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From: ccc_ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.lang.postscript
Subject: Re: PostScript Level II, contextual forms
Message-ID: <1330.26d576c4@waikato.ac.nz>
Date: 24 Aug 90 06:49:40 GMT
References: <9607@goofy.Apple.COM> <1289.26d27708@waikato.ac.nz> <1990Aug22.051728.16659@ico.isc.com>
Organization: University of Waikato, Hamilton, New Zealand
Lines: 56

In <1990Aug22.051728.16659@ico.isc.com>, rcd@ico.isc.com (Dick Dunn)
responds to my questions about support for contextual forms and interactive
WYSIWYG editing as follows:

"PostScript is the wrong level to make such a decision.  At the level of
PostScript, the output of text should be regarded as the output of a sequence
of glyphs which have no inherent semantics.  Characters are simply objects being
placed on the page or screen...it doesn't make sense to ascribe language-
dependent context to them."

So, you need another layer on top of PostScript to implement these functions.
Performance considerations aside, do you have a standard for this layer?
Or does this mean that programs that want to be writing-system-independent
cannot be operating-system-independent?

Remember, virtually *all* text drawing calls would have to go through
this extra layer; it no longer becomes possible to access PostScript directly,
unless you either a) add special cases to your code to handle all the
peculiarities of different writing systems, or b) you want your software
to be useful only in places where they use the Roman alphabet.

"Decisions have to be made upstream of PostScript anyway."

Dick mentioned text justification as an example. To be more specific, you
have the problem of deciding what's the optimum distribution of width
adjustments--how much to alter the spacing between words (for writing
systems that have spaces between words), and (if you really must) how much
you can alter character widths. Also the rules for varying character widths
depend on the writing system--for example, Arabic writing widens characters
by drawing extension bars between them. Then there's the problem of word
breaks at the ends of lines (the rules for finding word breaks are
writing-system-dependent), and hyphenation rules (if relevant).
Oh, and I forgot to mention automatic kerning...

If you have a separate text-rendition layer, you'd then have to maintain
*two* sets of information about each font: the standard PostScript font
dictionary, and all this extra information, in order to draw sensible-looking,
readable text with that font.

You can look at it another way: PostScript becomes just a low-level tool
for implementing a text-rendition and page-description system, rather
than being such a system in itself.

I'm not suggesting that you write PostScript programs to do page layout
(thought I agree it would become possible). But *somewhere* there needs to
be the information necessary to allow the application to do it--and it
needs to be available in a standard form, or portability goes out the window.

What do you think? What's the right way to do things?

Lawrence D'Oliveiro                       fone: +64-71-562-889
Computer Services Dept                     fax: +64-71-384-066
University of Waikato            electric mail: ldo@waikato.ac.nz
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+12:00
To someone with a hammer and a screwdriver, every problem looks
like a nail with threads.