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