Color Overlay Coffe function

coffe_color_overlay.coffee

@count_overlay = (color, overlay) ->
# First part: If Lower Layer Value > 127.5, then do the following -
# Value Unit = (255-Lower Layer Value)/127.5
# Min Value = Lower Layer Value - (255-Lower Layer Value)
# Overlay = (Upper Layer Value * Value Unit) + Min Value
# Second part: If Lower Layer Value < 127.5, then do the following -
# Value Unit=Lower Layer Value/127.5
# Overlay = Upper Layer Value * Value Unit
  color   = parseInt(color)
  overlay = parseInt(overlay)

  if color > 127.5
    val_unit    = (255 - color)/127.5
    min_val     = color - (255 - color)
    overlay_val = (overlay*val_unit) + min_val
  else
    val_unit    = color/127.5
    overlay_val = overlay*val_unit

  Math.round overlay_val