al_get_window_borders - Allegro 5 API

       If  that information is available returns TRUE and fills in the size of the window borders.  You can pass
       NULL for borders you do not want to retrieve.

       If the border information is not available returns FALSE.

              [UnstableAPI]: This is an experimental feature and currently only  partially  works  on  X11  and
              Windows.  The meaning of the upper border may change when menus are present.

       al_get_window_borders - Allegro 5 API

al_set_window_position(3alleg5), al_get_window_position(3alleg5)

       5.2.9

Allegro reference manual                                                          al_get_window_borders(3alleg5)

              #include <allegro5/allegro.h>

              bool al_get_window_borders(ALLEGRO_DISPLAY *display, int *left, int *top, int *right, int *bottom)