canvas实现星空动态背景

星空动态闪烁背景，用canvas实现

实现效果

脚本代码

//  实现星星背景
     $("#pageContent canvas").remove();
     var stars=""
     $("#pageContent").prepend(stars)
     setTimeout(()=>{
       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 = 1200;
     
     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;
     }
     
     function maxOrbit(x, y) {
       var max = Math.max(x, y),
         diameter = Math.round(Math.sqrt(max * max + max * max));
       return diameter / 2;
     }
     
     var 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) / 900000;
       this.alpha = random(2, 10) / 10;
     
       count++;
       stars[count] = this;
     }
     // 星星背景
     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 = 0.8;
       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();	
     },1000)