[HarfBuzz] Harfbuzz Sinhala (si) script support status update

[Harshula]

On Mon, 2012-07-23 at 02:36 +1000, Harshula wrote:
> Hi Behdad and Jonathan,
> 
> 1) I did a quick test of the latest commits. Basic Sinhala shaping seems
> to have improved for Bhashitha font (IIRC, the original version was for
> Windows) and gone backwards with GNU Free Font and LKLUG font.
> 
> The following file contains strings that represent the minimal shaping
> support required:
> http://git.savannah.gnu.org/cgit/sinhala.git/plain/patches/icu-sinhala-rendering.txt
> 
> This is how the output should look like:
> http://git.savannah.gnu.org/cgit/sinhala.git/plain/patches/icu-sinhala-rendering.png
> 
> FreeSerif font:
> http://ftp.gnu.org/gnu/freefont/freefont-ttf-20120503.zip
> 
> LKLUG font:
> http://sinhala.sourceforge.net/files/lklug.qa.ttf
> 
> Both Pango and ICU are able to shape the content of
> icu-sinhala-rendering.txt correctly using either FreeSerif or LKLUG
> fonts.

Here are more details about the problem. The new shaper renders කො
(ko) incorrectly with FreeSerif and LKLUG fonts but renders correctly
with Bhashitha font (IIRC, originated from Windows). The old shaper
renders the string correctly using all three fonts.

String: කො
Unicode Sequence: <U+0D9A,U+0DDC> (consonant + split dependent vowel)

<U+0DDC> = <U+0DD9><U+0DCF>

Using new shaper
----------------

Bhashitha:
 [uni0DD9=0+1091|uni0D9A=0+1744|uni0DCF=0+629]

FreeSerif:
 [e2_sinh=0+707|ka_sinh=0+915|o2_sinh=0+1308]

LKLUG:
 [uni0DD9=0+727|uni0D9A=0+913|uni0DDC=0+1329]

Using old shaper
----------------

Bhashitha:
 [uni0DD9=0+1091|uni0D9A=0+1744|uni0DCF=0+629]

FreeSerif:
 [e2_sinh=0+707|ka_sinh=0+915|aa2_sinh=0+336]

LKLUG:
 [uni0DD9=0+727|uni0D9A=0+913|uni0DCF=0+356]


NOTE: It appears LKLUG (using 'liga') and FreeSerif (using multiple
subs) construct U+0DDC from U+0DD9 and U+0DCF. However, Bhashitha
appears to deconstruct U+0DDC to form U+0DCF. I'm not good with font
rule construction, so it would be advisable for you to inspect the font
for accurate details.

Thanks again for adding the old shaper!!!

cya,
#