If I understand things right, Gdk operates in 32-bit coordinates
and employs a translation scrolling-type layer to cope with X11's 16-bit
restriction.  The X11 coordinates are not supposed to be visible to the
Gdk user, possibly with the exception of the function
gdk_window_get_internal_paint_info.

But gdk_window_get_origin returns X11 coordinates.  Hence for a very
large window -- the window of a foocanvas to be exact -- the coordinates
get clipped at +/- 16k.

My workaround is to get the offset via gdk_window_get_internal_paint_info.


Caution: _gdk_windowing_window_get_pointer seems to rely on getting X11
coordinates from gdk_window_get_origin.