Decompose transformed components across masters (#609)

* Alter the behaviour of DecomposeTransformedComponents filter to fully decompose a glyph when a transformed component is found.
* Make a note of which glyphs were decomposed by DecomposeTransformedComponents and decompose them in other masters too. Fixes decomposeTransformedComponents does not account for variable fonts #507.

Lib/ufo2ft/filters/decomposeTransformedComponents.py

@@ -8,20 +8,13 @@ class DecomposeTransformedComponentsFilter(BaseFilter):
     def filter(self, glyph):
         if not glyph.components:
             return False
-        transformedComponents = []
+        needs_decomposition = False
         for component in glyph.components:
             if component.transformation[:4] != Identity[:4]:
-                transformedComponents.append(component)
-        if not transformedComponents:
+                needs_decomposition = True
+                break
+        if not needs_decomposition:
             return False
-        specificComponents = [c.baseGlyph for c in transformedComponents]
-        ufo2ft.util.deepCopyContours(
-            self.context.glyphSet,
-            glyph,
-            glyph,
-            Transform(),
-            specificComponents=specificComponents,
-        )
-        for component in transformedComponents:
-            glyph.removeComponent(component)
+        ufo2ft.util.deepCopyContours(self.context.glyphSet, glyph, glyph, Transform())
+        glyph.clearComponents()
         return True

Lib/ufo2ft/preProcessor.py

@@ -7,6 +7,9 @@
 )
 from ufo2ft.filters import isValidFilter, loadFilters
 from ufo2ft.filters.decomposeComponents import DecomposeComponentsFilter
+from ufo2ft.filters.decomposeTransformedComponents import (
+    DecomposeTransformedComponentsFilter,
+)
 from ufo2ft.fontInfoData import getAttrWithFallback
 from ufo2ft.util import _GlyphSet
 
@@ -303,10 +306,20 @@ def __init__(
     def process(self):
         from cu2qu.ufo import fonts_to_quadratic
 
+        needs_decomposition = set()
+
         # first apply all custom pre-filters
         for funcs, ufo, glyphSet in zip(self.preFilters, self.ufos, self.glyphSets):
             for func in funcs:
-                func(ufo, glyphSet)
+                if isinstance(func, DecomposeTransformedComponentsFilter):
+                    needs_decomposition |= func(ufo, glyphSet)
+                else:
+                    func(ufo, glyphSet)
+        # If we decomposed a glyph in some masters, we must ensure it is decomposed in
+        # all masters. (https://github.com/googlefonts/ufo2ft/issues/507)
+        decompose = DecomposeComponentsFilter(include=needs_decomposition)
+        for ufo, glyphSet in zip(self.ufos, self.glyphSets):
+            decompose(ufo, glyphSet)
 
         # then apply all default filters
         for funcs, ufo, glyphSet in zip(self.defaultFilters, self.ufos, self.glyphSets):

tests/filters/decomposeTransformedComponents_test.py

@@ -1,6 +1,7 @@
 from ufo2ft.filters.decomposeTransformedComponents import (
     DecomposeTransformedComponentsFilter,
 )
+from ufo2ft.preProcessor import TTFInterpolatablePreProcessor
 
 
 class DecomposeTransformedComponentsFilterTest:
@@ -56,3 +57,39 @@ def test_transformed_components(self, FontClass):
         # nine.of has no outline and one component, it was not decomposed
         assert len(ufo["nine.of"]) == 0
         assert len(ufo["nine.of"].components) == 1
+
+    def test_decompose_compatibly(self, FontClass):
+        ufo1 = FontClass()
+        c = ufo1.newGlyph("comp")
+        c.width = 300
+        pen = c.getPen()
+        pen.moveTo((0, 0))
+        pen.lineTo((300, 0))
+        pen.lineTo((150, 300))
+        pen.closePath()
+
+        b = ufo1.newGlyph("base")
+        b.width = 300
+        pen = b.getPen()
+        pen.addComponent("comp", (0.5, 0, 0, 0.5, 0, 0))
+
+        ufo2 = FontClass()
+        c = ufo2.newGlyph("comp")
+        c.width = 600
+        pen = c.getPen()
+        pen.moveTo((0, 0))
+        pen.lineTo((600, 0))
+        pen.lineTo((300, 600))
+        pen.closePath()
+
+        b = ufo2.newGlyph("base")
+        b.width = 600
+        pen = b.getPen()
+        pen.addComponent("comp", (1, 0, 0, 1, 0, 0))
+
+        # Because ufo1.base needs decomposing, so should ufo2.base
+        glyphsets = TTFInterpolatablePreProcessor(
+            [ufo1, ufo2], filters=[DecomposeTransformedComponentsFilter(pre=True)]
+        ).process()
+        assert len(glyphsets[0]["base"]) == 1
+        assert len(glyphsets[1]["base"]) == 1