[GtkGLExt] Is it possible to use overlays with gtkglextmm?

["Haraldur Tristan Gunnarson" <harg pml ac uk>]

Greetings,

I have been writing, as my first significant project using OpenGL, a GUI
using gtkglextmm for viewing large datasets as a cloud of points. I have
some measuring tools that are currently rendered by drawing some of the
points and then the line or box of the tool while the user is dragging
the cursor. This works well with small datasets but gets sluggish with
the larger ones, particularly the ones that require caching. I would
like to use overlays as a conceptually and practically simple (I hope)
way of drawing the rulers (and so on) without having to redraw the
points each time.

How do I do this while using gtkglextmm? I found the method
Gdk::GL::Config::get_layer_plane() but no other obvious things in the
documentation. Looking at an example using WGL, it appears I need to
create an "layer context" for the overlay, but I do not see how to do
that in gtkglextmm. Does it work in a similar way and, if so, how?

Thanks in advance,

Haraldur

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