1IM_ITERATE(3)              Library Functions Manual              IM_ITERATE(3)
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NAME

6       im_iterate - PIO input from image
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SYNOPSIS

9       #include <vips/vips.h>
10       #include <vips/region.h>
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12       int im_iterate( im, start_fn, scan_fn, stop_fn, a, b )
13       IMAGE *im;
14       void *(*start_fn)();
15       int (*scan_fn)();
16       int (*stop_fn)();
17       void *a, *b;
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19       where, typically,
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21       void *start_fn( im, a, b )
22       IMAGE *im;
23       void *a, *b;
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25       int scan_fn( or, seq, a, b )
26       REGION *or;
27       void *seq;
28       void *a, *b;
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30       int stop_fn( seq, a, b )
31       void *seq;
32       void *a, *b;
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DESCRIPTION

35       im_iterate(3)  is  used for PIO image input. See `VIPS Library Program‐
36       mers' guide,' in the accompanying documentation, for an introduction to
37       this function.
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39       im_iterate(3)  makes  one or more regions on im, and starts one or more
40       sequences running over the image. im_iterate(3) guarantees that
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42          - scan_fn() will see each of the pels in im exactly once
43          - start_fn() and stop_fn() are both exclusive
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45       See the guide, the man page  for  im_generate(3),  and  the  source  to
46       im_deviate(3) for examples.
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48       On  machines  with  SVR4  threads  and several CPUs, im_generate(3) and
49       im_iterate(3) automatically  parallelise  programs.  You  can  set  the
50       desired concurrency level with the environment variable IM_CONCURRENCY,
51       for example
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53           example% setenv IM_CONCURRENCY 2
54           example% stats fred.v
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56       will run stats with enough concurrency to keep 2 CPUs  fully  occupied.
57       If IM_CONCURRENCY is not set, then it defaults to 1.
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RETURN VALUE

60       All functions return 0 on success and non-zero on error.
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SEE ALSO

63       im_generate(3), `VIPS Library Programmers' Guide,' in accompanying doc‐
64       umentation.
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67       National Gallery, 1993
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AUTHOR

70       J. Cupitt - 23/7/93
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74                                30 October 1992                  IM_ITERATE(3)
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