javascript - 我怎样才能从另一个网站得到这个 GIF？

Question

我正在创建一个网站，我想要一个在页面加载时自动运行的特定 gif 背景，这是网站的链接

http://contact-festival.com/

而且我想在艺术家阵容列表中使用移动的星星背景

我检查了我的开发者工具和网络，但似乎找不到来源

Answer 1

这些不是gifs。 这些是用 Canvas 标签和 javascript 编码制作的。

So here is an example below that you can use.

window.onload = function () {
  
  var element = "starfield";
  var bgColor = "#030304";
  var FPS = 30;
  var displacementRate = 5;
  var accelerationRate = 10;
  var maxSpeed = 100;
  var maxStars = 1000;

  
  var speedUp = setInterval(function(){
    if (accelerationRate > maxSpeed) {
     clearInterval(speedUp); 
    }
    accelerationRate = accelerationRate * 1.1;
  },100);

	var Star = function() {
		this.x = 0;
		this.y = 0;
		this.z = 0;
		this.maxDepth = 0;
		this.alpha = 0;
		this.radius = 0;

		this.dx = 0;
		this.dy = 0;
		this.dz = 0;
		this.ddx = 0;
		this.ddy = 0;

		this.drawInContext = function(ctx, deltaX, deltaY) {
			ctx.beginPath();
			ctx.fillStyle = "rgba(255, 255, 255," + this.alpha + ")";
			ctx.arc(this.x + deltaX, this.y + deltaY, this.radius, 0, Math.PI * 2, false);
			ctx.fill();
		};
	};

	var requestAnimationFrame =  
		window.requestAnimationFrame ||
		window.webkitRequestAnimationFrame ||
		window.mozRequestAnimationFrame ||
		window.msRequestAnimationFrame ||
		window.oRequestAnimationFrame ||
		function(callback) {
			return window.setTimeout(callback, 1000 / FPS);
		};

	function isCanvasSupported(element) {
		return !!(element.getContext && element.getContext("2d"));
	}

	function backingScale(context) {
		if ('devicePixelRatio' in window) {
			if (window.devicePixelRatio > 1) {
				return window.devicePixelRatio;
			}
		}

		return 1;
	}

	function StarField(canvasID) {
		this.canvas = document.getElementById(canvasID);
		if (!isCanvasSupported(this.canvas)) {
			this.canvas.className = "inactive";
			this.canvas.width = window.innerWidth;
			this.isCanvasEnabled = false;
			return this;
		}

		this.isCanvasEnabled = true;

		this.ctx = this.canvas.getContext("2d");
		this.scaleFactor = backingScale(this.ctx);
		this.stars = new Array();

		function newStar() {
			var star = new Star();
			star.x = Math.random() * this.canvas.width - this.originX;
			star.y = Math.random() * this.canvas.height - this.originY;
			star.z = star.max_depth = Math.max(this.canvas.width, this.canvas.height);
			star.alpha = Math.random();
			star.radius = Math.random();

			var xcoeff = star.x > 0 ? 1 : -1;
			var ycoeff = star.y > 0 ? 1 : -1;

			if (Math.abs(star.x) > Math.abs(star.y)) {
				star.dx = 1.0;
				star.dy = Math.abs(star.y / star.x);
			} else {
				star.dx = Math.abs(star.x / star.y);
				star.dy = 1.0;
			}

			star.dx *= xcoeff * (displacementRate / 10);
			star.dy *= ycoeff * (displacementRate / 10);
			star.dz = -1;

			star.ddx = (accelerationRate * star.dx) / 10;
			star.ddy = (accelerationRate * star.dy) / 10;

			return star;
		}

		function move(star) {
			star.x += star.dx;
			star.y += star.dy;
			star.z += star.dz;
	
			star.dx += star.ddx;
			star.dy += star.ddy;
		}

		function updateStars(ctx, stars) {
			for (var i=0; i<stars.length; i++) {
				move(stars[i]);

				if (stars[i].x < -this.originX || stars[i].x > this.originX || stars[i].y < -this.originY || stars[i].y > this.originY) {
					// Remove
					stars[i] = newStar();
				} else {
					// Paint
					var deltaX = this.originX;
					var deltaY = this.originY;
					stars[i].drawInContext(ctx, deltaX, deltaY);
				}
			}
		}

		this.configureGeometry = function() {
			// Ensure we are always at full width
			this.canvas.width = window.innerWidth;
			this.canvas.style.backgroundColor = bgColor;
			var ratio = 1;

			// Retina support
			// See http://www.html5rocks.com/en/tutorials/canvas/hidpi/
			if (this.scaleFactor > 1) {
				var devicePixelRatio = this.scaleFactor;
				var context = this.ctx;
				var backingStoreRatio = context.webkitBackingStorePixelRatio ||
										context.mozBackingStorePixelRatio ||
										context.msBackingStorePixelRatio ||
										context.oBackingStorePixelRatio ||
										context.backingStorePixelRatio || 1;
				ratio = devicePixelRatio / backingStoreRatio;

				// Upscale the canvas if the two ratios don't match
				if (devicePixelRatio !== backingStoreRatio) {
					var canvas = this.canvas;
					var oldWidth = canvas.width;
					var oldHeight = canvas.height;

					canvas.width = oldWidth * ratio;
					canvas.height = oldHeight * ratio;

					canvas.style.width = oldWidth + 'px';
					canvas.style.height = oldHeight + 'px';

					// Now scale the context to counter the fact that we've manually scaled our canvas element
					context.scale(ratio, ratio);
				}
			}

			// Starting origin of stars
			var logicalWidth = this.canvas.width / ratio;
			var logicalHeight = this.canvas.height / ratio;

			this.originX = logicalWidth / 2;
			this.originY = logicalHeight / 2;

			var numStars = logicalWidth / 2;
			this.numStars = numStars > maxStars ? maxStars : numStars;
		}

		this.render = function() {
			setTimeout(function() {
				// Drawing
				this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);

				updateStars(this.ctx, this.stars);

				requestAnimationFrame(render);

			}, 1000 / FPS);
		};

		// Configure origin and frames before creating initial batch of stars
		this.configureGeometry();

		for (var i=0; i<this.numStars; i++) {
			this.stars.push(newStar());
		}

		return this;
	}

	var starfield = StarField(element);
	if (starfield.isCanvasEnabled) {
		starfield.render();
	}

	// Make sure we adjust the canvas whenever the window resizes
	// Don't rely on CSS rules for 100% width because that causes rendering issues
	window.addEventListener('resize', resizeCanvas, false);
	function resizeCanvas() {
		if (starfield.isCanvasEnabled) {
			starfield.configureGeometry();
		} else {
			starfield.canvas.width = window.innerWidth;
		}
	}
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<canvas id="starfield" width="100%" height="400px"></canvas>