confette js not mine

NUM_CONFETTI = 350
COLORS = [[85,71,106], [174,61,99], [219,56,83], [244,92,68], [248,182,70]]
PI_2 = 2*Math.PI


canvas = document.getElementById "world"
context = canvas.getContext "2d"
window.w = 0
window.h = 0

resizeWindow = ->
  window.w = canvas.width = window.innerWidth
  window.h = canvas.height = window.innerHeight

window.addEventListener 'resize', resizeWindow, false

window.onload = -> setTimeout resizeWindow, 0

range = (a,b) -> (b-a)*Math.random() + a

drawCircle = (x,y,r,style) ->
  context.beginPath()
  context.arc(x,y,r,0,PI_2,false)
  context.fillStyle = style
  context.fill()

xpos = 0.5

document.onmousemove = (e) ->
  xpos = e.pageX/w

window.requestAnimationFrame = do ->
  window.requestAnimationFrame       ||
  window.webkitRequestAnimationFrame ||
  window.mozRequestAnimationFrame    ||
  window.oRequestAnimationFrame      ||
  window.msRequestAnimationFrame     ||
  (callback) -> window.setTimeout(callback, 1000 / 60)


class Confetti

  constructor: ->
    @style = COLORS[~~range(0,5)]
    @rgb = "rgba(#{@style[0]},#{@style[1]},#{@style[2]}"
    @r = ~~range(2,6)
    @r2 = 2*@r
    @replace()

  replace: ->
    @opacity = 0
    @dop = 0.03*range(1,4)
    @x = range(-@r2,w-@r2)
    @y = range(-20,h-@r2)
    @xmax = w-@r
    @ymax = h-@r
    @vx = range(0,2)+8*xpos-5
    @vy = 0.7*@r+range(-1,1)

  draw: ->
    @x += @vx
    @y += @vy
    @opacity += @dop
    if @opacity > 1
      @opacity = 1
      @dop *= -1
    @replace() if @opacity < 0 or @y > @ymax
    if !(0 < @x < @xmax)
      @x = (@x + @xmax) % @xmax
    drawCircle(~~@x,~~@y,@r,"#{@rgb},#{@opacity})")


confetti = (new Confetti for i in [1..NUM_CONFETTI])

window.step = ->
  requestAnimationFrame(step)
  context.clearRect(0,0,w,h)
  c.draw() for c in confetti
step();