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       IM_REGION_SIZEOF_LINE - macros for regions


       #include <vips/vips.h>

       int IM_REGION_LSKIP( reg )
       REGION *reg;

       int IM_REGION_N_ELEMENTS( reg )
       REGION *reg;

       int IM_REGION_SIZEOF_LINE( reg )
       REGION *reg;

       char *IM_REGION_ADDR( reg, x, y )
       REGION *reg;
       int x, y;


       These macros help to simplify address arithmetic for regions.

       IM_REGION_LSKIP(3) returns the number of *bytes* you should add to move
       down  a  scan line.  Remember that if your pointer has been cast to the
       type of the image pels, this will not be the correct amount to add! The
       value lskip returns can be changed by a call to im_prepare(3).

         returns the number of band elements across the

       IM_REGION_SIZEOF_LINE(3) returns sizeof( horizontal line across  region

       IM_REGION_ADDR(3)  returns  a pointer to the pixel at position (x,y) in
       the image on which reg has been defined. The  point  (x,y)  should  lie
       within the valid area for this region.

       If  the  macro DEBUG has been defined, then IM_REGION_ADDR(3) will also
       perform bounds checking. If you ask for the address of  a  pel  outside
       the rect reg->valid, then IM_REGION_ADDR(3) will print an error message
       of the form:

           IM_REGION_ADDR: point out of bounds, file "test.c", line 18
           (point x=50, y=0
            should have been within Rect left=0, top=0, width=50, height=50)

       and call abort(3).

       DEBUG needs to be defined *before* region.h is included. Either  define
       DEBUG  with  -D  in your Makefile, or have a #define DEBUG right at the
       top of your file.


       National Gallery, 1993


       IM_IMAGE_ADDR(3), im_malloc(3), im_open_local(3).


       J. Cupitt - 23/7/93

                                 11 April 1990                       MACROS(3)