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.
There now is a Python implementation of variation axes, because this
makes it (much) easier to build variable fonts from code. Therefore,
the definitions in otTables.py are not needed anymore.
I had broken this in e06166b83aa82582dab2e011520b1a77f72aa9f9.
Fix that, and other issues. Since I made that last commit, it has
become clear that SingleSubst works by adding delta and then doing
module 65536.
HarfBuzz was updated for this in 2011:
commit 52ebdff49d13f239efc886de935d47be9860f6e5
Author: Behdad Esfahbod <behdad@behdad.org>
Date: Tue Sep 27 12:38:16 2011 -0400
Fix GSUB lookuptype 1 subtype 1 delta wrapping
