[HarfBuzz] Language-specific forms in Scheherazade [was: Fwd: Re: Questions regarding hb_language_t]

Jonathan Kew jfkthame at googlemail.com
Mon Dec 16 23:52:54 PST 2013

On 16/12/13 15:21, Bob Hallissy wrote:

>> Looking briefly at the GSUB lookups, I don't see the language-specific
>> lookups I'd expect. In the 1.x font, it looks like we handled this
>> within the 'calt' feature (which is a little odd - I'd have expected
>> it in 'locl' - but perhaps we had a good reason for it at the time, I
>> forget).
> The good reason is that, at least at the time, MS shaper for Arabic
> didn't process locl.  And it still isn't listed as one of the features
> supported by their shaper in
> http://www.microsoft.com/typography/OpenTypeDev/arabic/intro.htm. Anyone
> know differently?

OK, that makes sense. It occurred to me after I sent the message that 
perhaps this was why we did it like that.

(Of course, even if they updated this in a new Windows version, you'd 
need to handle the forms in another feature if you want it to work for 
users on old OSes such as WinXP, where I doubt MS is pushing out many 
usp10 updates.)

> On this subject: I would have expected language-specific forms to work
> with Graphite rendering since the language table therein appears to work
> (at least it does with WorldPad -- admittedly using the old Graphite
> engine):

The language tags in my testcase were wrong, sorry. Should be "ur" and 
"sd" respectively. With those fixed, I get the expected lang-specific 
forms in Firefox Nightly using Graphite.


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