bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Fr Ml]

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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew, ..)

[Eli Zaretskii]

> From: Fr Ml <fr_ml@t-online.de>
> Date: Mon, 9 Nov 2020 07:10:38 +0100
> 
> Some time ago (maybe 3 months) I've noticed some problems with the bidi support (right-to-left languages)
> in outline-mode and org-mode.
> 
> One problem I can't reproduce: The characters have then a strange form but If I change the text scale
> (larger or smaller) it becomes normal.
> 
> The second problem I can reproduce, you can see it in the two images:
> 
> In this image: I have the option `bidi-paragraph-direction: nil` (the same if I put in the first line: `-*- mode:
> outline -*-`), to get the right direction for  Hebrew and Arabic. As you see the headline color isn't consistently
> brown. The English text don't have this problem.
> 
> [![The color of the headline changes, gets black. The direction is right to left][1]][1]

This is a known bug#43363, which was already fixed for the upcoming
Emacs 27.2.

> Actually, the first problem is bigger for me but I can't reproduce it; I think that both problems appeared a the
> same time. So maybe solving the second will solve the first one too(?)

Unlikely.  But you didn't say almost anything about this problem:
which characters take a "strange form", what is that strange form,
etc.  It's possible that an obscure bug related to Arabic shaping,
which was fixed just today (see bug#44521), is what you see.  (Do you
use Ivy or some similar add-on?)

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Eli Zaretskii]

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[Please use Reply All to CC the bug tracker as well.]

> From: Fr Ml <fr_ml@t-online.de>
> Date: Mon, 9 Nov 2020 18:34:07 +0100
> Thanks for the answer. Good news  that one problem is solved.
> 
> I didn't mention details because I assumed that's the same problem and it wasn't my main question there. I
> chose the reproducable proble. 
> 
> But now some details:
> - I don't use ivy or ido
> - The problem happens after "some time" of working with Emacs, usually not directly after starting Emacs.   
>   Example : the 3 attached pictures are of the same text file (not org or outline), but with different text sizes. I
> have just the Arabic word العربية in it. And I'm using a monospaced Font: Dejavu Sans Mono.
>   In 'text8correct.png' everything is fine, "text size": +8 word , if I decrease to +7, the shape is not correct the
> glyphs are too dense. It remains incorrect until the size +5. At +4 it becomes correct again.
>   But if I open the same file with a new Emacs process I don't have any problem!

I can only hope this is due to the same problem as was fixed in
bug#44521.  If not, let's hope someone will come up with a
reproducible recipe in the future.

> Also what happens:
> - Sometimes the letters don't have the correct form: a middle form for an ending letter 
> - Sometimes the letters are disconnected as in bug#44521.

I attach below the images you sent, so that they are stored with the
discussion:


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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Fr Ml]

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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Eli Zaretskii]

> Cc: 44528@debbugs.gnu.org
> From: Fr Ml <fr_ml@t-online.de>
> Date: Thu, 12 Nov 2020 08:14:30 +0100
> 
> in the INSTALL instruction of Emacs we read:
> (On GNU and Unix systems, Emacs needs the optional libraries "m17n-db",
> "libm17n-flt", "libotf" to correctly display such complex scripts as
> Indic and Khmer, and also for scripts that require Arabic shaping
> support (Arabic and Farsi).)
> 
> But I noticed that libm17n-flt isn't installed and it's not a package in the repository of Archlinux . I didn't need
> to install it before.
> 
> Can it be the problem? Or is it included in the other packages (m17n-db, libotf)?

This text is outdated: we nowadays prefer HarfBuzz, if available, as
our shaping engine.  Is your build using HarfBuzz?  You can tell by
looking at the value of the variable 'system-configuration-features'.

If your build doesn't use HarfBuzz, I suggest to install one that
does.

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Fr Ml]

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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Fr Ml]

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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Eli Zaretskii]

> Cc: 44528@debbugs.gnu.org
> From: Fr Ml <fr_ml@t-online.de>
> Date: Tue, 17 Nov 2020 11:04:05 +0100
> 
> I've made a new installation of Emacs (from the repository with pacman) and I've noticed that m17n-db and
> libotf are installed implicitly (because of dependency) with Emacs.
> Could this cause a problem with Harfbuzz (which is also installed implicitly with Emacs)?

I don't think so.

Start Emacs as "emacs -Q", then type "C-u C-x =" with point on some
character in the *scratch* buffer, and look at the line which says

              display: by this font (glyph code)

What does the following line say?

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Fr Ml]

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bug#44528: New bidi problems with outline-mode (Arabic, Hebrew,..)

[Eli Zaretskii]

> Cc: 44528@debbugs.gnu.org
> From: Fr Ml <fr_ml@t-online.de>
> Date: Wed, 18 Nov 2020 11:58:56 +0100
> 
> For 'l' (latin) and 'ع' (arabic):
> 
> l:     ftcrhb:-ADBO-Source Code Pro-normal-normal-normal-*-13-*-*-*-m-0-iso10646-1 (#x27)
> ع:     ftcrhb:-1ASC-Droid Serif-normal-normal-normal-*-13-*-*-*-*-0-iso10646-1 (#x1A)

The "hb" part of "ftcrhb" means that you are using HarfBuzz as the
shaping engine, so m17n libraries are only there as fallbacks (which
will probably never used).

IOW, your configuration is as good as it gets.

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew, ..)

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> I can only hope this is due to the same problem as was fixed in
> bug#44521.  If not, let's hope someone will come up with a
> reproducible recipe in the future.

(I'm going through old bug reports that unfortunately weren't resolved
at the time.)

Fr Ml, are you still seeing these problems in recent Emacs versions?

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#44528: New bidi problems with outline-mode (Arabic, Hebrew, ..)

[Lars Ingebrigtsen]

Lars Ingebrigtsen <larsi@gnus.org> writes:

> Fr Ml, are you still seeing these problems in recent Emacs versions?

More information was requested, but no response was given within a
month, so I'm closing this bug report.  If the problem still exists,
please respond to this email and we'll reopen the bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no