🚀 go-pugleaf

In article <1993Jan18.102504.18587@gate.esat.kuleuven.ac.be>, tytgat@esat.kuleuven.ac.be (John Tytgat) writes:
|> >also be rather hard, since you would need to have a postscript interpretter,
|> >which you don't need to read EPS files (since they're not really programs, but
|> >a postscript representation of a data structure), and then you would have
|> >problems with programs possibly not terminating, and it all gets a bit
|> >horrid.
|> 
|> Tsj, tsj, tsj.  PS is a real graphics language, so PS and EPS files can be
|> considered as programs (if all the procedures are defined).  And what do you
|> mean with "possibly not terminating programs" ???
|> 


It's possible to prove that one cannot generally prove that programs will
terminate, but that was done by Alan Turing a while back so I won't bother
with details.

To give a useful example though, there is a raytracing package written in
Postscript, popular amongst students for annoying departments' laser
printing services, since they typically take 3 hours to render a page, and
are rather hard to stop neatly since flushing the queue doesn't work -
the page has already reached the printer by the time you work out
something has gone wrong, and turning the printer off and on doesn't
go down well with queuing software.  (OK, so you can get round this, but
that's not really relevant to the topic.)

An importer to convert this into, say, an Artworks file would take quite
some time to execute, and it's not impossible to conceive of a scene that
would never finish rendering (just have zero loss reflections) so what
does the import do? 

It is precisely BECAUSE Postscript is a real language that you get problems.

On the other hand you'll only get these termination problems with stuff that
wouldn't print anyway.

However I am dubious as to the extent to which one can usefully interpret it
into a data structure, since it is a real language.  How does one deduce
that a function is, say, a graduated fill?


As for your comment that CC have the in house technology to do this,  do 
they?  Oh.  If you refer to the code in Showpage, that's rather different,
it's just interpretting postscript, and producing a bitmap, and the importers
on Artworks rely on known prologs to do conversions.

Ian