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Build most compact lookup representation

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This builds all possible representations of a contextual lookup and then selects the most copact
This commit is contained in:
Simon Cozens 2020-11-16 13:42:07 +00:00
parent f6fac3cbbf
commit 07b186a41e
1 changed files with 24 additions and 1 deletions
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25
Lib/fontTools/otlLib/builder.py
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@ -359,8 +359,31 @@ class ChainContextualBuilder(LookupBuilder):
rulesets = self.rulesets()
chaining = any(ruleset.hasPrefixOrSuffix for ruleset in rulesets)
for ruleset in rulesets:
# Determine format strategy. We try to build formats 1, 2 and 3
# subtables and then work out which is best. candidates list holds
# the subtables in each format for this ruleset (including a dummy
# "format 0" to make the addressing match the format numbers).
# We can always build a format 3 lookup by accumulating each of
# the rules into a list, so start with that.
candidates = [None, None, None, []]
for rule in ruleset.rules:
subtables.append(self.buildFormat3Subtable(rule, chaining))
candidates[3].append(self.buildFormat3Subtable(rule, chaining))
# Can we express the whole ruleset as a format 2 subtable?
classdefs = ruleset.format2ClassDefs()
if classdefs:
candidates[2] = [
self.buildFormat2Subtable(ruleset, classdefs, chaining)
]
if not ruleset.hasAnyGlyphClasses:
candidates[1] = [self.buildFormat1Subtable(ruleset, chaining)]
candidates = [x for x in candidates if x is not None]
winner = min(candidates, key=self.getCompiledSize_)
subtables.extend(winner)
# If we are not chaining, lookup type will be automatically fixed by
# buildLookup_
return self.buildLookup_(subtables)