Dos anyone have a small working example of using OpenGL in a libglade(mm) generated UI?

[Philipp Klaus Krause <pkk spth de>]

A few years ago I wrote an OpenGL application using glade for the rest
of the user interface. I used glademm C++ code generation, libgtkglextmm
to render to a widget derived from Gtk::DrawingArea.
Unfortunately glademm hasn't been updated for a long time, even back
then I often had to rewrite parts of the glademm-generated code myself
(glademm using old SigC:: vs me wantig to use sigc::, glademm not
knowing about newer GTK+ widgets, etc).
So i decided to give libglademm a try. However I have no idea how to
make this work. So far everything I tried resultet in runtime errors,
the derived widget not being used, etc. I didn't find an example of how
to use a derived widget that's not a top-level widget. Calling the
Gtk::DrawingArea constructor from my derived widget's constructor causes
a runtime error (set_gl_capability fails). gtkmm docs and Murray
rocomment to call the parent's constructor, they say it's necessary for
signal handling. However this is never done in any of the gtkglextmm
examples (they don't use libglademm though).

Does anyone have a working example of using OpenGL with libglade
(gtkglextmm with libglademm would be even better)?

Philipp