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css制作黑色星空效果

2015-04-17 ⁄ 文章标签： css特效 ⁄ 浏览次数：次

今天制作的是类似漫天星星缓缓流动的效果，如图

代码如下

<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()">
	</body>
</html>

css制作黑色星空效果

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