HTML canvas绘制椭圆

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>

<body>
  <canvas id = "Mycanvas" width="300" height="300" style="border:2px solid red;"></canvas>
 <script type="text/jscript">
   var canvas = document.getElementById("Mycanvas");
   var context = canvas.getContext("2d");
   var x = 100;
   var y = 100;
   var a = 50;
   var b = 30
   //选择a、b中的较大者作为arc方法的半径参数
   var r = (a > b) ? a : b; 
   var ratioX = a / r; //横轴缩放比率
   var ratioY = b / r; //纵轴缩放比率
   context.scale(ratioX, ratioY); //进行缩放（均匀压缩）
   context.beginPath();
   //从椭圆的左端点开始逆时针绘制
   context.arc(x , y , r, 0, 2 * Math.PI);
   context.fillStyle="#E2C1A7";
   context.fill();
   context.stroke();
 </script>
</body>
</html>
效果图：