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[feaLib] keep declaration order of ligatures within ligature set

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Fixes #3428
This commit is contained in:
Cosimo Lupo 2024-01-24 11:28:13 +00:00
parent 7cdac78423
commit f96b2128a1
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GPG Key ID: DF65A8A5A119C9A8
6 changed files with 48 additions and 34 deletions
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15
Lib/fontTools/otlLib/builder.py
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@ -1567,19 +1567,6 @@ def buildAlternateSubstSubtable(mapping):
return self
def _getLigatureKey(components):
# Computes a key for ordering ligatures in a GSUB Type-4 lookup.
# When building the OpenType lookup, we need to make sure that
# the longest sequence of components is listed first, so we
# use the negative length as the primary key for sorting.
# To make buildLigatureSubstSubtable() deterministic, we use the
# component sequence as the secondary key.
# For example, this will sort (f,f,f) < (f,f,i) < (f,f) < (f,i) < (f,l).
return (-len(components), components)
def buildLigatureSubstSubtable(mapping):
"""Builds a ligature substitution (GSUB4) subtable.
@ -1613,7 +1600,7 @@ def buildLigatureSubstSubtable(mapping):
# with fontTools >= 3.1:
# self.ligatures = dict(mapping)
self.ligatures = {}
for components in sorted(mapping.keys(), key=_getLigatureKey):
for components in sorted(mapping.keys(), key=self._getLigatureSortKey):
ligature = ot.Ligature()
ligature.Component = components[1:]
ligature.CompCount = len(ligature.Component) + 1

35
Lib/fontTools/ttLib/tables/otTables.py
View File

@ -1123,6 +1123,35 @@ class LigatureSubst(FormatSwitchingBaseTable):
self.ligatures = ligatures
del self.Format # Don't need this anymore
@staticmethod
def _getLigatureSortKey(components):
# Computes a key for ordering ligatures in a GSUB Type-4 lookup.
# When building the OpenType lookup, we need to make sure that
# the longest sequence of components is listed first, so we
# use the negative length as the key for sorting.
# Note, we no longer need to worry about deterministic order because the
# ligature mapping `dict` remembers the insertion order, and this in
# turn depends on the order in which the ligatures are written in the FEA.
# Since python sort algorithm is stable, the ligatures of equal length
# will keep the relative order in which they appear in the feature file.
# For example, given the following ligatures (all starting with 'f' and
# thus belonging to the same LigatureSet):
#
# feature liga {
# sub f i by f_i;
# sub f f f by f_f_f;
# sub f f by f_f;
# sub f f i by f_f_i;
# } liga;
#
# this should sort to: f_f_f, f_f_i, f_i, f_f
# This is also what fea-rs does, see:
# https://github.com/adobe-type-tools/afdko/issues/1727
# https://github.com/fonttools/fonttools/issues/3428
# https://github.com/googlefonts/fontc/pull/680
return -len(components)
def preWrite(self, font):
self.Format = 1
ligatures = getattr(self, "ligatures", None)
@ -1135,13 +1164,11 @@ class LigatureSubst(FormatSwitchingBaseTable):
# ligatures is map from components-sequence to lig-glyph
newLigatures = dict()
for comps, lig in sorted(
ligatures.items(), key=lambda item: (-len(item[0]), item[0])
):
for comps in sorted(ligatures.keys(), key=self._getLigatureSortKey):
ligature = Ligature()
ligature.Component = comps[1:]
ligature.CompCount = len(comps)
ligature.LigGlyph = lig
ligature.LigGlyph = ligatures[comps]
newLigatures.setdefault(comps[0], []).append(ligature)
ligatures = newLigatures

2
Tests/feaLib/data/spec4h1.ttx
View File

@ -147,8 +147,8 @@
<!-- SubTableCount=1 -->
<LigatureSubst index="0">
<LigatureSet glyph="c">
<Ligature components="s" glyph="c_s"/>
<Ligature components="t" glyph="c_t"/>
<Ligature components="s" glyph="c_s"/>
</LigatureSet>
</LigatureSubst>
</Lookup>

8
Tests/feaLib/data/spec5d1.ttx
View File

@ -62,16 +62,16 @@
<!-- SubTableCount=1 -->
<LigatureSubst index="0">
<LigatureSet glyph="one">
<Ligature components="fraction,two" glyph="onehalf"/>
<Ligature components="fraction,two.oldstyle" glyph="onehalf"/>
<Ligature components="slash,two" glyph="onehalf"/>
<Ligature components="fraction,two" glyph="onehalf"/>
<Ligature components="slash,two.oldstyle" glyph="onehalf"/>
<Ligature components="fraction,two.oldstyle" glyph="onehalf"/>
</LigatureSet>
<LigatureSet glyph="one.oldstyle">
<Ligature components="fraction,two" glyph="onehalf"/>
<Ligature components="fraction,two.oldstyle" glyph="onehalf"/>
<Ligature components="slash,two" glyph="onehalf"/>
<Ligature components="fraction,two" glyph="onehalf"/>
<Ligature components="slash,two.oldstyle" glyph="onehalf"/>
<Ligature components="fraction,two.oldstyle" glyph="onehalf"/>
</LigatureSet>
</LigatureSubst>
</Lookup>

16
Tests/mtiLib/data/mti/gsubligature.ttx.GSUB
View File

@ -16,20 +16,20 @@
<Ligature components="Jsmall" glyph="IJsmall"/>
</LigatureSet>
<LigatureSet glyph="f">
<Ligature components="f,b" glyph="ffb"/>
<Ligature components="f,h" glyph="ffh"/>
<Ligature components="f,i" glyph="ffi"/>
<Ligature components="f,k" glyph="ffk"/>
<Ligature components="f,l" glyph="ffl"/>
<Ligature components="f,t" glyph="fft"/>
<Ligature components="b" glyph="fb"/>
<Ligature components="f" glyph="ff"/>
<Ligature components="h" glyph="fh"/>
<Ligature components="f,b" glyph="ffb"/>
<Ligature components="f,h" glyph="ffh"/>
<Ligature components="f,k" glyph="ffk"/>
<Ligature components="i" glyph="fi"/>
<Ligature components="j" glyph="fj"/>
<Ligature components="k" glyph="fk"/>
<Ligature components="l" glyph="fl"/>
<Ligature components="f" glyph="ff"/>
<Ligature components="t" glyph="ft"/>
<Ligature components="b" glyph="fb"/>
<Ligature components="h" glyph="fh"/>
<Ligature components="k" glyph="fk"/>
<Ligature components="j" glyph="fj"/>
</LigatureSet>
<LigatureSet glyph="i">
<Ligature components="j" glyph="ij"/>

6
Tests/otlLib/builder_test.py
View File

@ -1051,11 +1051,11 @@ class BuilderTest(object):
func = lambda writer, font: value.toXML(writer, font, valueName="Val")
assert getXML(func) == ['<Val XPlacement="7" YPlacement="23"/>']
def test_getLigatureKey(self):
def test_getLigatureSortKey(self):
components = lambda s: [tuple(word) for word in s.split()]
c = components("fi fl ff ffi fff")
c.sort(key=builder._getLigatureKey)
assert c == components("fff ffi ff fi fl")
c.sort(key=otTables.LigatureSubst._getLigatureSortKey)
assert c == components("ffi fff fi fl ff")
def test_getSinglePosValueKey(self):
device = builder.buildDevice({10: 1, 11: 3})