[HarfBuzz] Lemongrass HarfBuzz Hackfest, end of day 4

[Shriramana Sharma]

On Mon, Jul 23, 2012 at 6:27 PM, Behdad Esfahbod <behdad at behdad.org> wrote:
> With HarfBuzz Indic shaper, our goal is to track Uniscribe shaping as closely
> as possible (while it makes sense).

Hi -- while I note your words within parans, I wonder why you have
chosen Uniscribe as the standard? Is it simply because it is widely
deployed? Despite MS's QA, there *might* be problems in Uniscribe's
rendering (I don't use Windows 7 so I'm not sure about its rendering)
-- in which case would the bug have to be fixed in Uniscribe first
before it can be done for HB? (Mind you, I'm just wondering here,
since I haven't actually run into such a sequence...)

> Jonathan, this is what's happening:
>
> Both Rachana and Raghu have 'half' lookups that subtitute C,H sequences with
> glyphs that are essentially ligatures of explicit halant on the consonant (not
> half forms really, from what I can see).  As such, our L-matra repositioning
> logic positions matras to the left of such glyphs.  In other words, since
> there is no explicit Halant glyph, matra is not repositioned.  This is exactly
> what the spec says, and works for Devanagari.  But Uniscribe seems to move it
> anyway.
>
> Is it the case that Malayalam does not have half forms?  If that is the case,
> that would explain, and we can adjust this.  What other scripts do not have
> half forms BTW?

FWIW, if by "half forms" you mean "C1-conjoining forms" (where in a
cluster C1 + Virama + C2, C2 remains as is and only C1 changes),
Malayalam does not have those. Previously the chillu-s (see the fag
end of the Malayalam code chart) were analysed as such, but no longer
since they were separately encoded. The dot reph is also functionally
a C1-conjoining form (in that it indicates a cluster-initial
consonant) but it is also encoded separately. So basically Malayalam
Unicode does not have any sequences C + Virama that map to a
conjoining form when followed by a consonant.

So it boils down to: if a Malayalam font is still providing mappings
for C + Virama (+ ZWJ) to chillu forms then it is not compliant with
current Unicode recommendations and should be fixed. Have you tested
with Lohit Malayalam?

(As for other scripts, Tamil also doesn't have any half-forms, but you
know that already.)

BTW I thought you were closing down the HB-Indic list?

-- 
Shriramana Sharma