A.P. Lawrence

printer filters

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From - Thu Jan 13 06:35:55 2000
Xref: world comp.unix.sco.misc:113866
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From: kevin@shady.com (Kevin Smith, ShadeTree Software, Inc.)
Newsgroups: comp.unix.sco.misc
Subject: Re: print filters
Date: 12 Jan 2000 22:58:22 -0500
Organization: ShadeTree Software, Inc.
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In article <387B2968.C656F3CE@squonk.net> "Brian K. White" <linut@squonk.net> writes:
>Kevin Smith wrote:
>> 
>> In article <38797A88.423347FF@squonk.net> "Brian K. White" <linut@squonk.net> writes:
...
>
>Right. per someone elses response, I did this and it works. thanks.
>However now it seems I want still more :)
>
>I have a program (not an important one for me, QCAD, gpl cad/drawing app) that
>just spits out ps data to the printer you pick (it has an option to print to
>file, and of course, since it's gpl and I compiled it myself, I could twiddle
>the source, but I'm looking for a real solution) so I set up another printer
>named ps4 that uses that same physical printer as p4, but I changed the
>printer interface so that the default filter was ps2epson instead of lp.cat.
>The idea was to pick "ps4" from inside the app and have graphics come out of
>the physical printer p4.
>text came out. here is what I did:
>
>I changed this:
>-------------------
>#Set up the default filter.
>if [  -x "${LOCALPATH}/lp.cat" ]
>then
>        LPCAT="${LOCALPATH}/lp.cat 0"
>else
>        LPCAT="cat"
>fi
>
>#If we are not using a filter, use the default one.
>if [ -z "${FILTER}" ]
>then
>        FILTER="${LPCAT}"
>fi
>
>
>to this:
>------------------
>LPCAT="${LOCALPATH}/ps2epson"
>FILTER="${LPCAT}"
>
>
>there is a ps2epson script in $LOCALPATH which at that point is
>/usr/spool/lp/bin
>
>but I don't see where $FILTER or $LPCAT are even used. 
>
>actually a few other apps just make the ps assumption too and if this worked
>that would be the best barring either getting magical detection of content
>type by the 
>spooler, or getting a real ps printer.

You don't say the source of the interface program.  If $FILTER or $LPCAT
are not used just don't bother with them and put your ps2epson whereever
the 'cat' is.

You could also add postscript processing to p4 as an option (-ops).
This is what I do for a laser printer.

At the top of the interface program...

    GS=/usr/local/bin/gs
    GSOPTS="-q -sDEVICE=ljet3 -dNOPAUSE"

Further down...

    ...
    options=$5
    shift; shift; shift; shift; shift
    mode=auto
    init=_init
    for o in $options
    do
        case $o in
         raw|g*)
            mode=raw
            init=_init_raw
            ;;
         2c)
            mode=2c
            init=_init_2c
            ;;
         ps)
            mode=ps
            init=_init_raw
            ;;
        esac
    done

Then in the actual print loop

    {
        # set printer width
        # send the file(s) to the standard out $copies times
        while       [ "$copies" -gt 0 ]
        do
                # Initialize the printer
                $init

                for file
                do
                    case $mode in
                     raw)
                        cat "$file"
                        ;;
                     2c)
                        ...
                        ;;
                     ps)
                        $GS $GSOPTS -sOUTPUTFILE=- "$file" </dev/null
                        ;;
                     auto|*)
                        ...
                    esac
                done
        done
    } | ... cat/netcat/whatever

Postscript output all starts with something like

    %!PS-Adobe-3.0

You could read and check the first line to autodetect.
Maybe something like (totally untested mind you)

    ps=`line`  (this should work since stdin is the file`
    case "$ps" in
     '$!PS-Adobe'*)
        (
            echo "$ps"
            cat
        ) | ghostscript...
        ;;
     *)
        echo "$ps"
        cat
        ;;
    esac

And finially and most importantly, you can't have to printers to the same
device.  Each queue is independent and you will mix output if you
are going to a serial or parallel devices.  It should work with network
printers as they normally only allow one connection at a time.
Normally though, I've found it best to do one of two things.

1) Handle every possibility in one interface script with -o options.
2) Create an interface script for each option but funnel them all
   through one final printer.  I.e. each script does

    {
        ... cat file ... whatever
    } | lp -dprinter

    The 'printer' interface can be totally dumb and just pass the job
    through or can take -oraw as a signal to pass stuff through
    untouched.
-- 
Do two rights make | Kevin Smith, ShadeTree Software, Philadelphia, PA, USA
a libertarian      | 001-215-487-3811  shady.com,kevin   bbs.cpcn.com,sysop
                   | dvtug.org,kevins--Deleware Valley Transit Users Group

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