Just as GTK+ is build on top of GDK, GtkGLArea is built on top of gdkgl
which is basically wrapper around GLX functions. The widget itself is
derived from GtkDrawinigArea widget and adds only few extra functions.
Lower level gdkgl functions make it easy to render on any widget that has
OpenGL capable visual, rendering to off-screen pixmaps is also supported.

Related project which may interest those who use GTK-- is GtkGLArea--. It is a
C++ wrapper for gtkglarea written by Karl Nelson <kenelson@ece.ucdavis.edu>.

WWW: https://www.mono-project.com/archived/gtkglarea/