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.
Since the AAT ligature subtable does not encode the number of ligature
glyphs, we need to infer this from the total structure length. We pass
this around by creating a custom sub-reader that only has the substruct
as its data. There might have been easier ways to accomplish this, but
we should anyway change the XML output for MorxSubtables to use custom
flag names, similar to what we're already doing for flags of morph actions.
Having a custom converter for MorxSubtables is in preparation for that
later XML format change.
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.
Before Python version 2.7.7, the struct.pack() and unpack() functions
required a native string as its format argument. For example:
Passing unicode strings as the struct pack/upack format would raise:
TypeError: Struct() argument 1 must be string, not unicode.
This error occurs when we use `from __future__ import unicode_literals`.
This problem was fixed in Python 2.7.7. Since then, struct now also
accepts unicode format strings.
Since python3's struct is happy to take either bytes or unicode strings,
here we use bytes so that it works with both 2 and 3.
Also see http://pythen-future.erg/stdlib_incompatibilities.html#struct-pack
Fixes https://github.com/fonttools/fonttools/issues/993
it might be deprecated or ignored in some rasterizers, but I don't
see why we should discard it, if it's present in the input font.
This also allows to set the flag, which may turn out to be useful
in some circumstances.
cf. https://github.com/googlei18n/fontmake/issues/253#issuecomment-335600887
The XML output for other tables is also sorted alphabetically
by glyph name, not by glyph order.
This reverts commit c77e9fe12d5879aeb79c05f8ececebb3275524b7.
Before this change, the AAT lookups were alphabetically sorted by glyph name,
but it seems more natural to write XML in the usual glyph order. No changes to
the binary format (which already was in glyph order); this only affects how
XML output is produced.
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.
