[XeTeX] Incorrect Bengali ZWJ behavior and v2 script spec

[Yves Codet]

Hello.

I had forgotten about ZWJ when I tested Devanagari script, because it's not used in Sanskrit, but in Hindi it is. With the tag 'deva' selected, I get the same result as Ian-Mathew: the sequence "consonant + virama + consonant" is correctly rendered as a conjunct consonant, but the sequence "consonant + virama + ZWJ + consonant" is rendered the same way, instead of "half-form of the first consonant + second consonant".

Best wishes,

Yves

Le 18 mars 2013 à 16:13, Ian-Mathew Hornburg <imhornburg at gmail.com> a écrit :

> Hello, and thanks to Khaled and contributors for their great work on this project! I do work in Indic scripts, and XeTeX has been immensely helpful in setting them.
> 
> 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.
> 
> However, when passing the bng2 script to the fonts, they both fail to render correctly at all. I might guess that something’s going wrong because the font contains both versions of the script tag, and I don’t know what happens on the HarfBuzz side when selecting which script to use when shaping a font.
> 
> Thanks in advance for any assistance!
> 
> 
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