al_acknowledge_resize - Allegro 5 API

       When the user receives a [resize event]ALLEGRO_EVENT_DISPLAY_RESIZE(3alleg5) from a resizable display, if
       they  wish the display to be resized they must call this function to let the graphics driver know that it
       can now resize the display.  Returns true on success.

       Adjusts the clipping rectangle to the full size of the backbuffer.   This  also  resets  the  backbuffers
       projection transform to default orthographic transform (see al_use_projection_transform(3alleg5)).

       Note  that  a  resize event may be outdated by the time you acknowledge it; there could be further resize
       events generated in the meantime.

       al_acknowledge_resize - Allegro 5 API

al_resize_display(3alleg5), ALLEGRO_EVENT(3alleg5)

Allegro reference manual                                                          al_acknowledge_resize(3alleg5)

              #include <allegro5/allegro.h>

              bool al_acknowledge_resize(ALLEGRO_DISPLAY *display)