[XeTeX] bug in polyglossia/sanskrit? (problem with diacritical marks)

[Steve White]

Hi Jonathan,

You may have a point, although I don't think it's the whole story.

(Most of what follows is font-techy. Upshot is: I did find suspicious
issues in FreeFont, and have now fixed them.)

The font feature in FreeSerif that positions generic marks like these is

mark ('generic marks above')

Indeed the 'dev2' script was different from the 'deva' script, being set
nly for language 'dflt'.  That is formally a bug, but I don't see why it
would matter here, as the "script" in which the problem happens is Latin
(the base characters beinig from the Latin range).

However, now that I look at the 'latn' script entries for that same feature...
it lacks the 'SAN ' language.  As I understand the logic, that would
result in the feature not being applied.

Now in the case of FreeFont, that should result in the mark crudely
appearing over the preceding character without GPOS placement, as these
marks have negative right bearing.

I have fixed these issues in FreeFont SVN.

It will be interesting to hear if they alleviate the issue in the newer
version of TL.  It might suggest triggers the effect.

Cheers!


On Thu, May 16, 2019 at 2:30 PM Jonathan Kew <jfkthame at gmail.com> wrote:
>
> On 16/05/2019 12:31, Ulrike Fischer wrote:
> > Am Mon, 13 May 2019 17:52:17 +0200 schrieb François Patte:
> >
> >> I have just made a fresh install of texlive 2019 and encountered a
> >> problem with the diacritical marks of romanized sanskrit.
> >
>
> Do the 'dev2' script tables in FreeSerif include positioning features
> for the various combining diacritics on Latin characters? I'm guessing
> not, in which case it's unsurprising that the results will be poor if
> you present it with accented Latin, yet request Devanagari shaping behavior.
>
> I'd expect romanized Sanskrit should be typeset with script=latn, or
> with no explicit script specification.
>
> JK
>
> > (copied from f.c.t.t):
> >
> > One can see it with plain xetex too, and it is not the font (I'm
> > forcing it to 2018), et it is not xdvipdfmx (it happens with tl19
> > and tl18 version). So it is quite probably an xetex engine bug.
> >
> > A plain xetex example:
> >
> > \XeTeXtracingfonts=1
> > \font\test="[C:/texlive/2018/texmf-dist/fonts/opentype/public/gnu-freefont/FreeSerif.otf]/OT:script=dev2;"
> > \test  ā ī ū ṛ ṝ ḷ ḹ ṭ ḍ ṅ ś ṣ ḥ
> > \bye
> >
> >
> > Comparing the versions gives
> > 2019:
> > Compiled with ICU version 63.1; using 63.1
> > Compiled with zlib version 1.2.11; using 1.2.11
> > Compiled with FreeType2 version 2.9.1; using 2.9.1
> > Compiled with Graphite2 version 1.3.13; using 1.3.13
> > Compiled with HarfBuzz version 2.3.1; using 2.3.1
> > Compiled with libpng version 1.6.36; using 1.6.36
> > Compiled with poppler version 0.68.0
> > Compiled with fontconfig version 2.13.1; using 2.13.1
> >
> > 2018:
> > Compiled with ICU version 61.1; using 61.1
> > Compiled with zlib version 1.2.11; using 1.2.11
> > Compiled with FreeType2 version 2.9.1; using 2.9.1
> > Compiled with Graphite2 version 1.3.11; using 1.3.11
> > Compiled with HarfBuzz version 1.7.6; using 1.7.6
> > Compiled with libpng version 1.6.34; using 1.6.34
> > Compiled with poppler version 0.64.0
> > Compiled with fontconfig version 2.13.0; using 2.13.0
> >
> > The first suspect is HarfBuzz.
> >
> >
> >
> >
>