root / pykota / trunk / docs / filterpykota.sgml @ 922

<!-- $Id$ -->

<chapter>
  <title id="filter">The pykota filter</title>
  
  <para>Last modified on $Date$</para>
  
  <para>
    To account for pages or eventually ink usage, you must plug your accounting
    system into <application>CUPS</application>. One way to do this without having
    to modify <application>CUPS</application> itself, is by using a <firstterm>filter</firstterm>.
  </para>
  
  <para>
    A filter is a computer program which takes data in one format as its input, and outputs the
    same data but transformed into another format. <application>CUPS</application> already
    contains many filters. For example there's one filter named <application>pstops</application> which accepts 
    PostScript data as its input, and, as its name implies, outputs PostScript data too, but after having
    eventually rearranged the pages to fit several pages on a single sheet of paper, or other manipulations
    like that.
  </para>
  
  <para>
    The <application>pstops</application> filter described above is also in charge of doing basic page
    accounting, but <application>PyKota</application> currently doesn't use this facility since it may
    prove to be unreliable depending on the drivers used or if a paper jam occur for example.
  </para>
  
  <para>
    So to do its own accounting, <application>PyKota</application> has its own filter, named <application>pykota</application>,
    which you have to plug into the different set of filters used by <application>CUPS</application>. The procedure to 
    install the <application>pykota</application> filter is described in the 
    <xref linkend="installation" endterm="installation"> chapter.
  </para>
  
  <para>
    Currently the <application>pykota</application> filter is used at the very last stage of the print mechanism,
    just before the final data is sent to the printer, but it may eventually be used earlier with some
    modifications to <application>CUPS</application>'s filtering configuration. This is not tested yet, but this
    may be the solution to use <application>PyKota</application> with printers which really needs to have
    a <literal>*cupsFilter</literal> line in their <acronym>PPD</acronym> file, i.e. non-postscript printers.
  </para>
  
  <para>
    The <application>pykota</application> filter really is the only thing which depends on <application>CUPS</application>,
    so it is probable that a next version of <application>PyKota</application> will support other printing environments.
  </para>
  
</chapter>

<!--

$Log$
Revision 1.2  2003/03/25 09:32:06  jalet
Improved documentation.

Revision 1.1  2003/02/08 00:03:35  jalet
Documentation skeleton added


-->