"Finally, all the prep work is done for the user interface
of our drawing application, and we're ready to begin drawing.
Drawing functions are not resident in the GTK+ library but are part
of another library known as the GIMP Drawing Kit (GDK). In this
article we will concentrate on writing simple callbacks for the
Line, Circle, and Rectangle menu items in our program. Eventually
we'll add the ability for the user to show us where to draw (let
them select the endpoints of a line with their mouse or size a
circle or rectangle interactively). But for now, let's simply draw
a line, a circle and a rectangle when asked."