星空旋转特效

 1 function random(min, max) {
 2   if (arguments.length < 2) {
 3     max = min;
 4     min = 0;
 5   }
 6   if (min > max) {
 7     const hold = max;
 8     max = min;
 9     min = hold;
10   }
11   return Math.floor(Math.random() * (max - min + 1)) + min;
12 }
13 
14 // 星星移动范围，值越大范围越小
15 function maxOrbit(x, y) {
16   const max = Math.max(x, y);
17   const diameter = Math.round(Math.sqrt(max * max + max * max));
18   return diameter / 2;
19 }
20 
21 export default class Star {
22   constructor(ctx, canvas2, w, h, maxStars) {
23     this.ctx = ctx;
24     this.canvas2 = canvas2;
25 
26     this.orbitRadius = random(maxOrbit(w, h));
27     this.radius = random(60, this.orbitRadius) / 8;
28     // 星星大小
29     this.orbitX = w / 2;
30     this.orbitY = h / 2;
31     this.timePassed = random(0, maxStars);
32     // 转动速度
33     this.speed = random(this.orbitRadius) / 500000;
34     // 透明度-闪烁效果
35     this.alpha = random(2, 10) / 10;
36   }
37 
38   draw() {
39     const x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX;
40     const y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY;
41     const twinkle = random(10);
42 
43     if (twinkle === 1 && this.alpha > 0) {
44       this.alpha -= 0.05;
45     } else if (twinkle === 2 && this.alpha < 1) {
46       this.alpha += 0.05;
47     }
48 
49     this.ctx.globalAlpha = this.alpha;
50     this.ctx.drawImage(this.canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
51     this.timePassed += this.speed;
52   }
53 }

 1 import 'jquery';
 2 import Star from './star';
 3 
 4 const hue = 217;
 5 const stars = [];
 6 const maxStars = 1300; // 星星数量
 7 
 8 export default class Stars {
 9   constructor(canvas) {
10     this.ctx = canvas.getContext('2d');
11     this.w = canvas.width = canvas.clientWidth;
12     this.h = canvas.height = canvas.clientHeight;
13 
14     const canvas2 = document.createElement('canvas');
15     const ctx2 = canvas2.getContext('2d');
16     canvas2.width = 100;
17     canvas2.height = 100;
18     const half = canvas2.width / 2;
19     const gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
20     gradient2.addColorStop(0.025, '#CCC');
21     gradient2.addColorStop(0.1, `hsl(${hue}, 61%, 33%)`);
22     gradient2.addColorStop(0.25, `hsl(${hue}, 64%, 6%)`);
23     gradient2.addColorStop(1, 'transparent');
24 
25     ctx2.fillStyle = gradient2;
26     ctx2.beginPath();
27     ctx2.arc(half, half, half, 0, Math.PI * 2);
28     ctx2.fill();
29 
30     for (let i = 0; i < maxStars; i++) {
31       stars[i] = new Star(this.ctx, canvas2, this.w, this.h, maxStars);
32     }
33   }
34 
35   animation() {
36     this.ctx.globalCompositeOperation = 'source-over';
37     this.ctx.globalAlpha = 0.5; // 尾巴
38     this.ctx.fillStyle = `hsla(${  hue  }, 64%, 6%, 2)`;
39     this.ctx.fillRect(0, 0, this.w, this.h)
40 
41     this.ctx.globalCompositeOperation = 'lighter';
42     for (let i = 1, l = stars.length; i < l; i++) {
43       stars[i].draw();
44     };
45 
46     window.requestAnimationFrame(this.animation.bind(this));
47   }
48 }

import Stars from 'utils/star/index.js'

const canvas = document.getElementById('canvas');
const stars = new Stars(canvas);
stars.animation();

1 #canvas {
2     position: absolute;
3     left: 0;
4     top: 0;
5     z-index: -1;
6     display: inline-block;
7     width: 100%;
8     height: 100%;
9   }