def open_entity(entity)
  if gui = @gui
    position = entity.position
    window = Boleite::GUI::Window.new
    window.header_text = "#{position.x}x#{position.y} #{entity.template.name}"
    window.size = Boleite::Vector2f.new(200.0, 200.0)
    window.set_next_to @window
    window.add_close_button do
      unless gui.nil?
        gui.remove_root window
      end
    end
    gui.add_root window
    @entity_windows << window
  end
end