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

[Alan Munn]

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.

For sample images of the output see this StackExchange question where the issue was first raised: http://tex.stackexchange.com/q/89352/2693

Here's a small plain TeX document which shows that the new numbers are accessible, but the alpha codes are not: (I've done this in plain TeX because of a current bug in fontspec that makes the Graphite renderer inaccessible.)

-Alan

% !TEX TS-program = XeTeX
% This document assumes version 1.510 of Gentium Plus
% This command should work, but doesn't
\font\lowalpha="Gentium Plus/GR:lopr=1" at 12 pt
% These commands work instead
\font\lowfont="Gentium Plus/GR:1819242610=1" at 12 pt
\font\regfont="Gentium Plus/GR:1819242610=0" at 12 pt

\lowalpha má \qquad should have low profile diacritic

\lowfont má \qquad has low profile diacritic

\regfont má \qquad has regular profile diacritic

 
\bye

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-- 
Alan Munn
amunn at gmx.com