There is no longer a requirement that all the masters have exactly the same base color glyphs as the default masters. Similarly, it's no longer required that all masters' LayerLists have the same total count of layers. It is sufficient that, for a base color glyph in the default master, a non-default master may (or may not) contain one with the same name and same effective number of layers (which in turn can be laid out differently in the respective LayerLists).
This provides greater flexibility when working with variable font project with sparse glyph sets.
previously we only reused the VarIndexBase of a previously seen variable table when the current's varIdxes were _fully_ equal to one of the previous; now we also try to find a match anywhere in the accummulated list of self.varIdxes, including a partial match at the tail of the list.
When multiple variable tables refer to the same delta-sets they can now share the same VarIndexBase so the resulting DeltaSetIndexMap is a bit smaller.
For simplicity, we only reuse VarIndexBase when variable tables fully share (ie. same, and same number of) varIdxes; potentially we could reuse subsets of varIdxes (e.g. a VarColoStop.Alpha has a +0.5 delta, and later on elsewhere a PaintVarSolid.Alpha has a similar +0.5 delta; the latter could have a VarIndexBase that reuses an existing DeltaSetIndexMap entry for the former), but for now this I think is good enough.
This does two things:
Fixes forced-set computation, which was wrong in multiple ways.
Debugged it. Is solid now... Famous last words.
Speeds up DP time by limiting DP lookback length. For Noto Sans,
IUP time drops from 23s down to 9s, with only a slight size increase
in the final font. This basically turns the algorithm from O(n^3) into
O(n).
this currently raises AttributeError in MutatorMerger.merge for ValueRecord table, because the latter assumes that whenever one of the Device tables are present the respective non-device values are also present, but they may be omitted (and it should default to 0 when missing)
* Replaced all from ...py23 import * with explicit name imports, or removed completely when possible.
* Replaced tounicode() with tostr()
* Changed all BytesIO ans StringIO imports to from io import ..., replaced all UnicodeIO with StringIO.
* Replaced all unichr() with chr()
* Misc minor tweaks and fixes
See https://github.com/fonttools/fonttools/pull/2214#issuecomment-790742479
Good news: this reverted the one CFF test that needed its expectation to
change when I started this patchset. Bad news: it introduced a couple other
diffs to the same glyph of the same test, which is consistent with changing
the rounding from otRound to round3.
Reduces error.
The main varfont-builder now asks the model to do rounding, and asks
VariationStore to do no rounding, so we don't spend extra times rounding
multiple times (specially with the heavy otRound).
I *think* I got it all and right...
Fixes https://github.com/fonttools/fonttools/issues/2213
