What is Gnome? a desktop environment and a development platform that is a framework for building graphical applications
GtkButton widget documentation
Gnome Developer Home Page with overview, architecture tools etc.
Overview of the GNOME platform
Gnome User Guide, System Adminstration Guide
Ruby Gnome2 (also here for version history)
Cairo Graphics Tutorial (Python Based)
Note Rectangle point of confusion: http://www.cairographics.org/manual/cairo-cairo-t.html#id2618849
Cairo::Rectangle object is for
Cairo::Context#clip_rectangle_list (*) not
Cairo::Context#rectangle.