drawing lines on picture

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

Ok, it must be trivial for  most of you but if someone could give me a
clue, I would be glad...

I have to draw a grid on an image which can be resized by a mouse click
& drag, any advices will be welcomed.
Where can I find some documentation (I have already read GTK tutorial,
but without success) ?

regards

Thomas GAUDIN, a poor student who may not pass his exams.