<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>非零环绕原则</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‘); context.beginPath(); context.arc(400,400,300,0,Math.PI*2,false); context.arc(400,400,150,0,Math.PI*2,true); context.closePath(); context.fillStyle = "#058"; context.shadowColor = "gray"; context.shadowOffsetX = 10; context.shadowOffsetY = 10; context.shadowBlur = 10; context.fill(); }else{ alert(‘当前游览器不支持Canvas，请更换游览器后再试！‘); } } </script> </body> </html>
canvas-9NonZeroAroundPrinciples.html
原文：http://www.cnblogs.com/cynthia-wuqian/p/4989151.html