[gs-bugs] [Bug 692000] pdfwrite: incorrect treatment of substitution-based Type 3 Fonts

bugzilla-daemon at ghostscript.com bugzilla-daemon at ghostscript.com
Mon Feb 28 16:05:58 UTC 2011


http://bugs.ghostscript.com/show_bug.cgi?id=692000

--- Comment #5 from Ken Sharp <ken.sharp at artifex.com> 2011-02-28 16:05:57 UTC ---
(In reply to comment #4)

> > if the type 3 font does nothing but reposition glyphs from
> > the type 1 font, then the type 1 font is incorrect
> 
> While the task of the type 3 font is indeed to reposition (or, better,
> relative-position) the diacritic marks, what makes such repositioning necessary
> is not a problem with the type 1 font, but rather inherent aspects of
> letter-vowel combinations.  These aspects, as well as the type 3 technique used
> to overcome the challenges that they present, are described in Sivan Toledo's
> short article on the topic, which can be found at
> http://www.tau.ac.il/~stoledo/Pubs/vowels.ps

I've read the document, and I'm still of the opinion that this is the wrong way
to solve the problem. Its a clever solution, indeed very clever, but in my
opinion the real way to solve this is in the typesetting application, not the
PostScript interpreter. 

As is demonstrated by the Distiller output, the same effect can be achieved by
simply placing each glyph from the type 1 font in the correct position. It
seems to me better to do this in a 'typesetting' application which really ought
to know about the properties of the text, rather than building intelligence
into the PostScript program. 

After all, the typesetting program is already responsible for placing all the
other glyphs, adding this ability would seem like the correct solution, rather
than placing the burden on the PostScript interpreter.

Indeed the author notes that there are problems with this approach since the
code is unable to take into account the text to left and right of the glyph
being marked, which looks like it is potentially important (presumably to avoid
clashing of vowels).

This approach is rather like trying to write Arabic text by having the
PostScript interpreter apply kashidas and generate the initial, medial and
terminal glyphs rather than having the typesetting application do it using all
its information about surrounding text.

As I said, I'll leave it open as an enhancement.

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