| from __future__ import print_function, division, absolute_import, unicode_literals |
| |
| __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) |
