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From: liam@cs.qmc.ac.uk (William Roberts)
Newsgroups: comp.lang.postscript
Subject: Re: Want Laser Prep walkthrough
Summary: LaserPrep is a moving target
Keywords: PostSCript, LaserPrep
Message-ID: <788@sequent.cs.qmc.ac.uk>
Date: 15 Dec 88 16:57:54 GMT
References: <456@grand.UUCP> <3265@bgsuvax.UUCP>
Reply-To: liam@cs.qmc.ac.uk (William Roberts)
Organization: Computer Science Dept, Queen Mary College, University of London, UK.
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I have plans to write a paper entitled something like

         A Short History of the Apple LaserPrep:
        The Primrose Path to the Enternal Bonfire

This will demonstrate the way in which the Apple LaserPrep code
has moved further and further away from good taste and decency,
resulting in the current state of affairs in which the code
conforms almost to the letter of the document structuring
conventions whilst being utterly against the spirit!

For example: the "od" routine used during document setup.

DSC2 says that every page should be independent of every other
page: LaserPrep 67 does this by calling od at the start of the
document (in a correctly labelled document setup section) which
includes

 newpath clippath
 mark
  {transform{itransform moveto}}
  {transform{itransform lineto}}
  {6 -2 roll transform 6 -2 roll transform 6 -2 roll transform
    {itransform 6 2 roll itransform 6 2 roll itransform 6 2 roll curveto}}
  {{closepath}}
  pathforall newpath
 counttomark array astore /gc xdf

What does this do? Answer: it sets the current path to be the
current clipping region, then uses pathforall to walk through
the path, producing for each element of the path the point(s)
involved *IN DEVICE COORDINATES* and an instruction to turn
them back into current coordinates and then execute the
appropriate path constructor. It then puts these instructions
into an array and saves it under the name "gc".

For example, if the clipping path is

        100 100 moveto
        100 200 lineto
        200 200 lineto
        200 100 lineto
        closepath

gc will be

        352 3776 {itransform moveto}
        352 2590 {itransform lineto}
       1552 2590 {itransform lineto}
       1552 3376 {itransform lineto}
       {closepath}

The start of each page involves executing gc to set up the
clipping path for that page.

This is obscene (Apple are you listening?). Why is it necessary
to use device coordinates? If it were not for the cost to me,
I'd buy a copy of the PostScript Green Book and send it to the
LaserPrep writers. There is no justification for the grotesque
code that is contained in current laserprep files.

Incidentally, if anyone out there expects to be able to use
modern Apple PostScript inside things like psfig, then they
might as well forget it now and not waste time trying to
pretend that this stuff can be used in the same way as the
early LaserPreps.

Can anyone suggest a good place to publish such a paper?
-- 

William Roberts         ARPA: liam@cs.qmc.ac.uk  (gw: cs.ucl.edu)
Queen Mary College      UUCP: liam@qmc-cs.UUCP
LONDON, UK              Tel:  01-975 5250