[XeTeX] 'locl' feature with Arabic script

[Khaled Hosny]

On Tue, Jan 03, 2012 at 04:39:49PM +0000, Jonathan Kew wrote:
> On 3 Jan 2012, at 16:25, Khaled Hosny wrote:
> 
> > I don't get the 'locl' feature to work with Arabic script, the attached
> > sample should give diagonal dots not rounded ones (it does if processed
> > with luatex). 'locl' feature works just fine with Latin script in other
> > fonts.
> > 
> > Is this a XeTeX bug, feature or even a known limitation? The font might
> > be buggy off course (though it works with other OpenType engines as
> > well), but I want to be sure before putting much effort debugging the
> > font.
> 
> Known limitation of XeTeX (or rather, of the ICU layout engine
> implementation it's using).... the Arabic shaper doesn't support the
> 'locl' feature, sorry.

I see, that is what I suspected.

> (Note, btw, that 'locl' isn't mentioned in the MS spec for Arabic
> shaping, at
> http://www.microsoft.com/typography/otfntdev/arabicot/features.aspx.
> Nevertheless, I think it should be implemented.)

IIRC, this was stated as an oversight in some recent discussion over the
OpenType mailing list.

> As a possible workaround, you could implement language-specific
> variants of a supported feature such as 'ccmp' and include the
> appropriate localized-form substitutions there.

Good idea, I'll try that. Thanks :)

Regards,
 Khaled