1 files changed, 105 insertions, 0 deletions
diff --git a/Lib/fontTools/pens/qu2cuPen.py b/Lib/fontTools/pens/qu2cuPen.py
new file mode 100644
index 00000000..7e400f98
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+++ b/Lib/fontTools/pens/qu2cuPen.py
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+# Copyright 2016 Google Inc. All Rights Reserved.
+# Copyright 2023 Behdad Esfahbod. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from fontTools.qu2cu import quadratic_to_curves
+from fontTools.pens.filterPen import ContourFilterPen
+from fontTools.pens.reverseContourPen import ReverseContourPen
+import math
+
+
+class Qu2CuPen(ContourFilterPen):
+    """A filter pen to convert quadratic bezier splines to cubic curves
+    using the FontTools SegmentPen protocol.
+
+    Args:
+
+        other_pen: another SegmentPen used to draw the transformed outline.
+        max_err: maximum approximation error in font units. For optimal results,
+            if you know the UPEM of the font, we recommend setting this to a
+            value equal, or close to UPEM / 1000.
+        reverse_direction: flip the contours' direction but keep starting point.
+        stats: a dictionary counting the point numbers of cubic segments.
+    """
+
+    def __init__(
+        self,
+        other_pen,
+        max_err,
+        all_cubic=False,
+        reverse_direction=False,
+        stats=None,
+    ):
+        if reverse_direction:
+            other_pen = ReverseContourPen(other_pen)
+        super().__init__(other_pen)
+        self.all_cubic = all_cubic
+        self.max_err = max_err
+        self.stats = stats
+
+    def _quadratics_to_curve(self, q):
+        curves = quadratic_to_curves(q, self.max_err, all_cubic=self.all_cubic)
+        if self.stats is not None:
+            for curve in curves:
+                n = str(len(curve) - 2)
+                self.stats[n] = self.stats.get(n, 0) + 1
+        for curve in curves:
+            if len(curve) == 4:
+                yield ("curveTo", curve[1:])
+            else:
+                yield ("qCurveTo", curve[1:])
+
+    def filterContour(self, contour):
+        quadratics = []
+        currentPt = None
+        newContour = []
+        for op, args in contour:
+            if op == "qCurveTo" and (
+                self.all_cubic or (len(args) > 2 and args[-1] is not None)
+            ):
+                if args[-1] is None:
+                    raise NotImplementedError(
+                        "oncurve-less contours with all_cubic not implemented"
+                    )
+                quadratics.append((currentPt,) + args)
+            else:
+                if quadratics:
+                    newContour.extend(self._quadratics_to_curve(quadratics))
+                    quadratics = []
+                newContour.append((op, args))
+            currentPt = args[-1] if args else None
+        if quadratics:
+            newContour.extend(self._quadratics_to_curve(quadratics))
+
+        if not self.all_cubic:
+            # Add back implicit oncurve points
+            contour = newContour
+            newContour = []
+            for op, args in contour:
+                if op == "qCurveTo" and newContour and newContour[-1][0] == "qCurveTo":
+                    pt0 = newContour[-1][1][-2]
+                    pt1 = newContour[-1][1][-1]
+                    pt2 = args[0]
+                    if (
+                        pt1 is not None
+                        and math.isclose(pt2[0] - pt1[0], pt1[0] - pt0[0])
+                        and math.isclose(pt2[1] - pt1[1], pt1[1] - pt0[1])
+                    ):
+                        newArgs = newContour[-1][1][:-1] + args
+                        newContour[-1] = (op, newArgs)
+                        continue
+
+                newContour.append((op, args))
+
+        return newContour