drawing a grid on an image

[Thomas Gaudin <Thomas Gaudin emi u-bordeaux fr>]

Hi,

I'm not yet familiar with GTK and I'd like to know how to add a grid
(whose size should changed by mouse draging)  onto a picture, anybody
knows if an existing application based on GTK does that kind of thing ?
will I have to make a custom widget ?
shall I use two differents layers ?
If only I could draw one line over my picture (but not in), I think I
would manage for the rest.

thanks

Thomas Gaudin