al_resize_display - Allegro 5 API

       Resize  the  display.   Returns  true  on  success, or false on error.  This works on both fullscreen and
       windowed displays, regardless of the ALLEGRO_RESIZABLE flag.

       Adjusts the clipping rectangle to the full size of the backbuffer.

       al_resize_display - Allegro 5 API

al_acknowledge_resize(3alleg5)

Allegro reference manual                                                              al_resize_display(3alleg5)

              #include <allegro5/allegro.h>

              bool al_resize_display(ALLEGRO_DISPLAY *display, int width, int height)