bool al_get_monitor_info(int adapter, ALLEGRO_MONITOR_INFO *info)
Get information about a monitor's position on the desktop. adapter is a number from 0 to al_get_num_video_adapters()-1.
On Windows, use al_set_new_display_flags(3alleg5) to switch between Direct3D and OpenGL backends, which will often have different adapters available.
Returns true on success, false on failure.