Role for objects that will be passed into UAV::Pilot::SDL::Window as children.

The method draw will be called on the object to draw itself. It will be passed the UAV::Pilot::SDL::Window object. This is the only method that is required for the class doing the role to implement.

The update_window_rect method is passed an UAV::Pilot::SDL::Window, and is called after draw. The default implementation will call <UAV::Pilot::SDL::Window-update_rect>>, but you may wish to override this if you have other means of updating your drawing area.

The add_to_window method should be called on the object after construction and passed an UAV::Pilot::SDL::Window object. A second optional parameter is the float value (default bottom). The handler will add itself as a child to this window. The default code for the method in the role will do this for you, adding the child at the bottom.

Also has width and height attributes. They are read-only attributes, but can be set with the _set_width and _set_height methods. These methods should be considered private to the class.