al_set_current_opengl_context - Allegro 5 API

       Make  the OpenGL context associated with the given display current for the calling thread.  If there is a
       current target bitmap which belongs to a different OpenGL context, the target bitmap will be  changed  to
       NULL.

       Normally  you  do  not  need  to  use  this  function,  as the context will be made current when you call
       al_set_target_bitmap(3alleg5) or al_set_target_backbuffer(3alleg5).  You might need it if you created  an
       OpenGL  “forward compatible” context.  Then al_get_backbuffer(3alleg5) only returns NULL, so it would not
       work to pass that to al_set_target_bitmap(3alleg5).

Allegro reference manual                                                  al_set_current_opengl_context(3alleg5)

       al_set_current_opengl_context - Allegro 5 API

              #include <allegro5/allegro_opengl.h>

              void al_set_current_opengl_context(ALLEGRO_DISPLAY *display)