[HarfBuzz] Shaping Thai text

[Theppitak Karoonboonyanan]

Oops. Forgot to Cc: list.

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

On Thu, Feb 3, 2011 at 2:35 PM, Theppitak Karoonboonyanan
<thep at linux.thai.net> wrote:
> On Thu, Feb 3, 2011 at 1:39 PM, Peter Hunter <phunter at atex.com> wrote:
>> I'm using Harfbuzz (not Harfbuzz-ng) for shaping Thai text (using HB_BasicShape/HB_HeuristicPosition)
>>
>> Not being familiar with the Thai language, I've been told that the vowels/marks are positioned "too high", (particularly compared to MS wordPad/Notepad)
>> At least with the fonts I have access to, the vowels/marks are already configured to an appropriate height for most situations and do not require the extra adjustment provided in "positionCluster"
>>
>> Disabling the extra adjustment however causes a problem with the positioning of the combining above marks when used in conjunction with 0xe1b,0xe1d,0xe1f characters( PO PLA, PO FA and PO FAN). (These characters all have a trailing vertical stem that overlaps the combining above marks when left at their default position)
>> In wordpad/notepad these marks are left at their design height, but positioned left aligned with the base character.
>> (The fonts appear to have been designed for this situation, but I don't know if that is true for Thai fonts in general)
>
> I also see this weird rendering on Qt applications, and confirm that this is
> considered sub-optimal typography. Pango, on the other hand, positions
> the glyphs more elegantly, either by the aids of PUA glyphs or OpenType
> GPOS feature.
>
> (The PUA solution is still retained for compatibility with Windows, where
> the lack of OpenType feature is a norm for Thai fonts, so users can still
> use fonts designed for Windows on it.)
>
>> So, I'd like to know if this issue has been resolved in "-ng" or if anyone else has experienced and/or resolved this problem
>
> I wonder how to test HarfBuzz-ng per se to find it out. To my understanding,
> HarfBuzz-ng is being used in Pango, but the shaping engine which
> provides the proper positioning is in Pango layer, not HarfBuzz-ng.
>
> Regards,
> --
> Theppitak Karoonboonyanan
> http://linux.thai.net/~thep/
>