JavaScript 动态星空背景实现教程

<canvas id="canvas"></canvas>

/*css reset */
body,p,div,ol,ul,li,dl,dt,dd,h1,h2,h3,h4,h5,h6,form,input,iframe,nav {
 margin: 0;
 padding: 0;
}
html,body {
 width: 100%;
 height: 100%;
}
body {
 font: 14px Microsoft YaHei;
 -webkit-text-size-adjust:100%;
 -moz-user-select: none;
 -webkit-user-select: none;
 user-select: none;
 position: relative;
 background: #000;
}

#canvas {
 width: 100%;
 height: 100%;
 display: block;
 opacity: .8;
}

// 音量大小,0.01-1


//宇宙特效
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 = 1100;    //星星数量,默认1300
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, '#CCC');
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;
}

function maxOrbit(x, y) {
 var max = Math.max(x, y),
 diameter = Math.round(Math.sqrt(max * max + max * max));
 return diameter / 2;
 //星星移动范围，值越大范围越小，
}

var Star = function() {

 this.orbitRadius = random(maxOrbit(w, h));
 this.radius = random(60, this.orbitRadius) / 10;  //星星大小,值越大星星越小,默认8
 
 this.orbitX = w / 2;
 this.orbitY = h / 2;
 this.timePassed = random(0, maxStars);
 this.speed = random(this.orbitRadius) / 80000;  //星星移动速度,值越大越慢,默认5W
 
 this.alpha = random(2, 10) / 10;

 count++;
 stars[count] = this;
}

Star.prototype.draw = function() {
 var x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX,
 y = Math.cos(this.timePassed) * this.orbitRadius + 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 = 0.5;         //尾巴
 ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
 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();