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【JS】 canvas标签用法

作者:羊村村长 / 发布于2014/11/7/ 718


	<script type="text/javascript" src="script/excanvas.js"></script>
	function getheatMap(){
	 //坐标
	 var aXY = [[25, 20], [26, 30]];
	 var canvas=document.getElementById('myCanvas');
	 if($.browser.msie){
	 canvas=window.G_vmlCanvasManager.initElement(canvas);
	 }
	 var context=canvas.getContext('2d');
	
	 //设置填充样式，透明度为0.1
	 context.fillStyle = 'rgba(255,30,0,0.1)';
	 var pi2 = Math.PI * 2;
	 for (var i = 0, len = aXY.length; i < len; i++) {
	 var x = aXY[i][0], y = aXY[i][1];
	 context.beginPath();
	 context.arc(x, y, 6, 0, pi2, true);
	 context.closePath();
	 context.fill();
	 }
	 var imgd = context.getImageData(0, 0, 1200, 2000);
	 var pix = imgd.data;
	 for (var i = 0, n = pix.length; i < n; i += 4) {
	 var a = pix[i+3]; //alpha
	 pix[i ] = 128 * Math.sin((1 / 256 * a - 0.5 ) * Math.PI ) + 200;
	 pix[i+1] = 128 * Math.sin((1 / 128 * a - 0.5 ) * Math.PI ) + 127;
	 pix[i+2] = 256 * Math.sin((1 / 256 * a + 0.5 ) * Math.PI );
	 pix[i+3] = pix[i+3] * 0.8;
	 }
	 context.putImageData(imgd, 0, 0);
	 }

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　canvas　

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