HTML5运用canvas标签画椭圆
<!doctype html>
<html>
<head>
<title>画出一个椭圆</title>
</head>
<body>
<!-- 画出我的画布 -->
<canvas id="can1" width="500px" height="500px" style="border:1px solid
black"></canvas>
<script type="text/javascript">
//获取画布
var canvas = document.getElementById("can1");
//获取画笔
var cxt = canvas.getContext("2d");
cxt.beginPath();
//设置填充颜色
cxt.fillStyle = "red";
var a=120;
var b=160;
var x=250;
var y=250;
//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
cxt.scale(ratioX, ratioY); //进行缩放（均匀压缩）
//从椭圆的左端点开始逆时针绘制
cxt.moveTo((x + a) / ratioX , y / ratioY);
cxt.arc(x / ratioX, y / ratioY, r, 0, 2 * Math.PI);
cxt.fill();
cxt.closePath();
</script>
</body>
</html>
