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instancer: only keep unique FeatureVariationRecords

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After partial instancing, multiple FeatureVariationRecords may end up with
the same set of conditions (e.g. if one references two axes, one of which
is dropped, and a subsequent one also references the same axis that was
kept in the preceding record's condition set, and the min/max values are
the same for both records).
Therefore, we make sure only the first unique record with a given
configuration of conditions is kept. Any additional records with identical
conditions will never match the current context so they can be dropped.
This commit is contained in:
Cosimo Lupo 2019-05-29 18:28:03 +01:00
parent 60754aab8e
commit 11c662ee4d
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GPG Key ID: 20D4A261E4A0E642
1 changed files with 25 additions and 1 deletions
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26
Lib/fontTools/varLib/instancer.py
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@ -415,12 +415,35 @@ def instantiateFeatureVariations(varfont, location):
varfont[tableTag].prune_lookups()
def _featureVariationRecordIsUnique(rec, seen):
conditionSet = []
for cond in rec.ConditionSet.ConditionTable:
if cond.Format != 1:
# can't tell whether this is duplicate, assume not seen
return False
conditionSet.append(
(cond.AxisIndex, cond.FilterRangeMinValue, cond.FilterRangeMaxValue)
)
# besides the set of conditions, we also include the FeatureTableSubstitution
# version to identify unique FeatureVariationRecords, even though only one
# version is currently defined. It's theoretically possible that multiple
# records with same conditions but different substitution table version be
# present in the same font for backward compatibility.
recordKey = frozenset([rec.FeatureTableSubstitution.Version] + conditionSet)
if recordKey in seen:
return False
else:
seen.add(recordKey) # side effect
return True
def _instantiateFeatureVariations(table, fvarAxes, location):
pinnedAxes = set(location.keys())
axisOrder = [axis.axisTag for axis in fvarAxes if axis.axisTag not in pinnedAxes]
axisIndexMap = {axisTag: axisOrder.index(axisTag) for axisTag in axisOrder}
featureVariationApplied = False
uniqueRecords = set()
newRecords = []
for i, record in enumerate(table.FeatureVariations.FeatureVariationRecord):
@ -454,7 +477,8 @@ def _instantiateFeatureVariations(table, fvarAxes, location):
if retainRecord and newConditions:
record.ConditionSet.ConditionTable = newConditions
newRecords.append(record)
if _featureVariationRecordIsUnique(record, uniqueRecords):
newRecords.append(record)
if applies and not featureVariationApplied:
assert record.FeatureTableSubstitution.Version == 0x00010000