这是一款html5 canvas炫酷旋转银河系星空背景特效。该特效通过canvas来绘制银河系星盘，并制作星系旋转的效果，非常炫酷。

使用方法

HTML结构

该旋转银河系星空背景特效的HTML结果只需要一个元素即可。

JavaScript

然后通过下面的js代码来在canvas上绘制银河系，以及制作动画效果。

"use strict";

var canvas = document.getElementById('canvas'),

ctx = canvas.getContext('2d'),

w = canvas.width = window.innerWidth,

h = canvas.height = window.innerHeight,

hue = 217,

stars = [],

count = 0,

maxStars = 1400;

// Cache gradient

var canvas2 = document.createElement('canvas'),

ctx2 = canvas2.getContext('2d');

canvas2.width = 100;

canvas2.height = 100;

var half = canvas2.width/2,

gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);

gradient2.addColorStop(0.025, '#fff');

gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');

gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');

gradient2.addColorStop(1, 'transparent');

ctx2.fillStyle = gradient2;

ctx2.beginPath();

ctx2.arc(half, half, half, 0, Math.PI * 2);

ctx2.fill();

// End cache

function random(min, max) {

if (arguments.length < 2) {

max = min;

min = 0;

}

if (min > max) {

var hold = max;

max = min;

min = hold;

}

return Math.floor(Math.random() * (max - min + 1)) + min;

}

var Star = function() {

this.orbitRadius = random(w / 2 - 50);

this.radius = random(100, this.orbitRadius) / 10;

this.orbitX = w / 2;

this.orbitY = h / 2;

this.timePassed = random(0, maxStars);

this.speed = random(this.orbitRadius) / 100000;

this.alpha = random(2, 10) / 10;

count++;

stars[count] = this;

}

Star.prototype.draw = function() {

var x = Math.sin(this.timePassed + 1) * this.orbitRadius + this.orbitX,

y = Math.cos(this.timePassed) * this.orbitRadius/2 + this.orbitY,

twinkle = random(10);

if (twinkle === 1 && this.alpha > 0) {

this.alpha -= 0.05;

} else if (twinkle === 2 && this.alpha < 1) {

this.alpha += 0.05;

}

ctx.globalAlpha = this.alpha;

ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);

this.timePassed += this.speed;

}

for (var i = 0; i < maxStars; i++) {

new Star();

}

function animation() {

ctx.globalCompositeOperation = 'source-over';

ctx.globalAlpha = 0.8;

ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 1)';

ctx.fillRect(0, 0, w, h)

ctx.globalCompositeOperation = 'lighter';

for (var i = 1, l = stars.length; i < l; i++) {

stars[i].draw();

};

window.requestAnimationFrame(animation);

}

animation();