JS 绘制椭圆

Canvas 还没有提供直接绘制椭圆的功能,下面使用 bezierCurveTo() 来绘制椭圆。

圆也是使用 arc 来绘制的,在新版的 JS 中提供了 ellipse 来绘制椭圆,但是很多浏览器都还不支持

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="http://cdn.bootcss.com/jquery/3.2.1/jquery.min.js"></script>
<style media="screen">
canvas {
border: 1px solid grey;
}
</style>
</head>
<body>
<canvas id="canvas" width="500" height="300">Your browser does not support canvas.</canvas>
<script>
var canvas = $('#canvas').get(0);
var ctx = canvas.getContext('2d');
drawEllipse(ctx, 100, 100, 80, 120);
drawEllipse(ctx, 200, 200, 200, 80);
function drawEllipse(context, centerX, centerY, width, height) {
context.beginPath();
context.moveTo(centerX, centerY - height / 2);
context.bezierCurveTo(
centerX + width / 2, centerY - height / 2,
centerX + width / 2, centerY + height / 2,
centerX, centerY + height / 2
);
context.bezierCurveTo(
centerX - width / 2, centerY + height / 2,
centerX - width / 2, centerY - height / 2,
centerX, centerY - height / 2
);
context.closePath();
context.stroke();
}
</script>
</body>
</html>