[HarfBuzz] Malayalam [was: Lemongrass HarfBuzz Hackfest, end of day 4]

[Jonathan Kew]

On 23/7/12 13:57, Behdad Esfahbod wrote:
>
> Also noticed that post-base 'LA' is not correctly rendered for 'സ്പ്ലേ'.
> This one is more interesting.  And we differ from Uniscribe, and I see why.
>
> 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?
>

AFAIK, Malayalam doesn't have half forms (although it does have a bunch 
of possible ligated conjunct forms). So perhaps it's appropriate to 
position the left-matra after "half" forms (that are really composites 
of consonant with visible halant [candrakala] form). That's also what 
seems to be happening with the Rachana font under Apple's Core Text 
shaper, FWIW.

Another issue to check is the handling of a sequence with vowel-matra 
followed by virama, such as <U+0D38,0D41,0D4D>. I notice that we differ 
from Core Text on this one (using the Lohit Malayalam font) - our shaper 
appears to use a ligature of the u-matra and virama, whereas Core Text 
doesn't ligate them. I haven't tried Uniscribe yet to see what it gives.

JK