bug#34035: 26.1; Arabic shadda-kasrah renders incorrectly

[Stephen Berman]

On Fri, 11 Jan 2019 12:34:12 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Cc: craven@gmx.net,  34035@debbugs.gnu.org
>> Date: Fri, 11 Jan 2019 10:47:11 +0100
>> 
>> > Please show the entire output of "C-x =" 
>> 
>> I assume you meant `C-u C-x ='
>> 
>> >                                          (I presume you invoke it on
>> > the position of sin?).
>> 
>> Yes.  Here's the output on master:
>> 
>> ==============================================================================
>>              position: 1 of 3 (0%), column: 0
>>             character: س‎ (displayed as س‎) (codepoint 1587, #o3063, #x633)
>>               charset: unicode (Unicode (ISO10646))
>> code point in charset: 0x0633
>>                script: arabic
>>                syntax: w     which means: word
>>              category: .:Base, R:Right-to-left (strong), b:Arabic
>>              to input: type "s" with arabic input method
>>           buffer code: #xD8 #xB3
>>             file code: #xD8 #xB3 (encoded by coding system utf-8-unix)
>>               display: composed to form "سِّ" (see below)
>> 
>> Composed with the following character(s) "ِّ" using this font:
>>   xft:-PfEd-DejaVu Sans-normal-normal-semicondensed-*-15-*-*-*-*-0-iso10646-1
>> by these glyphs:
>>   [0 2 1587 1377 16 0 16 6 4 nil]
>>   [0 2 0 6022 0 -15 -10 13 -11 [-16 2 0]]
>> 
>> Character code properties: customize what to show
>>   name: ARABIC LETTER SEEN
>>   general-category: Lo (Letter, Other)
>>   decomposition: (1587) ('س')
>> ==============================================================================
>
> This clearly says that Emacs uses DejaVu Sans for this grapheme
> cluster, so I wonder what does "switch the font to Symbola" mean in
> this case.  Can you tell what you did to switch to Symbola?

I started emacs with -Q, then I selected the "Set Default Font..." entry
from the Options menu, clicked on "Symbola Regular" and pressed the
select button.  After doing that, `C-u C-x =' on a character in
*scratch* shows this:

xft:-UFAS-Symbola-normal-normal-semicondensed-*-15-*-*-*-*-0-iso10646-1 (#x37)

I don't know why the Arabic character info is different, but the display
is correct with Symbola as default font, but not with DejaVu.

>> On the harfbuzz branch the output is the same except for the glyphs:
>> 
>>   [0 2 1587 6022 0 1 6 16 -8 [0 3 0]]
>>   [0 2 1587 1377 16 0 16 6 4 nil]
>> 
>> Note the second line here is identical to the first line of glyphs on
>> master.
>
> I would hardly call this "identical", since the offsets are also
> different.  But I don't think that matters at this point.

I don't know if it's significant, but it's only first glyph line from
the harfbuzz build:
[0 2 1587 6022 0 1 6 16 -8 [0 3 0]]
that differs from the second glyph line from the master build:
[0 2 0 6022 0 -15 -10 13 -11 [-16 2 0]]
The second glyph line from the harfbuzz build:
[0 2 1587 1377 16 0 16 6 4 nil]
is identical to the first glyph line from the master build:
[0 2 1587 1377 16 0 16 6 4 nil]

Steve Berman