al_get_opengl_fbo - Allegro 5 API

       Returns the OpenGL FBO id internally used by the given bitmap if it uses one, otherwise returns zero.  No
       attempt will be made to create an FBO if the bitmap is not owned by the current display.

       The  FBO  returned  by  this  function  will  only  be freed when the bitmap is destroyed, or if you call
       al_remove_opengl_fbo(3alleg5) on the bitmap.

              Note: In Allegro 5.0.0 this function only returned an FBO which had  previously  been  created  by
              calling  al_set_target_bitmap(3alleg5).   It  would not attempt to create an FBO itself.  This has
              since been changed.

       al_get_opengl_fbo - Allegro 5 API

al_remove_opengl_fbo(3alleg5), al_set_target_bitmap(3alleg5)

Allegro reference manual                                                              al_get_opengl_fbo(3alleg5)

              #include <allegro5/allegro_opengl.h>

              GLuint al_get_opengl_fbo(ALLEGRO_BITMAP *bitmap)