Looks like Unsicribe responds to the 'mymr' tag by zeroing marks
GDEF_LATE instead of generic-shaper UNICODE_LATE. Implement that.
Fixes
Bug 81775 - Incorrect Rendering with harfbuzz-ng myanmar unicode
https://bugs.freedesktop.org/show_bug.cgi?id=81775
Micro-test added based on Padauk.
Follows the order of the Arabic/Syriac specs. Also don't stop
between rlig and calt in non-Arabic scripts.
Micro-tests for Arabic and Mongolian added for the latter.
Originally we fixed those in 79d1007a50.
However, fonts like MongolianWhite don't have GDEF, but have IgnoreMarks
in their LigatureSubstitute init/etc features. We were synthesizing a
GDEF class of mark for Mongolian Variation Selectors and as such the
ligature lookups where not matching. Uniscribe doesn't do that.
I tried with more sophisticated fixes, like, if there is no GDEF and
a lookup-flag mismatch happens, instead of rejecting a match, try
skipping that glyph. That surely produces some interesting behavior,
but since we don't want to support fonts missing GDEF more than we have
to, I went for this simpler fix which is to always mark
default-ignorables as base when synthesizing GDEF.
Micro-test added.
Fixes rest of https://bugs.freedesktop.org/show_bug.cgi?id=65258
If pre-base reordering Ra is NOT formed (or formed and then
broken up), we should consider that Ra as base. This is
observable when there's a left matra or dotreph that positions
before base.
Now, it might be that we shouldn't do this if the Ra happend
to form a below form. We can't quite deduce that right now...
Micro test added. Also at:
https://code.google.com/a/google.com/p/noto-alpha/issues/detail?id=186#c29
Behdad Esfahbod