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       im_region_buffer,           im_region_image,          im_region_region,
       im_region_position, im_region_equalsregion - attach data to region


       #include <vips/vips.h>

       int im_region_buffer( reg, r )
       REGION *reg;
       Rect *r;

       int im_region_image( reg, r )
       REGION *reg;
       Rect *r;

       int im_region_region( reg, treg, r, x, y )
       REGION *reg, treg;
       Rect *r;
       int x, y;

       int im_region_position( reg, x, y )
       REGION *reg;
       int x, y;

       int im_region_equalsregion( REGION *reg1, REGION *reg2 )


       These functions are used to say where exactly input from or output to a
       region  goes. Briefly, im_region_buffer(3) gives a region its own piece
       of local storage, im_region_image(3) links the region to an image,  and
       im_region_region(3) links the region to another region.

       im_region_region(3)  is  the most powerful of the three --- you can use
       it  to  avoid  copy  operations.  See  the  source  for  im_extract(3),
       im_insert(3),  im_copy(3),  im_embed(3), and im_lrmerge(3) for examples
       of its use, and see also im_prepare_copy(3).

       im_region_buffer(3) clips Rect r against the size  of  the  image  upon
       which  reg  is  defined,  then searches for any calculated pixels which
       enclose that area. If there are any suitable pixels already, the region
       is set to point to them.  Otherwise, a fresh buffer is allocated.

       If  region->buffer->done is set, then the region is already calculated.
       Otherwise, the pixels need to be calculated.

       im_region_buffer(3) is called by im_prepare(3) just before it calls the
       user generate function.

       im_region_image(3)  attaches  reg to the image on which it was defined.
       The image has to be SETBUF, MMAPIN, MMAPINRW, or OPENIN  ---  ie.,  the
       types passed by im_incheck(3).

       im_region_region(3)  redirects  reg  to  treg.  treg  can be defined on
       another image. r is clipped  against  the  size  of  reg’s  image,  and
       against treg->valid.  treg has to have pel data associated with it (ie.
       memory local to treg, memory that is part of the image on which treg is
       defined,  or  even memory from a third region), and the pel data has to
       be in a form which is compatible with reg, ie. BandFmt and  Bands  must
       be the same.

       r  becomes the valid field in reg, (x,y) is the top left-hand corner of
       the area in treg to which valid is mapped.

       im_region_position(3) changes reg->valid, so that reg->valid.left ==  x
       and  reg-> == y. width and height are clipped against the size
       of the image. If x < 0 or y < 0 or the clipped rect has zero  width  or
       height, the call fails.

       This   function  affects  the  way  that  pels  are  addressed  by  the
       IM_REGION_ADDR(3) macro. It does not affect the pels themselves! It has
       the effect of moving the area of pels a region represents. This call is
       used by im_extract(3).

       im_region_equalsregion(3) tests for reg1 and reg2 are identical, ie.:

          IM_REGION_ADDR( reg1, x, y ) ==
            IM_REGION_ADDR( reg2, x, y ) &&
          *IM_REGION_ADDR( reg1, x, y ) ==
            *IM_REGION_ADDR( reg2, x, y )

       It is used internally by VIPS, but may be useful to applications.


       All int-valued functions return zero on success and non-zero on  error.


       National Gallery, 1993


       J. Cupitt - 23/7/93

                                 11 April 1990            REGION-OPERATIONS(3)