[HarfBuzz] Tai Tham NGA, SAKOT is not Kinzi

[Richard Wordingham]

On Thu, 4 Apr 2013 13:10:53 +0700
Theppitak Karoonboonyanan <thep at linux.thai.net> wrote:

> On Thu, Apr 4, 2013 at 1:10 AM, Richard Wordingham
> <richard.wordingham at ntlworld.com> wrote:
> > 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:

> Is that recommended by Unicode? Why using <SAKOT, LA> when
> MEDIAL LA is available? Especially for Lao Tham, there are two
> variants of MEDIAL LA (U+1A56 SIGN MEDIAL LA, and the other similar to
> U+1A57 SIGN LA TANG LAI). So, one should be explicit which one to use,
> the situation similar to U+1A63 VOWEL AA and U+1A64 VOWEL TALL AA.

MEDIAL LA and LA TANG LAI are given in the code charts.  L2/07-007 give
the form of <SAKOT, LA>.  It is very similar to LA TANG LA, but without
the horizontal cross-piece.  Words with 'ho nam' are very variable
between <HIGH HA, SAKOT, LA> and <HIGH HA, MEDIAL LA>.

> Now I wonder how far MAI KANG & MAI KANG LAI is shifted to the left in
> Khuen/Lanna.

In Tai Khuen, or at least, printed material, MAI KANG LAI is placed
between the two consonants.  The typeset course notes from Wat Suan Dok
(Chiang Mai, Northern Thai) clearly show it on the first base consonant.

> For Lao Tham, the shift is not as far as the position on "boomaa".
> It's just shifted at most to the middle between the consonant and
> vowel AA. But for "booma", it's centered right above BA.

That's what I've seen a lot of in Northern Thai.  However, material that
has been written using a computer font (I don't about mechanical
printing) has <AA, MAI KANG> that looks like THAI CHARACTER SARA AM in
so far as the position of the MAI KANG is considered.  I think of that
as a Bangkok style.  A relevant divide is what happens to the tone
mark - does it stay on the middle of the consonant, or does it join the
mai kang?  When searching a document for examples, one sees just how
large a proportion of the cases in Thai are the word น้ำ 'water', but
this word is no use as an example in Tai Tham because NA and AA merge
and MAI KANG and TONE-2 then naturally occur together.  Fortunately,
whether the tone mark goes after or above MAI KANG is naturally handled
by GPOS.

> The former, if it's really to be done for Tham, is similar to the
> case of Thai SARA AM (U+0E33), which has already been handled by
> rendering engines.

The problem is not in doing the rearrangement of <HIGH TA, TONE-1, AA,
MAI KANG> to <HIGH TA, MAI KANG, TONE-1, AA>; it is that it is wanted
for some styles but not for others.  There is also the complication that
<NA, TONE-2, AA, MAI KANG> needs to be rearranged in all styles so
that TONE-2 may be placed on or to the right of MAI KANG.

The SEA shaper appears not to handle it.  Unfortunately, I'm finding it
hard to see what the HarfBuzz shaper does just from reading the code. 

Richard.