Add a 'struct vo *vo' argument to the x11_common.c functions that
access the variable so it's available as vo->opts->vo_ontop. To keep
VOs using the old API working create a global vo variable that is set
to the currently used old vo. "vo_ontop" will be #defined to
"global_vo->opts->vo_ontop", and x11_common.h will add defines like
the following when it is included by old VOs:
#define vo_x11_ontop() vo_x11_ontop(global_vo)
so that they will call the function according to the new declaration.
Uoti Urpala