[HarfBuzz] Thai below-base normalization

[Jonathan Kew]

On 21/1/14 03:56, Theppitak Karoonboonyanan wrote:
> Hi,
>
> I'm trying to typeset Patani Malay text using Thai script as guided by
> the Royal Institute, and I have some problems with Phinthu-
> modified consonants with below-base vowel combined.
>
> See the sample text captured from the book here:
>
> http://linux.thai.net/~thep/shots/20140121-patani-sample-marked.jpg

Interesting. Are there any cases (in Thai or other languages) where the 
Phinthu *is* written below the Sara-U or Sara-UU vowel?

The comment in hb-unicode-private.hh suggests that Uniscribe behaves the 
same as (current) harfbuzz here. There appear to be only two examples of 
this in our thai-wikipedia word list, but I just checked, and Uniscribe 
does indeed render the Phinthu dot *below* the vowel in both cases:
   <U+0E1B,U+0E3A,U+0E38,U+0E04,U+0E04,U+0E42,U+0E25>
and
   <U+0E28,U+0E23,U+0E32,U+0E27,U+0E3A,U+0E38,U+0E12,U+0E34>
Is this the correct rendering for those strings?

>
> The text is also attached as testbv.txt.
>
> With Harfbuzz 0.9.25, I get Phinthu (U+0E3A), the consonant
> modifier, below the vowel, not right below the consonant as
> expected:
>
> http://linux.thai.net/~thep/shots/20140121-patani-bv-before.png
>
> In hb-unicode-private.hh, the combining class for U+0E3A is
> modified from 103 to 3. I believe there must be some reason
> behind this, but it prevents some ethnic languages from being
> properly rendered. AFAIK, there are some other languages that
> create new consonants this way.
>
> I try reverting this (with the attached 01_thai-ccc.patch) and get
> the proper rendering:
>
> http://linux.thai.net/~thep/shots/20140121-patani-bv-after.png
>
> Is the change reasonable?
>
> In case you asked for the font I use, it's here:
>
> http://linux.thai.net/~thep/tmp/thai-ethnic/TTFGaruda.ttf
>
> Regards,
> -Thep.
>
>
>
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