html 5 canvas 绘制太极demo

　　一个练习canvas的小案例。其中若有小问题，欢迎大神拍砖……^_*

　　代码效果预览地址：http://code.w3ctech.com/detail/2500

1     <div class="container">
2         <canvas id="myCanvas" width="400" height="400" ></canvas>
3     </div>

 1         * {
 2             padding: 0;
 3             margin: 0;
 4         }
 5 
 6         body {
 7             background-color: #d5d3d4;
 8         }
 9 
10         .container {
11             width: 500px;
12             height: 500px;
13             position: relative;
14             top: 80px;
15             left: 50%;
16             transform: translateX(-50%);
17             background-color: #fff;
18             border-radius: 10px;
19             box-shadow: 0 0 5px #c2bfbf;
20         }
21         #myCanvas{
22             border:1px solid #000;
23             position:relative;
24             top: 50px;
25             left: 50px;
26             transform:translate(-50%,-50%);
27             border-radius:50%;
28             animation: myfirst 30s linear infinite;
29         }
30         @keyframes myfirst
31         {
32             0%   {transform:rotate(0deg);}
33             100% {transform:rotate(360deg);}
34         }

 1         window.onload = function () {
 2             var canvas=document.getElementById("myCanvas");
 3             var ctx=canvas.getContext("2d");
 4             ctx.beginPath();
 5             ctx.arc(200, 100, 100, -0.5 * Math.PI, 0.5 * Math.PI, false);
 6             ctx.arc(200, 300, 100, 1.5 * Math.PI, 0.5 * Math.PI, true);
 7             ctx.arc(200, 200, 200, 0.5 * Math.PI, 1.5 * Math.PI, false);
 8             ctx.closePath();
 9             ctx.fillStyle = "black";
10             ctx.fill();
11 
12             ctx.beginPath();
13             ctx.arc(200, 100, 25, 0 * Math.PI, 2 * Math.PI, false);
14             ctx.fillStyle = "white";
15             ctx.fill();
16             ctx.beginPath();
17             ctx.arc(200, 300, 25, 0 * Math.PI, 2 * Math.PI, false);
18             ctx.fillStyle = "black";
19             ctx.fill();
20         }