How to do_size_allocate properly in a gtk.Viewport subclass

[Joel Hedlund]

Hi!

I've raised this issue on #pygtk and #gtk+ but with no luck. I haven't 
been able to solve this even with aid of google, the pygtk reference and 
the gtk C source, so pretty please help?

I'm making an application that you can think of as an image viewer. I 
want to display a widget in a gtk.Viewport. The widget can have any size 
from tiny to humungous. I don't want the viewport to ever give the 
widget a larger size allocation than requested, and I don't want the 
viewport to ever resize to accomodate a large widget. It should rather 
leave grey areas around the widget/show only a portion of the widget.

To do this I have subclassed gtk.Viewport (MyViewport) and overrided the 
do_size_allocate method:

>     def do_size_allocate(self, allocation):
>         self.allocation = allocation
>         child_req = self.child.get_child_requisition()
>         child_alloc = gtk.gdk.Rectangle(0, 0, *child_req)
>         self.child.size_allocate(child_alloc)
>         self.props.hadjustment.update(allocation.width, child_alloc.width)
>         self.props.vadjustment.update(allocation.height, child_alloc.height)
>         if self.flags() & gtk.REALIZED:
>             self.window.move_resize(*self.allocation)
>             self.child.window()

When I add a very large widget (a gtk.DrawingArea) to MyViewport only 
the originally visible portion of the widget is redrawn when I resize 
the window using the mouse, and the grey area around widget gets 
littered with grey lines that are not redrawn if you minimize and 
restore the window. I assume this comes from that the proper gdk windows 
haven't been updated, and that the grey lines are remnants of old 
Viewport borders.

In gtk_viewport_size_allocate in gtkviewport.c, gdk_window_move_resize 
is called on three gdk windows: viewport->window, viewport->view_window 
and viewport->bin_window, but in pygtk I only have gtk.Viewport.window. 
I assume that this is the problem? If so, how can I fix this? Or is 
there something else that I have overlooked?

And another relevant question: am I overcomplicating this? Is there some 
kind of flag that I could set on a vanilla viewport to accomplish this?

Thanks in advance,
Joel