def draw(alpha = 0xff, z_index = 0, color = 0xffffff, over_color = 0xcccccc)
      return unless @visible
      unless @img
        bottom = @y + (@open ? @max_h : @h) + @scale_y
        b_color = (alpha << 24)
        G.window.draw_quad @x - @scale_x, @y - @scale_y, b_color,
                           @x + @w + @scale_x, @y - @scale_y, b_color,
                           @x + @w + @scale_x, bottom, b_color,
                           @x - @scale_x, bottom, b_color, z_index
        @buttons.each do |b|
          c = (alpha << 24) | (b.state == :over ? over_color : color)
          G.window.draw_quad b.x, b.y, c,
                             b.x + b.w, b.y, c,
                             b.x + b.w, b.y + b.h, c,
                             b.x, b.y + b.h, c, z_index + 1 if b.visible
        end
      end
      @buttons[0].draw(alpha, z_index, color)
      @buttons[1..-1].each { |b| b.draw alpha, z_index + 1, color }
    end
def draw(alpha = 0xff, z_index = 0, color = 0xffffff, over_color = 0xcccccc)
      return unless @visible
      unless @img
        bottom = @y + (@open ? @max_h : @h) + @scale_y
        b_color = (alpha << 24)
        G.window.draw_quad @x - @scale_x, @y - @scale_y, b_color,
                           @x + @w + @scale_x, @y - @scale_y, b_color,
                           @x + @w + @scale_x, bottom, b_color,
                           @x - @scale_x, bottom, b_color, z_index
        @buttons.each do |b|
          c = (alpha << 24) | (b.state == :over ? over_color : color)
          G.window.draw_quad b.x, b.y, c,
                             b.x + b.w, b.y, c,
                             b.x + b.w, b.y + b.h, c,
                             b.x, b.y + b.h, c, z_index + 1 if b.visible
        end
      end
      @buttons[0].draw(alpha, z_index, color)
      @buttons[1..-1].each { |b| b.draw alpha, z_index + 1, color }
    end
Draws the drop-down list.

 Parameters:
 [alpha] (+Fixnum+) The opacity with which the drop-down list will be
         drawn. Allowed values vary between 0 (fully transparent) and 255
         (fully opaque).
 [z_index] (+Fixnum+) The z-order to draw the object. Objects with larger
           z-orders will be drawn on top of the ones with smaller z-orders.
 [color] Color of the buttons, if no image was provided, or color to apply
         a filter to the images.
 [over_color] Color of the buttons when the mouse is over them (when no
              image was provided).