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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 format
	    (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  performance.
	    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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