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al_lock_bitmap_region(3)   Library Functions Manual   al_lock_bitmap_region(3)

NAME
       al_lock_bitmap_region - Allegro 5 API

SYNOPSIS
	      #include <allegro5/allegro.h>

	      ALLEGRO_LOCKED_REGION *al_lock_bitmap_region(ALLEGRO_BITMAP *bitmap,
		 int x,	int y, int width, int height, int format, int flags)

DESCRIPTION
       Like  al_lock_bitmap(3),	 but only locks	a specific area	of the bitmap.
       If the bitmap is	a video	bitmap,	only that area of the texture will  be
       updated	when  it  is  unlocked.	 Locking only the region you indend to
       modify will be faster than locking the whole bitmap.

	      Note: Using the ALLEGRO_LOCK_WRITEONLY with a blocked pixel for-
	      mat  (i.e. formats  for  which  al_get_pixel_block_width(3)   or
	      al_get_pixel_block_height(3)  do	not  return 1) requires	you to
	      have the region be aligned to the	block width for	 optimal  per-
	      formance.	 If it is not, then the	function will have to lock the
	      region  with  the	ALLEGRO_LOCK_READWRITE instead in order	to pad
	      this region with valid data.

SEE ALSO
       ALLEGRO_LOCKED_REGION(3), ALLEGRO_PIXEL_FORMAT(3), al_unlock_bitmap(3)

Allegro	reference manual			      al_lock_bitmap_region(3)

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