<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>canvas</title>
<script type="text/javascript" src="../js/jQuery.js"></script>
<style type="text/css">
*{
margin: 0;
padding: 0;
outline: none;
border: none;
}
#canvas{
margin: auto auto;
width: 7rem;
margin: .25rem 0 0 1.5rem;
border: 1px solid black;
}
</style>
</head>
<body>
<canvas id="canvas" width="1000" height="600"></canvas>
</body>
</html>
<script type="text/javascript">
/**
* rem 布局初始化
*/
$('html').css('font-size', $(window).width()/10);
/**
* 获取 canvas 画布
* 获取 canvas 绘图上下文环境
*/
var canvas = $('#canvas')[0];
var cxt = canvas.getContext('2d');
/**
* 扩展context('2d'), 绘制五角星的方法
*/
CanvasRenderingContext2D.prototype.fillFiveStar = function(fiveStar){
this.beginPath();
this.lineWidth = 10;
var x = 0, y = 0;
for(var i = 0; i < 5; i++){
x = Math.cos((18+72*i-fiveStar.RotationAngle)/180*Math.PI);
x = x*fiveStart.bigRadius+fiveStar.offsetX;
y = -Math.sin((18+72*i-fiveStar.RotationAngle)/180*Math.PI);
y = y*fiveStart.bigRadius+fiveStar.offsetY;
this.lineTo(x,y);
x = Math.cos((54+i*72-fiveStar.RotationAngle)/180*Math.PI);
x = x*fiveStart.smallRadius+fiveStar.offsetX;
y = -Math.sin((54+i*72-fiveStar.RotationAngle)/180*Math.PI);
y = y*fiveStart.smallRadius+fiveStar.offsetY;
this.lineTo(x,y);
}
this.closePath();
this.stroke();
}
/**
* 调用扩展的方法
*/
var fiveStart = {
bigRadius: 200,
smallRadius: 30,
offsetX: 400,
offsetY: 300,
RotationAngle: 0
}
cxt.fillFiveStar(fiveStart);
</script>