bug#17261: Some combining characters don't combine (Emacs 24 regression)

bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Max Shinn]

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Certain combining characters---such as the combining vector
arrow (0x20D7, a⃗) and the combining circle (0x20DD, a⃝)---do not
combine properly under most fonts on Emacs 24.3.1 under Debian GNU/Linux
x86_64, GTK 3.4.2.  In Emacs 23.3.1, these characters worked properly
under several fonts (for instance, Droid Sans Mono), whereas in Emacs
24, they only work properly with the FreeMono font.  The precise
behavior I am observing on Emacs 24 is where the base character and the
combining character sit side-by-side instead of superimposed on one
another.

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bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Eli Zaretskii]

> Date: Sun, 13 Apr 2014 10:49:44 -0500
> From: Max Shinn <max@maxshinnpotential.com>
> 
> Certain combining characters---such as the combining vector
> arrow (0x20D7, a⃗) and the combining circle (0x20DD, a⃝)---do not
> combine properly under most fonts on Emacs 24.3.1 under Debian GNU/Linux
> x86_64, GTK 3.4.2.  In Emacs 23.3.1, these characters worked properly
> under several fonts (for instance, Droid Sans Mono), whereas in Emacs
> 24, they only work properly with the FreeMono font.  The precise
> behavior I am observing on Emacs 24 is where the base character and the
> combining character sit side-by-side instead of superimposed on one
> another.

Looks like some side effect of changes in how we select fonts.  Where
Emacs 23 would force the base character to use the font that could
display the combining character, Emacs 24 now does not, which disables
auto-composition because Emacs can only compose characters that come
from the same font.  So the only way to display those characters as
composed is to select a buffer font that can display them.

bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Stefan Kangas]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Sun, 13 Apr 2014 10:49:44 -0500
>> From: Max Shinn <max@maxshinnpotential.com>
>>
>> Certain combining characters---such as the combining vector
>> arrow (0x20D7, a⃗) and the combining circle (0x20DD, a⃝)---do not
>> combine properly under most fonts on Emacs 24.3.1 under Debian GNU/Linux
>> x86_64, GTK 3.4.2.  In Emacs 23.3.1, these characters worked properly
>> under several fonts (for instance, Droid Sans Mono), whereas in Emacs
>> 24, they only work properly with the FreeMono font.  The precise
>> behavior I am observing on Emacs 24 is where the base character and the
>> combining character sit side-by-side instead of superimposed on one
>> another.
>
> Looks like some side effect of changes in how we select fonts.  Where
> Emacs 23 would force the base character to use the font that could
> display the combining character, Emacs 24 now does not, which disables
> auto-composition because Emacs can only compose characters that come
> from the same font.  So the only way to display those characters as
> composed is to select a buffer font that can display them.

Does that mean that the behaviour is not a bug, or should it be fixed?

Best regards,
Stefan Kangas

bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Sat, 21 Sep 2019 11:51:02 +0200
> Cc: Max Shinn <max@maxshinnpotential.com>, Kenichi Handa <handa@gnu.org>, 17261@debbugs.gnu.org
> 
> > Looks like some side effect of changes in how we select fonts.  Where
> > Emacs 23 would force the base character to use the font that could
> > display the combining character, Emacs 24 now does not, which disables
> > auto-composition because Emacs can only compose characters that come
> > from the same font.  So the only way to display those characters as
> > composed is to select a buffer font that can display them.
> 
> Does that mean that the behaviour is not a bug, or should it be fixed?

I don't think it's a bug, no.

bug#17261: Some combining characters don't combine (Emacs 24 regression)

[Stefan Kangas]

tags 17261 + notabug
close 17261
thanks

Eli Zaretskii <eliz@gnu.org> writes:

> > Does that mean that the behaviour is not a bug, or should it be fixed?
>
> I don't think it's a bug, no.

No further comments within 5 weeks, so I'll go ahead and close this.

Best regards,
Stefan Kangas