Hey Mike! also nice to see u!

GDI stands for "Graphics Device Interface".
The GDI is for all cinds of "window-outputs".
So it is for a text, for 2d grafix,.... for the visual things....
also for the printer (is also a visual output wink ).
So, yes its also for drawing windows button.

cheers
Marcel

A8c, Blender, FlStudio, Unity3d