[XeTeX] Contextual Ligature Problems with OT Tamil Font Converted to AAT

[Blake Wentworth]

Greetings,
I have recently been using Tamil fonts sold by the font developer Xenotype Technologies, which are conversions of OpenType fonts to AAT.  The aim was to allow me to use Tamil fonts other than the default InaiMathi font  with Mac OS X's keyboard driver for Tamil,  Murasu Anjal.  Initial use of these fonts led to none of the contextual ligatures appearing in my pdf document, though everything looked fine in the TeXShop front-end.  I have no real knowledge of font development, but include the workaround subsequently provided by Xenotype Technologies over the course of my correspondence with them, in the hope that this may help others or allow for a fix, if indeed a bug is at work.  I would be delighted to know where the source of the initial problem lies, if knowledgeable XeTeX users would be so kind as to help me.
With thanks, 
--Blake Wentworth

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Hi Blake,

I've got one more theory...the Tamil fonts contain both OpenType
tables and AAT (Mac) tables. It's possible that XeTeX is identifying
the font as an OpenType font (which it technically is) because it
finds those tables first and stops processing the font for native
tables. This was an issue when 10.5 was first released and Apple had
to modify the way the system identified fonts.

At any rate, it's worth a try so I've attached a copy of the Surya
font without the OpenType specific tables, leaving only the native
Mac tables. Before you try this out, be sure to remove the existing
version and maybe restart to force the font cache to reset, then
install the attached version.

[Note: I installed this latter font, and contextual ligatures then worked properly. Xenotype's response follows.]

Glad this worked! A little surprised that it hasn't been addressed already in XeTeX. Perhaps, if you have occasion to be in any of the XeTeX forums, you might be able to submit this as a bug and offer others this possible solution if they're running into the same problem.

However, there is a down side to not having those OpenType Tables in the fonts - though it may not matter to you - several applications can only work with OpenType tables, not the native Mac tables. Most notable are all of the Adobe applications.

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Yale University
Director, South Asian Language Program
South Asian Studies Council
Luce Hall, Suite 210
34 Hillhouse Ave
New Haven CT 06520-8206