GNU bug report logs - #20173
24.4; Rendering misallocates combining marks on ligatures

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Richard Wordingham <richard.wordingham <at> ntlworld.com>
Subject: bug#20173: closed (Re: bug#20173: 24.4; Rendering misallocates
 combining marks on ligatures)
Date: Mon, 17 Aug 2020 22:46:03 +0000

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Your bug report

#20173: 24.4; Rendering misallocates combining marks on ligatures

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 20173 <at> debbugs.gnu.org.

-- 
20173: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=20173
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Stefan Kangas <stefan <at> marxist.se>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Richard Wordingham <richard.wordingham <at> ntlworld.com>,
 20173-done <at> debbugs.gnu.org
Subject: Re: bug#20173: 24.4;
 Rendering misallocates combining marks on ligatures
Date: Mon, 17 Aug 2020 22:45:26 +0000

Eli Zaretskii <eliz <at> gnu.org> writes:

>> Date: Fri, 27 Mar 2015 09:04:44 +0000
>> From: Richard Wordingham <richard.wordingham <at> ntlworld.com>
>> Cc: 20173 <at> debbugs.gnu.org
>>
>> On Tue, 24 Mar 2015 19:03:38 +0200
>> Eli Zaretskii <eliz <at> gnu.org> wrote:
>>
>> > > Date: Tue, 24 Mar 2015 08:28:28 +0000
>> > > From: Richard Wordingham <richard.wordingham <at> ntlworld.com>
>> > > Cc: 20173 <at> debbugs.gnu.org
>>
>> > > You might want to first check whether composed Arabic is
>> > > usable. Doesn't making each word a grapheme cluster makes editing
>> > > unpleasant?
>>
>> > I don't know; I don't speak or write any of the languages that use the
>> > Arabic script.  I expect the users that do to come up and ask for
>> > features they miss.  We already allow deletion of single codepoints,
>> > even when they are composed; we might as well provide similar features
>> > for movement or whatever.
>>
>> I forgot that grapheme clustering is done in m17n, not Emacs itself.
>> The m17n code (in ARAB-OTF.flt) is reasonable - it clusters letters
>> with combining marks.  It *seems* I have a problem with tpu-forward-char
>> and tpu-backward-char; it's as though there's an initialisation fault
>> which stops them stepping through the Arabic compositions at first.  It
>> may be an issue with the presumably underlying forward-char and
>> backward-char; I haven't investigated further.  I'll have to record
>> the exact actions provoking the problem before I formally record a bug.
>
> Please try in "emacs -Q" without activating the TPU emulation.

More information was requested, but none was given within 5 years, so
I'm closing this bug.  If this is still an issue, please reply to this
email (use "Reply to all" in your email client) and we can reopen the
bug report.

Best regards,
Stefan Kangas

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From: Richard Wordingham <richard.wordingham <at> ntlworld.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.4; Rendering misallocates combining marks on ligatures
Date: Mon, 23 Mar 2015 01:06:26 +0000

When a ligature of two base characters has two combining marks on the
first component but none on the second, the second combining mark is
rendered as though it applied to the second component. A good example
is the Arabic sequence لَّا (lam, shadda, fatha, alef - <U+0644, U+0651,
U+064E, U+0627), where the shadda is rendered on the lam part of
lam-alif ligature and the fatha on the alif part.  This problem is not
restricted to right-to-left scripts; I encountered the problem when
debugging left-to-right rendering.  Lam-alif is one of the most
reliably generated ligatures bearing marks on different components.

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