How to get GdkNativeWindow from GdkWindow? (need during iteration of display, using gdk)

[Mike Cookson <cook60020tmp mail ru>]

Hi all.
I'm developing window docker - tool, allowing to turn any toplevel window into panel. It should check all toplevel windows in default display for properties (name, role, class, type, probably something else) and create panel on the same screen, which should grab window into GtkSocket widget (also grouping by props is planned).

Iteration looks very easy - i just get default display and iterate screens and toplevel windows. But in order to grab window - i need to get its ID. I saw x11-specific lookup functions, to get GDK objects from X11 objects; but in this case i need reverce operation. However, i saw also function to get default XDisplay object, but in this case iteration may be done only with X11 API.

Currently i got tool, that grabs one window, with synopsis: "window-docker WID" (could also be extended to grab set of windows, placing them in one or more rows).