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HTML

              
                canvas#canvas
h1#title Rays & Particles
form
	label#ray-count(for="ray-input") Rays: 50
	input(type="range" id="ray-input" min="0" max="100")
		
	label#particle-count(for="particle-input") Particles: 50
	input(type="range" id="particle-input" min="0" max="100")
a#codepen-link(href='https://www.codepen.io/seanfree' target='_blank')
a.v2-link(href='https://codepen.io/seanfree/pen/bRvxMw' target='_blank') Click here to see Version II
              
            
!

CSS

              
                #canvas
	position: absolute
	z-index: 0
	top: 0
	left: 0
	height: 100vh
	width: 100vw
	background-image: linear-gradient(#4f4f34, #1f1f12)

#title
	position: absolute
	top: 60%
	left: 0
	z-index: 1
	width: 100%
	margin: 0
	padding: 0
	font-family: 'Raleway', sans-serif
	font-size: 3em
	text-align: center
	color: #ffffff
	mix-blend-mode: overlay

form
	position: absolute
	padding: 30px
	width: 200px
	mix-blend-mode: overlay
	font-size: 1.1em
	z-index: 1

label
	display: block
	text-align: center
	font-family: 'Raleway', sans-serif
	color: #fff

input[type=range] 
	-webkit-appearance: none
	margin-bottom: 18px
	width: 100%

	&:focus
		outline: none

	&::-webkit-slider-runnable-track 
		width: 100%
		height: 2px
		cursor: pointer
		background: white

	&::-webkit-slider-thumb 
		height: 16px
		width: 16px
		border-radius: 50%
		background: white
		cursor: pointer
		-webkit-appearance: none
		margin-top: -7px

	&::-moz-range-track 
		width: 100%
		height: 2px
		cursor: pointer
		background: white

	&::-moz-range-thumb 
		height: 16px
		width: 16px
		border-radius: 50%
		border: 2px solid white
		background: transparent
		cursor: pointer
		-webkit-appearance: none
		margin-top: -7px

.v2-link
	position: absolute
	bottom: 30px
	left: 30px
	color: rgba(255,255,255,0.6)
	font-family: 'Open Sans Condensed', sans-serif
	font-size: 1.2em
	text-decoration: none
	mix-blend-mode: overlay
	&:hover
		color: rgba(255,255,255,1)
		text-decoration: underline
	

#codepen-link
	position: absolute
	right: 30px
	bottom: 30px
	height: 40px
	width: 40px
	z-index: 10
	border-radius: 50%
	background-image: url('https://s3-us-west-2.amazonaws.com/s.cdpn.io/544318/logo.jpg')
	background-position: center center
	background-size: cover
	opacity: 0.5
	transition: all 0.25s

	&:hover
		opacity: 1
		box-shadow: 0 0 6px #6f6f6f
              
            
!

JS

              
                (function(window, document, undefined) {
	//IIFE's are pretty neat http://benalman.com/news/2010/11/immediately-invoked-function-expression/
	var canvas,
		ctx, //main (visible) canvas/context
		osCanvas,
		osCtx, //offscreen canvas/context
		rect,
		height,
		width,
		objects,
		numParticles,
		numRays, //objects array + totals
		pInput,
		rInput,
		rCount,
		pCount,
		title; //DOM elements

	var Ray = function() {
		this.ctx = osCtx; //locally cache offscreen 2d context for more effecient animation

		this.angle = 85 * Math.PI / 180; //105 deg in radians

		this.init = function() {
			this.velocity = 0.25 - Math.random() * 0.5; //velocity of x-axis
			this.len = canvas.height / 2 + Math.random() * (canvas.height / 2); //length of ray between half and full window height
			this.start = {
				//start/top of ray
				x: Math.random() * (canvas.width + 100) - 50,
				y: 0
			};
			this.end = {
				//end/bottom of ray
				x: this.start.x + this.len * Math.cos(this.angle), //use sine and cosine to calculate end point based on start point, length and angle
				y: this.start.y + this.len * Math.sin(this.angle) //start at point, add length then 'rotate' to final point by multiplying sine/cosine of angle
			};
			this.ttl = 100 + Math.random() * 200; //total lifespan of ray 'time to live'
			this.life = 0; //current lifespan of ray
			this.width = 0.5 + Math.random() * 4; //random width between 0.5 an 4.5
			this.hue = Math.round(45 + Math.random() * 15).toString(); //random yellow hue between 45 and 60 (degrees)
			this.saturation = Math.round(20 + Math.random() * 40).toString(); //random saturation between 40% and 60%
		};

		this.color = function() {
			//generate gradient
			var alpha = wave(this.life, this.ttl) * 0.005, //fade in/fade out alpha
				color1 =
					"hsla(" +
					this.hue +
					"," +
					this.saturation +
					"%," +
					"60%," +
					alpha.toString() +
					")", //start color of ray gradient
				color2 = "hsla(50,20%,20%,0)", //bottom color of ray gradient (transparent)
				gradient = ctx.createLinearGradient(
					this.start.x,
					this.start.y,
					this.end.x,
					this.end.y
				);

			gradient.addColorStop(0, color1);
			gradient.addColorStop(1, color2);

			return gradient;
		};

		this.draw = function() {
			//draw the ray
			this.ctx.beginPath();
			this.ctx.strokeStyle = this.color();
			this.ctx.lineWidth = this.width;
			this.ctx.moveTo(this.start.x, this.start.y);
			this.ctx.lineTo(this.end.x, this.end.y);
			this.ctx.stroke();
			this.ctx.closePath();
		};

		this.update = function() {
			if (this.life > this.ttl) {
				//re-initialize when lifespan expires
				this.init();
			}
			this.life++; //add to current life
			this.start.x += this.velocity; //move both ends of line
			this.end.x += this.velocity;
		};

		this.init(); //initialize when new ray is created

		return this; //return local scope
	};

	var Particle = function() {
		this.ctx = osCtx; //locally cache offscren 2d context for more effecient animation

		this.init = function() {
			this.position = {
				//random x,y position
				x: Math.random() * width,
				y: height / 2 + Math.random() * height / 2
			};
			this.velocity = {
				//random velocity on x-axis and y-axis
				x: 0.5 - Math.random() * 1,
				y: 0.5 - Math.random() * 1
			};
			this.ttl = 100 + Math.random() * 200; //total lifespan of particle
			this.life = 0; //current life of particle
			this.size = 1 + Math.random() * 10; //random size
		};

		this.color = function() {
			//generate hsla color
			var alpha = wave(this.life, this.ttl) * 0.005, //fade in/fade out alpha
				color = "hsla(50,50%,25%," + alpha.toString() + ")";
			return color;
		};

		this.draw = function() {
			//draw the particle
			this.ctx.beginPath();
			this.ctx.fillStyle = this.color();
			this.ctx.arc(this.position.x, this.position.y, this.size, 0, Math.PI * 2);
			this.ctx.fill();
			this.ctx.closePath();
		};

		this.update = function() {
			if (this.life > this.ttl) {
				this.init();
			} else {
				this.life++;
				this.position.x += this.velocity.x;
				this.position.y += this.velocity.y;
			}
		};

		this.init(); //initialize when new particle is created

		return this; //return local scope
	};

	function onResize() {
		//allows for resizing without effecting previously drawn objects
		rect = canvas.getBoundingClientRect();
		height = rect.height;
		width = rect.width;

		canvas.height = osCanvas.height = height;
		canvas.width = osCanvas.width = width;
	}

	function requestAnimationFrame() {
		//vendor prefixing + fallback
		return (
			window.requestAnimationFrame ||
			window.webkitRequestAnimationFrame ||
			window.mozRequestAnimationFrame ||
			window.oRequestAnimationFrame ||
			window.msRequestAnimationFrame ||
			function(callback) {
				window.setTimeout(callback, 1000 / 60);
			}
		);
	}

	function wave(t, a) {
		//function credit to http://stackoverflow.com/questions/26590800/how-can-we-increment-and-then-decrement-a-counter-without-conditionals
		return Math.abs((t + a / 2) % a - a / 2);
	}

	function setTitle() {
		//set title based on current objects being drawn
		var titleStr;
		if (numRays > 0 && numParticles > 0) titleStr = "Rays &amp; Particles";
		else if (numRays > 0 && numParticles === 0) titleStr = "Rays";
		else if (numRays === 0 && numParticles > 0) titleStr = "Particles";
		else if (numRays === 0 && numParticles === 0) titleStr = "¯\\_(ツ)_/¯";

		title.innerHTML = titleStr;
	}

	function createObjects() {
		numRays = parseInt(rInput.value); //pull values from range inputs, convert to integers
		numParticles = parseInt(pInput.value);

		setTitle();

		objects = [];

		for (var i = 0; i < numRays; i++) {
			//instantiate rays/particles
			var ray = new Ray();
			objects.push(ray);
		}

		for (var i = 0; i < numParticles; i++) {
			var particle = new Particle();
			objects.push(particle);
		}
	}

	function render(c1, c2) {
		c1.clearRect(0, 0, width, height); //clear previously drawn frames
		c2.clearRect(0, 0, width, height);
		c2.shadowBlur = 30; //add a 'glow' to rays/particles
		c2.shadowColor = "white";
		c2.globalCompositeOperation = "lighter"; //lighter composite operation for more of a 'glow'
		for (var i = 0, len = objects.length; i < len; i++) {
			//draw offscreen/update objects (rays and particles in same array)
			var obj = objects[i];
			obj.update();
			obj.draw();
		}
		c1.drawImage(osCanvas, 0, 0); //copy offscreen canvas to main canvas
	}

	function loop() {
		//animation loop
		render(ctx, osCtx);
		window.requestAnimationFrame(loop);
	}

	function init() {
		//initialize canvas/globals
		canvas = document.getElementById("canvas"); //main (on-screen) canvas / context
		ctx = canvas.getContext("2d");

		osCanvas = document.createElement("canvas"); //secondary (off-screen) canvas / context
		osCtx = osCanvas.getContext("2d");

		//get the DOM elements
		title = document.getElementById("title");

		rInput = document.getElementById("ray-input");
		rCount = document.getElementById("ray-count");

		rInput.oninput = function() {
			rCount.innerHTML = "Rays: " + this.value.toString();
			createObjects();
		};

		pInput = document.getElementById("particle-input");
		pCount = document.getElementById("particle-count");

		pInput.oninput = function() {
			pCount.innerHTML = "Particles: " + this.value.toString();
			createObjects();
		};

		onResize(); //set canvas size
		createObjects(); //create rays/particles
		loop(); //do a barrel roll
	}

	window.onload = init;
	window.onresize = onResize;
	window.requestAnimationFrame = requestAnimationFrame();
})(this, document);

              
            
!
999px

Console