[HarfBuzz] Tai Tham NGA, SAKOT is not Kinzi

[Richard Wordingham]

On Wed, 3 Apr 2013 11:01:48 +0700
Theppitak Karoonboonyanan <thep at linux.thai.net> wrote:

> On Wed, Apr 3, 2013 at 4:53 AM, Richard Wordingham
> <richard.wordingham at ntlworld.com> wrote:
> > On 7 January 2013, Behdad Esfahbod replied to Theppitak
> > Karoonboonyaan:
> >
> >>> - Final NGA (U+1A59) with virama following is not reordered after
> >>>   the next base consonant (at the end of line 4).

> So, my proposal for Lao Tham is to apply above rule with U+1A58
> instead.

Of course, this rule should not be applied for Tai Khuen, at least, not
for the modern style.

> And Lao Tham fonts can then provide two identical glyphs for U+1A58
> and U+1A59, with only the former affected by the rule.
 
> > A noteworthy example is Northern Thai _tanglai_ <LOW TA, MAI KANG
> > LAI, SIGN LA, AA, SAKOT, YA> 'all', 'many', where MAI KANG LAI
> > almost always starts above the initial consonant.  This may be
> > because SIGN LA is part of the same syllable as LOW TA.  The
> > textbook showing it between consonants shows it, in this case,
> > between SIGN LA and the vowel AA.

Correction: For SIGN LA, read SAKOT, LA.

> > Is there a problem with supporting this variety in positioning?
 
> Can it be distinguished with the presence of following SAKOT?
 
> For example:
 
> <SA, MAI KANG LAI, LOW KHA, VOWEL E, VOWEL AA>
> = MAI KANG LAI above SA
 
> <SA, MAI KANG LAI, SAKOT, LOW KHA, VOWEL E, VOWEL AA>
> = MAI KANG LAI above LOW KHA

I believe a Tai Khuen font would render them as:

1) SA, MAI KANG LAI, E, LOG KHA, AA
2) E, SA.KHA, MAI KANG LAI, AA

where SA.KHA is a vertical stack.

Also note that _tanglai_ is <LOW TA, MAI KANG LAI, SAKOT, LA, AA,
SAKOT, YA>, but the LA is subscript.  (I should have typed it first and
then written out the code points.  It might exist with SIGN LA instead
of SAKOT, LA, but I haven't noticed it written that way.)

So that idea would not work.

I'm not sure that we should be encoding writings with MAI KANG LAI
on the first and on the second consonant differently any more than
we encode _dam_ differently depending on whether the MAI KANG is
written on the DA or the AA.  In either case, we encode it <DA, AA, MAI
KANG> and leave it to the renderer to decide, do we not?  (Obviously
the position is significant in contractions like boomaa <BA, MAI KANG,
TONE-1, SAKOT, MA, AA>.)  I must admit I had thought that a shaper
would have problems with words like _tam_ <TA, TONE-1, AA, MAI KANG>
(optionally swapping TONE-1 and MAI KANG) and would need special
processing for words like _luup_ <RA, UU, SAKOT, BA>, which looks just
like the Sanskrit fragment <RA, SAKOT, BA, UU>.  

Richard.