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| <h3 class="sectionHead"><span class="titlemark">3.4 </span> <a |
| id="x23-1030003.4"></a>Programming in-place functions</h3> |
| <!--l. 3--><p class="noindent" >VIPS includes a little support for in-place functions — |
| functions which operate directly on an image, both |
| reading and writing from the same descriptor via the data |
| pointer. This is an extremely dangerous way to handle IO, |
| since any bugs in your program will trash your input |
| image. |
| <!--l. 8--><p class="indent" > Operations of this type should call <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_rwcheck()</span></span></span> |
| instead of <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_incheck()</span></span></span>. <span class="obeylines-h"><span class="verb"><span |
| class="pcrr7t-">im_rwcheck()</span></span></span> tries to get |
| a descriptor ready for in-place writing. For example, a |
| function which cleared an image to black might be written |
| as: |
| <div class="verbatim" id="verbatim-171"> |
| #include <stdio.h> |
|  <br />#include <memory.h> |
|  <br /> |
|  <br />#include <vips/vips.h> |
|  <br /> |
|  <br />int |
|  <br />black_inplace( IMAGE ⋆im ) |
|  <br />{ |
|  <br />   /⋆ Check that we can RW to im. |
|  <br />    ⋆/ |
|  <br />   if( im_rwcheck( im ) ) |
|  <br />      return( -1 ); |
|  <br /> |
|  <br />   /⋆ Zap the image! |
|  <br />    ⋆/ |
|  <br />   memset( im->data, 0, |
|  <br />      IM_IMAGE_SIZEOF_LINE( im ) ⋆ |
|  <br />      im->Ysize ); |
|  <br /> |
|  <br />   return( 0 ); |
|  <br />} |
| </div> |
| <!--l. 35--><p class="nopar" > |
| <!--l. 37--><p class="indent" > This function might be called from an application |
| as: |
| |
| |
| |
| <div class="verbatim" id="verbatim-172"> |
| #include <stdio.h> |
|  <br />#include <stdlib.h> |
|  <br /> |
|  <br />#include <vips/vips.h> |
|  <br /> |
|  <br />void |
|  <br />zap( char ⋆name ) |
|  <br />{ |
|  <br />   IMAGE ⋆im; |
|  <br /> |
|  <br />   if( !(im = im_open( name, "rw" )) || |
|  <br />      black_inplace( im ) || |
|  <br />      im_updatehist( im, "zap image" ) || |
|  <br />      im_close( im ) ) |
|  <br />      error_exit( "failure!" ); |
|  <br />} |
| </div> |
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