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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.

       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 it's data	inter-
       nally, call with	al_get_bitmap_format(bitmap) as	the format or use  AL-
       LEGRO_PIXEL_FORMAT_ANY.	 Locking  in the native	format will usually be

	      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)

Allegro	reference manual				     al_lock_bitmap(3)


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