"""Module to build FeatureVariation tables:
https://docs.microsoft.com/en-us/typography/opentype/spec/chapter2#featurevariations-table
NOTE: The API is experimental and subject to change.
"""
from fontTools.misc.dictTools import hashdict
from fontTools.misc.intTools import bit_count
from fontTools.ttLib import newTable
from fontTools.ttLib.tables import otTables as ot
from fontTools.ttLib.ttVisitor import TTVisitor
from fontTools.otlLib.builder import buildLookup, buildSingleSubstSubtable
from collections import OrderedDict
from .errors import VarLibError, VarLibValidationError
[docs]
def addFeatureVariations(font, conditionalSubstitutions, featureTag="rvrn"):
"""Add conditional substitutions to a Variable Font.
The `conditionalSubstitutions` argument is a list of (Region, Substitutions)
tuples.
A Region is a list of Boxes. A Box is a dict mapping axisTags to
(minValue, maxValue) tuples. Irrelevant axes may be omitted and they are
interpretted as extending to end of axis in each direction. A Box represents
an orthogonal 'rectangular' subset of an N-dimensional design space.
A Region represents a more complex subset of an N-dimensional design space,
ie. the union of all the Boxes in the Region.
For efficiency, Boxes within a Region should ideally not overlap, but
functionality is not compromised if they do.
The minimum and maximum values are expressed in normalized coordinates.
A Substitution is a dict mapping source glyph names to substitute glyph names.
Example:
# >>> f = TTFont(srcPath)
# >>> condSubst = [
# ... # A list of (Region, Substitution) tuples.
# ... ([{"wdth": (0.5, 1.0)}], {"cent": "cent.rvrn"}),
# ... ([{"wght": (0.5, 1.0)}], {"dollar": "dollar.rvrn"}),
# ... ]
# >>> addFeatureVariations(f, condSubst)
# >>> f.save(dstPath)
The `featureTag` parameter takes either a str or a iterable of str (the single str
is kept for backwards compatibility), and defines which feature(s) will be
associated with the feature variations.
Note, if this is "rvrn", then the substitution lookup will be inserted at the
beginning of the lookup list so that it is processed before others, otherwise
for any other feature tags it will be appended last.
"""
# process first when "rvrn" is the only listed tag
featureTags = [featureTag] if isinstance(featureTag, str) else sorted(featureTag)
processLast = "rvrn" not in featureTags or len(featureTags) > 1
_checkSubstitutionGlyphsExist(
glyphNames=set(font.getGlyphOrder()),
substitutions=conditionalSubstitutions,
)
substitutions = overlayFeatureVariations(conditionalSubstitutions)
# turn substitution dicts into tuples of tuples, so they are hashable
conditionalSubstitutions, allSubstitutions = makeSubstitutionsHashable(
substitutions
)
if "GSUB" not in font:
font["GSUB"] = buildGSUB()
else:
existingTags = _existingVariableFeatures(font["GSUB"].table).intersection(
featureTags
)
if existingTags:
raise VarLibError(
f"FeatureVariations already exist for feature tag(s): {existingTags}"
)
# setup lookups
lookupMap = buildSubstitutionLookups(
font["GSUB"].table, allSubstitutions, processLast
)
# addFeatureVariationsRaw takes a list of
# ( {condition}, [ lookup indices ] )
# so rearrange our lookups to match
conditionsAndLookups = []
for conditionSet, substitutions in conditionalSubstitutions:
conditionsAndLookups.append(
(conditionSet, [lookupMap[s] for s in substitutions])
)
addFeatureVariationsRaw(font, font["GSUB"].table, conditionsAndLookups, featureTags)
def _existingVariableFeatures(table):
existingFeatureVarsTags = set()
if hasattr(table, "FeatureVariations") and table.FeatureVariations is not None:
features = table.FeatureList.FeatureRecord
for fvr in table.FeatureVariations.FeatureVariationRecord:
for ftsr in fvr.FeatureTableSubstitution.SubstitutionRecord:
existingFeatureVarsTags.add(features[ftsr.FeatureIndex].FeatureTag)
return existingFeatureVarsTags
def _checkSubstitutionGlyphsExist(glyphNames, substitutions):
referencedGlyphNames = set()
for _, substitution in substitutions:
referencedGlyphNames |= substitution.keys()
referencedGlyphNames |= set(substitution.values())
missing = referencedGlyphNames - glyphNames
if missing:
raise VarLibValidationError(
"Missing glyphs are referenced in conditional substitution rules:"
f" {', '.join(missing)}"
)
[docs]
def overlayFeatureVariations(conditionalSubstitutions):
"""Compute overlaps between all conditional substitutions.
The `conditionalSubstitutions` argument is a list of (Region, Substitutions)
tuples.
A Region is a list of Boxes. A Box is a dict mapping axisTags to
(minValue, maxValue) tuples. Irrelevant axes may be omitted and they are
interpretted as extending to end of axis in each direction. A Box represents
an orthogonal 'rectangular' subset of an N-dimensional design space.
A Region represents a more complex subset of an N-dimensional design space,
ie. the union of all the Boxes in the Region.
For efficiency, Boxes within a Region should ideally not overlap, but
functionality is not compromised if they do.
The minimum and maximum values are expressed in normalized coordinates.
A Substitution is a dict mapping source glyph names to substitute glyph names.
Returns data is in similar but different format. Overlaps of distinct
substitution Boxes (*not* Regions) are explicitly listed as distinct rules,
and rules with the same Box merged. The more specific rules appear earlier
in the resulting list. Moreover, instead of just a dictionary of substitutions,
a list of dictionaries is returned for substitutions corresponding to each
unique space, with each dictionary being identical to one of the input
substitution dictionaries. These dictionaries are not merged to allow data
sharing when they are converted into font tables.
Example::
>>> condSubst = [
... # A list of (Region, Substitution) tuples.
... ([{"wght": (0.5, 1.0)}], {"dollar": "dollar.rvrn"}),
... ([{"wght": (0.5, 1.0)}], {"dollar": "dollar.rvrn"}),
... ([{"wdth": (0.5, 1.0)}], {"cent": "cent.rvrn"}),
... ([{"wght": (0.5, 1.0), "wdth": (-1, 1.0)}], {"dollar": "dollar.rvrn"}),
... ]
>>> from pprint import pprint
>>> pprint(overlayFeatureVariations(condSubst))
[({'wdth': (0.5, 1.0), 'wght': (0.5, 1.0)},
[{'dollar': 'dollar.rvrn'}, {'cent': 'cent.rvrn'}]),
({'wdth': (0.5, 1.0)}, [{'cent': 'cent.rvrn'}]),
({'wght': (0.5, 1.0)}, [{'dollar': 'dollar.rvrn'}])]
"""
# Merge same-substitutions rules, as this creates fewer number oflookups.
merged = OrderedDict()
for value, key in conditionalSubstitutions:
key = hashdict(key)
if key in merged:
merged[key].extend(value)
else:
merged[key] = value
conditionalSubstitutions = [(v, dict(k)) for k, v in merged.items()]
del merged
# Merge same-region rules, as this is cheaper.
# Also convert boxes to hashdict()
#
# Reversing is such that earlier entries win in case of conflicting substitution
# rules for the same region.
merged = OrderedDict()
for key, value in reversed(conditionalSubstitutions):
key = tuple(
sorted(
(hashdict(cleanupBox(k)) for k in key),
key=lambda d: tuple(sorted(d.items())),
)
)
if key in merged:
merged[key].update(value)
else:
merged[key] = dict(value)
conditionalSubstitutions = list(reversed(merged.items()))
del merged
# Overlay
#
# Rank is the bit-set of the index of all contributing layers.
initMapInit = ((hashdict(), 0),) # Initializer representing the entire space
boxMap = OrderedDict(initMapInit) # Map from Box to Rank
for i, (currRegion, _) in enumerate(conditionalSubstitutions):
newMap = OrderedDict(initMapInit)
currRank = 1 << i
for box, rank in boxMap.items():
for currBox in currRegion:
intersection, remainder = overlayBox(currBox, box)
if intersection is not None:
intersection = hashdict(intersection)
newMap[intersection] = newMap.get(intersection, 0) | rank | currRank
if remainder is not None:
remainder = hashdict(remainder)
newMap[remainder] = newMap.get(remainder, 0) | rank
boxMap = newMap
# Generate output
items = []
for box, rank in sorted(
boxMap.items(), key=(lambda BoxAndRank: -bit_count(BoxAndRank[1]))
):
# Skip any box that doesn't have any substitution.
if rank == 0:
continue
substsList = []
i = 0
while rank:
if rank & 1:
substsList.append(conditionalSubstitutions[i][1])
rank >>= 1
i += 1
items.append((dict(box), substsList))
return items
#
# Terminology:
#
# A 'Box' is a dict representing an orthogonal "rectangular" bit of N-dimensional space.
# The keys in the dict are axis tags, the values are (minValue, maxValue) tuples.
# Missing dimensions (keys) are substituted by the default min and max values
# from the corresponding axes.
#
[docs]
def overlayBox(top, bot):
"""Overlays ``top`` box on top of ``bot`` box.
Returns two items:
* Box for intersection of ``top`` and ``bot``, or None if they don't intersect.
* Box for remainder of ``bot``. Remainder box might not be exact (since the
remainder might not be a simple box), but is inclusive of the exact
remainder.
"""
# Intersection
intersection = {}
intersection.update(top)
intersection.update(bot)
for axisTag in set(top) & set(bot):
min1, max1 = top[axisTag]
min2, max2 = bot[axisTag]
minimum = max(min1, min2)
maximum = min(max1, max2)
if not minimum < maximum:
return None, bot # Do not intersect
intersection[axisTag] = minimum, maximum
# Remainder
#
# Remainder is empty if bot's each axis range lies within that of intersection.
#
# Remainder is shrank if bot's each, except for exactly one, axis range lies
# within that of intersection, and that one axis, it extrudes out of the
# intersection only on one side.
#
# Bot is returned in full as remainder otherwise, as true remainder is not
# representable as a single box.
remainder = dict(bot)
extruding = False
fullyInside = True
for axisTag in top:
if axisTag in bot:
continue
extruding = True
fullyInside = False
break
for axisTag in bot:
if axisTag not in top:
continue # Axis range lies fully within
min1, max1 = intersection[axisTag]
min2, max2 = bot[axisTag]
if min1 <= min2 and max2 <= max1:
continue # Axis range lies fully within
# Bot's range doesn't fully lie within that of top's for this axis.
# We know they intersect, so it cannot lie fully without either; so they
# overlap.
# If we have had an overlapping axis before, remainder is not
# representable as a box, so return full bottom and go home.
if extruding:
return intersection, bot
extruding = True
fullyInside = False
# Otherwise, cut remainder on this axis and continue.
if min1 <= min2:
# Right side survives.
minimum = max(max1, min2)
maximum = max2
elif max2 <= max1:
# Left side survives.
minimum = min2
maximum = min(min1, max2)
else:
# Remainder leaks out from both sides. Can't cut either.
return intersection, bot
remainder[axisTag] = minimum, maximum
if fullyInside:
# bot is fully within intersection. Remainder is empty.
return intersection, None
return intersection, remainder
[docs]
def cleanupBox(box):
"""Return a sparse copy of `box`, without redundant (default) values.
>>> cleanupBox({})
{}
>>> cleanupBox({'wdth': (0.0, 1.0)})
{'wdth': (0.0, 1.0)}
>>> cleanupBox({'wdth': (-1.0, 1.0)})
{}
"""
return {tag: limit for tag, limit in box.items() if limit != (-1.0, 1.0)}
#
# Low level implementation
#
[docs]
def addFeatureVariationsRaw(font, table, conditionalSubstitutions, featureTag="rvrn"):
"""Low level implementation of addFeatureVariations that directly
models the possibilities of the FeatureVariations table."""
featureTags = [featureTag] if isinstance(featureTag, str) else sorted(featureTag)
processLast = "rvrn" not in featureTags or len(featureTags) > 1
#
# if a <featureTag> feature is not present:
# make empty <featureTag> feature
# sort features, get <featureTag> feature index
# add <featureTag> feature to all scripts
# if a <featureTag> feature is present:
# reuse <featureTag> feature index
# make lookups
# add feature variations
#
if table.Version < 0x00010001:
table.Version = 0x00010001 # allow table.FeatureVariations
varFeatureIndices = set()
existingTags = {
feature.FeatureTag
for feature in table.FeatureList.FeatureRecord
if feature.FeatureTag in featureTags
}
newTags = set(featureTags) - existingTags
if newTags:
varFeatures = []
for featureTag in sorted(newTags):
varFeature = buildFeatureRecord(featureTag, [])
table.FeatureList.FeatureRecord.append(varFeature)
varFeatures.append(varFeature)
table.FeatureList.FeatureCount = len(table.FeatureList.FeatureRecord)
sortFeatureList(table)
for varFeature in varFeatures:
varFeatureIndex = table.FeatureList.FeatureRecord.index(varFeature)
for scriptRecord in table.ScriptList.ScriptRecord:
if scriptRecord.Script.DefaultLangSys is None:
raise VarLibError(
"Feature variations require that the script "
f"'{scriptRecord.ScriptTag}' defines a default language system."
)
langSystems = [lsr.LangSys for lsr in scriptRecord.Script.LangSysRecord]
for langSys in [scriptRecord.Script.DefaultLangSys] + langSystems:
langSys.FeatureIndex.append(varFeatureIndex)
langSys.FeatureCount = len(langSys.FeatureIndex)
varFeatureIndices.add(varFeatureIndex)
if existingTags:
# indices may have changed if we inserted new features and sorted feature list
# so we must do this after the above
varFeatureIndices.update(
index
for index, feature in enumerate(table.FeatureList.FeatureRecord)
if feature.FeatureTag in existingTags
)
axisIndices = {
axis.axisTag: axisIndex for axisIndex, axis in enumerate(font["fvar"].axes)
}
hasFeatureVariations = (
hasattr(table, "FeatureVariations") and table.FeatureVariations is not None
)
featureVariationRecords = []
for conditionSet, lookupIndices in conditionalSubstitutions:
conditionTable = []
for axisTag, (minValue, maxValue) in sorted(conditionSet.items()):
if minValue > maxValue:
raise VarLibValidationError(
"A condition set has a minimum value above the maximum value."
)
ct = buildConditionTable(axisIndices[axisTag], minValue, maxValue)
conditionTable.append(ct)
records = []
for varFeatureIndex in sorted(varFeatureIndices):
existingLookupIndices = table.FeatureList.FeatureRecord[
varFeatureIndex
].Feature.LookupListIndex
combinedLookupIndices = (
existingLookupIndices + lookupIndices
if processLast
else lookupIndices + existingLookupIndices
)
records.append(
buildFeatureTableSubstitutionRecord(
varFeatureIndex, combinedLookupIndices
)
)
if hasFeatureVariations and (
fvr := findFeatureVariationRecord(table.FeatureVariations, conditionTable)
):
fvr.FeatureTableSubstitution.SubstitutionRecord.extend(records)
fvr.FeatureTableSubstitution.SubstitutionCount = len(
fvr.FeatureTableSubstitution.SubstitutionRecord
)
else:
featureVariationRecords.append(
buildFeatureVariationRecord(conditionTable, records)
)
if hasFeatureVariations:
if table.FeatureVariations.Version != 0x00010000:
raise VarLibError(
"Unsupported FeatureVariations table version: "
f"0x{table.FeatureVariations.Version:08x} (expected 0x00010000)."
)
table.FeatureVariations.FeatureVariationRecord.extend(featureVariationRecords)
table.FeatureVariations.FeatureVariationCount = len(
table.FeatureVariations.FeatureVariationRecord
)
else:
table.FeatureVariations = buildFeatureVariations(featureVariationRecords)
#
# Building GSUB/FeatureVariations internals
#
[docs]
def buildGSUB():
"""Build a GSUB table from scratch."""
fontTable = newTable("GSUB")
gsub = fontTable.table = ot.GSUB()
gsub.Version = 0x00010001 # allow gsub.FeatureVariations
gsub.ScriptList = ot.ScriptList()
gsub.ScriptList.ScriptRecord = []
gsub.FeatureList = ot.FeatureList()
gsub.FeatureList.FeatureRecord = []
gsub.LookupList = ot.LookupList()
gsub.LookupList.Lookup = []
srec = ot.ScriptRecord()
srec.ScriptTag = "DFLT"
srec.Script = ot.Script()
srec.Script.DefaultLangSys = None
srec.Script.LangSysRecord = []
srec.Script.LangSysCount = 0
langrec = ot.LangSysRecord()
langrec.LangSys = ot.LangSys()
langrec.LangSys.ReqFeatureIndex = 0xFFFF
langrec.LangSys.FeatureIndex = []
srec.Script.DefaultLangSys = langrec.LangSys
gsub.ScriptList.ScriptRecord.append(srec)
gsub.ScriptList.ScriptCount = 1
gsub.FeatureVariations = None
return fontTable
[docs]
def makeSubstitutionsHashable(conditionalSubstitutions):
"""Turn all the substitution dictionaries in sorted tuples of tuples so
they are hashable, to detect duplicates so we don't write out redundant
data."""
allSubstitutions = set()
condSubst = []
for conditionSet, substitutionMaps in conditionalSubstitutions:
substitutions = []
for substitutionMap in substitutionMaps:
subst = tuple(sorted(substitutionMap.items()))
substitutions.append(subst)
allSubstitutions.add(subst)
condSubst.append((conditionSet, substitutions))
return condSubst, sorted(allSubstitutions)
[docs]
class ShifterVisitor(TTVisitor):
def __init__(self, shift):
self.shift = shift
@ShifterVisitor.register_attr(ot.Feature, "LookupListIndex") # GSUB/GPOS
def visit(visitor, obj, attr, value):
shift = visitor.shift
value = [l + shift for l in value]
setattr(obj, attr, value)
@ShifterVisitor.register_attr(
(ot.SubstLookupRecord, ot.PosLookupRecord), "LookupListIndex"
)
def visit(visitor, obj, attr, value):
setattr(obj, attr, visitor.shift + value)
[docs]
def buildSubstitutionLookups(gsub, allSubstitutions, processLast=False):
"""Build the lookups for the glyph substitutions, return a dict mapping
the substitution to lookup indices."""
# Insert lookups at the beginning of the lookup vector
# https://github.com/googlefonts/fontmake/issues/950
firstIndex = len(gsub.LookupList.Lookup) if processLast else 0
lookupMap = {}
for i, substitutionMap in enumerate(allSubstitutions):
lookupMap[substitutionMap] = firstIndex + i
if not processLast:
# Shift all lookup indices in gsub by len(allSubstitutions)
shift = len(allSubstitutions)
visitor = ShifterVisitor(shift)
visitor.visit(gsub.FeatureList.FeatureRecord)
visitor.visit(gsub.LookupList.Lookup)
for i, subst in enumerate(allSubstitutions):
substMap = dict(subst)
lookup = buildLookup([buildSingleSubstSubtable(substMap)])
if processLast:
gsub.LookupList.Lookup.append(lookup)
else:
gsub.LookupList.Lookup.insert(i, lookup)
assert gsub.LookupList.Lookup[lookupMap[subst]] is lookup
gsub.LookupList.LookupCount = len(gsub.LookupList.Lookup)
return lookupMap
[docs]
def buildFeatureVariations(featureVariationRecords):
"""Build the FeatureVariations subtable."""
fv = ot.FeatureVariations()
fv.Version = 0x00010000
fv.FeatureVariationRecord = featureVariationRecords
fv.FeatureVariationCount = len(featureVariationRecords)
return fv
[docs]
def buildFeatureRecord(featureTag, lookupListIndices):
"""Build a FeatureRecord."""
fr = ot.FeatureRecord()
fr.FeatureTag = featureTag
fr.Feature = ot.Feature()
fr.Feature.LookupListIndex = lookupListIndices
fr.Feature.populateDefaults()
return fr
[docs]
def buildFeatureVariationRecord(conditionTable, substitutionRecords):
"""Build a FeatureVariationRecord."""
fvr = ot.FeatureVariationRecord()
fvr.ConditionSet = ot.ConditionSet()
fvr.ConditionSet.ConditionTable = conditionTable
fvr.ConditionSet.ConditionCount = len(conditionTable)
fvr.FeatureTableSubstitution = ot.FeatureTableSubstitution()
fvr.FeatureTableSubstitution.Version = 0x00010000
fvr.FeatureTableSubstitution.SubstitutionRecord = substitutionRecords
fvr.FeatureTableSubstitution.SubstitutionCount = len(substitutionRecords)
return fvr
[docs]
def buildFeatureTableSubstitutionRecord(featureIndex, lookupListIndices):
"""Build a FeatureTableSubstitutionRecord."""
ftsr = ot.FeatureTableSubstitutionRecord()
ftsr.FeatureIndex = featureIndex
ftsr.Feature = ot.Feature()
ftsr.Feature.LookupListIndex = lookupListIndices
ftsr.Feature.LookupCount = len(lookupListIndices)
return ftsr
[docs]
def buildConditionTable(axisIndex, filterRangeMinValue, filterRangeMaxValue):
"""Build a ConditionTable."""
ct = ot.ConditionTable()
ct.Format = 1
ct.AxisIndex = axisIndex
ct.FilterRangeMinValue = filterRangeMinValue
ct.FilterRangeMaxValue = filterRangeMaxValue
return ct
[docs]
def findFeatureVariationRecord(featureVariations, conditionTable):
"""Find a FeatureVariationRecord that has the same conditionTable."""
if featureVariations.Version != 0x00010000:
raise VarLibError(
"Unsupported FeatureVariations table version: "
f"0x{featureVariations.Version:08x} (expected 0x00010000)."
)
for fvr in featureVariations.FeatureVariationRecord:
if conditionTable == fvr.ConditionSet.ConditionTable:
return fvr
return None
[docs]
def sortFeatureList(table):
"""Sort the feature list by feature tag, and remap the feature indices
elsewhere. This is needed after the feature list has been modified.
"""
# decorate, sort, undecorate, because we need to make an index remapping table
tagIndexFea = [
(fea.FeatureTag, index, fea)
for index, fea in enumerate(table.FeatureList.FeatureRecord)
]
tagIndexFea.sort()
table.FeatureList.FeatureRecord = [fea for tag, index, fea in tagIndexFea]
featureRemap = dict(
zip([index for tag, index, fea in tagIndexFea], range(len(tagIndexFea)))
)
# Remap the feature indices
remapFeatures(table, featureRemap)
[docs]
def remapFeatures(table, featureRemap):
"""Go through the scripts list, and remap feature indices."""
for scriptIndex, script in enumerate(table.ScriptList.ScriptRecord):
defaultLangSys = script.Script.DefaultLangSys
if defaultLangSys is not None:
_remapLangSys(defaultLangSys, featureRemap)
for langSysRecordIndex, langSysRec in enumerate(script.Script.LangSysRecord):
langSys = langSysRec.LangSys
_remapLangSys(langSys, featureRemap)
if hasattr(table, "FeatureVariations") and table.FeatureVariations is not None:
for fvr in table.FeatureVariations.FeatureVariationRecord:
for ftsr in fvr.FeatureTableSubstitution.SubstitutionRecord:
ftsr.FeatureIndex = featureRemap[ftsr.FeatureIndex]
def _remapLangSys(langSys, featureRemap):
if langSys.ReqFeatureIndex != 0xFFFF:
langSys.ReqFeatureIndex = featureRemap[langSys.ReqFeatureIndex]
langSys.FeatureIndex = [featureRemap[index] for index in langSys.FeatureIndex]
if __name__ == "__main__":
import doctest, sys
sys.exit(doctest.testmod().failed)