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  Raster API introduction for the Common UNIX Printing System (CUPS).

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<h2 class='title'><a name="OVERVIEW">Overview</a></h2>

<p>The CUPS raster API provides a standard interface for reading and writing
CUPS raster streams which are used for printing to raster printers. Because the
raster format is updated from time to time, it is important to use this API to
avoid incompatibilities with newer versions of CUPS.</p>

<p>CUPS raster files (<code>application/vnd.cups-raster</code>) consists of
a stream of raster page descriptions produced by one of the RIP filters such as
<var>pstoraster</var>, <var>imagetoraster</var>, or
<var>cgpdftoraster</var>. CUPS raster files are referred to using the
<a href='#cups_raster_t'><code>cups_raster_t</code></a> type and are
opened using the <a href='#cupsRasterOpen'><code>cupsRasterOpen</code></a>
function. For example, to read raster data from the standard input, open
file descriptor 0:</p>

<pre class="example">
#include &lt;cups/raster.h&gt;>

<a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
</pre>

<p>Each page of data begins with a page dictionary structure called
<a href="#cups_page_header2_t"><code>cups_page_header2_t</code></a>. This
structure contains the colorspace, bits per color, media size, media type,
hardware resolution, and so forth used for the page. You read the page header
using the
<a href="#cupsRasterReadHeader2"><code>cupsRasterReadHeader2</code></a>
function:</p>

<pre class="example">
#include &lt;cups/raster.h&gt;>

<a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
<a href="#cups_page_header2_t">cups_page_header2_t</a> header;

while (<a href="#cupsRasterReadHeader2">cupsRasterReadHeader2</a>(ras, &amp;header))
{
  /* setup this page */

  /* read raster data */

  /* finish this page */
}
</pre>

<p>After the page dictionary comes the page data which is a full-resolution,
possibly compressed bitmap representing the page in the printer's output
colorspace. You read uncompressed raster data using the
<a href="#cupsRasterReadPixels"><code>cupsRasterReadPixels</code></a>
function. A <code>for</code> loop is normally used to read the page one line
at a time:</p>

<pre class="example">
#include &lt;cups/raster.h&gt;>

<a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
<a href="#cups_page_header2_t">cups_page_header2_t</a> header;
int page = 0;
int y;
char *buffer;

while (<a href="#cupsRasterReadHeader2">cupsRasterReadHeader2</a>(ras, &amp;header))
{
  /* setup this page */
  page ++;
  fprintf(stderr, "PAGE: %d %d\n", page, header.NumCopies);

  /* allocate memory for 1 line */
  buffer = malloc(header.cupsBytesPerLine);

  /* read raster data */
  for (y = 0; y &lt; header.cupsHeight; y ++)
  {
    if (<a href="#cupsRasterReadPixels">cupsRasterReadPixels</a>(ras, buffer, header.cupsBytesPerLine) == 0)
      break;

    /* write raster data to printer */
  }

  /* finish this page */
}
</pre>

<p>When you are done reading the raster data, call the
<a href="#cupsRasterClose"><code>cupsRasterClose</code></a> function to free
the memory used to read the raster file:</p>

<pre class="example">
<a href="#cups_raster_t">cups_raster_t</a> *ras;

<a href="#cupsRasterClose">cupsRasterClose</a>(ras);
</pre>