[HarfBuzz] Regression with ZWJ in Indic scripts

[Khaled Hosny]

I was doing something like:

  script = hb_script_from_string (engine->script, -1)
  language = hb_language_from_string (engine->language, -1)
  hb_buffer_set_script (buffer, script)
  hb_buffer_set_language (buffer, language)

But this didn’t work for, say, ‘bng2’ script, now I understand that the
_from_string() functions take ISO tags, so now I do something like:

  script = hb_ot_tag_to_script (hb_tag_from_string (engine->script, -1));
  language = hb_ot_tag_to_language (hb_tag_from_string (engine->language, -1));

since users of XeTeX are expected to pass OpenType script and language
tags (macro package can provide user friendly names). Now I’m not sure
if passing version 1/version 2 tags for Indic scripts really make
HaarfBuzz use them, or there is some internal magic to do the right
thing, I was about to ask :)

Regards,
Khaled

On Tue, Mar 19, 2013 at 05:56:22AM -0400, Behdad Esfahbod wrote:
> BTW, how do you pass OpenType script tag to HarfBuzz?!
> 
> On 13-03-18 03:15 PM, Khaled Hosny wrote:
> > The issue reported below seems to be a regression in 0.9.13, basically
> > ZWJ seems to be completely ignored, with 0.9.12 I get the desired
> > output.
> > 
> > Regards,
> > Khaled
> > 
> > ----- Forwarded message from Ian-Mathew Hornburg <imhornburg at gmail.com> -----
> > 
> > From: Ian-Mathew Hornburg <imhornburg at gmail.com>
> > To: xetex at tug.org
> > Subject: [XeTeX] Incorrect Bengali ZWJ behavior and v2 script spec
> > Reply-To: Unicode-based TeX for Mac OS X and other platforms <xetex at tug.org>
> > 
> > I may have identified two possible bugs in 0.9999.0: the release notes
> > indicate that the version-2 OpenType Indic script tags are now supported,
> > and I’ve been testing various Bengali-script fonts with the git version of
> > XeTeX and a current install of TeX Live 2012 to check them for correct
> > shaping behavior. I’ve posted a MWE reproducing some examples from the
> > Microsoft standard here: [http://pastebin.com/mgAX8c7U].
> > 
> > Microsoft ships two Bengali fonts (Vrinda and Shonar Bangla; both v6.80)
> > with Windows 8 that support both the older (beng) and newer (bng2) Bengali
> > script specs. (Older versions of each are shipped with Windows 7 and other
> > Microsoft products.) The fonts behave correctly when using the beng script
> > feature, with the exception of a particular ZWJ sequence: the Microsoft
> > spec [https://www.microsoft.com/typography/OpenTypeDev/bengali/intro.htm]
> > says that the sequence of consonant-hasant-ZWJ-consonant should prevent a
> > ligature of the two consonants, then render a half-form of the first
> > consonant. XeTeX currently fails to suppress the ligature.
> > 
> > ----- End forwarded message -----
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> > 
> 
> -- 
> behdad
> http://behdad.org/