[HarfBuzz] Decomposition and soft dotted characters

[Denis Jacquerye]

Showing <U+0131, U+0308> instead of <U+0456, U+0308> is better, but
what do you do with <U+012F, U+0308> (with i-ogonek), <U+0268, U+0308>
(with i-bar) or even <U+2071, U+0308> (with superscript i). There’s a
point where fonts should just know better.

On Mon, Aug 5, 2013 at 3:33 AM, Khaled Hosny <khaledhosny at eglug.org> wrote:
> On Sun, Aug 04, 2013 at 05:54:46PM -0400, Behdad Esfahbod wrote:
>> On 13-08-04 03:15 PM, Khaled Hosny wrote:
>> > Hi All,
>> >
>> > This TeX.SE question[1] shows an “interesting” effect of decomposition
>> > and soft dotted characters; Gentium lacks ї (U+0457, CYRILLIC SMALL
>> > LETTER YI) so HarfBuzz decomposes it into і (U+0456) and U+0308 so we
>> > end up with three dots.
>> >
>> > Not sure what to do here though, but IMO unless the font has lookups to
>> > remove the soft dot,
>>
>> If the font has i and U+0308 but not rules to compose them, it's a font bug.
>> Avoiding the sequence is just working around a font bug that cannot be
>> detected (easily).
>
> Well, if the ‘dtls’ feature were part of the official OpenType registry
> and fonts were to implement it, it would have been a nice way to support
> soft dotting more systematically…
>
>> > such decomposition is wrong and should be avoided
>> > as it would just fool applications depending on HarfBuzz output to
>> > determine if font fallback is needed or not since, IMO, using a fallback
>> > font is better here.
>>
>> But then if the user has the i,U+0308 sequence they would hit the bug still
>> and there's no way to avoid that.
>
> Good point.
>
>> At any rate, something to reconsider if / when we add itemization support.
>> Right now we don't tell apps whether the font supports the sequence or not.
>> The app chooses the font and we just do our best at shaping with it.
>
> One could check the cmap to see if the font supports the code point or
> not (like Firefox does, AFAIK), but then he loses HarfBuzz’s fine
> grained composition/decomposition, which I’m trying to avoid. But for
> this particular case I’m convinced it is a font bug.
>
> Regards,
> Khaled
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-- 
Denis Moyogo Jacquerye
African Network for Localisation http://www.africanlocalisation.net/
Nkótá ya Kongó míbalé --- http://info-langues-congo.1sd.org/
DejaVu fonts --- http://www.dejavu-fonts.org/