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<html>
<head>
<title>星空</title>
<META http-equiv="X-UA-Compatible" content="IE=edge"></META>
<META http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<script>
var BW = 800; //canvas width
var BH = 600; //canvas height
var MAX_STAR_SIZE = 3;
var MAX_STAR_SPEED = 1;
var STAR_COUNT = 120;
var BGCOLOR = "black";
var ctx;
var stars = [];
function rndf(n){
return Math.floor(Math.random()*n);
}
function rndc(n){
return Math.ceil(Math.random()*n);
}
function Star(){
this.reset = function(){
this.x = 0;
this.y = rndf(BH);
this.size = rndc(MAX_STAR_SIZE);
this.vx = MAX_STAR_SPEED*this.size/MAX_STAR_SIZE;
this.vy = 0;
this.color = "rgba("+rndf(255)+", "+rndf(255)+", "+rndf(255)+", 0.5)";
};
this.reset();
this.x = rndf(BW);
}
function render(){
ctx.globalCompositeOperation = "source-over";
ctx.fillStyle = "rgba(0, 0, 0, 0.3)";
ctx.fillRect(0, 0, BW, BH);
ctx.globalCompositeOperation = "lighter";
for(var i = 0; i < STAR_COUNT; ++i){
var p = stars[i];
ctx.beginPath();
var gradient = ctx.createRadialGradient(p.x, p.y, 0, p.x, p.y, p.size);
gradient.addColorStop(0, "white");
gradient.addColorStop(0.4, "white");
gradient.addColorStop(0.4, p.color);
gradient.addColorStop(1, "black");
ctx.fillStyle = gradient;
ctx.arc(p.x, p.y, p.size, Math.PI*2, false);
ctx.fill();
p.x += p.vx;
p.y += p.vy;
if(p.x<=0 || p.x>=BW || p.y<=0 || p.y>=BH){
p.reset();
}
}
}
function init(){
if (!window.console){
console = {log:function(){},debug:function(){}};
}
//create canvas
var cv = document.createElement(‘canvas‘);
cv.width = BW;
cv.height = BH;
cv.style.background = BGCOLOR;
document.body.appendChild(cv);
ctx = cv.getContext("2d");
//create all stars
for(var i=0;i<STAR_COUNT;++i){
var s = new Star();
stars.push(s);
}
setInterval(render, 33);
};
</script>
</head>
<body onload="init()">
<div>http://www.999jiujiu.com/</div>
</body>
</html>
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原文地址：http://www.cnblogs.com/life6688/p/4597498.html
