From: John Hudson (john@tiro.ca)
Date: Fri Feb 16 2007 - 15:01:38 CST
Lokesh Joshi wrote:
> Here's the Microsoft Thai OT spec. section about invalid combining marks:
> http://www.microsoft.com/typography/otfntdev/thaiot/shaping.aspx
> Therefore, I'm inclined to think that more relaxed checking is in order.
> This, unfortunately, will require a redesign of the Thai engine. Perhaps
> this should be done in conjunction w/ the work for Thai and Lao OpenType
> processing, and perhaps the generic mark checking. (Tickets 2382, 2386,
> 4740)
I dob't think that Thai OT spec is sufficiently recent to be used as a reliable reference
(note document date: February 2002). Most of the OT script-specific specs are acknowledged
by MS to be obsolete and in need of revision, since they do not necessarily reflect
current shaping engine behaviour. I know that the Thai engine in Uniscribe was revised for
the Office 2007 and Vista releases because I was testing it against some older fonts and
found that some of my older methods for kerning tall vowels off stacks were no longer
working, requiring updates to the fonts. [Note: I don't blame MS for this; the kerning
method I had used wasn't the most sensible, it just happened to work with the older
version of the shaping engine. The new method I came up with to work with the new engine
is a lot more robust.] I don't know if any of these changes relate specifically to
definition of invalid sequences.
John Hudson
-- Tiro Typeworks www.tiro.com Vancouver, BC tiro@tiro.com Do not begin to paddle unless you intend always to paddle. - St Jean de Brébeuf, instructions for missionaries, 1637
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