gdk_window_set_back_pixmap()

["Matt Hoosier" <matt hoosier gmail com>]

A couple of weeks ago, I asked here whether anybody had a good
technique to prevent the initial tiling-to-white that happens when a
GtkWindow first is mapped and exposed.

One solution that was offered is to install a "realize" signal handler
which just does this:

 gdk_window_set_back_pixmap (w->window, NULL, FALSE);

This causes the contents of the underlying X11 window to be either
transparent, or a snapshot of the underlying root window [I can't
entirely tell from the documentation:
http://developer.gnome.org/doc/API/2.0/gdk/gdk-Windows.html#gdk-window-set-back-pixmap].
Disregarding which of those two approaches happens, the result is not
to show the logical conents of the window until it's rendered under
its own power.  At least visually, the result is much smoother.

Are there down-sides to this; that is, why does Gtk not use this trick
by default?

--Matt