<!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>