[cairo] Layered stroke / fill

[Lockert Fredrick]

Greetings,

I'm currently programming a very simple gtkmm/cairo application, where
the user can draw lines, circles, rectangles, etc, in real time.

There's one problem I've got though, and I can't quite figure out how
to fix it. When the user draws out rectangles, they "merge" into each
other, rather then being painted on top of each other. I'm sure this
is an easy fix, but I couldn't find an answer after searching the web
and the documentation (probably used the wrong keywords...)

Here's what I've currently got:
http://fureloka.com/files/dev/gtkmm/gtkmm_rectangle_drawing.png

Here's what I wish to achieve:
http://fureloka.com/files/dev/gtkmm/win32_api_rectangle_drawing.png

Source:
http://fureloka.com/files/dev/gtkmm/main.cpp
http://fureloka.com/files/dev/gtkmm/drawarea.h
http://fureloka.com/files/dev/gtkmm/drawarea.cpp

I would really really appreciate it, if someone could point me in the
right direction!

Cheers,
Fredrick