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| __all__ = ["maxCtxFont"] | |
| def maxCtxFont(font): | |
| """Calculate the usMaxContext value for an entire font.""" | |
| maxCtx = 0 | |
| for tag in ("GSUB", "GPOS"): | |
| if tag not in font: | |
| continue | |
| table = font[tag].table | |
| if not table.LookupList: | |
| continue | |
| for lookup in table.LookupList.Lookup: | |
| for st in lookup.SubTable: | |
| maxCtx = maxCtxSubtable(maxCtx, tag, lookup.LookupType, st) | |
| return maxCtx | |
| def maxCtxSubtable(maxCtx, tag, lookupType, st): | |
| """Calculate usMaxContext based on a single lookup table (and an existing | |
| max value). | |
| """ | |
| # single positioning, single / multiple substitution | |
| if (tag == "GPOS" and lookupType == 1) or ( | |
| tag == "GSUB" and lookupType in (1, 2, 3) | |
| ): | |
| maxCtx = max(maxCtx, 1) | |
| # pair positioning | |
| elif tag == "GPOS" and lookupType == 2: | |
| maxCtx = max(maxCtx, 2) | |
| # ligatures | |
| elif tag == "GSUB" and lookupType == 4: | |
| for ligatures in st.ligatures.values(): | |
| for ligature in ligatures: | |
| maxCtx = max(maxCtx, ligature.CompCount) | |
| # context | |
| elif (tag == "GPOS" and lookupType == 7) or (tag == "GSUB" and lookupType == 5): | |
| maxCtx = maxCtxContextualSubtable(maxCtx, st, "Pos" if tag == "GPOS" else "Sub") | |
| # chained context | |
| elif (tag == "GPOS" and lookupType == 8) or (tag == "GSUB" and lookupType == 6): | |
| maxCtx = maxCtxContextualSubtable( | |
| maxCtx, st, "Pos" if tag == "GPOS" else "Sub", "Chain" | |
| ) | |
| # extensions | |
| elif (tag == "GPOS" and lookupType == 9) or (tag == "GSUB" and lookupType == 7): | |
| maxCtx = maxCtxSubtable(maxCtx, tag, st.ExtensionLookupType, st.ExtSubTable) | |
| # reverse-chained context | |
| elif tag == "GSUB" and lookupType == 8: | |
| maxCtx = maxCtxContextualRule(maxCtx, st, "Reverse") | |
| return maxCtx | |
| def maxCtxContextualSubtable(maxCtx, st, ruleType, chain=""): | |
| """Calculate usMaxContext based on a contextual feature subtable.""" | |
| if st.Format == 1: | |
| for ruleset in getattr(st, "%s%sRuleSet" % (chain, ruleType)): | |
| if ruleset is None: | |
| continue | |
| for rule in getattr(ruleset, "%s%sRule" % (chain, ruleType)): | |
| if rule is None: | |
| continue | |
| maxCtx = maxCtxContextualRule(maxCtx, rule, chain) | |
| elif st.Format == 2: | |
| for ruleset in getattr(st, "%s%sClassSet" % (chain, ruleType)): | |
| if ruleset is None: | |
| continue | |
| for rule in getattr(ruleset, "%s%sClassRule" % (chain, ruleType)): | |
| if rule is None: | |
| continue | |
| maxCtx = maxCtxContextualRule(maxCtx, rule, chain) | |
| elif st.Format == 3: | |
| maxCtx = maxCtxContextualRule(maxCtx, st, chain) | |
| return maxCtx | |
| def maxCtxContextualRule(maxCtx, st, chain): | |
| """Calculate usMaxContext based on a contextual feature rule.""" | |
| if not chain: | |
| return max(maxCtx, st.GlyphCount) | |
| elif chain == "Reverse": | |
| return max(maxCtx, st.GlyphCount + st.LookAheadGlyphCount) | |
| return max(maxCtx, st.InputGlyphCount + st.LookAheadGlyphCount) | |