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HTML5技术里面的canvas如何绘制星空效果

html head titlecanvas绘制星空效果/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_x('canvas'); cv.width = BW; cv.height = BH; cv.style.background = BGCOLOR; document.body.a(cv); ctx = cv.getContext("2d"); //create all stars for(var i=0;iSTAR_COUNT;++i){ var s = new Star(); stars.push(s); } setInterval(render, 33); }; /script /head body onLoad="init()" /body /html 原文来自：