[XeTeX] Incorrect rendering of Vedic Sanskrit accents

[Zdenek Wagner]

2015-05-22 21:14 GMT+02:00 David M. Jones <dmj at dmj.ams.org>:
> Mike Maxwell's original post hasn't shown up here yet, so I'm lumping
> two responses together.
>
>> Date: Fri, 22 May 2015 12:24:49 -0600
>> From: Bobby de Vos <devos.bobby at gmail.com>
>> Reply-To: "XeTeX (Unicode-based TeX) discussion." <xetex at tug.org>
>>
>> On 2015-05-22 10:49, maxwell wrote:
>> > On 2015-05-22 10:14, David M. Jones wrote:
>> >> ...
>> >> P.S. There's actually a third class of bug that is clearly visible in
>> >> the table at the top of my document, but which I didn't mention
>> >> explicitly: XeTeX won't typeset one of the Devanagari combining
>> >> characters in isolation without adding a prothetic dotted circle
>> >> (U+25CC).
>> >
>> > I was waiting for someone who knows more about this than I do to
>> > answer, but I'll display my ignorance.
>> >
>> > Afaik that's not a bug, that's the way combining characters are
>> > *supposed* to render when they don't have any character to combine
>
> This is, I think, debatable, as shown by the fact that XeTeX does
> *not* add the dotted circle for any of the combining diacritical in
> the 0300 block, and LuaTeX doesn't add them for the Devanagari marks.
> So at the very least, this is a matter of consistency.
>
The requirement of the Indic specification is to display the dotted
circle if the mark cannot be combined. HarfBuzz implements correctly
the specification and XeTeX makes use of HarfBuzz. Luatex breaks the
specification but the bug is not considered as serious as the fix is
needed. It is possible that it will remain in LuaTeX forever,
although, strictly speaking, i is a bug.

>> > with.  There's a way to prevent that; I _think_ it's to precede the
>> > combining character by a non-breaking space (U+00A0).  But I haven't
>> > tried that.
>
> You're correct: that is the suggested Unicode coding and it does in
> fact work. (I thought I tried it before and it didn't work, but either
> I'm misremembering or it was before I upgraded to the latest XeTeX.)
>
>> Some minority languages (that is, not the dominate language using a
>> particular script) often use combining marks in ways not envisioned in
>> order to extend the script to cover all the sounds in the minority
>> language. So for those minority languages, having a dotted circle show
>> up is not very helpful.
>
> Arguably, it never is -- if you want a dotted circle, you can add it
> yourself, whereas it's not at all unusual to want to show combining
> marks in isolation in, say, textbooks.
>
> But I admit this is an edge case, which is probabably why I decided
> against drawing attention to it in my original sourceforge bug report.
> I wish I had stuck to my earlier resolve.
>
> Cheers,
> David.
>
>> Bobby
>>
>> --
>> Bobby de Vos
>> /devos.bobby at gmail.com/
>>

Zdeněk Wagner
http://hroch486.icpf.cas.cz/wagner/
http://icebearsoft.euweb.cz



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