unveil.coffee

# https://github.com/luis-almeida/unveil/blob/master/jquery.unveil.js
$.fn.unveil = (th = 0, callback = ->) ->
  $w = $ window
  images = $ @
  @one 'unveil', ->
    if (source = @getAttribute 'data-src')
      @setAttribute 'src', source
      callback()
  unveil = =>
    inview = @filter ->
      $e = $ @
      return if $e.is ':hidden'
      wt = $w.scrollTop()
      wb = wt + $w.height()
      et = $e.offset().top
      eb = et + $e.height()
      return eb >= wt - th and et <= wb + th
    loaded = inview.trigger 'unveil'
    images = images.not loaded
  $w.scroll unveil
  $w.resize unveil
  setTimeout unveil, 200
  return @