class Bitmap
  def outline_rect(x, y, width, height, color, thickness = 1)
    fill_rect(x, y, width, thickness, color)
    fill_rect(x, y, thickness, height, color)
    fill_rect(x, y + height - thickness, width, thickness, color)
    fill_rect(x + width - thickness, y, thickness, height, color)
  end
end