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al_get_backbuffer(3)                                      al_get_backbuffer(3)

NAME
       al_get_backbuffer - Allegro 5 API

SYNOPSIS

              #include <allegro5/allegro.h>

              ALLEGRO_BITMAP *al_get_backbuffer(ALLEGRO_DISPLAY *display)

DESCRIPTION
       Return a special bitmap representing the back-buffer of the display.

       Care should be taken when using the backbuffer bitmap (and its
       sub-bitmaps) as the source bitmap (e.g as the bitmap argument to
       al_draw_bitmap(3)).  Only untransformed operations are hardware
       accelerated.  This consists of al_draw_bitmap(3) and
       al_draw_bitmap_region(3) when the current transformation is the
       identity.  If the tranformation is not the identity, or some other
       drawing operation is used, the call will be routed through the memory
       bitmap routines, which are slow.  If you need those operations to be
       accelerated, then first copy a region of the backbuffer into a
       temporary bitmap (via the al_draw_bitmap(3) and
       al_draw_bitmap_region(3)), and then use that temporary bitmap as the
       source bitmap.

Allegro reference manual                                  al_get_backbuffer(3)