html5 canvas裁剪区域

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<!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>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

<title>canvas裁剪区域</title>

<script src="js/modernizr.js"></script>

</head>

<body>

<script type="text/javascript">

window.addEventListener('load',eventWindowLoaded,false);

function eventWindowLoaded(){

	canvasApp();

}

function canvasSupport(){

	return Modernizr.canvas;

}

function canvasApp(){

	if(!canvasSupport()){

		return;

	}else{

		var theCanvas = document.getElementById('canvas')

		var context = theCanvas.getContext("2d")

	}

	drawScreen();

	function drawScreen(){

		context.fillStyle = "green";

		context.fillRect(10,10,200,200);

		context.save();

		context.beginPath();

		context.rect(0,0,50,50);

		context.clip();

		//红色圆

		context.beginPath();

		context.strokeStyle="red";

		context.lineWidth=5;

		context.arc(100,100,100,(Math.PI/180)*0,(Math.PI/180)*360,false);

		//整理

		context.stroke();

		context.closePath();

		context.restore();

		//再次裁剪整个画布

		context.beginPath();

		context.rect(0,0,200,200);

		context.clip();

		//绘制一个没有裁剪的蓝线

		context.beginPath();

		context.strokeStyle="blue";

		context.lineWidth=5;

		context.arc(100,100,50,(Math.PI/180)*0,(Math.PI/180)*360,false);

		//整圆

		context.stroke();

		context.closePath();

	}

}

</script>

<canvas id="canvas" width="500" height="500">

你的浏览器无法使用canvas

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</canvas>

</body>

</html>