al_set_clipping_rectangle - Allegro 5 API

       Set the region of the target bitmap or display that pixels get clipped to.  The default is to clip pixels
       to the entire bitmap.

       al_set_clipping_rectangle - Allegro 5 API

al_get_clipping_rectangle(3alleg5), al_reset_clipping_rectangle(3alleg5)

Allegro reference manual                                                      al_set_clipping_rectangle(3alleg5)

              #include <allegro5/allegro.h>

              void al_set_clipping_rectangle(int x, int y, int width, int height)