After the Ngapi hackfest work, we were assuming that fonts
won't use presentation features to choose specific forms
(eg. conjuncts). As such, we were using auto-joiner behavior
for such features. It proved to be troublesome as many fonts
used presentation forms ('pres') for example to form conjuncts,
which need to be disabled when a ZWJ is inserted.
Two examples:
U+0D2F,U+200D,U+0D4D,U+0D2F with kartika.ttf
U+0995,U+09CD,U+200D,U+09B7 with vrinda.ttf
What we do now is to never do magic to ZWJ during GSUB's main input
match for Indic-style shapers. Note that backtrack/lookahead are still
matched liberally, as is GPOS. This seems to be an acceptable
compromise.
As to the bug that initially started this work, that one needs to
be fixed differently:
Bug 58714 - Kannada u+0cb0 u+200d u+0ccd u+0c95 u+0cbe does not
provide same results as Windows8
https://bugs.freedesktop.org/show_bug.cgi?id=58714
New numbers:
BENGALI: 353689 out of 354188 tests passed. 499 failed (0.140886%)
DEVANAGARI: 707305 out of 707394 tests passed. 89 failed (0.0125814%)
GUJARATI: 366349 out of 366457 tests passed. 108 failed (0.0294714%)
GURMUKHI: 60706 out of 60747 tests passed. 41 failed (0.067493%)
KANNADA: 951030 out of 951913 tests passed. 883 failed (0.0927606%)
KHMER: 299070 out of 299124 tests passed. 54 failed (0.0180527%)
LAO: 53611 out of 53644 tests passed. 33 failed (0.0615167%)
MALAYALAM: 1048102 out of 1048334 tests passed. 232 failed (0.0221304%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271666 out of 271847 tests passed. 181 failed (0.0665816%)
TAMIL: 1091753 out of 1091754 tests passed. 1 failed (9.15957e-05%)
TELUGU: 970555 out of 970573 tests passed. 18 failed (0.00185457%)
TIBETAN: 208469 out of 208469 tests passed. 0 failed (0%)
Ouch, how did things ever work without this?! The added test that has a
dot-reph as well as a pre-base reordering Ra perfectly demonstrates the
bug (tested with Nirmala font from Win8 for example). Testing suggests
that Win8 shaper has the *exact* same bug / behavior that we used to
have. Odd.
With FreeSerif, it seems that the 'ccmp' feature does ligature
substituttions. That was then causing syllable match failures. We now
find syllables before any features have been applied.
Test sequence: U+0D9A,U+0DCA,U+200D,U+0DBB,U+0DCF
The d1d69ec52e change broke Kannada badly,
since it was ligating consonants, pushing matra out, and then ligating
with the matra. Adjust for that. See comments.
This commit: a3313e5400 broke MarkMarkPos
when one of the marks itself is a ligature. That regressed 26 Tibetan
tests (up from zero!). Fix that. Tibetan back to zero.
The font is forming a post-base consonant in some samples, and Uniscribe
positions top matra on the post-base. Do the same.
Gurmukhi failures down from 59 to 41 (0.0674242%).
Uniscribe is buggy and sometimes /eats/ a mark next to a non-joiner.
Most of Malayalam failures where actually hitting this bug.
Ignore test output with two zero-width space glyphs. This is a hack
until we build up the test suite infrastructure better.
Bengali went down by 9, Devanagari by 2, Kannada by 130, Malayalm down
from 1197 to 307, Sinhala down by 16, Telugu down by 26. New stats:
BENGALI: 353996 out of 354285 tests passed. 289 failed (0.0815727%)
DEVANAGARI: 693573 out of 693628 tests passed. 55 failed (0.00792932%)
GUJARATI: 366489 out of 366506 tests passed. 17 failed (0.0046384%)
GURMUKHI: 60750 out of 60809 tests passed. 59 failed (0.0970251%)
KANNADA: 951086 out of 951913 tests passed. 827 failed (0.0868777%)
KHMER: 299094 out of 299124 tests passed. 30 failed (0.0100293%)
MALAYALAM: 1048109 out of 1048416 tests passed. 307 failed (0.0292823%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271715 out of 271847 tests passed. 132 failed (0.0485567%)
TAMIL: 1091837 out of 1091837 tests passed. 0 failed (0%)
TELUGU: 970550 out of 970573 tests passed. 23 failed (0.00236973%)
Just put it before base, which is what's expected.
Malayalam failures down from 1559 to 1197 (0.114172%).
BENGALI: 353988 out of 354285 tests passed. 297 failed (0.0838308%)
DEVANAGARI: 693571 out of 693628 tests passed. 57 failed (0.00821766%)
GUJARATI: 366489 out of 366506 tests passed. 17 failed (0.0046384%)
GURMUKHI: 60750 out of 60809 tests passed. 59 failed (0.0970251%)
KANNADA: 950956 out of 951913 tests passed. 957 failed (0.100534%)
KHMER: 299094 out of 299124 tests passed. 30 failed (0.0100293%)
MALAYALAM: 1047219 out of 1048416 tests passed. 1197 failed (0.114172%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271699 out of 271847 tests passed. 148 failed (0.0544424%)
TAMIL: 1091837 out of 1091837 tests passed. 0 failed (0%)
TELUGU: 970524 out of 970573 tests passed. 49 failed (0.00504856%)
The sequence Ra,H,Ya in Bengali is ambigious and Unicode encoded that to
get Ya-Phalaa, one would place ZWJ before Halant. Ie. a ZWJ,H sequence
requests subjoining, while a H,ZWJ requests Half form. Implement that.
Bengali failures go down from 377 to 297 (0.0838308%).
Gujarati is down by 4 to 17 (0.0046384%).
Kannada is down by 226 to 957 (0.100534%).
Current status:
BENGALI: 353988 out of 354285 tests passed. 297 failed (0.0838308%)
DEVANAGARI: 693571 out of 693628 tests passed. 57 failed (0.00821766%)
GUJARATI: 366489 out of 366506 tests passed. 17 failed (0.0046384%)
GURMUKHI: 60750 out of 60809 tests passed. 59 failed (0.0970251%)
KANNADA: 950956 out of 951913 tests passed. 957 failed (0.100534%)
KHMER: 299094 out of 299124 tests passed. 30 failed (0.0100293%)
MALAYALAM: 1046857 out of 1048416 tests passed. 1559 failed (0.148701%)
ORIYA: 42320 out of 42329 tests passed. 9 failed (0.021262%)
SINHALA: 271699 out of 271847 tests passed. 148 failed (0.0544424%)
TAMIL: 1091837 out of 1091837 tests passed. 0 failed (0%)
TELUGU: 970524 out of 970573 tests passed. 49 failed (0.00504856%)
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