源代码：
<html>
<div style="width:200px;height:200px;"id="cloud">test canvas</div>
<canvas style="display:none;"id="can"width="200"height="200"></canvas>
<script>(function() {
var canvas = document.getElementById('can'), context;
if(!canvas.getContext) {
alert('你的浏览器不支持 canvas!');
return;
}
context = canvas.getContext('2d');
context.fillStyle = 'red';
context.beginPath();
context.moveTo(75,40);
context.bezierCurveTo(75,37,70,25,50,25);
context.bezierCurveTo(20,25,20,62.5,20,62.5);
context.bezierCurveTo(20,80,40,102,75,120);
context.bezierCurveTo(110,102,130,80,130,62.5);
context.bezierCurveTo(130,62.5,130,25,100,25);
context.bezierCurveTo(85,25,75,37,75,40);
context.fill();
var url = context.canvas.toDataURL();
document.getElementById('cloud').style.backgroundImage = 'url("' + url + '")';
})();
</script>
</html> 效果如下：
实现原理：
