al_convert_memory_bitmaps - Allegro 5 API
If you create a bitmap when there is no current display (for example because you
have not called al_create_display(3) in the current thread) and are using the
ALLEGRO_CONVERT_BITMAP bitmap flag (which is set by default) then the bitmap
will be created successfully, but as a memory bitmap. This function converts
all such bitmaps to proper video bitmaps belonging to the current display.
Note that video bitmaps get automatically converted back to memory
bitmaps when the last display is destroyed.
This operation will preserve all bitmap flags except
ALLEGRO_VIDEO_BITMAP and ALLEGRO_MEMORY_BITMAP.