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| Raster API introduction for 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>Two kinds of CUPS filters use the CUPS raster API - raster image processor |
| (RIP) filters such as <code>pstoraster</code> and <code>cgpdftoraster</code> |
| (macOS) that produce CUPS raster files and printer driver filters that |
| convert CUPS raster files into a format usable by the printer. Printer |
| driver filters are by far the most common.</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 <cups/raster.h> |
| |
| <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.</p> |
| |
| <blockquote><b>Note:</b> |
| |
| <p>Do not confuse the colorspace in the page header with the PPD |
| <tt>ColorModel</tt> keyword. <tt>ColorModel</tt> refers to the general type of |
| color used for a device (Gray, RGB, CMYK, DeviceN) and is often used to |
| select a particular colorspace for the page header along with the associate |
| color profile. The page header colorspace (<tt>cupsColorSpace</tt>) describes |
| both the type and organization of the color data, for example KCMY (black |
| first) instead of CMYK and RGBA (RGB + alpha) instead of RGB.</p> |
| |
| </blockquote> |
| |
| <p>You read the page header using the |
| <a href="#cupsRasterReadHeader2"><code>cupsRasterReadHeader2</code></a> |
| function:</p> |
| |
| <pre class="example"> |
| #include <cups/raster.h> |
| |
| <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, &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 <cups/raster.h> |
| |
| <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, &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 < header.cupsHeight; y ++) |
| { |
| if (<a href="#cupsRasterReadPixels">cupsRasterReadPixels</a>(ras, buffer, header.cupsBytesPerLine) == 0) |
| break; |
| |
| /* write raster data to printer on stdout */ |
| } |
| |
| /* 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> |
| |
| |
| <h2 class='title'><a name="TASKS">Functions by Task</a></h2> |
| |
| <h3><a name="OPENCLOSE">Opening and Closing Raster Streams</a></h3> |
| |
| <ul class="code"> |
| |
| <li><a href="#cupsRasterClose" title="Close a raster stream.">cupsRasterClose</a></li> |
| <li><a href="#cupsRasterOpen" title="Open a raster stream.">cupsRasterOpen</a></li> |
| |
| </ul> |
| |
| <h3><a name="READING">Reading Raster Streams</a></h3> |
| |
| <ul class="code"> |
| |
| <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> |
| <li><a href="#cupsRasterReadHeader2" title="Read a raster page header and store it in a version 2 page header structure.">cupsRasterReadHeader2</a></li> |
| <li><a href="#cupsRasterReadPixels" title="Read raster pixels.">cupsRasterReadPixels</a></li> |
| |
| </ul> |
| |
| <h3><a name="WRITING">Writing Raster Streams</a></h3> |
| |
| <ul class="code"> |
| |
| <li><a href="#cupsRasterInterpretPPD" title="Interpret PPD commands to create a page header.">cupsRasterInterpretPPD</a></li> |
| <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> |
| <li><a href="#cupsRasterWriteHeader2" title="Write a raster page header from a version 2 page header structure.">cupsRasterWriteHeader2</a></li> |
| <li><a href="#cupsRasterWritePixels" title="Write raster pixels.">cupsRasterWritePixels</a></li> |
| |
| </ul> |