<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Canvas</title>
</head>
<style type="text/css">
body{margin:20px auto; padding:0; width:800px; }
canvas{border:dashed 2px #CCC}
</style>
<script type="text/javascript">
function $$(id){
return document.getElementById(id);
}
function pageLoad(){
var can = $$(‘can‘);
var cans = can.getContext(‘2d‘);
var objImg = new Image();
objImg.src = ‘lin.jpg‘;
objImg.onload = function (){
cans.drawImage(objImg,0,0,800,600);
}
cans.beginPath();
cans.arc(400,300,200,0,Math.PI*2,1);
cans.closePath();
cans.clip();
}
function img_click(){
var can = $$(‘can‘);
var cans = can.getContext(‘2d‘);
cans.clearRect(0,0,800,600);
}
</script>
<body onload="pageLoad();">
<canvas id="can" width="800px" height="600px" onclick="img_click(this);"></canvas>
</body>
</html>
原文：http://www.cnblogs.com/babysay123/p/4654030.html