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

[Khaled Hosny]

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.

You can simply access Graphite features by their labels in this case:

 \font\lowfont="Gentium Plus/GR:Low-profile diacritics=1"

This will, hopefully, be fixed for next XeTeX.

Regards,
Khaled