set_display_switch_callback (3) - Linux Man Pages
set_display_switch_callback: Installs a switching notification callback. Allegro game programming library.
set_display_switch_callback - Installs a switching notification callback. Allegro game programming library.
int set_display_switch_callback(int dir, void (*cb)());
Installs a notification callback for the switching mode that was
previously selected by calling set_display_switch_mode(). The direction
parameter can either be SWITCH_IN or SWITCH_OUT, depending whether you
want to be notified about switches away from your program or back to your
program. You can sometimes install callbacks for both directions at the
same time, but not every platform supports this. You can install several
switch callbacks, but no more than eight on any platform.
Returns zero on success, decreasing the number of empty callback slots by
one. Returns -1 if the request is impossible for the current platform or
you have reached the maximum number of allowed callbacks.