<!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{
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');
/**
* 绘制一片星空
*/
cxt.fillStyle = 'black';
cxt.fillRect(0, 0, canvas.width, canvas.height);
for(var i = 0; i <= 300; i++){
var fiveStart = {};
fiveStart.Radius = Math.random()*6+6;
fiveStart.offsetX = Math.random()*canvas.width;
fiveStart.offsetY = Math.random()*canvas.height;
fiveStart.RotationAngle = Math.random()*360;
drawFiveStar(cxt, fiveStart);
}
/**
* 控制五角星的方法
*/
function drawFiveStar(cxt, fiveStart){
cxt.save();
cxt.translate(fiveStart.offsetX, fiveStart.offsetY); //相对于原点的偏移量
cxt.rotate(fiveStart.RotationAngle/180*Math.PI); //图形旋转(弧度)
cxt.scale(fiveStart.Radius, fiveStart.Radius); //图形缩放( X轴的倍数, Y轴的倍数 )
fiveStartPath(cxt);
cxt.fillStyle = "yellow";
cxt.fill();
cxt.restore();
}
/**
* 绘制标准五角星路径的方法
*/
function fiveStartPath(cxt){
cxt.beginPath();
var x = 0; y = 0;
for(var i = 0; i < 5; i++){
x = Math.cos((18+72*i)/180*Math.PI);
y = Math.sin((18+72*i)/180*Math.PI);
cxt.lineTo(x, 0-y);
x = Math.cos((54+72*i)/180*Math.PI)/2.0;
y = Math.sin((54+72*i)/180*Math.PI)/2.0;
cxt.lineTo(x, 0-y);
}
cxt.closePath();
}
</script>
