Role for objects that will be passed into
UAV::Pilot::SDL::Window as children.
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.
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.
height attributes. They are read-only attributes, but can be set with the
_set_height methods. These methods should be considered private to the class.