why not animated?

[hanmac]

hi i have this:

class Window_Base
  
  #--------------------------------------------------------------------------
  # * Object Initialization
  #     x      : window x-coordinate
  #     y      : window y-coordinate
  #     width  : window width
  #     height : window height
  #--------------------------------------------------------------------------
  alias wskin_init initialize
  def initialize(x, y, width, height)
    wskin_init(x, y, width, height) 
    @window_skin = RPG::Cache.windowskin(@windowskin_name)
    @skin_part=Bitmap.new(192,128)
    @max = @window_skin.height / 128
    @skin_part.blt(0, 0, @window_skin, Rect.new(0, 0, 192, 128))
    self.windowskin = @skin_part
    @blink_count=0
    self.stretch = $game_system.windowskin_stretch
  end

  def update
    super
    #Animates the Window Skin
    @blink_count = (@blink_count + 1) % (@max*5)
    if @blink_count % 5 == 0
      @skin_part.clear
      @skin_part.blt(0, 0, @window_skin, Rect.new(0, @blink_count * 128 / 5, 192, 128))
      self.windowskin = @skin_part
    end
  end
end

the skin should be animated but i did not funktion