filter/api-raster.shtml

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   2   Raster API introduction for CUPS.
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  13
  14 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
  15
  16 <p>The CUPS raster API provides a standard interface for reading and writing
  17 CUPS raster streams which are used for printing to raster printers. Because the
  18 raster format is updated from time to time, it is important to use this API to
  19 avoid incompatibilities with newer versions of CUPS.</p>
  20
  21 <p>Two kinds of CUPS filters use the CUPS raster API - raster image processor
  22 (RIP) filters such as <code>pstoraster</code> and <code>cgpdftoraster</code>
  23 (macOS) that produce CUPS raster files and printer driver filters that
  24 convert CUPS raster files into a format usable by the printer. Printer
  25 driver filters are by far the most common.</p>
  26
  27 <p>CUPS raster files (<code>application/vnd.cups-raster</code>) consists of
  28 a stream of raster page descriptions produced by one of the RIP filters such as
  29 <var>pstoraster</var>, <var>imagetoraster</var>, or
  30 <var>cgpdftoraster</var>. CUPS raster files are referred to using the
  31 <a href='#cups_raster_t'><code>cups_raster_t</code></a> type and are
  32 opened using the <a href='#cupsRasterOpen'><code>cupsRasterOpen</code></a>
  33 function. For example, to read raster data from the standard input, open
  34 file descriptor 0:</p>
  35
  36 <pre class="example">
  37 #include &lt;cups/raster.h&gt;>
  38
  39 <a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
  40 </pre>
  41
  42 <p>Each page of data begins with a page dictionary structure called
  43 <a href="#cups_page_header2_t"><code>cups_page_header2_t</code></a>. This
  44 structure contains the colorspace, bits per color, media size, media type,
  45 hardware resolution, and so forth used for the page.</p>
  46
  47 <blockquote><b>Note:</b>
  48
  49   <p>Do not confuse the colorspace in the page header with the PPD
  50   <tt>ColorModel</tt> keyword. <tt>ColorModel</tt> refers to the general type of
  51   color used for a device (Gray, RGB, CMYK, DeviceN) and is often used to
  52   select a particular colorspace for the page header along with the associate
  53   color profile. The page header colorspace (<tt>cupsColorSpace</tt>) describes
  54   both the type and organization of the color data, for example KCMY (black
  55   first) instead of CMYK and RGBA (RGB + alpha) instead of RGB.</p>
  56
  57 </blockquote>
  58
  59 <p>You read the page header using the
  60 <a href="#cupsRasterReadHeader2"><code>cupsRasterReadHeader2</code></a>
  61 function:</p>
  62
  63 <pre class="example">
  64 #include &lt;cups/raster.h&gt;>
  65
  66 <a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
  67 <a href="#cups_page_header2_t">cups_page_header2_t</a> header;
  68
  69 while (<a href="#cupsRasterReadHeader2">cupsRasterReadHeader2</a>(ras, &amp;header))
  70 {
  71   /* setup this page */
  72
  73   /* read raster data */
  74
  75   /* finish this page */
  76 }
  77 </pre>
  78
  79 <p>After the page dictionary comes the page data which is a full-resolution,
  80 possibly compressed bitmap representing the page in the printer's output
  81 colorspace. You read uncompressed raster data using the
  82 <a href="#cupsRasterReadPixels"><code>cupsRasterReadPixels</code></a>
  83 function. A <code>for</code> loop is normally used to read the page one line
  84 at a time:</p>
  85
  86 <pre class="example">
  87 #include &lt;cups/raster.h&gt;>
  88
  89 <a href="#cups_raster_t">cups_raster_t</a> *ras = <a href="#cupsRasterOpen">cupsRasterOpen</a>(0, CUPS_RASTER_READ);
  90 <a href="#cups_page_header2_t">cups_page_header2_t</a> header;
  91 int page = 0;
  92 int y;
  93 char *buffer;
  94
  95 while (<a href="#cupsRasterReadHeader2">cupsRasterReadHeader2</a>(ras, &amp;header))
  96 {
  97   /* setup this page */
  98   page ++;
  99   fprintf(stderr, "PAGE: %d %d\n", page, header.NumCopies);
 100
 101   /* allocate memory for 1 line */
 102   buffer = malloc(header.cupsBytesPerLine);
 103
 104   /* read raster data */
 105   for (y = 0; y &lt; header.cupsHeight; y ++)
 106   {
 107     if (<a href="#cupsRasterReadPixels">cupsRasterReadPixels</a>(ras, buffer, header.cupsBytesPerLine) == 0)
 108       break;
 109
 110     /* write raster data to printer on stdout */
 111   }
 112
 113   /* finish this page */
 114 }
 115 </pre>
 116
 117 <p>When you are done reading the raster data, call the
 118 <a href="#cupsRasterClose"><code>cupsRasterClose</code></a> function to free
 119 the memory used to read the raster file:</p>
 120
 121 <pre class="example">
 122 <a href="#cups_raster_t">cups_raster_t</a> *ras;
 123
 124 <a href="#cupsRasterClose">cupsRasterClose</a>(ras);
 125 </pre>
 126
 127
 128 <h2 class='title'><a name="TASKS">Functions by Task</a></h2>
 129
 130 <h3><a name="OPENCLOSE">Opening and Closing Raster Streams</a></h3>
 131
 132 <ul class="code">
 133
 134         <li><a href="#cupsRasterClose" title="Close a raster stream.">cupsRasterClose</a></li>
 135         <li><a href="#cupsRasterOpen" title="Open a raster stream.">cupsRasterOpen</a></li>
 136
 137 </ul>
 138
 139 <h3><a name="READING">Reading Raster Streams</a></h3>
 140
 141 <ul class="code">
 142
 143         <li><a href="#cupsRasterReadHeader" title="Read a raster page header and store it in a version 1 page header structure.">cupsRasterReadHeader</a> <span class="info">Deprecated in CUPS 1.2/macOS 10.5</span></li>
 144         <li><a href="#cupsRasterReadHeader2" title="Read a raster page header and store it in a version 2 page header structure.">cupsRasterReadHeader2</a></li>
 145         <li><a href="#cupsRasterReadPixels" title="Read raster pixels.">cupsRasterReadPixels</a></li>
 146
 147 </ul>
 148
 149 <h3><a name="WRITING">Writing Raster Streams</a></h3>
 150
 151 <ul class="code">
 152
 153         <li><a href="#cupsRasterInterpretPPD" title="Interpret PPD commands to create a page header.">cupsRasterInterpretPPD</a></li>
 154         <li><a href="#cupsRasterWriteHeader" title="Write a raster page header from a version 1 page header structure.">cupsRasterWriteHeader</a> <span class="info">Deprecated in CUPS 1.2/macOS 10.5</span></li>
 155         <li><a href="#cupsRasterWriteHeader2" title="Write a raster page header from a version 2 page header structure.">cupsRasterWriteHeader2</a></li>
 156         <li><a href="#cupsRasterWritePixels" title="Write raster pixels.">cupsRasterWritePixels</a></li>
 157
 158 </ul>