text: // https://codepen.io/whqet/pen/Auzch
  //
  // when animating on canvas, it is best to use requestAnimationFrame instead of setTimeout or setInterval
  // not supported in all browsers though and sometimes needs a prefix, so we need a shim
  window.requestAnimFrame = ( function() {
  	return window.requestAnimationFrame ||
  				window.webkitRequestAnimationFrame ||
  				window.mozRequestAnimationFrame ||
  				function( callback ) {
  					window.setTimeout( callback, 1000 / 60 );
  				};
  })();
  
  // now we will setup our basic variables for the demo
  var canvas = document.getElementById( 'scene' ),
  		ctx = canvas.getContext( '2d' ),
  		// full screen dimensions
  		cw = 300, //window.innerWidth,
  		ch = 300, //window.innerHeight,
  		// firework collection
  		fireworks = [],
  		// particle collection
  		particles = [],
  		// starting hue
  		hue = 120,
  		// when launching fireworks with a click, too many get launched at once without a limiter, one launch per 5 loop ticks
  		limiterTotal = 5,
  		limiterTick = 0,
  		// this will time the auto launches of fireworks, one launch per 80 loop ticks
  		timerTotal = 80,
  		timerTick = 0,
  		mousedown = false,
  		// mouse x coordinate,
  		mx,
  		// mouse y coordinate
  		my;
  
  // set canvas dimensions
  canvas.width = cw;
  canvas.height = ch;
  
  // now we are going to setup our function placeholders for the entire demo
  
  // get a random number within a range
  function random( min, max ) {
  	return Math.random() * ( max - min ) + min;
  }
  
  // calculate the distance between two points
  function calculateDistance( p1x, p1y, p2x, p2y ) {
  	var xDistance = p1x - p2x,
  			yDistance = p1y - p2y;
  	return Math.sqrt( Math.pow( xDistance, 2 ) + Math.pow( yDistance, 2 ) );
  }
  
  // create firework
  function Firework( sx, sy, tx, ty ) {
  	// actual coordinates
  	this.x = sx;
  	this.y = sy;
  	// starting coordinates
  	this.sx = sx;
  	this.sy = sy;
  	// target coordinates
  	this.tx = tx;
  	this.ty = ty;
  	// distance from starting point to target
  	this.distanceToTarget = calculateDistance( sx, sy, tx, ty );
  	this.distanceTraveled = 0;
  	// track the past coordinates of each firework to create a trail effect, increase the coordinate count to create more prominent trails
  	this.coordinates = [];
  	this.coordinateCount = 3;
  	// populate initial coordinate collection with the current coordinates
  	while( this.coordinateCount-- ) {
  		this.coordinates.push( [ this.x, this.y ] );
  	}
  	this.angle = Math.atan2( ty - sy, tx - sx );
  	this.speed = 2;
  	this.acceleration = 1.05;
  	this.brightness = random( 50, 70 );
  	// circle target indicator radius
  	this.targetRadius = 1;
  }
  
  // update firework
  Firework.prototype.update = function( index ) {
  	// remove last item in coordinates array
  	this.coordinates.pop();
  	// add current coordinates to the start of the array
  	this.coordinates.unshift( [ this.x, this.y ] );
  
  	// cycle the circle target indicator radius
  	if( this.targetRadius < 8 ) {
  		this.targetRadius += 0.3;
  	} else {
  		this.targetRadius = 1;
  	}
  
  	// speed up the firework
  	this.speed *= this.acceleration;
  
  	// get the current velocities based on angle and speed
  	var vx = Math.cos( this.angle ) * this.speed,
  			vy = Math.sin( this.angle ) * this.speed;
  	// how far will the firework have traveled with velocities applied?
  	this.distanceTraveled = calculateDistance( this.sx, this.sy, this.x + vx, this.y + vy );
  
  	// if the distance traveled, including velocities, is greater than the initial distance to the target, then the target has been reached
  	if( this.distanceTraveled >= this.distanceToTarget ) {
  		createParticles( this.tx, this.ty );
  		// remove the firework, use the index passed into the update function to determine which to remove
  		fireworks.splice( index, 1 );
  	} else {
  		// target not reached, keep traveling
  		this.x += vx;
  		this.y += vy;
  	}
  }
  
  // draw firework
  Firework.prototype.draw = function() {
  	ctx.beginPath();
  	// move to the last tracked coordinate in the set, then draw a line to the current x and y
  	ctx.moveTo( this.coordinates[ this.coordinates.length - 1][ 0 ], this.coordinates[ this.coordinates.length - 1][ 1 ] );
  	ctx.lineTo( this.x, this.y );
  	ctx.strokeStyle = 'hsl(' + hue + ', 100%, ' + this.brightness + '%)';
  	ctx.stroke();
  
  	ctx.beginPath();
  	// draw the target for this firework with a pulsing circle
  	ctx.arc( this.tx, this.ty, this.targetRadius, 0, Math.PI * 2 );
  	ctx.stroke();
  }
  
  // create particle
  function Particle( x, y ) {
  	this.x = x;
  	this.y = y;
  	// track the past coordinates of each particle to create a trail effect, increase the coordinate count to create more prominent trails
  	this.coordinates = [];
  	this.coordinateCount = 5;
  	while( this.coordinateCount-- ) {
  		this.coordinates.push( [ this.x, this.y ] );
  	}
  	// set a random angle in all possible directions, in radians
  	this.angle = random( 0, Math.PI * 2 );
  	this.speed = random( 1, 10 );
  	// friction will slow the particle down
  	this.friction = 0.95;
  	// gravity will be applied and pull the particle down
  	this.gravity = 1;
  	// set the hue to a random number +-50 of the overall hue variable
  	this.hue = random( hue - 50, hue + 50 );
  	this.brightness = random( 50, 80 );
  	this.alpha = 1;
  	// set how fast the particle fades out
  	this.decay = random( 0.015, 0.03 );
  }
  
  // update particle
  Particle.prototype.update = function( index ) {
  	// remove last item in coordinates array
  	this.coordinates.pop();
  	// add current coordinates to the start of the array
  	this.coordinates.unshift( [ this.x, this.y ] );
  	// slow down the particle
  	this.speed *= this.friction;
  	// apply velocity
  	this.x += Math.cos( this.angle ) * this.speed;
  	this.y += Math.sin( this.angle ) * this.speed + this.gravity;
  	// fade out the particle
  	this.alpha -= this.decay;
  
  	// remove the particle once the alpha is low enough, based on the passed in index
  	if( this.alpha <= this.decay ) {
  		particles.splice( index, 1 );
  	}
  }
  
  // draw particle
  Particle.prototype.draw = function() {
  	ctx. beginPath();
  	// move to the last tracked coordinates in the set, then draw a line to the current x and y
  	ctx.moveTo( this.coordinates[ this.coordinates.length - 1 ][ 0 ], this.coordinates[ this.coordinates.length - 1 ][ 1 ] );
  	ctx.lineTo( this.x, this.y );
  	ctx.strokeStyle = 'hsla(' + this.hue + ', 100%, ' + this.brightness + '%, ' + this.alpha + ')';
  	ctx.stroke();
  }
  
  // create particle group/explosion
  function createParticles( x, y ) {
  	// increase the particle count for a bigger explosion, beware of the canvas performance hit with the increased particles though
  	var particleCount = 30;
  	while( particleCount-- ) {
  		particles.push( new Particle( x, y ) );
  	}
  }
  
  // main demo loop
  function launchFireworks() {
  	// this function will run endlessly with requestAnimationFrame
  	requestAnimFrame( launchFireworks );
  
  	// increase the hue to get different colored fireworks over time
  	//hue += 0.5;
  
    // create random color
    hue= random(0, 360 );
  
  	// normally, clearRect() would be used to clear the canvas
  	// we want to create a trailing effect though
  	// setting the composite operation to destination-out will allow us to clear the canvas at a specific opacity, rather than wiping it entirely
  	ctx.globalCompositeOperation = 'destination-out';
  	// decrease the alpha property to create more prominent trails
  	ctx.fillStyle = 'rgba(0, 0, 0, 0.5)';
  	ctx.fillRect( 0, 0, cw, ch );
  	// change the composite operation back to our main mode
  	// lighter creates bright highlight points as the fireworks and particles overlap each other
  	ctx.globalCompositeOperation = 'lighter';
  
  	// loop over each firework, draw it, update it
  	var i = fireworks.length;
  	while( i-- ) {
  		fireworks[ i ].draw();
  		fireworks[ i ].update( i );
  	}
  
  	// loop over each particle, draw it, update it
  	var i = particles.length;
  	while( i-- ) {
  		particles[ i ].draw();
  		particles[ i ].update( i );
  	}
  
  	// launch fireworks automatically to random coordinates, when the mouse isn't down
  	if( timerTick >= timerTotal ) {
  		if( !mousedown ) {
  			// start the firework at the bottom middle of the screen, then set the random target coordinates, the random y coordinates will be set within the range of the top half of the screen
  			fireworks.push( new Firework( cw / 2, ch, random( 0, cw ), random( 0, ch / 2 ) ) );
  			timerTick = 0;
  		}
  	} else {
  		timerTick++;
  	}
  
  	// limit the rate at which fireworks get launched when mouse is down
  	if( limiterTick >= limiterTotal ) {
  		if( mousedown ) {
  			// start the firework at the bottom middle of the screen, then set the current mouse coordinates as the target
  			fireworks.push( new Firework( cw / 2, ch, mx, my ) );
  			limiterTick = 0;
  		}
  	} else {
  		limiterTick++;
  	}
  }
  
  // mouse event bindings
  // update the mouse coordinates on mousemove
  canvas.addEventListener( 'mousemove', function( e ) {
  	mx = e.pageX - canvas.offsetLeft;
  	my = e.pageY - canvas.offsetTop;
  });
  
  // toggle mousedown state and prevent canvas from being selected
  canvas.addEventListener( 'mousedown', function( e ) {
  	e.preventDefault();
  	mousedown = true;
  });
  
  canvas.addEventListener( 'mouseup', function( e ) {
  	e.preventDefault();
  	mousedown = false;
  });
  /*
  
  // once the window loads, we are ready for some fireworks!
  window.onload = loop;
  */
  