html 5画圆
如果要创建一个弧形的画布，我们可以使用 arc() 方法。
语法：arc(定义一个中心点，半径，起始角度，结束角度，和绘图方向：顺时针或逆时针)
代码：
JavaScript Code复制内容到剪贴板
context.arc(centerX, centerY, radius, startingAngle, endingAngle, antiClockwise);
HTML5 Canvas Arc 例子：
XML/HTML Code复制内容到剪贴板
<!DOCTYPE HTML>
<html>
<head>
<title>html5 canvas Arc</title>
<style>
body {margin: 0px;padding: 0px;}
#myCanvas {border: 1px solid #9C9898; margin:0 auto;margin-top:200px; margin-left:100px;}
</style> www.zzzyk.com
<script>
window.onload = function(){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
var centerX = 288;
var centerY = 160;
var radius = 75;
var startingAngle = 1.1 * Math.PI;
var endingAngle = 1.9 * Math.PI;
var counterclockwise = false;
context.arc(centerX, centerY, radius, startingAngle, endingAngle, counterclockwise);
context.lineWidth = 15;
context.strokeStyle = "black"; // line color
context.stroke();
};
</script>
</head>
<body>
<canvas id="myCanvas" width="578" height="200">
</canvas>
</body>
</html>
补充：web前端 , HTML 5 ,
