canvas = document.getElementById('canvas')
ctx = canvas.getContext('2d')
ctx.globalCompositeOperation = 'lighter'

var resize = function(){
  ctx.canvas.width  = window.innerWidth
  ctx.canvas.height = window.innerHeight
}
resize()
window.addEventListener('resize',resize)

Particle = function(opacity,oFade,size,sFade,innerSizeFactor,x,ySpeed,ySpeedFade,xSpeed,xSpeedFade){
  this.d = false
  this.o = opacity
  this.oF = oFade
  this.s = size
  this.sF = sFade
  this.iSF = innerSizeFactor
  this.iS = this.s*this.iSF
  this.x = x
  this.xS = xSpeed
  this.xSF = xSpeedFade
  this.yS = ySpeed
  this.ySF = ySpeedFade
  this.y = ctx.canvas.height
}
Particle.prototype.update = function(){
  if(this.d == false){
    var o = this.o-this.oF*dt
    if(o<0){this.d = true}else{this.o=o}
    var s = this.s-this.sF*dt
    if(s<0){this.d = true}else{this.s=s}
    this.iS -= this.sF*this.iSF*dt
    this.yS -= this.ySF*dt
    this.xS -= this.xSF*dt
    this.x -= this.xS*dt
    this.y -= this.yS*dt
  }
}
Particle.prototype.draw = function(){
  if(this.d == false){
    ctx.setTransform(1,0,0,1,this.x,this.y)
    var grd = ctx.createRadialGradient(this.s,this.s,this.iS,this.s,this.s,this.s)
    ctx.globalAlpha = this.o
    grd.addColorStop(0,'#fa631a')
    grd.addColorStop(1,'rgba(255,255,255,0)')
    ctx.fillStyle=grd
    ctx.fillRect(0,0,this.s*2,this.s*2)
  }
}
window.requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
                              window.webkitRequestAnimationFrame || window.msRequestAnimationFrame

var t,dt,to,
    particles = [],
    n = 0

loop = function(){
  n += 1
  t = performance.now()
  dt = t-to
  to = t
  for(var i=0;i<canvas.width/300;i++){
  particles.push(new Particle(
    Math.random()*8+0.01,//opacity
    Math.random()*0.0001,//oFade
    Math.random()*5,//size
    Math.random()*0.003+0.002,//sFade
    Math.random()*0.5,//innerSizeFactor
    Math.random()*canvas.width,//x
    Math.random()*0.1+0.38,//ySpeed
    Math.random()*0.00001,//ySpeedFade
    Math.random()*-0.2,//xSpeed
    Math.random()*0.00006-0.00003//xSpeedFade
  ))
  }
  while(particles.length > 500){particles.shift()}
	ctx.setTransform(1,0,0,1,0,0)
	ctx.clearRect(0,0,canvas.width,canvas.height)
  for(var i=0;i < particles.length;i++){
    particles[i].draw()
  }
  for(var i=0;i < particles.length;i++){
    particles[i].update()
  }
  window.requestAnimationFrame(loop)
}

to = performance.now()
window.requestAnimationFrame(loop)