al_update_display_region - Allegro 5 API

       Does  the  same  as  al_flip_display(3alleg5),  but tries to update only the specified region.  With many
       drivers this is not possible, but for some it can improve performance.  If this is  not  supported,  this
       function  falls  back  to  the  behavior of al_flip_display(3alleg5).  You can query the support for this
       function using al_get_display_option(display, ALLEGRO_UPDATE_DISPLAY_REGION).

       al_update_display_region - Allegro 5 API

al_flip_display(3alleg5), al_get_display_option(3alleg5)

Allegro reference manual                                                       al_update_display_region(3alleg5)

              #include <allegro5/allegro.h>

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