canvas制作星空旋转效果

 canvas制作星空旋转效果

/*
* @params:config:{id: String, canvas自己的idclass: String, canvas外框的class，用来获取宽高color: '#306468', // rgb(34, 103, 96) 星星颜色Hsl值hue: 1,星星颜色HslbackgroundColor: '#101524', 背景色maxStars: 1000, 星星数量time: 30000， 转动时长
}
* */
export function stars(config) {const canvas = document.getElementById(config.id);const box = document.getElementsByClassName(config.class);const ctx = canvas.getContext('2d');const w = canvas.width = box[0] ? box[0].offsetWidth : 300;const h = canvas.height = box[0] ? box[0].offsetHeight : 300;const hue = config.hue;const stars = [];let count = 0;const maxStars = config.maxStars;const canvas2 = document.createElement('canvas');const ctx2 = canvas2.getContext('2d');canvas2.width = 100;canvas2.height = 100;const half = canvas2.width / 2;const gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);gradient2.addColorStop(0.025, config.color);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();function random(min, max) {if (arguments.length < 2) {max = min;min = 0;}if (min > max) {const hold = max;max = min;min = hold;}return Math.floor(Math.random() * (max - min + 1)) + min;}function maxOrbit(x, y) {const max = Math.max(x, y);const diameter = Math.round(Math.sqrt(max * max + max * max));return diameter / 2;}const Star = function() {this.orbitRadius = random(maxOrbit(w, h));this.radius = random(60, this.orbitRadius) / 12;this.orbitX = w / 2;this.orbitY = h / 2;this.timePassed = random(0, maxStars);this.speed = random(this.orbitRadius) / config.time;this.alpha = random(2, 10) / 10;count++;stars[count] = this;};Star.prototype.draw = function() {const x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX;const y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY;const 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 (let i = 0; i < maxStars; i++) {new Star();}function animation() {ctx.globalCompositeOperation = 'source-over';ctx.globalAlpha = 0.8;ctx.fillStyle = config.backgroundColor;ctx.fillRect(0, 0, w, h);ctx.globalCompositeOperation = 'lighter';for (let i = 1, l = stars.length; i < l; i++) {stars[i].draw();}window.requestAnimationFrame(animation);}animation();
}

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