Zooming in GtkDrawingArea

["gao chaowei" <chaoweigao hotmail com>]

I hope i get help here. I put a message several days ago, untill now i have 
not seen response. I feel worry because my supervisor ...
My Program:

GtkDrawingArea darea;
draw_arc(....);
...
Finally a tree is displayed(maybe large).

My question is:

How can i zoom in or zoom out what i have drawing in an efficient way. If 
other way can achieve this goal. Anybody have idea? Wait for your help!!

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