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Re: Display of Lao script

From: Stephen Berman
Subject: Re: Display of Lao script
Date: Fri, 20 Oct 2017 13:48:36 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/27.0.50 (gnu/linux)

On Tue, 17 Oct 2017 19:40:27 +0300 Eli Zaretskii <address@hidden> wrote:

> [Adding Handa-san, in the hope that he could comment on this.]
>> From: Stephen Berman <address@hidden>
>> Date: Tue, 17 Oct 2017 01:14:03 +0200
>> Is this difference expected?  I'm not familiar with the Lao script, so I
>> don't know if one of the displays is wrong, though this quote from
>> https://en.wikipedia.org/wiki/Lao_alphabet seems to suggest that either
>> way is possible: "Vowels can be written above, below, in front of, or
>> behind consonants, with some vowel combinations written before, over and
>> after."  This is m17n-lib-1.7.0 and libotf-0.9.13 from
>> http://www.nongnu.org/m17n/, which are AFAIK the latest released
>> versions (there's a patch for Bengali in etc/PROBLEMS, but I don't know
>> of any problem report about Lao).  (Regardless if what's correct, my
>> aesthetic impression is that the first display, without m17n and libotf,
>> looks better; however, I do know that the Arabic example in HELLO is
>> correctly displayed only with these libraries).
> I see a better display here, on MS-Windows.  Can you try a different
> font, perhaps one that is advertised to have good support for the Lao
> script?  AFAIK, libotf/libm17n (as any other shaping engine) depend on
> font capabilities to some extent.

I haven't yet tried a font specialized for Lao, but I did try Symbola,
and with that the Lao HELLO example appears as it does in Emacs without
m17n-lib and libotf (with one exeption, see below) -- though the font
used to display the Lao is not Symbola but DejaVu Sans.  Then I realized
what the difference is: Symbola is a variable pitch font, while my
default font is DejaVu Sans Mono (also the default with -Q).  And
indeed, using DejaVu Sans (not Mono) as the default font displays the
Lao as in Emacs without m17n-lib and libotf (but in the latter Emacs
it's the same display also with DejaVu Sans Mono) -- with the exception
of the character LAO LETTER HO SUNG, which is composed with LAO TONE MAI
THO, but in the display, the latter appears over the following
character, while in the Emacs without m17n-lib and libotf it appears
over the character it is composed with (which I assume is correct).  The
other three character compositions in the Lao example appear the same in
Emacs both without and with m17n-lib and libotf -- but again, in the
latter only with variable pitch DejaVu Sans.  So this does seem to be a
problem in the m17n-lib and/or libotf code.

Steve Berman

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