[HarfBuzz] Tai Tham NGA, SAKOT is not Kinzi

[Theppitak Karoonboonyanan]

On Thu, May 2, 2013 at 2:28 AM, Richard Wordingham
<richard.wordingham at ntlworld.com> wrote:
> On Wed, 1 May 2013 15:50:54 +0700
> Theppitak Karoonboonyanan <thep at linux.thai.net> wrote:
>
>> On Wed, May 1, 2013 at 2:39 PM, Richard Wordingham
>> <richard.wordingham at ntlworld.com> wrote:
>
>> > (b) That word is not a problem for a Tai Khuen font.  How should a
>> > Lao Tham font handle it?
>
>> No need to handle it, because Mai Kang Lai is not that heavily used
>> in Lao Tham. It should rather be spelt as ᩋᩢ᩠ᨦᨠᩕᩥ᩠ᩈ instead.
>
> That depends on whether one expects to have to choose the font
> according to the spelling habits of the font.  I would hope a font
> could handle all the languages, though of cause it need not be beautiful
> for all languages.

I've just recalled a style in a book, which has been mimicked in the
attached image for "ᨸᩩᩕᩥᩈᩮᩣ" (puriso) in the first line. (I can take a photo
of the evidence if you like.)

So, I can imagine the rendering style for "ᩋᩘᨠᩕᩥ᩠ᩈ" as in the second line.

>> >  How would it handle the Pali word _sankilesa_
>> > spelt with MAI KANG LAI - I would expect text written for a Tai
>> > Khuen font to use MAI KANG LAI.
>>
>> The conflict like this is usually avoided in Lao Tham manuscripts by
>> using alternative spelling, probably ᩈᨦ᩠ᨠᩥᩃᩮᩈ. (I haven't found a real
>> sample of this yet,
>> just imply it from the tendency of other cases.)
>
> That is what I would expect - but see my comment above.  Possibly a Lao
> Tham font could protect itself by adding GSUB rules such as
>
> <KA, MAI KANG LAI> becomes <NGA, <SAKOT KA>> before SIGN I, though
> the rearrangement is not nice.  Perhaps the solution for a Lao Tham font
> is a special <KA, MAI KANG LAI> ligature that looks very like <NGA,
> SAKOT,
> KA>.

Or just cram the two marks into one column. It's already needed for the
word "ᩈᩘᨥᩴ" (sangkhang).

>> > (i) ᩁᩘᩈᩦ <RA, MAI KANG LAI, SA, SIGN II> 'ray of light'
>> > (ii) ᩈᩘᨠᩕᩣᨶ᩠ᨲᩴ <HIGH SA, MAI KANG LAI, HIGH KA, MEDIAL RA, AA, NA,
>> > SAKOT, HIGH TA, RA HAAM> 'songkran'
>
>> So, the question is for Lanna. Do such spellings exist, and how are
>> they handled? If they exist, yes, the rendering engine 'must' handle
>> it.
>
> The problem with handling the differences when reordering is that Lao
> Tham reorders <MAI KANG LAI, HIGH KA, MEDIAL RA>, but the MFL style
> does not.  This gives us at least three different reordering behaviours.

Three? Shift, no shift, and what else?

> As to whether these spellings exist, I wish I had manuscript evidence.
>
>> >  I'm still some way
>> > from being ready to test the ability of GPOS to undo shaping.  The
>> > sort of GPOS rule I have in mind is:
>
>> > Context (lookup type 7): consonant consonant <MAI KANG LAI>
>> > Lookup for context: At position 0, mark to base (lookup type 4),
>> > skipping bases and other marks, to position MAI KANG LAI on the
>> > consonant.
>
>> > In example (i) above, rearrangement would deliver <g(RA), g(SA),
>> > g(MAI KANG LAI), g(SIGN II)>, and we need to be able to attach MAI
>> > KANG LAI to RA.  I don't know if this sort of rule works.
>>
>> I think having the rendering engine do it should be simpler.
>
> The problem is that the reordering logic is not very flexible.  We may
> need GPOS rules to handle the exceptions that vary from style to style.

Gotta check this. It's beyond my knowledge.

Regards,
--
Theppitak Karoonboonyanan
http://linux.thai.net/~thep/
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