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Find ligature glyph names by parsing the GSUB using fonttools.feaLib
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from fontTools.feaLib.parser import Parser | |
from fontTools.feaLib.ast import * | |
from io import StringIO | |
""" | |
RoboFont Script | |
- Type: Mastering | |
- Purpose: To find ligature by parsing the features. | |
- Specifications: | |
- Parse the substitutions in the current font features using fontTools.feaLib | |
- Find lookup references in the provided feature tags | |
- Find ligature statements only inside the the provided feature tags or lookup references | |
- Collect name of ligature glyphs and return it as a set | |
- Publish Date: 10 August 2021 | |
- Author: Bahman Eslami | |
- License: MIT | |
""" | |
def getFeatureFileFeaLibAstElementFromFont(font): | |
featurefile = StringIO(font.features.text) | |
featurefile.name = font.path | |
parser = Parser(featurefile, font.keys()) | |
return parser.parse() | |
def getLigaturesInFeaLibAstElement(e, featureTags, lookupNames): | |
ligatureNames = set() | |
if type(e) is FeatureBlock: | |
if e.name not in featureTags: | |
return set() | |
elif type(e) is LookupBlock: | |
if e.name not in lookupNames: | |
return set() | |
if hasattr(e, 'statements'): | |
for s in e.statements: | |
ligatureNames.update(getLigaturesInFeaLibAstElement(s, featureTags, lookupNames)) | |
if type(e) is MultipleSubstStatement: | |
ligatureNames.add(e.replacement) | |
elif type(e) is LigatureSubstStatement: | |
ligatureNames.add(e.replacement) | |
return ligatureNames | |
def getLookupNamesInFeaLibAstElement(e, featureTags): | |
lookupNames = set() | |
if type(e) is FeatureBlock: | |
if e.name not in featureTags: | |
return set() | |
if hasattr(e, 'statements'): | |
for s in e.statements: | |
lookupNames.update(getLookupNamesInFeaLibAstElement(s, featureTags)) | |
if type(e) is LookupReferenceStatement: | |
lookupNames.add(e.lookup.name) | |
elif type(e) is LookupBlock: | |
lookupNames.add(e.name) | |
return lookupNames | |
def getGlyphNamesFromListOfAstGlyphNames(astGlyphList): | |
return set([g.glyph for g in astGlyphList if type(g) is GlyphName]) | |
def getLigatureAlternates(e, ligatureNames): | |
if hasattr(e, 'statements'): | |
for s in e.statements: | |
ligatureNames.update(getLigatureAlternates(s, ligatureNames)) | |
if type(e) is SingleSubstStatement: | |
glyphs = getGlyphNamesFromListOfAstGlyphNames(e.glyphs) | |
if glyphs - ligatureNames == set(): | |
ligatureNames.update(getGlyphNamesFromListOfAstGlyphNames(e.replacements)) | |
return ligatureNames | |
def getLigaturesInFont(font, featureTags): | |
""" | |
Returns a set of glyph names which are ligatures. The featureTags argument is an iterable | |
which defines which features should be parsed. | |
""" | |
features = getFeatureFileFeaLibAstElementFromFont(font) | |
lookupNames = getLookupNamesInFeaLibAstElement(features, featureTags) | |
ligatureNames = getLigaturesInFeaLibAstElement(features, featureTags, lookupNames) | |
while True: | |
numLigas = len(ligatureNames) | |
ligatureNames = getLigatureAlternates(features, ligatureNames) | |
if len(ligatureNames) == numLigas: | |
break | |
return ligatureNames | |
if __name__ == "__main__": | |
font = CurrentFont() | |
featureTags = set(["liga", "dlig", "rlig"]) | |
ligas = getLigaturesInFont(font, featureTags) | |
print(ligas) |
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