def do_draw(self):
pass<EOL>
Draw any shapes or images associated with this widget.

This method is called by `_draw()` after it checks to make sure the 
widget is attached to the root of the GUI hierarchy and that the 
`rect`, `group`, and `batch` attributes have all been set.  

This method is called both to draw the widget for the first time and to 
update it subsequently.  This usually means that you need to check to 
see if your graphics objects and resources need to be initialized yet.