[HarfBuzz] Discovering 'vert' feature

[Konstantin Ritt]

Let's maybe not add some hacky workaround for broken/buggy fonts?

Anyways, I like Jonathan's proposition (I was proposing quite similar patch
something like a year ago); if it solves the described issue w/o additional
hacks, here is yeat another +1 from me.

Regards,
Konstantin

2014-10-10 12:46 GMT+04:00 Jonathan Kew <jfkthame at gmail.com>:

> On 10/10/14 02:12, Behdad Esfahbod wrote:
>
>> I'm helping Dominik port Chrome's vertical text support to HarfBuzz, and
>> we've
>> hit a buggy font in Windows, that we need to work around.
>>
>> "SimSun" on Windows 7, only declares the 'vert' feature under script
>> 'hani'
>> (fine) language-system "CHN ".  No tag maps to "CHN ".  It's a font bug.
>>
>> In Windows 8 family, someone **tried** to fix it.  They tweaked the
>> features
>> until it worked for them.  So it has the 'vert' feature for script
>> 'hani', now
>> in language system "ZHS " as well as "CHN ", but also for script 'latn' as
>> default language-system.  So now, if the itemizer failed to mark the
>> correct
>> script, HarfBuzz tries 'latn' and gets the right feature.  But if it looks
>> under 'hani' but there's no language tag, it still fails.
>>
>> So, I'm tempted to try this fixup: if feature is 'vert', and we found no
>> feature, then walk the feature list and enable the first feature found
>> that
>> has tag 'vert'.
>>
>> How does that sound?
>>
>> https://github.com/behdad/harfbuzz/issues/63
>>
>>
> Sounds like it would probably work, but this makes me really uneasy - it's
> too much of a hack. Yuck.
>
> Here's a proposal for an alternative fixup that *maybe* feels more
> acceptable to me (maybe, because I haven't thought about it for very long,
> and perhaps it's just as hackish really):
>
> If the script we're using has no matching langSys for the buffer's
> language, and if there's also no default langSys defined, then look for the
> "typical" language system(s) for the script (e.g. ENG for 'latn') -
> allowing this to be a list of tags, so that for 'hani', for instance, we
> could list ZHS, ZHT, JAN ... and we could append the unofficial CHN here.
>
> So we'd need to have a mapping of script tag -> langSys tag(s), often just
> one "prototypical" language that uses the script, but sometimes several
> candidates. This would address the comparable issue of a font that (for
> example) provides features only under arab/ARA (or deva/HIN), and is
> presented with text tagged as Persian (or Nepali)... ISTM it'd be better to
> use the Arabic- (or Hindi-) language features here than to fail altogether.
>
> (This is obviously related, though not identical, to the idea of Pango's
> pango_script_get_sample_language function.)
>
> WDYT?
>
>
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