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al_lock_bitmap(3)					     al_lock_bitmap(3)

       al_lock_bitmap -	Allegro	5 API

	      #include <allegro5/allegro.h>

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

       Lock  an	entire bitmap for reading or writing.  If the bitmap is	a dis-
       play 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:

       o 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.

       o 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 pix-
	 els before unlocking the bitmap again,	so be careful when using  this

       o 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 ALLE-
       GRO_PIXEL_FORMAT_ANY.  Locking in the native  format  will  usually  be
       faster.	 If  the bitmap	format is compressed, using ALLEGRO_PIXEL_FOR-
       MAT_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(3)'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_PRE-
       SERVE_TEXTURE flag.

	      Note:  While a bitmap is locked, you can not use any drawing op-
	      erations on it (with the sole exception of  al_put_pixel(3)  and

       ALLEGRO_LOCKED_REGION(3), ALLEGRO_PIXEL_FORMAT(3), al_unlock_bitmap(3),
       al_lock_bitmap_region(3), al_lock_bitmap_blocked(3), al_lock_bitmap_re-

Allegro	reference manual				     al_lock_bitmap(3)


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