When enforcing symmetry, add a point at the origin if currently it's an even number of points

Author: code-monet

gremlin/spline.py

@@ -177,8 +177,10 @@ def _enforce_symmetry(self) -> None:
             p2.x = -p1.x
             p2.y = -p1.y
 
-        if count % 2 != 0:
+        if count % 2:  # Odd number of points.
             self.points[int(count / 2)] = Point2D(0.0, 0.0)
+        else:
+            self.points.insert(int(count / 2), Point2D(0.0, 0.0))
 
     def _default_points(self) -> CoordinateList:
         return [(-1.0, -1.0), (1.0, 1.0)]
@@ -254,8 +256,11 @@ def _enforce_symmetry(self) -> None:
             p2.x = -p1.x
             p2.y = -p1.y
 
-        if count % 2 != 0:
+        if count % 2:  # Odd number of points.
             self.points[int(count / 2)] = Point2D(0.0, 0.0)
+        else:
+            self.points.insert(int(count / 2), Point2D(0.0, 0.0))
+            self.z.insert(int(count / 2), 0.0)
 
     def fit(self) -> None:
         """Computes the second derivatives for the control points."""
@@ -408,8 +413,15 @@ def _enforce_symmetry(self) -> None:
             if cp1.handle_right is not None:
                 cp2.handle_left = cp2.center - (cp1.handle_right - cp1.center)
 
-        if count % 2 != 0:
+        if count % 2:  # Odd number of points.
             self._control_points[int(count / 2)].center = Point2D(0.0, 0.0)
+        else:
+            self._control_points.insert(
+                int(count / 2),
+                CubicBezierSpline.ControlPoint(
+                    Point2D(0, 0), Point2D(-0.05, 0), Point2D(+0.05, 0)
+                ),
+            )
 
     def _default_points(self) -> CoordinateList:
         return [(-1.0, -1.0), (-0.95, -0.95), (0.95, 0.95), (1.0, 1.0)]

test/integration/action_plugins/test_response_curve.py

@@ -374,9 +374,9 @@ def test_cubic_spline_asymmetric(
             (1, 1.0),
             (0.75, 0.58125),
             (0.5, 0.2),
-            (0.25, 0.1048),
+            (0.25, 0.1),
             (0, 0.0),
-            (-0.25, -0.1048),
+            (-0.25, -0.1),
             (-0.5, -0.2),
             (-0.75, -0.58125),
             (-1, -1.0),