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From: heiney@wsl.dec.com (Bob Heiney)
Newsgroups: comp.lang.postscript
Subject: Re: showpage-layering (eg. print-odd-pages-only)
Keywords: showpage,troff,word-perfect,PSPRINT,problems
Message-ID: <1990Aug14.163226.1253@wrl.dec.com>
Date: 14 Aug 90 16:32:26 GMT
References: <30532.26c6bf13@ccavax.camb.com>
Sender: news@wrl.dec.com (News)
Reply-To: heiney@wsl.dec.com (Bob Heiney)
Organization: DEC Western Software Lab
Lines: 57

The best way to achieve what you want would be to exploit the page
comments that
a good PostScript file gives you.  By putting "%!-PS-Adobe-2.0" (or
other version #)
at the top, documents claim that they will follow a set of conventions
that would
easily give you the tools you need.  You can get "struct.ps" from the
Adobe file
server if you want to see what's in the lastest version of the conventions.

Unfortunately, in the words of Brian Reid (who came up with the original
commenting
conventions):

	"They're one of those things that everyone agrees is a great idea, easy
	 easy to do, etc. -- but no one follows them."

I foolishly whipped up an awk script to do segmentation of large files. 
I was at
Berkeley at the time, and was constantly annoyed by people printing HUGE
ps files.
My 1000 byte job was always next in the queue after one of those monsters.  So,
since I occasionally need to print big ps files too, I decided to write
a segmenter
that would split the ps file into n page chunks.  That way no one would
curse my
name when I printed large documents.

Unfortunately, the absolute worst thing about this whole matter is that
while few
(I can count them on one hand... :-( ) applications *actually* follow
the document
structuring (a.k.a. commenting) conventions, almost *ALL* claim they do
by putting "%!-PS-Adobe-2.0" at the top of their code.  This the
requires artificial intelligence
from the paging software to have it figure out what's going on.  The
most common
problem is that pages are not independent like they're supposed to be. 
On the Mac,
for example, the first time a font is used, a revectoring is done.  Since this
revectoring is crucial, and only done once, if you don't execute the page that
the revectoring occurs on, you'll get an error.

I wish I had some more helpful advice, but since messing around with
showpage is
bound to be hairy, and since people don't follow the commenting
conventions, I think
this is one of those "fix it by hand when you really have to do it" kind
of problems.  That or you can write really smart software.

In the end, I think the best solution would be for all applications to either
generate properly structured code, or stop claiming that they are
compliant when
they're not.

Bob Heiney
Graphics Consultant