[filterPen] add decomposing filter pens

Lib/fontTools/pens/filterPen.py

@@ -1,5 +1,7 @@
-from fontTools.pens.basePen import AbstractPen
-from fontTools.pens.pointPen import AbstractPointPen
+from __future__ import annotations
+
+from fontTools.pens.basePen import AbstractPen, DecomposingPen
+from fontTools.pens.pointPen import AbstractPointPen, DecomposingPointPen
 from fontTools.pens.recordingPen import RecordingPen
 
 
@@ -150,8 +152,8 @@ class FilterPointPen(_PassThruComponentsMixin, AbstractPointPen):
     ('endPath', (), {})
     """
 
-    def __init__(self, outPointPen):
-        self._outPen = outPointPen
+    def __init__(self, outPen):
+        self._outPen = outPen
 
     def beginPath(self, **kwargs):
         self._outPen.beginPath(**kwargs)
@@ -161,3 +163,79 @@ def endPath(self):
 
     def addPoint(self, pt, segmentType=None, smooth=False, name=None, **kwargs):
         self._outPen.addPoint(pt, segmentType, smooth, name, **kwargs)
+
+
+class _DecomposingFilterPenMixin:
+    """Mixin class that decomposes components as regular contours.
+
+    Shared by both DecomposingFilterPen and DecomposingFilterPointPen.
+
+    Takes two required parameters, another (segment or point) pen 'outPen' to draw
+    with, and a 'glyphSet' dict of drawable glyph objects to draw components from.
+
+    The 'skipMissingComponents' and 'reverseFlipped' optional arguments work the
+    same as in the DecomposingPen/DecomposingPointPen. Both are False by default.
+
+    In addition, the decomposing filter pens also take the following two options:
+
+    'include' is an optional set of component base glyph names to consider for
+    decomposition; the default include=None means decompose all components no matter
+    the base glyph name).
+
+    'decomposeNested' (bool) controls whether to recurse decomposition into nested
+    components of components (this only matters when 'include' was also provided);
+    if False, only decompose top-level components included in the set, but not
+    also their children.
+    """
+
+    # raises MissingComponentError if base glyph is not found in glyphSet
+    skipMissingComponents = False
+
+    def __init__(
+        self,
+        outPen,
+        glyphSet,
+        skipMissingComponents=None,
+        reverseFlipped=False,
+        include: set[str] | None = None,
+        decomposeNested: bool = True,
+    ):
+        super().__init__(
+            outPen=outPen,
+            glyphSet=glyphSet,
+            skipMissingComponents=skipMissingComponents,
+            reverseFlipped=reverseFlipped,
+        )
+        self.include = include
+        self.decomposeNested = decomposeNested
+
+    def addComponent(self, baseGlyphName, transformation, **kwargs):
+        # only decompose the component if it's included in the set
+        if self.include is None or baseGlyphName in self.include:
+            # if we're decomposing nested components, temporarily set include to None
+            include_bak = self.include
+            if self.decomposeNested and self.include:
+                self.include = None
+            try:
+                super().addComponent(baseGlyphName, transformation, **kwargs)
+            finally:
+                if self.include != include_bak:
+                    self.include = include_bak
+        else:
+            _PassThruComponentsMixin.addComponent(
+                self, baseGlyphName, transformation, **kwargs
+            )
+
+
+class DecomposingFilterPen(_DecomposingFilterPenMixin, DecomposingPen, FilterPen):
+    """Filter pen that draws components as regular contours."""
+
+    pass
+
+
+class DecomposingFilterPointPen(
+    _DecomposingFilterPenMixin, DecomposingPointPen, FilterPointPen
+):
+    """Filter point pen that draws components as regular contours."""
+
+    pass