[omega] Question about the paper published in EuroTeX 2005
Yannis Haralambous
yannis.haralambous at enst-bretagne.fr
Mon Mar 14 13:31:27 CET 2005
Benjamin Bayart answered by the following:
> Si on dit que "k-" est un glyphe different pour "c", ca sonne faux. Par
> contre, si on dit que "k-k" est une chaine de glyphes differente, dans
> cette langue, pour la chaine de caracteres "ck", alors ca sonne juste.
> La notion de "variantes de glyphe" devrait donc etre comprise dans un
> contexte, et pas de maniere absolue. Le cas des "d" de Zapfino est
> different parce que le contexte ne jour que graphiquement et pas au
> niveau linguistique, mais il me semble que ca rentre dans le meme
> cadre.
(in English: if we say that "k-" is a different glyph for "c", that
sounds wrong. But, on the contrary, if we say that "k-k" is a different
glyph string, in this language, for the character string "ck", that
sounds OK. The notion of "glyph variant " should be understood in a
context, and not in absolute way. The case of Zapfino "d" glyphs is
different because the context is only graphical and not linguistic,
but it seems that the frame is the same)
My answer:
we need an atomic unit for algorithms (like OTPs, paragraph builder,
etc.) to operate. Let us take again the example of backen: I agree that
saying that "k" is a variant glyph of "c" is absurd. But suppose now
that in our font we have an `ak' ligature. Then, when the word is
hyphenated "bak-ken", I would indeed like to have that ligature in the
part "bak-". Which means that the algorithm must detect a "k" texteme
to be able to apply the ligature. So even if it sounds absurd to have a
"c" with a "k" glyph, maybe this is how the engine sees it.
My argument about "pseudo" is that we weren't very precise yet on what
we mean when talk of a "glyph". A TeX charnode contains a number which
is the position of a glyph in the current font. So in some sense this
is both concrete and abstract. Concrete because we obtain one and only
image (when I say glyph 97 of font CMR10 at size 10 points, this is a
unique image, modulo the version changes by Knuth, and this no matter
how I get there, be it bitmap or vector outlines). Abstract because
being only a table position we can change fonts, and provided we have
the same glyph encoding we can get something else.
So the question is: how abstract must a "texteme glyph reference" be?
How many levels of specification do we have? When we say that we want
glyph=a, do we mean just any a (default font) at any size (default
size)? a in a font named foo? a in a font named foo version 1.01? in a
given size? using a specific outline?
In TeX this problem was avoided by using *only* TFM. TeX knows only
about TFM and if we want to combine TFM with real-world fonts then all
the ambiguity of identifying a font is outside the scope of TeX. Omega
will soon read OpenType fonts directly. In a TTF-flavored OpenType font
you must go through GSUB/GPOS to access certain glyphs (not accessible
from cmap), otherwise the only way is through glyph indexes which are
not reliable, so the problem of identifying a glyph in a texteme is a
hot topic.
But first of all, we should be very clear about what we are talking
about when we say "glyph". (Vocabulary, terminology, taxonomy: sounds
like a talk by Chris, Joachim and Christina???)
--
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| Yannis Haralambous, Ph.D. yannis.haralambous at enst-bretagne.fr |
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