1IM_IOCHECK(3) Library Functions Manual IM_IOCHECK(3)
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6 im_demand_hint - hint on demand style for im_generate(3)
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9 #include <vips/vips.h>
10 #include <vips/region.h>
11 int im_demand_hint( im, hint, in1, in2, ..., NULL )
13 IMAGE *im, *in1, *in2, ...;
14 im_demand_type hint;
15 int im_demand_hint_array( im, hint, in )
17 IMAGE *im, **in;
18 im_demand_type hint;
19
21 im_demand_hint(3) suggests to im_generate(3) the sorts of demand with
22 which this image processing operation would be happiest.
23 im is the image this operation is generating. hint is the demand style
25 this operation would like (see below), and in1 ... is a NULL-termi‐
26 nated list of the image upon which this output image directly depends,
27 that is, the images which this operation will call im_prepare(3) for.
28 This list of parent images is necessary, as im_demand_hint(3) needs to
30 know what demand style this operation's ancestors have requested. If an
31 ancestor of this operation has specified a very restrictive demand
32 style, then this operation must fall back to that restrictive style and
33 ignore the hint given in this call to im_demand_hint(3).
34 VIPS currently supports three demand styles. More may be added in the
36 future. These demand styles are given below in order of increasing
37 restrictiveness. When demanding output from a pipeline, im_generate(3)
38 will use the most restrictive of the styles requested by the operations
39 in the pipeline.
40 IM_THINSTRIP
42 This operation would like to output strips the width of the image and a
43 few pels high. This is option suitable for point-to-point operations,
44 such as those in the arithmetic package.
45 This option is only efficient for cases where each output pel depends
47 upon the pel in the corresponding position in the input image.
48 IM_FATSTRIP
50 This operation would like to output strips the width of the image and
51 as high as possible. This option is suitable for area operations which
52 do not violently transform coordinates, such as im_conv(3).
53 IM_SMALLTILE
55 This is the most general demand format, and is the default. Output is
56 demanded in small (around 100x100 pel) sections. This style works rea‐
57 sonably efficiently, even for bizzare operations like 45 degree rotate.
58 im_demand_hint_array(3) works exactly as im_demand_hint(3), but expects
60 a pointer to a NULL-terminated array of parent images as its third
61 argument. You may use im_allocate_input_array(3), if you wish, to build
62 this structure.
63 As an example, here is part of the code for im_invert(3). In this oper‐
65 ation, each output pel depends upon the corresponding input pel. In
66 other words, there is no coordinate transformation in im_prepare(3).
67 This style of operation is most efficient with IM_THINSTRIP IO.
68 int im_invert( IMAGE *in, IMAGE *out )
70 {
71 if( in->Coding != NOCODING ) {
72 im_errormsg( "im_invert: input coded" );
73 return( -1 );
74 }
75 if( in->BandFmt != FMTUCHAR ) {
76 im_errormsg( "im_invert: input not UCHAR" );
77 return( -1 );
78 }
79 if( im_piocheck( in, out ) )
80 return( -1 );
81 if( im_cp_desc( out, in ) )
82 return( -1 );
83 if( im_demand_hint( out, IM_THINSTRIP, in, NULL ) )
84 return( -1 );
85 if( im_generate( out,
86 im_start_one, inv_gen, im_stop_one, in, NULL ) )
87 return( -1 );
88 return( 0 );
89 }
90
93 All functions returns 0 on success and non-zero on error.
94
96 im_generate(3), im_prepare(3). `VIPS Library Programmers' Guide,' in
97 accompanying documentation.
98
100 National Gallery
101
103 J. Cupitt - 3/9/93
104 11 April 1990 IM_IOCHECK(3)