It should be possible to do:
clutter_stage_set_fullscreen (stage, TRUE);
clutter_actor_show (stage);
and have the stage be full screen as soon as it is shown.
Currently, we need to call clutter_actor_realize() prior to calling
set_fullscreen(), otherwise the backing X window will not be set,
and ClutterStageX11 will silently discard the change.
If set_fullscreen() was called prior to realization, ClutterStageX11
should delay setting the fullscreen hint until the realize() chain
has been successfully executed.
http://bugzilla.clutter-project.org/show_bug.cgi?id=2515
b8e5603a85