How can I improve my Turkish Small Capitals (XeTeX)

Question

Status update

In a private email, Bogusław Jackowski (to whom my sincere thanks) has recognised this as a bug in the TeX Gyre fonts. As the TeX Gyre team are all working hard on another piece of the TeX Gyre project, he cannot commit to a date for fixing this, but his best estimate is sometime next year.

---

Turkish characters to small caps and Turkish characters to uppercase attempt to address the tribulations of those of us who need to deal with the dotted letter i/İ, in full-size and small capitals. As far as I can see, all the answers address the pdftex engine.

Here's my MWE to illustrate my annoyance:

\documentclass[a4paper,12pt]{article}
\usepackage{fontspec}
\setmainfont{TeX Gyre Adventor}
\begin{document}
\noindent
{\Huge
  \textsc{Eb\.ı} \.Incelemesi\\[6pt]
  \textsc{Eb\.{}\kern -0.215em ı} \.Incelemesi
}
\end{document}

and here's the output:

Now, can anyone, please, explain to me:

1. (Curiosity) Why is the dot accent over the B so badly out-of-joint?
2. (Real question) Given that (a) none of my fonts appears to have the TRK feature; (b) although they have a small caps dotted İ, the position in the glyph table varies, and the Unicode code point, of course, is at some random location in the Private Area; and (c) the time I spent hand-tuning the "-0.215em" will almost certainly need to be spent again if I change fonts; then what better and more robust method is there for producing the second line?

---

Further to EGreg's interesting comment, I 'made up' a new MWE, with an extra ı just to emphasize the problem:

\documentclass[a4paper,12pt]{article}
\usepackage{fontspec}
\setmainfont[%
  Script=Latin,
  Language=Turkish,
  ]{TeX Gyre Adventor}
\begin{document}
\noindent
{\Huge
  \textsc{Ebiı} İncelemesi\\[6pt]
}
\end{document}

Here's the output; the dot is still missing:

---

So now I'm getting irritated with myself, and I add another option:

\setmainfont[%
  Script=Latin,
  Language=Turkish,
  Letters=UppercaseSmallCaps,
  ]{TeX Gyre Adventor}

which gives the same result.

Then I switched to Brill, with the same options, and got this:

which, of course, is not what I want, as EBİ is now all uppercase, not SC.

At which point I'm going to sleep on it. What's the correct behaviour for Letters=UppercaseSmallCaps?

Answer 1

This seems to be a bug in the implementation of the TRK feature in the TeX Gyre fonts. Here's an example:

\documentclass[a4paper,12pt]{article}
\usepackage{fontspec}
\usepackage{polyglossia}
\setmainfont{Brill}
\setmainlanguage{turkish}
\newfontfamily{\termes}[Language=Turkish]{TeX Gyre Termes}
\begin{document}
\textsc{Ebi} İncemelesi \textsc{ıIiİ}

\termes
\textsc{Ebi} İncemelesi \textsc{ıIiİ}

\end{document}

and here's the result

The log file makes clear that the TRK feature is selected for both fonts:

.................................................
. fontspec info: "defining-font"
. 
. Font family 'TeXGyreTermes(0)' created for font 'TeX Gyre Termes' with
. options [Language=Turkish].
. 
. This font family consists of the following shapes:
. 
. * 'normal' with NFSS spec.:
. <->"TeX Gyre Termes/ICU:script=latn;language=TRK;"
. 
. * 'small caps' with NFSS spec.:
. <->"TeX Gyre Termes/ICU:script=latn;language=TRK;+smcp;"

[...]

. fontspec info: "defining-font"
. 
. Font family 'Brill(1)' created for font 'Brill' with options
. [,Language=Turkish].
. 
. This font family consists of the following shapes:
. 
. * 'normal' with NFSS spec.:
. <->"Brill/ICU:script=latn;language=TRK;"
. 
. * 'small caps' with NFSS spec.:
. <->"Brill/ICU:script=latn;language=TRK;+smcp;"

[...]

---

Here's the relevant part of the interaction between polyglossia and fontspec (line numbers from polyglossia.sty):

253 \def\xpg@addfontfeature@lang#1#2{% #1 is langtag, #2 is langname
254   % Turkish is a special case: tag can be TRK or TUR
255   \edef\tmp@Turkish{Turkish}%
256   \edef\tmp@@langname{#2}%
257   %  \ifstrequal{#2}{Turkish}%
258   \ifx\tmp@@langname\tmp@Turkish
259     \fontspec_if_language:nTF {TRK}%
260       {\addfontfeature{Language=Turkish}}%
261       {\fontspec_if_language:nTF {TUR}%
262         {\addfontfeature{Language=Turkish}}%
263         {}}%
264     % else not Turkish
265   \else
266      \edef\tmp@@langparam{Language=#2}%
267      \expandafter\expandafter\expandafter\fontspec_if_language:nTF \expandafter{#1}%
268       {\expandafter\expandafter\expandafter\addfontfeature\expandafter{\tmp@@langparam}}%
269       {}%
270   \fi
271 }

Essentially, the Language=... option is passed to the defined font families (and fontspec creates a new one, as results from the log file reported above). The fact that Turkish is treated in a special way is a happy coincidence.

If you're not using polyglossia, then you should define a font family for Turkish anyway, or \textsc won't give the expected result on "i" when a non-Turkish language is involved.

Answer 2

The fontspec accent code looks a bit suspect to me.

if you drop back to the classic TeX accent command but using the dot accent from Unicode position things look a bit better. The alignment still seems slightly off for the full size I.

\documentclass[a4paper,12pt]{article}

\def\dotabove#1{{\accent729 #1}}

\usepackage{fontspec}
\setmainfont{TeX Gyre Adventor}
\begin{document}

\Huge
  \textsc{Eb\.ı} \.Incelemesi


  \textsc{Eb\.{}\kern -0.215em ı} \.Incelemesi

  \textsc{Eb\dotabove ı} \dotabove Incelemesi

\end{document}