最先绘制的黑色背景怎么不显示了，求老师解答下，谢谢了

源自：8-2 globalAlpha和globalCompositeOperation

<!DOCTYPE html>

<html>

<head>

<title>Document</title>

<style>

*{margin:0;}

#canvas{margin:0 auto;display: block; background: #ccc;}

</style>

</head>

<body>

var canvas=document.getElementById('canvas');

var cxt=canvas.getContext('2d');

cxt.save();

cxt.beginPath();

cxt.fillStyle="#000"

cxt.fillRect(0,0,600,600);

cxt.beginPath();

cxt.fillStyle="#f00"

cxt.fillRect(0,0,600,600);

cxt.globalCompositeOperation="destination-out";

cxt.beginPath();

cxt.fillStyle="#00f"

cxt.fillRect(200,200,200,200);

cxt.beginPath();

cxt.arc(200,200,50,0,2*Math.PI);

cxt.fillStyle="#0f0";

cxt.fill();

cxt.beginPath();

cxt.fillStyle="#00f"

cxt.fillRect(400,400,100,100);

cxt.restore();

</script>

</body>

</html>

提问者：xxAzz 2015-03-13 17:27

最先绘制的黑色背景怎么不显示了，求老师解答下 ，谢谢了