ALLEGRO_VERTEX_CACHE_SIZE - Allegro 5 API

       Defines  the  size  of  the transformation vertex cache for the software renderer.  If you pass less than
       this many vertices to the primitive rendering functions you will get a speed boost.   This  also  defines
       the size of the cache vertex buffer, used for the high-level primitives.  This corresponds to the maximum
       number of line segments that will be used to form them.

Allegro reference manual                                                      ALLEGRO_VERTEX_CACHE_SIZE(3alleg5)

       ALLEGRO_VERTEX_CACHE_SIZE - Allegro 5 API

              #include <allegro5/allegro_primitives.h>

              #define ALLEGRO_VERTEX_CACHE_SIZE 256