Originally Posted by Iņigo
A GtkLabel does not own a GdkWindow (i.e. an X window), so I guess this trick performs a full screen refresh. Am I correct?
Yes, a full refresh. Although I am not sure why it works (worked?). Maybe it has to do with the total area that needs an update. If you draw something at the top and then update a GtkLabel at the bottom, it leads to a full-refresh.
(see also sysd/src/display.c)