in COLRv1 all scalar values have associated varIdx to support variations. I want to load them as
immutable namedtuples, and also I want to dump them as simple XML tags with 'value' and 'varIdx'
attributes, instead of normal otTables (i.e. with nested Value and VarIdx sub-elements) as
that would make them too verbose in the XML dump.
So I made a custom _NamedTupleConverter, as a base class for VariableScalar, etc.; sub-classes
must provide a tupleClass and a list of converterClasses for each namedtuple field.
The ExtendMode enum has also a custom converter to dump it as string in the XML, and load it
as IntEnum.
fixup
We don't need to cast to int when using the round function from py23,
as this is a backport of python3's built-in round and thus it returns
an int when called with a single argument.
The AAT `ankr` anchor point table is an auxiliary table for `kerx`,
used to store anchor overrides in case the glyph itself does not
supply the needed anchors as control points. Among the fonts that
come pre-installed with MacOS 10.12.6, `ankr` is used by a handful
of non-Latin fonts such as “Myanmar MN”, “Devanagari Sangam MN”,
and “Arial HB”.
https://developer.apple.com/fonts/TrueType-Reference-Manual/RM06/Chap6ankr.html
Other metamorphosis types are not yet supported and will raise an error
upon decompilation. The TTX tool catches the error and continues to emit
a hexdump of the table contents, just as before this change.
Interestingly, this can handle the examples from the AAT specification
(which are part of the unit tests), and also most AAT fonts on my disk.
However, some other AAT fonts such as Apple Chancery cannot be decompiled.
The failure seems to be a general problem with how fonttools decompiles
AAT lookups of format 4, and unrelated to this present change.
After this change, fonttools is able to dump the `lcar` table of
the AppleChancery font to XML. However, the resulting XML cannot
be compiled back to TrueType, yet. So, something is still broken
with the implementation of AAT lookups. Need to do more testing
before the support for table `lcar` can be added to fonttools.
API Change:
This will change XML output for GSUB/GPOS/GDEF/MATH/BASE/JSTF/...
Scripts that set the Version for those to 1.0 or other float values
also need fixing. A warning is emitted when code or XML needs fix.
