#--------------------------------------------------------------------------
  # * Load Bitmap
  #--------------------------------------------------------------------------
  def self.load_bitmap(folder_name, filename, hue = 0)
    @cache = {} if @cache == nil
    path = folder_name + filename
    if not @cache.include?(path) or @cache[path].disposed?
      if filename.empty?
        @cache[path] = Bitmap.new(32, 32)
      else
        @cache[path] = Bitmap.new(path)
      end
    end
    if hue == 0
      return @cache[path]
    else
      key = [path, hue]
      if not @cache.include?(key) or @cache[key].disposed?
        @cache[key] = @cache[path].clone
        @cache[key].hue_change(hue)
      end
      return @cache[key]
    end
  end
end