al_create_display - Allegro 5 API

       Create a display, or window, with the specified dimensions.  The parameters of the display are determined
       by  the  last  calls  to  al_set_new_display_*.   Default parameters are used if none are set explicitly.
       Creating a new display will automatically make it the  active  one,  with  the  backbuffer  selected  for
       drawing.

       Returns NULL on error.

       Each  display  that  uses OpenGL as a backend has a distinct OpenGL rendering context associated with it.
       See al_set_target_bitmap(3alleg5) for the discussion about rendering contexts.

       al_create_display - Allegro 5 API

al_set_new_display_flags(3alleg5),                                    al_set_new_display_option(3alleg5),
       al_set_new_display_refresh_rate(3alleg5),                            al_set_new_display_adapter(3alleg5),
       al_set_new_window_title(3alleg5) al_set_window_position(3alleg5)

Allegro reference manual                                                              al_create_display(3alleg5)

              #include <allegro5/allegro.h>

              ALLEGRO_DISPLAY *al_create_display(int w, int h)