ALLEGRO_GET_EVENT_TYPE - Allegro 5 API

       Make  an  event  type  identifier, which is a 32-bit integer.  Usually, but not necessarily, this will be
       made from four 8-bit character codes, for example:

              #define MY_EVENT_TYPE   ALLEGRO_GET_EVENT_TYPE('M','I','N','E')

       IDs  less  than  1024  are  reserved  for  Allegro  or  its  addons.   Don’t  use  anything  lower   than
       ALLEGRO_GET_EVENT_TYPE(0, 0, 4, 0).

       You  should try to make your IDs unique so they don’t clash with any 3rd party code you may be using.  Be
       creative.  Numbering from 1024 is not creative.

       If you need multiple identifiers, you could define them like this:

              #define BASE_EVENT   ALLEGRO_GET_EVENT_TYPE('M','I','N','E')
              #define BARK_EVENT   (BASE_EVENT + 0)
              #define MEOW_EVENT   (BASE_EVENT + 1)
              #define SQUAWK_EVENT (BASE_EVENT + 2)

              /* Alternatively */
              enum {
                 BARK_EVENT = ALLEGRO_GET_EVENT_TYPE('M','I','N','E'),
                 MEOW_EVENT,
                 SQUAWK_EVENT
              };

       ALLEGRO_GET_EVENT_TYPE - Allegro 5 API

ALLEGRO_EVENT(3alleg5), ALLEGRO_USER_EVENT(3alleg5), ALLEGRO_EVENT_TYPE_IS_USER(3alleg5)

Allegro reference manual                                                         ALLEGRO_GET_EVENT_TYPE(3alleg5)

              #include <allegro5/allegro.h>

              #define ALLEGRO_GET_EVENT_TYPE(a, b, c, d)   AL_ID(a, b, c, d)