oracular (3) al_lock_bitmap.3alleg5.gz

NAME

       al_lock_bitmap - Allegro 5 API

SYNOPSIS

              #include <allegro5/allegro.h>

              ALLEGRO_LOCKED_REGION *al_lock_bitmap(ALLEGRO_BITMAP *bitmap,
                 int format, int flags)

DESCRIPTION

       Lock  an entire bitmap for reading or writing.  If the bitmap is a display bitmap it will be updated from
       system memory after the bitmap is unlocked (unless locked read only).  Returns NULL if the bitmap  cannot
       be  locked,  e.g. the  bitmap was locked previously and not unlocked.  This function also returns NULL if
       the format is a compressed format.

       Flags are:

       • ALLEGRO_LOCK_READONLY - The locked region will not be written to.  This can be faster if the bitmap  is
         a video texture, as it can be discarded after the lock instead of uploaded back to the card.

       • ALLEGRO_LOCK_WRITEONLY  - The locked region will not be read from.  This can be faster if the bitmap is
         a video texture, as no data need to be read from the video card.  You  are  required  to  fill  in  all
         pixels before unlocking the bitmap again, so be careful when using this flag.

       • ALLEGRO_LOCK_READWRITE - The locked region can be written to and read from.  Use this flag if a partial
         number of pixels need to be written to, even if reading is not needed.

       format indicates the pixel format that the returned buffer will be in.  To lock in the same format as the
       bitmap  stores  its  data  internally,  call  with  al_get_bitmap_format(bitmap)  as  the  format  or use
       ALLEGRO_PIXEL_FORMAT_ANY.  Locking in the native format will usually be faster.  If the bitmap format  is
       compressed, using ALLEGRO_PIXEL_FORMAT_ANY will choose an implementation defined non-compressed format.

       On  some  platforms,  Allegro  automatically  backs  up the contents of video bitmaps because they may be
       occasionally lost (see discussion in al_create_bitmap(3alleg5)’s documentation).   If  you’re  completely
       recreating  the  bitmap  contents  often (e.g.  every frame) then you will get much better performance by
       creating the target bitmap with ALLEGRO_NO_PRESERVE_TEXTURE flag.

              Note: While a bitmap is locked, you can not use any  drawing  operations  on  it  (with  the  sole
              exception of al_put_pixel(3alleg5) and al_put_blended_pixel(3alleg5)).

SEE ALSO

       ALLEGRO_LOCKED_REGION(3alleg5),         ALLEGRO_PIXEL_FORMAT(3alleg5),         al_unlock_bitmap(3alleg5),
       al_lock_bitmap_region(3alleg5), al_lock_bitmap_blocked(3alleg5), al_lock_bitmap_region_blocked(3alleg5)