In OT kern subtable header, the format is the high byte of 'coverage'
bit mask (bits 8-15), and the low byte (bits 0-7) is the actual coverage
bits.
In AAT kern, it's the opposite: the coverage flags are the high byte,
whereas the subtable format is the low byte.
Also adjusted the test data, and set coverage to 1 for OT kern subtable
(which means the usual horizontal kerning).
- When compiling kern subtables for version=1.0 kern tables (AAT)
the subtable header was written incorrectly: there is no version,
the length is a uint32 and there's an additional uint16 for
tupleIndex
- Use the 'coverage' low byte to select subtable "format", instead
of the 'version' field, only present in OT kern subtable header.
The getkern method was failing with AttributeError on 'unknown'
subtable formats, as their class only has 'format' instead of
'version' attribute. The 'version' attribute is renamed to
'format' also to avoid confusion, but the old one is kept for
backward compatiblity. In the only implemeted subtable class,
'format' becomes a class attribute rather than instance's
(it must always be 0).
- KernTable_format_0 now takes an 'apple=False' argument, used to
know the different headers and whether to read/write tupleIndex.
- minor pep8 whitespace and indentation fixes
- A new 'tupleIndex' attribute is written out to TTX for apple
kern subtables. Old ttx files which lack that attribute will
still be read (with a warning) and will default to tupleIndex=0
when recompiled or dumped with current fonttools.
Fixes#1089
This also fixes fonttools/fonttools/issues/1030.
Although the roundtrip is generally possible when a VariationStore is built from source font data using the Superpolator model, it is possible to build region definitions that do not follow this model. Behdad cited the Skia "Q" example, where the tail of the Q is affected by two regions defined as:
min=0 peak=0.5 max=0.51 delta=+10
min=0.49 peak=0.5 max=0.51 delta=-10
Beyond composing ligatures, AAT finite-state transducers can also
execute insertion actions without rewriting existing glyphs. The
corresponding actions have almost the same structure as ligature
actions, so we can share a lot of the plumbing within fonttools.
This renaming is in preparation of a larger change to support `morx`
ables with insertions.
Before this change, we were emitting XML with numeric values for `morx`
coverage flags. Now, we emit XML that makes more sense to human readers.
XML files from previous versions of fonttools can still be parsed.
Before this change, the following glyph class:
@Vowels = [@Vowels.lc @Vowels.uc y Y];
Would be written back as:
@Vowels = [@Vowels.lc = [a e i o u]; @Vowels.uc = [A E I O U]; y Y];
Which is clearly invalid. It seems for GlyphClass.asFea() to work
correctly here we should be using GlyphClassName not GlyphClass
for the nested classes (similar to the code at the beginning of
parse_glyphclass_()).
