ALLEGRO_EVENT_SOURCE - Allegro 5 API

       An  event  source  is any object which can generate events.  For example, an ALLEGRO_DISPLAY can generate
       events,  and  you   can   get   the   ALLEGRO_EVENT_SOURCE   pointer   from   an   ALLEGRO_DISPLAY   with
       al_get_display_event_source(3alleg5).

       You may create your own “user” event sources that emit custom events.

       ALLEGRO_EVENT_SOURCE - Allegro 5 API

ALLEGRO_EVENT(3alleg5), al_init_user_event_source(3alleg5), al_emit_user_event(3alleg5)

Allegro reference manual                                                           ALLEGRO_EVENT_SOURCE(3alleg5)

              #include <allegro5/allegro.h>

              typedef struct ALLEGRO_EVENT_SOURCE ALLEGRO_EVENT_SOURCE;