[luatex] Problem with babel-greek (harfbuzz?)

[Ulrike Fischer]

Am Tue, 17 Oct 2023 09:51:55 +0300 schrieb Nikos Platis:

> Dear all,
> 
> I came across a rather strange issue while using lualatex with babel-greek.
> I am posting here because I believe it is mostly related to lua(la)tex and
> less to babel-greek.
> 
> Here is an MWE:
> 
> ----------------------------
> % !TeX program = lualatex
> 
> \documentclass{book}
> 
> \usepackage[sf,bf]{titlesec}
> 
> \usepackage[greek]{babel}
> \babelfont[greek]{rm}{Times New Roman}
> \babelfont[greek]{sf}{Arial}
> 
> % \usepackage{polyglossia}
> % \setmainlanguage{greek}
> % \newfontfamily\greekfont[Script=Greek]{Times New Roman}
> % \newfontfamily\greekfontsf[Script=Greek]{Arial}
> 
> % \usepackage[no-math]{fontspec}
> % \defaultfontfeatures{Ligatures=TeX}
> % \setmainfont{Times New Roman}
> % \setsansfont{Arial}
> % \usepackage{xgreek}
> 
> \begin{document}
> 
> \tableofcontents
> 
> \chapter{Πρώτο Κεφάλαιο}
> Καλησπέρα \TeX. Πρώτο Κεφάλαιο.
> 
> \end{document}
> ----------------------------
> 
> I was compiling this on fully updated Arch Linux with lualatex from texlive
> (not Arch Linux packages). The result is the attached pdf file. You can see
> the strange accents in "Περιεχόμενα" and "Κεφάλαιο". You can also see that,
> for example, "Κεφάλαιο" appears correctly in the text.
> 
> After a lot of testing, I found out that this happens only for lualatex
> (not xelatex) with babel-greek (not polyglossia or xgreek) (only in the
> "stock" strings, "Περιεχόμενα", "Κεφάλαιο") and lualatex from texlive (not
> with lualatex from the Arch Linux package).
> 
> [....]
> The crucial difference is probably in harfbuzz. But how can this impact the
> output in the ways described above?

The harfbuzz version is not relevant. 

In the faulty words the ά is not U+03AC (alpha with tonos) but U+3B1
(alpha) with a following U+0301 (combining acute accent) (and
similar for the other char with accent).

If the greek hyphenation patterns are used an discretionary is
inserted between char and accent and that disturbs the placement:

\documentclass{book}

\usepackage{babel}
\usepackage{fontspec}
\setmainfont{Times New Roman}
\setsansfont{Arial}
\textwidth=1pt
\begin{document}
\selectlanguage{greek}
\showoutput

Κεφάλαιο 
Κεφάλαιο

\sffamily 
Κεφάλαιο 
Κεφάλαιο

\end{document}

basically it means that the greek hyphenation patterns needs a
correction, see https://tex.stackexchange.com/a/340164/2388 and
https://tex.stackexchange.com/q/330180/2388 for a similar problem
with russian.

You can avoid the problem by using the harfbuzz renderer, e.g.
    \babelfont[greek]{sf}[Renderer=harfbuzz]{Arial}
It typically suppress some problematic hyphenation points as it
builds clusters earlier. (polyglossia uses harfbuzz by default,
that's why you don't see the problem there).

Another option is to redefine \contentsname and \chaptername and to
remove the accent introduced by babel-greek here:

\addto\captionsgreek{\renewcommand\chaptername{Κεφάλαιο}%
\renewcommand\contentsname{Περιεχόμενα}}


The real fix is naturally to correct the hyphenation patterns. 
 


-- 
Ulrike Fischer 
http://www.troubleshooting-tex.de/