When implementing Greek in a font, I realized that using the polytonic version some glyphs point instead to those of the monotonic version.
This happens both in LibreOffice and with LaTeX, although I specify the composition engine I use, namely Lualatex, the <polutonicogreek> option.
I state that the accents of monotonic and polytonic are slightly different.
The fact is that the glyphs (polythonic) with the grave accent, which should be those with oxia, point instead to the glyphs (monotonic) with tonos (unless I, instead of using keyboard shortcuts to write, directly enter the glyph with the correct unicode value).
Of course, this problem doesn't show up in the professional fonts I've checked, but I haven't found the same solutions. In some there is a lookup of ccmp, in others of the Contextual Alternates with replacement rules. But honestly, I didn't understand how to proceed.
How do you solve the problem of the correct coupling between monotonic and polytonic, precisely in relation to these accents?
Thank you
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but it does not produce any results, because it does not make replacements. Is there something wrong with the system or the syntax?
There are some "duplicate" Greek characters that exist for compatibility with legacy systems, also known as compatibility characters. They are canonically and semantically equivalent. Most fonts, search engines and other software will work with and display both versions identically. The Greek Keyboard in use will make a decision to input one or the other.
The duplicated characters preserved a false distinction of legacy code tables, following Greek spelling reform in the 1980s. The Unicode database initially established normalizing rules and since 2016 has formally deprecated and removed the versions from the Greek extended range, leaving the basic range.There are sixteen (16) affected characters:
Or do you mean that in any case the character used is U + 03AC (ie alphatonos) and instead never the duplicate U + 1F71?
Not all environments apply normalisation, so you may get different results in different apps/platforms with the same fonts.
There's no really robust way around this other than to make the two identical (or to make the polytonic and monotonic separate fonts). Making them identical also makes sense if one takes the view that the tonos is the oxia, that the monotonic system didn't create a new accent, but simply got rid of all-except-one of the existing accents (and reformed some of the rules around its use).
So yes, LibreOffice and Lualatex are environments, and may be part of larger environments — host operating systems, as well as default algorithms or preference settings within the applications — that could affect what is happening to text.
Yes, that's the one. Sorry, I thought I had included a link, but it didn't work.
In any case, as you can see from the attached screen, the replacement seems correct in the lookup window.
Now, the problem is to understand what is wrong with the lookup I have indicated above, because in any case it operates (if I'm not wrong) after the normalization of the text to be composed has been carried out.
Now, your substitution seems to depend on the PGR language system tag, so in order to work it requires that you are able to tag text in your environment in a way that invokes the PGR language system feature lookups in the font. This is far from the most robust aspect of OpenType Layout, with varying levels and methods of support. So there are quite a lot of ways it can fail.
A last question. The replacement works fine if I set, in the metadata of the lookup,
grek{PGR, dflt}
: what inconveniences can the fact of adding <dflt> produce?That replacement takes place even if I use monotonic Greek?
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Hmm. I've thought of another way you could get your oxia form to substitute only and specifically in polytonic setting, but it's a bit crazy (and would only work for sequences of polytonic words containing at least one other polytonic accent). Probably too silly to consider a viable solution.
You'd be better off making separate polytonic and monotonic fonts if you really want the accent forms to differ. That's what I do when I have language-specific forms that I want to be really reliably used, e.g. Tiro Devanagari Hindi, Tiro Devanagari Marathi, Tiro Devanagari Sanskrit.
a) Decompose all combined diacritics to letter + mark combinations using the ccmp feature.
b) Ensure marks are identified as such in the GDEF table.
c) Use GPOS mark anchor attachment to correctly position marks on letters.
d) Add rclt feature substitution tonos -> oxia in chaining context of other polytonic marks (i.e. look behind and ahead for varia, perismoneni, etc.) and set the lookup flag to not process base glyphs.
The last step, the lookup flag, is the reason for the initial decomposition: you want to get to a state where you can process the mark glyphs independent of the letters.
That would work for any sequences of polytonic words that contain multiple accent types. Obviously it wouldn't work for a string that only contained the tonos, as there would be no context to trigger the substitution. There would also be an issue in some environments that don't process the word space as part of a string, so won't catch context from adjacent words.
As you can see from the image, on the left Adobe Garamond Premiere Pro itself presents the problem of using in the polytonic the acute accents of the monotonic, slightly different from the polytonic causing a lack of homogeneity in the rendering (see the third line). On the right the final rendering of the font I'm working on.
Thanx a lot for your cooperatiom!