</body>
</html>