al_set_new_bitmap_format - Allegro 5 API

       Sets the pixel format (ALLEGRO_PIXEL_FORMAT(3alleg5)) for newly created bitmaps.  The default format is 0
       and means the display driver will choose the best format.

       al_set_new_bitmap_format - Allegro 5 API

ALLEGRO_PIXEL_FORMAT(3alleg5), al_get_new_bitmap_format(3alleg5), al_get_bitmap_format(3alleg5)

Allegro reference manual                                                       al_set_new_bitmap_format(3alleg5)

              #include <allegro5/allegro.h>

              void al_set_new_bitmap_format(int format)