My memory from when I looked into this several years ago is that this is built 
into HarfBuzz at a fairly low level: If you try to typeset a combining 
character in isolation, HarfBuzz supplies the dotted circle. My impression is 
that's because that's the way UniScribe did it and/or an an overly rigid 
interpretation of the "Fallback Rendering" paragraph in section 5.13 of the 
Unicode Standard (v 13.0.0).

You might be able to get rid of the dotted circle by attaching the combining 
character to an invisible character such as U+00A0 NO-BREAK SPACE.   Try

    \char"A0\XeTeXglyph\XeTeXglyphindex "yaPhalaa_gran"

I haven't tried this with the Noto Grantha font, but it works with, for example 
combining vowel signs in Sanskrit fonts:

    \documentclass{article}
    \usepackage{fontspec}
    \pagestyle{empty}
    % Murty Hindi 1.01: http://www.murtylibrary.com/mcli-fonts.php
    \def\nagarifont{Murty Hindi}
    \newfontfamily\1[Script=Devanagari]{\nagarifont}
    \begin{document}
    {\1\char"0924}
    {\1\char"093E}
    {\1\char"A0\char"093E}
    \end{document}


Cheers,
David.
________________________________________
From: XeTeX <xetex-bounces+dmj=ams....@tug.org> on behalf of François Patte 
<francois.pa...@mi.parisdescartes.fr>
Sent: Tuesday, April 6, 2021 5:42 PM
To: xetex@tug.org
Subject: Re: [XeTeX] using glyph from private use area

Le 06/04/2021 à 18:49, Yannis Haralambous a écrit :
> salut François !
>
> I would suggest
>
> \XeTeXglyph\XeTeXglyphindex"yaPhalaa_gran"
>
> but be sure to leave a blank space after the closing double quote
> otherwise you will get nothing…

Thank you, both of you. This does the trick, only the dotted circle
remains which I can't remove... I tried to play with \XeTeXcharglyph
without any success:
"You can't use `\XeTeXcharglyph' in restricted horizontal mode." is the
result of my attempts.

Is it possible to get rid of this circle?

Thank you for your help.

F.


--
François Patte
UFR de mathématiques et informatique
Laboratoire CNRS MAP5, UMR 8145
Université Paris Descartes
45, rue des Saints Pères
F-75270 Paris Cedex 06
Tél. +33 (0)6 7892 5822
http://www.math-info.univ-paris5.fr/~patte
FSF
https://www.fsf.org/blogs/community/presenting-shoetool-happy-holidays-from-the-fsf




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