From: Pip Cet <pipcet@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: valizadeh.ho@gmail.com, 41005@debbugs.gnu.org, nicholasdrozd@gmail.com
Subject: bug#41005: problem with rendering Persian text in Emacs 27
Date: Sat, 06 Jun 2020 09:11:36 +0000 [thread overview]
Message-ID: <875zc4zhh3.fsf@gmail.com> (raw)
In-Reply-To: <831rmsa7ln.fsf@gnu.org> (Eli Zaretskii's message of "Sat, 06 Jun 2020 12:04:04 +0300")
Eli Zaretskii <eliz@gnu.org> writes:
>> From: Pip Cet <pipcet@gmail.com>
>> Cc: valizadeh.ho@gmail.com, 41005@debbugs.gnu.org, nicholasdrozd@gmail.com
>> Date: Sat, 06 Jun 2020 08:38:39 +0000
>>
>> >> Given these two bugs, I wonder whether it wouldn't be more reasonable
>> >> always to let HarfBuzz guess the direction, at least for Emacs-27:
~~~~~~~~~~~~~~~~~~~~~
I should have been clearer here and said I was only concerned with Emacs 27.
>> >> scripts which change direction, if they are supported by HarfBuzz, won't
>> >> work anyway.
>> >
>> > Please explain "scripts that change direction" and "won't work
>> > anyway", I don't think I understand that part.
>>
>> I think your example (RLO..PDF in RTL text) is better: that won't work
>> anyway, right now, because if, for example, you type
>>
>> <HEBREW LETTER SHIN> <RIGHT-TO-LEFT OVERRIDE> f i
>>
>> and have set the char table to treat "fi" as a ligature, the result will
>> (at least sometimes) be an "fi" ligature, but it should look like the
>> word "if".
>
> That's not how shaping engines work, at least not how HarfBuzz does
> AFAIU. It gets the characters in the logical order, so it always
> wants to see "fi", even if the directionality of the characters was
> overridden, and it also wants to know the local text directionality.
> What is produced from that depends on the font: if it has different
> ligatures for "fi" in different directions, then HarfBuzz should give
> us back the ligature appropriate for the direction it was passed.
>
> (Personally, I think that when some text uses a directional override,
> they don't intend to see ligatures, because the override is mostly for
> treating characters as independent of the surrounding context. But
> this is eventually up to the font to specify. AFAIU, Arabic shaping
> works differently in different directional contexts, for example.)
>
>> > The reason we don't let HarfBuzz guess in all cases is because the
>> > resolved bidi level, when we have it, is a more accurate indication of
>> > the required direction.
>>
>> Yes, but we'll still cache the wrong direction.
>
> Why "wrong"? We will cache the same direction as we passed to
> HarfBuzz, and thus the produced glyphs will be consistent with the
> cached direction. And if we ever need to display the same sequence of
> characters with a different direction, the cached sequence will fail
> to match, and we will call HarfBuzz again to produce glyphs for this
> other direction. That sounds TRT to me.
You're absolutely correct, sorry for wasting so much of your time with
this: caching directions is the right thing, I was just concerned about
what to do in Emacs 27 where AIUI we don't want to cache directions...
> Once the caching of direction is
> implemented, my point is that passing the direction to HarfBuzz and
> caching it will produce better results for text in a directional
> override than if we let HarfBuzz guess the direction.
Again, I agree. Sorry for the misunderstanding.
next prev parent reply other threads:[~2020-06-06 9:11 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-01 18:02 bug#41005: problem with rendering Persian text in Emacs 27 hossein valizadeh
2020-05-01 18:51 ` Eli Zaretskii
[not found] ` <CAMyfNNp7FiFgAN5EVcVauawiy8ZB7U+eKY7qOeqZOnbMQfs5iQ@mail.gmail.com>
2020-06-03 14:34 ` Eli Zaretskii
2020-06-03 17:24 ` Nicholas Drozd
2020-06-03 18:01 ` Eli Zaretskii
2020-06-04 2:39 ` hossein valizadeh
2020-06-04 3:01 ` hossein valizadeh
2020-06-04 4:01 ` Eli Zaretskii
2020-06-04 4:10 ` Eli Zaretskii
2020-06-04 6:27 ` hossein valizadeh
2020-06-04 8:28 ` Pip Cet
2020-06-04 13:15 ` Eli Zaretskii
2020-06-04 19:52 ` Pip Cet
2020-06-05 4:46 ` hossein valizadeh
2020-06-05 6:21 ` Eli Zaretskii
2020-06-05 11:07 ` Basil L. Contovounesios
2020-06-05 12:32 ` hossein valizadeh
2020-06-05 12:53 ` Eli Zaretskii
2020-06-05 13:05 ` Pip Cet
2020-06-05 14:13 ` Eli Zaretskii
2020-06-06 8:38 ` Pip Cet
2020-06-06 9:04 ` Eli Zaretskii
2020-06-06 9:11 ` Pip Cet [this message]
2020-06-06 9:24 ` Eli Zaretskii
2020-06-06 13:09 ` Pip Cet
2020-06-05 14:23 ` hossein valizadeh
2020-06-05 14:25 ` Eli Zaretskii
2020-06-05 6:39 ` Pip Cet
2020-06-05 8:01 ` Eli Zaretskii
2020-06-05 8:41 ` Pip Cet
2020-06-05 11:42 ` Eli Zaretskii
2020-07-21 12:40 ` Amin Bandali
2020-07-21 13:34 ` Robert Pluim
2020-07-21 17:53 ` Amin Bandali
2020-07-21 18:27 ` Eli Zaretskii
2020-07-22 2:12 ` Amin Bandali
2020-07-22 14:20 ` Eli Zaretskii
2020-07-24 4:11 ` Amin Bandali
2020-07-24 6:09 ` Eli Zaretskii
2020-07-25 4:19 ` Amin Bandali
2020-07-25 6:48 ` Eli Zaretskii
2020-07-25 15:53 ` Amin Bandali
2020-07-25 16:28 ` Eli Zaretskii
2020-07-25 16:44 ` Amin Bandali
2020-07-25 16:56 ` Eli Zaretskii
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