canvas 绘制八卦图

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<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>canvas绘制八卦图</title>
</head>

<body>
<center>
<canvas id="canvas" width="600" height="500"></canvas>
<script>
var canvas=document.getElementById("canvas");
var context=canvas.getContext('2d');

//1.先绘制一个完整的空心圆
context.beginPath();
context.arc(250,250,200,0,Math.PI*2);
context.stroke();

//2.绘制半黑半白默认为黑色
context.beginPath();
context.arc(250,250,200,Math.PI*3/2,Math.PI/2,true);
context.fill();

//3.绘制一黑一白两个半圆
context.fillStyle="white";
context.beginPath();
context.arc(250,150,100,0,Math.PI*2);
context.fill();

context.fillStyle="black";
context.beginPath();
context.arc(250,350,100,0,Math.PI*2);
context.fill();

//4.绘制两个小圆
context.fillStyle="black";
context.beginPath();
context.arc(250,150,30,0,Math.PI*2);
context.fill();

context.fillStyle="white";
context.beginPath();
context.arc(250,350,30,0,Math.PI*2);
context.fill();
</script>
</center>
</body>
</html>

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