131 lines
3.6 KiB
Groff
131 lines
3.6 KiB
Groff
.TH IM_IOCHECK 3 "11 April 1990"
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.SH NAME
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im_demand_hint \- hint on demand style for im_generate(3)
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.SH SYNOPSIS
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#include <vips/vips.h>
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int im_demand_hint( im, hint, in1, in2, ..., NULL )
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.br
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IMAGE *im, *in1, *in2, ...;
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.br
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im_demand_type hint;
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int im_demand_hint_array( im, hint, in )
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.br
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IMAGE *im, **in;
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.br
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im_demand_type hint;
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.SH DESCRIPTION
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.B im_demand_hint(3)
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suggests to im_generate(3) the sorts of demand with which this image processing
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operation would be happiest.
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.B im
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is the image this operation is generating.
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.B hint
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is the demand style this operation would like (see below), and
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.B in1 ...
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is a NULL-terminated list of the image upon which this output image directly
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depends, that is, the images which this operation will call im_prepare(3) for.
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This list of parent images is necessary, as im_demand_hint(3) needs to know
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what demand style this operation's ancestors have requested. If an ancestor of
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this operation has specified a very restrictive demand style, then this
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operation must fall back to that restrictive style and ignore the hint given
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in this call to im_demand_hint(3).
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VIPS currently supports three demand styles. More may be added in the future.
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These demand styles are given below in order of increasing restrictiveness.
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When demanding output from a pipeline, im_generate(3) will use the most
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restrictive of the styles requested by the operations in the pipeline.
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IM_THINSTRIP
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.br
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This operation would like to output strips the width of the image and a few
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pels high. This is option suitable for point-to-point operations, such as
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those in the arithmetic package.
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This option is only efficient for cases where each output pel depends upon the
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pel in the corresponding position in the input image.
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IM_FATSTRIP
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.br
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This operation would like to output strips the width of the image and as high
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as possible. This option is suitable for area operations which do not
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violently transform coordinates, such as im_conv(3).
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IM_SMALLTILE
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.br
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This is the most general demand format, and is the default. Output is
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demanded in small (around 100x100 pel) sections. This style works reasonably
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efficiently, even for bizzare operations like 45 degree rotate.
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IM_ANY
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.br
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This image is not being demand-read from a disc file (even indirectly) so any
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demand style is OK. It's used for things like
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.B im_black(3)
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where the pixels are calculated.
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.B
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im_demand_hint_array(3)
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works exactly as im_demand_hint(3), but expects a pointer to a NULL-terminated
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array of parent images as its third argument. You may use
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im_allocate_input_array(3), if you wish, to build this structure.
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As an example, here is part of the code for im_invert(3). In this operation,
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each output pel depends upon the corresponding input pel. In other words,
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there is no coordinate transformation in im_prepare(3). This style of
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operation is most efficient with IM_THINSTRIP IO.
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int im_invert( IMAGE *in, IMAGE *out )
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.br
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{
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.br
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if( in->Coding != NOCODING ) {
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.br
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im_errormsg( "im_invert: input coded" );
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.br
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return( -1 );
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.br
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}
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.br
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if( in->BandFmt != FMTUCHAR ) {
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.br
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im_errormsg( "im_invert: input not UCHAR" );
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.br
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return( -1 );
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.br
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}
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.br
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if( im_piocheck( in, out ) )
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.br
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return( -1 );
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.br
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if( im_cp_desc( out, in ) )
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.br
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return( -1 );
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.br
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if( im_demand_hint( out, IM_THINSTRIP, in, NULL ) )
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.br
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return( -1 );
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.br
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if( im_generate( out,
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.br
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im_start_one, inv_gen, im_stop_one, in, NULL ) )
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.br
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return( -1 );
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.br
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return( 0 );
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.br
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}
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.SH RETURN VALUE
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All functions returns 0 on success and non-zero on error.
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.SH SEE ALSO
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im_generate(3), im_prepare(3).
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.SH COPYRIGHT
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National Gallery
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.SH AUTHOR
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J. Cupitt \- 3/9/93
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