Apparently if there is C,V,ZWJ,C, the first C will be base, but if
it's C,ZWJ,V,C, the second one will be.
Note that Uniscribe implements this differently, by breaking syllable in
the case of C,ZWJ,V,C and putting the first consonant in one syllable
and the rest in the next syllable.
Sinhala failures down from 208 to 158 (0.0581209%). No changes to
Khmer.
Sinhala does not have half forms. And most (all?) consonants can be
base, except when preceded by ZWJ, which would request a subjoined form.
Hence switch the base algorithm to categorize with Khmer, start search
at start, and stop at a ZWJ.
Also, mark all pos=base consonants after base to be subjoined. Mark
base itself to have pos=base.
Finally, adjust Sinhala's reph position to after-main.
Brings down Sinhala failures from 455 to 328 (0.120656%).
If, say, a H,ZWJ,C ligature was formed, we don't want the code to detec
that as a Halant. So, ignore ligatures when matching category in
final_reordering.
Sinhala failures down from 514 to 455 (0.167374%).
In Sinhala, Rakar is formed by Al-Lakuna,ZWJ,Ra. If you put that at the
end of a Consonant,Matra syllable, you get a dotted-circle from
Uniscribe. Apparently adding a ZWJ before the Al-Lakuna "fixes" that.
And people have been encoding that sequence... So, allow a forced
"ZWJ,Virama,ZWJ,Ra" sequence at the of syllables.
Fixes some 100 or more of Sinhala failures. Now at 622 only (0.23%).
POS_BASE can disappear if base ligated backward. Define base as last
with position not after base.
Fixes a few hundred of Sinhala failures with Iskoola Pota.
Normally, we attach the Halant to the previous character and move it
with it. For after-base consonants however, the Halant "belongs" to the
consonant after, so attach it so.
This fixes Bengali sequences involving post-base consonant Ya, which
should ligate with the Halant to form Ya Phala, but previously a
reordered matras was blocking the ligation.
Seems like this is what Uniscribe is doing, and does not break any fonts
we tested (with Devanagari, Malayalam, Khmer, and Bengali), while fixing
some Ra Phala sequences for Bengali with Vrinda. Fixes another 2% of
Bengali failures (a couple more to go).
The spec says: "[{M}+[N]+[H]]", and that's what Uniscribe implements.
We instead do: "{M+[N]+[H]}", which means we allow Nukta and Halant
after all Matras, not just the last one. It makes more sense.
In the case of Consonant,LeftMatra,Halant, Uniscribe leaves the Halant
where it is, but we want to move it with the Matra as that makes more
logical sense.
U+0985 BENGALI LETTER A followed by U+09D7 BENGALI AU LENGTH MARK.
According to Bobby de Vos on the mailing list, this results in a dotted
circle with most shaping engines, but is a legitimate sequence in this
minority language.
We reached the consensus on the list to NOT implement dotted-circle
in HarfBuzz.
Behdad Esfahbod