Scrolledwindow, layout and drawing area

["fzamperini tiscali it" <fzamperini tiscali it>]

Hi,
    I have to draw a picture inside a top level window that has many 
other widgets (like side panes, menu bar etc.); I need zooming and 
panning features, so I went for a scrolled window => layout => 
drawingarea.
To achieve zooming I handle the scroll event by scaling the original 
size pixbuf and copying it to an off screen pixbuf that is copied on 
the drawingarea in the expose_event handler. I want the minimum zoom 
value to fit the picture in the scrolled window, and the maximum to be 
the actual picture size (let's suppose that the actual picture size is 
always greater than the scrolled window viewport).
I read the documentation but I miss something about the GtkLayout; 
these are the steps that I'm taking when zooming:
- nothing to do with the scrolledwindow
- layout: I resize it (gtk_layout_set_size()) to the _scaled_ picture 
size (remember, always greater or equal to the "viewport")
- drawingarea: I resize it to fit the layout 
(gtk_widget_set_size_request()), that is to the scaled picture size.
I took these steps because I think that the layout should hold the 
whole scaled picture, and its scrolling features make it move around 
behind the top level window; the only visible part, though, will be 
that corresponding to the scrolledwindow rectangle.
When I do this in my application I cannot make the drawing area to fit 
the layout (it works only the first time I do that), so I see the 
picture zooming just in the portion of the viewport that corresponds to 
the starting drawingarea rectangle.
Does anyone knows if something is wrong with this approach?
Thank you for any help

Federico Zamperini



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