html5 convas如何绘制gif动图?

html5 convas可以用来绘制gif动图么,绘制图片可以,但是动图怎么实现呢?

麻烦会的小伙伴能提供个简单的demo看一下。谢谢

<!DOCTYPE HTML>
 2 <html>
 3     <head>
 4         <meta charset="utf-8" />
 5         <title>canvas上画动态图,视频也可以画</title>
 6         
 7         <script type="text/javascript">
 8             window.onload = function() {
 9                 var img = document.getElementById(\'img1\');
10                 var can = document.getElementById(\'can\');
11                 var cxt = can.getContext(\'2d\');
12                 
13                 
14                 setInterval(function (){cxt.drawImage(img, 0, 0);}, 20);
15             }
16         </script>
17     </head>
18     
19     <body>
20         <p>准备绘制的动态图片:</p>
21         <img id="img1" src="ex.gif" alt="你的浏览器不支持img标签"></img>
22         <p>canvas画布上绘制的动态图片:</p>
23         <canvas id="can" width="800px" height="600px" style="background-color: #CCCCCC">你的浏览器不支持canvas标签</canvas>
24     </body>
25 </html>