al_lock_vertex_buffer - Allegro 5 API

       Locks  a  vertex  buffer  so you can access its data.  Will return NULL if the parameters are invalid, if
       reading is requested from a write only buffer, or if the buffer is already locked.

       Parameters:

       • buffer - Vertex buffer to lock

       • offset - Vertex index of the start of the locked range

       • length - How many vertices to lock

       • flags - ALLEGRO_LOCK_READONLY, ALLEGRO_LOCK_WRITEONLY or ALLEGRO_LOCK_READWRITE

       al_lock_vertex_buffer - Allegro 5 API

ALLEGRO_VERTEX_BUFFER(3alleg5), al_unlock_vertex_buffer(3alleg5)

Allegro reference manual                                                          al_lock_vertex_buffer(3alleg5)

       5.1.3

              #include <allegro5/allegro_primitives.h>

              void* al_lock_vertex_buffer(ALLEGRO_VERTEX_BUFFER* buffer, int offset,
                 int length, int flags)