Although the GTK distribution comes with many types of widgets that
should cover most basic needs, there may come a time when you need to
create your own new widget type. Since GTK uses widget inheritance
extensively, and there is already a widget that is close to what you want,
it is often possible to make a useful new widget type in
just a few lines of code. But before starting work on a new widget, check
around first to make sure that someone has not already written
it. This will prevent duplication of effort and keep the number of
GTK widgets out there to a minimum, which will help keep both the code
and the interface of different applications consistent. As a flip side
to this, once you finish your widget, announce it to the world so
other people can benefit. The best place to do this is probably the
gtk-list.
Complete sources for the example widgets are available at the place you
got this tutorial, or from:
http://www.gtk.org/~otaylor/gtk/tutorial/
