[HarfBuzz] 'calt' in Indic shaper

[Behdad Esfahbod]

[+harfbuzz]

On 13-08-06 06:12 AM, Jonathan Kew wrote:
> On 6/8/13 02:51, Behdad Esfahbod wrote:
>> On 13-08-05 05:55 PM, Jonathan Kew wrote:
>>>
>>> where we seem to be choosing an alternate form for U+0AAF that makes it look
>>> like it's ligated with the preceding U+0A9C, but I failed to find what feature
>>> is causing this.
>>
>> Looks to me like it's coming from a 'calt' lookup...  FeatureIndex=38,
>> Lookup=50, recursing into Lookup=155.  Disabling 'calt' inhibits it.  Looks
>> legit to me.  WDYT?
>>
> 
> Ah yes, thanks - I must've mis-followed an index somewhere on my first time
> through the GSUB.
> 
> So apparently Uniscribe isn't applying 'calt' by default in Gujarati. That
> kinda seems reasonable, given that the Indic specs refer to it as
> "Discretionary presentation forms", although it differs from Adobe's
> registration of the feature (targeted at cursive Latin fonts), which says it
> should be active by default.
> 
> In the interests of consistency with Uniscribe (and therefore to minimize
> surprises for font developers), I think we should probably remove it from the
> Indic shaper.

But it sounds like an interesting feature for font developers.  How about
other features that we apply that Uniscribe may not be applying?  clig, curs,
rclt?  But then again I see that the MS spec singles calt out.  I'll push this
out, but like to hear from John Hudson and other Indic font developers.

Cheers,
-- 
behdad
http://behdad.org/