Merge pull request #3042 from fonttools/conditionset-consult-avar

Conditionset: consult avar to normalize values

Lib/fontTools/feaLib/ast.py

@@ -2065,7 +2065,7 @@ class ConditionsetStatement(Statement):
         self.conditions = conditions
 
     def build(self, builder):
-        builder.add_conditionset(self.name, self.conditions)
+        builder.add_conditionset(self.location, self.name, self.conditions)
 
     def asFea(self, res="", indent=""):
         res += indent + f"conditionset {self.name} " + "{\n"

Lib/fontTools/feaLib/builder.py

@@ -34,7 +34,7 @@ from fontTools.otlLib.error import OpenTypeLibError
 from fontTools.varLib.varStore import OnlineVarStoreBuilder
 from fontTools.varLib.builder import buildVarDevTable
 from fontTools.varLib.featureVars import addFeatureVariationsRaw
-from fontTools.varLib.models import normalizeValue
+from fontTools.varLib.models import normalizeValue, piecewiseLinearMap
 from collections import defaultdict
 import itertools
 from io import StringIO
@@ -947,11 +947,7 @@ class Builder(object):
         feature_vars = {}
         has_any_variations = False
         # Sort out which lookups to build, gather their indices
-        for (
-            script_,
-            language,
-            feature_tag,
-        ), variations in self.feature_variations_.items():
+        for (_, _, feature_tag), variations in self.feature_variations_.items():
             feature_vars[feature_tag] = []
             for conditionset, builders in variations.items():
                 raw_conditionset = self.conditionsets_[conditionset]
@@ -1572,10 +1568,11 @@ class Builder(object):
     def add_vhea_field(self, key, value):
         self.vhea_[key] = value
 
-    def add_conditionset(self, key, value):
-        if not "fvar" in self.font:
+    def add_conditionset(self, location, key, value):
+        if "fvar" not in self.font:
             raise FeatureLibError(
-                "Cannot add feature variations to a font without an 'fvar' table"
+                "Cannot add feature variations to a font without an 'fvar' table",
+                location,
             )
 
         # Normalize
@@ -1592,6 +1589,18 @@ class Builder(object):
             for tag, (bottom, top) in value.items()
         }
 
+        # NOTE: This might result in rounding errors (off-by-ones) compared to
+        # rules in Designspace files, since we're working with what's in the
+        # `avar` table rather than the original values.
+        if "avar" in self.font:
+            mapping = self.font["avar"].segments
+            value = {
+                axis: tuple(
+                    piecewiseLinearMap(v, mapping[axis]) for v in condition_range
+                )
+                for axis, condition_range in value.items()
+            }
+
         self.conditionsets_[key] = value
 
     def makeOpenTypeAnchor(self, location, anchor):

Tests/feaLib/builder_test.py

@@ -975,6 +975,57 @@ class BuilderTest(unittest.TestCase):
                 f'{name}.fea:{line}:12: Ambiguous "ignore {sub}", there should be least one marked glyph'
             )
 
+    def test_condition_set_avar(self):
+        """Test that the `avar` table is consulted when normalizing user-space
+        values."""
+
+        features = """
+            languagesystem DFLT dflt;
+
+            lookup conditional_sub {
+                sub e by a;
+            } conditional_sub;
+
+            conditionset test {
+                wght 600 1000;
+            } test;
+
+            variation rlig test {
+                lookup conditional_sub;
+            } rlig;
+        """
+
+        def make_mock_vf():
+            font = makeTTFont()
+            font["name"] = newTable("name")
+            addFvar(font, [("wght", 0, 0, 1000, "Weight")], [])
+            del font["name"]
+            return font
+
+        # Without `avar`:
+        font = make_mock_vf()
+        addOpenTypeFeaturesFromString(font, features)
+        assert (
+            font.tables["GSUB"]
+            .table.FeatureVariations.FeatureVariationRecord[0]
+            .ConditionSet.ConditionTable[0]
+            .FilterRangeMinValue
+            == 0.6  # user-space 600
+        )
+
+        # With `avar`, shifting the positive midpoint 0.5 a bit to the right:
+        font = make_mock_vf()
+        font["avar"] = newTable("avar")
+        font["avar"].segments = {"wght": {-1.0: -1.0, 0.0: 0.0, 0.5: 0.625, 1.0: 1.0}}
+        addOpenTypeFeaturesFromString(font, features)
+        assert (
+            font.tables["GSUB"]
+            .table.FeatureVariations.FeatureVariationRecord[0]
+            .ConditionSet.ConditionTable[0]
+            .FilterRangeMinValue
+            == 0.7  # user-space 600 shifted to the right,
+        )
+
 
 def generate_feature_file_test(name):
     return lambda self: self.check_feature_file(name)