[HarfBuzz] Tai Tham / Lanna (iso15924="lana") shaping question

Andrew Cunningham lang.support at gmail.com
Wed May 23 15:48:21 PDT 2012

I think what Ed is saying is that Tai Tham follows a similar model to
Myanmar rather than a pure Indic model, where you have a distinct medials
vs subjoined consonants wher subjoined consonants require a virama and
medials don't

Par of a fundamental change between myanar in unicode 4.1 and 5.1

Will look at my sources to confirm for Tai Tham.


On Thursday, 24 May 2012, Behdad Esfahbod <behdad at behdad.org> wrote:
> Hi Thep,
> Humm, the message from Ed hat you are replying to never made it to me or
> the list.  Replies inline.
> On 05/23/2012 06:53 AM, Theppitak Karoonboonyanan wrote:
>> Hi, Ed, Behdad,
>> On Sun, May 20, 2012 at 3:45 AM, Ed Trager <ed.trager at gmail.com> wrote:
>>> On Fri, May 18, 2012 at 5:48 PM, Behdad Esfahbod <behdad at behdad.org>
>>>> On 05/18/2012 04:02 PM, Ed Trager wrote:
>>>>> In Tai Tham, U+1A6E VOWEL SIGN E needs to be shifted all the way to
>>>>> the left so that the final visual appearance would be:
>>>> Are you sure?  Without U+1A60 TAI THAM SIGN SAKOT before the subjoined
>>>> consonant?  Reading Unicode suggests that you need that sign betwee PA
and LA.
>>> For most subjoined consonants, yes, that's true.  But note in
>>> particular that U+1A56 MEDIAL LA and U+1A57 MEDIAL LA TANG LAI were
>>> encoded separately.  In the case of these two "LA" signs, I believe
>>> there are two reasons justifying the separate encoding:
>>> (1) These are variant forms of the same subjoined letter LA:
>>> apparently, there is no other good way to do it other than encoding
>>> both.
>>> (2) Both of these LA signs can be part of triple consonant clusters,
>>> i.e. "KLW" appears in the common word Thai / Tai word for banana,
>>> กล้วย, "klwy" .  In Tai Tham, both the L and the W appear as
>>> below-base stacked forms (and actually the "y" is also a subjoined
>>> form, but it's kind of hanging off the right side of the whole stack).
> I'm not questioning the separate encoding.  I don't care :-).  What I'm
> is that you need a SAKOT before them for them to be considered part of the
> same syllable according to the Indic OpenType spec and my implementation.
> Now, if you think Unicode intended these to subjoin without a SAKOT, then
> like you to point me to documentation about that.
> If that is the case, we would need changes to the Indic machine.  Not
> impossible, but I first want to make sure that it is indeed the case.
> behdad
>>> There are some other separately-encoded subjoining consonant signs:
>>> U+1A5B, U+1A5C, U+1A5D, U+1A5E.
>> Please also count U+1A55 (MEDIAL RA) in the rule, although it's not a
>> subjoined form.
>> Regards,
>> -Thep.
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Andrew Cunningham
Senior Project Manager, Research and Development
State Library of Victoria

andrewc at vicnet.net.au
lang.support at gmail.com
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