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<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>Document</title> </head> <body> <canvas id="canvas" style="margin:0 auto;border:1px #ddd solid"> The current browser does not support Canvas, can replace the browser a try! </canvas> <script> window.onload = function(){ var canvas = document.getElementById(‘canvas‘); canvas.width = 1024; canvas.height = 768; if(canvas.getContext(‘2d‘)){ var context = canvas.getContext(‘2d‘); // 整个系统的透明度设置 context.globalAlpha = 0.7; for(var i=0;i<100;i++){ var R = Math.floor(Math.random()*255); var G = Math.floor(Math.random()*255); var B = Math.floor(Math.random()*255); context.fillStyle = "rgb(" + R + "," + G + "," + B + ")"; context.beginPath(); context.arc(Math.random()*canvas.width,Math.random()*canvas.height,Math.random()*100,0,2*Math.PI) context.closePath(); context.fill(); } }else{ alert(‘当前游览器不支持Canvas，请更换游览器后再试！‘); } } </script> </body> <script> /*global globalAlpha globalCompositeOperation = "source-over"(default) sourse-atop sourse-in sourse-out destination-over //前面绘制的覆盖了后面绘制的图形 destination-atop destination-in destination-out lighter copy xor */ </script> </html>
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原文地址：http://www.cnblogs.com/cynthia-wuqian/p/4988522.html
