[cups.general] writing/using user-written filters with CUPS -- need a little help ...

[Mark Sornson]

I have CUPS installed on Tru64 UNIX.
Tru64 UNIX ships BSD-style printing by default.

I'd like to port a filter from the BSD
environment into CUPS.  What I don't quite
'get' is the mapping of BSD-to-CUPS (which
definitely isn't one-for-one, even though
the filter/backend architecture looks
similar enough).  In particular I don't
fully understand how to associate a new
filter with a particular printer/print-queue.

In BSD, you simply go into /etc/printcap
and change either or both "if" and "of"
entries to point to ones filter of choice.
[Knowing the difference between how a
filter is called as "of" vs "if" is a side
issue that doesn't matter.]  All data is
then piped through the filter; whether or
not the filter understands it is separate
issue.

Rather than say how I think CUPS works
(since I don't fully understand it, yet),
I gratefully extend thanks in advance to
anyone who can offer 'how to' comments
(and/or how-you-did-it-war-stories), or
pointers to similar material.

Additionally, the CUPS documentation says
that certain environment variables are
available to filters, including one that
points to a PPD file.  Is it possible to
use this environment variable to point to
something other than a PPD file (say,
something with a similar logical purpose,
to describe printer attributes)?  If so,
how do I set the environment variable value?

Thanks in advance.
-mark.