gtk_drawing_area and scrollbar

[Jozef Botka <jozob zoznam sk>]

Hi, I have written an app., which read a file, parses it, and draws the contents to a gdk_pixmap 
simultaneously. After then the gdk_pixmap is drawn to gtk_drawing_area...............

I have also written some functions, which after clicking buttons zoomIN/OUT or move(left,right,up,down),  
recalculate coordinates of the content, that is going to be drawn to pixmap >> drawing_area, but does not 
recalculate the size of pixmap or drawing_area(I don't want it). It does not recalculate the size of pixmap 
and drawing_area, because if it is too high I get a seg. fault or some other error(ofcourse...). 
I hope you understand it, as I think it is not the "common" way to do that things like that.

....All that works, but I know, it is a primitive solution.

I want to know, how to solve "this problem". So I have a simple question, how to work out better scrolling 
using scrollbar. Or can you navigate me through the right way how make a (CAD) like app?

Thank you