extend Drawing Area class

[Jeff Simpson <llcooljeff gmail com>]

(also posted to glade-users):

I'm hoping somebody can point me in the right direction for a project
I'm working on. Basically, I need to add a few extra functions to the
DrawingArea object, and I'd like to use Glade / gtkmm as much as
possible. The code needs to be in C++ due to some already existing
functions that I'd like to not have to re-write.

Can anybody point me in the right direction for how to create a new
custom class/object based on DrawingArea? I'd like it to have all the
existing functions of DrawingArea (draw_line, etc) but also have a few
customized functions. Thanks for any help!

 - Jeff