57 lines
1.2 KiB
TeX
57 lines
1.2 KiB
TeX
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\section{Programming in-place functions}
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VIPS includes a little support for in-place functions --- functions
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which operate directly on an image, both reading and writing from the same
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descriptor via the data pointer. This is an extremely dangerous way to
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handle IO, since any bugs in your program will trash your input image.
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Operations of this type should call \verb+im_rwcheck()+ instead of
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\verb+im_incheck()+. \verb+im_rwcheck()+ tries to get a descriptor ready
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for in-place writing. For example, a function which cleared an image to
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black might be written as:
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\begin{verbatim}
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#include <stdio.h>
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#include <memory.h>
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#include <vips/vips.h>
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int
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black_inplace( IMAGE *im )
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{
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/* Check that we can RW to im.
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*/
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if( im_rwcheck( im ) )
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return( -1 );
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/* Zap the image!
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*/
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memset( im->data, 0,
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IM_IMAGE_SIZEOF_LINE( im ) *
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im->Ysize );
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return( 0 );
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}
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\end{verbatim}
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This function might be called from an application as:
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\begin{verbatim}
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#include <stdio.h>
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#include <stdlib.h>
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#include <vips/vips.h>
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void
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zap( char *name )
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{
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IMAGE *im;
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if( !(im = im_open( name, "rw" )) ||
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black_inplace( im ) ||
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im_updatehist( im, "zap image" ) ||
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im_close( im ) )
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error_exit( "failure!" );
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}
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\end{verbatim}
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