Source code for fontTools.varLib.featureVars

"""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 popCount
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) """ _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() # setup lookups lookupMap = buildSubstitutionLookups(font["GSUB"].table, allSubstitutions) # 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, featureTag)
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: -popCount(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 spills 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) exactlyOne = False fullyInside = False for axisTag in bot: if axisTag not in intersection: fullyInside = False 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 exactlyOne: return intersection, bot exactlyOne = 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.""" # # if there is no <featureTag> feature: # make empty <featureTag> feature # sort features, get <featureTag> feature index # add <featureTag> feature to all scripts # make lookups # add feature variations # if table.Version < 0x00010001: table.Version = 0x00010001 # allow table.FeatureVariations table.FeatureVariations = None # delete any existing FeatureVariations varFeatureIndices = [] for index, feature in enumerate(table.FeatureList.FeatureRecord): if feature.FeatureTag == featureTag: varFeatureIndices.append(index) if not varFeatureIndices: varFeature = buildFeatureRecord(featureTag, []) table.FeatureList.FeatureRecord.append(varFeature) table.FeatureList.FeatureCount = len(table.FeatureList.FeatureRecord) sortFeatureList(table) 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 = [varFeatureIndex] axisIndices = {axis.axisTag: axisIndex for axisIndex, axis in enumerate(font["fvar"].axes)} 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 varFeatureIndices: existingLookupIndices = table.FeatureList.FeatureRecord[varFeatureIndex].Feature.LookupListIndex records.append(buildFeatureTableSubstitutionRecord(varFeatureIndex, lookupIndices + existingLookupIndices)) featureVariationRecords.append(buildFeatureVariationRecord(conditionTable, records)) 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): """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 lookupMap = {} for i, substitutionMap in enumerate(allSubstitutions): lookupMap[substitutionMap] = i # 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)]) 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 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)