[XeTeX] Graphite font feature changes in Gentium Plus and XeTeX

[Khaled Hosny]

On Sun, Jan 06, 2013 at 09:53:50AM -0500, Alan Munn wrote:
> On Jan 6, 2013, at 4:53 AM, Khaled Hosny wrote:
> 
> > On Sat, Jan 05, 2013 at 05:13:56PM -0500, Alan Munn wrote:
> >> Hi everyone. 
> >> 
> >> The most recent version of the Gentium font
> >> http://scripts.sil.org/cms/scripts/page.php?site_id=nrsi&id=Gentium_download
> >> has changed from numeric feature IDs to alpha feature IDs.  However,
> >> XeTeX does not seem to be able to deal with the new alpha IDs, instead
> >> converts them into huge numeric IDs instead.
> >> 
> >> Attached is a modified version of aat-info.tex adjusted to show use
> >> the Graphite renderer. When run with the old version of Gentium Plus
> >> (1.504) it correctly reports the 4 digit ID codes.  For example, the
> >> low profile diacritics ID used to be 1054.
> >> 
> >> When run with the new version of Gentium (1.510) it reports different
> >> numbers.  Now the low profile diacritic ID should be 'lopr' but XeTeX
> >> thinks it's 1819242610.
> > 
> > The alpha numeric features id are represented internally as unsigned
> > integers, is 1819242610 is (('l'<<24)|('o'<<16)|('p'<<8)|'r'), and since
> > such tags were not used when XeTeX got its Graphite support, it simply
> > returns the integer value.
> 
> Hi Khaled, that's what I suspected.
>  
> > 
> > You can simply access Graphite features by their labels in this case:
> > 
> > \font\lowfont="Gentium Plus/GR:Low-profile diacritics=1"
> 
>  That doesn't seem to work, however:

Sorry it should be “True” not “1” or whatever the string printed by
\XeTeXselectorname. BTW, the Gentium Plus documentation suggests “High
angle” and “Low angle”, but that is incorrect.

Development version of XeTeX already supports alpha numeric tags for
Graphite, and they are treated like OpenType tags. But I’m not sure how
to handle the \XeTeXfeaturecode here, may be it is possible to convert
the integer tag to string with some black TeX macro magic, but I
wouldn’t know.

Regards,
Khaled