make PathPen curveTo/qCurveTo accept variable number of points

When constructing a pathops.Path using the PathPen, we should handle variable number of point arguments to curveTo and qCurveTo, following fontTools' BasePen which is the blueprint of all segment-based pens.

https://github.com/fonttools/fonttools/blob/35856412485bce4a1e6c08cceb52c7a87c75c4ee/Lib/fontTools/pens/basePen.py#L274-L329

Also see unified-font-object/ufo-spec#211

and googlefonts/ufo2ft#468 (comment)

src/python/pathops/__init__.py

@@ -14,6 +14,7 @@
     PathOpsError,
     UnsupportedVerbError,
     OpenPathError,
+    NumberOfPointsError,
     bits2float,
     float2bits,
     decompose_quadratic_segment,

src/python/pathops/_pathops.pxd

@@ -247,7 +247,7 @@ cdef class PathPen:
 
     cpdef lineTo(self, pt)
 
-    cpdef curveTo(self, pt1, pt2, pt3)
+    # def curveTo(self, *points)
 
     # def qCurveTo(self, *points)
 

src/python/pathops/_pathops.pyx

@@ -54,6 +54,10 @@ cdef class OpenPathError(PathOpsError):
     pass
 
 
+cdef class NumberOfPointsError(PathOpsError):
+    pass
+
+
 # Helpers to convert to/from a float and its bit pattern
 
 cdef inline int32_t _float2bits(float x):
@@ -891,16 +895,35 @@ cdef class PathPen:
     cpdef lineTo(self, pt):
         self.path.lineTo(pt[0], pt[1])
 
-    cpdef curveTo(self, pt1, pt2, pt3):
-        # support BasePen "super-beziers"? Nah.
-        self.path.cubicTo(
-            pt1[0], pt1[1],
-            pt2[0], pt2[1],
-            pt3[0], pt3[1])
+    def curveTo(self, *points):
+        num_offcurves = len(points) - 1
+        if num_offcurves == 2:
+            pt1, pt2, pt3 = points
+            self.path.cubicTo(
+                pt1[0], pt1[1],
+                pt2[0], pt2[1],
+                pt3[0], pt3[1])
+        elif num_offcurves == 1:
+            pt1, pt2 = points
+            self.path.quadTo(pt1[0], pt1[1], pt2[0], pt2[1])
+        elif num_offcurves == 0:
+            pt = points[0]
+            self.path.lineTo(pt[0], pt[1])
+        else:
+            # support BasePen "super-beziers"? Nah.
+            raise NumberOfPointsError(
+                "curveTo requires between 1 and 3 points; got %d" % len(points)
+            )
 
     def qCurveTo(self, *points):
-        for pt1, pt2 in _decompose_quadratic_segment(points):
-            self._qCurveToOne(pt1, pt2)
+        num_offcurves = len(points) - 1
+        if num_offcurves > 0:
+            for pt1, pt2 in _decompose_quadratic_segment(points):
+                self._qCurveToOne(pt1, pt2)
+        elif num_offcurves == 0:
+            self.lineTo(points[0])
+        else:
+            raise NumberOfPointsError("qCurveTo requires at least 1 point; got 0")
 
     cdef _qCurveToOne(self, pt1, pt2):
         self.path.quadTo(pt1[0], pt1[1], pt2[0], pt2[1])

tests/pathops_test.py

@@ -11,6 +11,7 @@
     ArcSize,
     Direction,
     simplify,
+    NumberOfPointsError,
 )
 
 import pytest
@@ -106,6 +107,56 @@ def test_decompose_join_quadratic_segments(self):
             ('qCurveTo', ((1.0, 1.0), (2.0, 2.0), (3.0, 3.0))),
             ('closePath', ())]
 
+    def test_qCurveTo_varargs(self):
+        path = Path()
+        pen = path.getPen()
+        pen.moveTo((0, 0))
+        pen.qCurveTo((1, 1))
+        pen.closePath()
+
+        items = list(path)
+        assert len(items) == 3
+        # qcurve without offcurves is stored internally as a line
+        assert items[1][0] == PathVerb.LINE
+        assert items[1][1] == ((1.0, 1.0),)
+
+        assert list(path.segments) == [
+            ('moveTo', ((0.0, 0.0),)),
+            ('lineTo', ((1.0, 1.0),)),
+            ('closePath', ()),
+        ]
+
+        with pytest.raises(
+            NumberOfPointsError, match="qCurveTo requires at least 1 point; got 0"
+        ):
+            pen.qCurveTo()
+
+    def test_curveTo_varargs(self):
+        path = Path()
+        pen = path.getPen()
+        pen.moveTo((0, 0))
+        pen.curveTo((1, 1), (2, 2), (3, 3))  # a cubic
+        pen.curveTo((4, 4), (5, 5))  # a quadratic
+        pen.curveTo((6, 6))  # a line
+        pen.closePath()
+
+        assert list(path.segments) == [
+            ('moveTo', ((0.0, 0.0),)),
+            ('curveTo', ((1.0, 1.0), (2.0, 2.0), (3.0, 3.0))),
+            ('qCurveTo', ((4.0, 4.0), (5.0, 5.0))),
+            ('lineTo', ((6.0, 6.0),)),
+            ('closePath', ()),
+        ]
+
+        with pytest.raises(
+            NumberOfPointsError, match="curveTo requires between 1 and 3 points; got 0"
+        ):
+            pen.curveTo()
+        with pytest.raises(
+            NumberOfPointsError, match="curveTo requires between 1 and 3 points; got 4"
+        ):
+            pen.curveTo((0, 0), (1, 1), (2, 2), (3, 3))
+
     def test_last_implicit_lineTo(self):
         # https://github.com/fonttools/skia-pathops/issues/6
         path = Path()