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       im_rect_marginadjust,    im_rect_includespoint,   im_rect_includesrect,
       im_rect_intersectrect,       im_rect_isempty,        im_rect_unionrect,
       im_rect_normalise,   im_rect_equalsrect,   im_rect_dup,  IM_RECT_RIGHT,
       IM_RECT_BOTTOM, IM_RECT_HCENTRE, IM_RECT_VCENTRE  -  rectangle  algebra


       #include <vips/vips.h>

       typedef struct {
            int left, top, width, height;
       } Rect;

       #define IM_RECT_RIGHT(R) ((R)->left + (R)->width)
       #define IM_RECT_BOTTOM(R) ((R)->top + (R)->height)
       #define IM_RECT_HCENTRE(R) ((R)->left + (R)->width / 2)
       #define IM_RECT_VCENTRE(R) ((R)->top + (R)->height / 2)

       void im_rect_marginadjust( Rect *r, int n );
       int im_rect_includespoint( Rect *r, int x, int y );
       int im_rect_includesrect( Rect *r1, Rect *r2 );
       void im_rect_intersectrect( Rect *r1, Rect *r2, Rect *r3 );
       int im_rect_isempty( Rect *r );
       void im_rect_unionrect( Rect *r1, Rect *r2, Rect *r3 );
       int im_rect_equalsrect( Rect *r1, Rect *r2 );
       Rect *im_rect_dup( Rect *r );
       void im_rect_normalise( Rect *r );


       These  functions  perform  simple algebra on Rect structs. There should
       also be a set of functions to do rectlist algebra.

       im_rect_marginadjust(3) expands a Rect by n units up,  down,  left  and
       right.  Negative expansions shrink the Rect.

       im_rect_includespoint(3)  returns  non-zero  if point (x,y) lies within
       Rect r.

       im_rect_includesrect(3) returns non-zero if  Rect  r2  lies  completely
       within Rect r1.

       im_rect_intersectrect(3)  fills  Rect r3 with the intersection of Rects
       r1 and r2.

       im_rect_isempty(3) returns non-zero if Rect r  has  either  width  less
       than or equal to 0 or height less than or equal to 0.

       im_rect_unionrect(3) fills Rect r3 with the bounding box of Rect r1 and
       Rect r2. A proper union operation requires lists of rectangles,  sadly.

       im_rect_equalsrect(3) returns non-zero if r1 and r2 are identical.

       im_rect_dup(3) allocates memory for a new Rect structure and copies the
       elements of r into it. It returns a pointer to the new struct, or  NULL
       on error.

       im_rect_normalise(3)  flips r so that the same pixels are enclosed, but
       width and height are guaranteed >=0.


       im_prepare(3), im_region_create(3)


       National Gallery, 1992


       J. Cupitt

                                  2 May 1991                           Rect(3)