1.程序代码：

<!doctype html>
<html>
<head>
    <meta charset="utf-8">
    <title>旋转的星空</title>
    <style type="text/css">
        body{background: black;padding: 0;margin: 0; overflow:hidden}
        .header{margin: 0 auto;width: 100%;height: 100%;background-color: #000;position: relative;}
    </style>
</head>
<body>
<div class="header"><canvas id="canvas"></canvas></div>
<script>
    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 = 3000;//星星数量
    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) / 8;
//星星大小
        this.orbitX = w / 2;
        this.orbitY = h / 2;
        this.timePassed = random(0, maxStars);
        this.speed = random(this.orbitRadius) / 50000;
//星星移动速度
        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();
</script>
</body>
</html>

2.效果图：

 

# html # javascript # 前端
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