Bezier Spline: Add a more generalized insertion utility

This logic is from the curve sundivide node, used to add points with
proper handles in between two existing points. However, the same logic
is used for trimming of Bezier splines, and possibly interactive point
insertion in the future, so it's helpful as a general utility.

The logic is converted to depend on a bezier spline instead of being
static. A temporary segment spline can be used for the latter use case.

1 files changed, 40 insertions, 0 deletions

diff --git a/source/blender/blenkernel/intern/spline_bezier.cc b/source/blender/blenkernel/intern/spline_bezier.cc
index 02d26ac715b..b6764f65631 100644
--- a/source/blender/blenkernel/intern/spline_bezier.cc
+++ b/source/blender/blenkernel/intern/spline_bezier.cc
@@ -333,6 +333,46 @@ void BezierSpline::correct_end_tangents() const
   }
 }
 
+/**
+ * De Casteljau Bezier subdivision.
+ * \param index: The index of the segment's start control point.
+ * \param next_index: The index of the control point at the end of the segment. Could be 0,
+ * if the spline is cyclic.
+ * \param parameter: The factor along the segment, between 0 and 1. Note that this is used
+ * directly by the calculation, it doesn't correspond to a portion of the evaluated length.
+ *
+ * <pre>
+ *           handle_prev         handle_next
+ *                x----------------x
+ *               /                  \
+ *              /      x---O---x     \
+ *             /        result        \
+ *            /                        \
+ *           O                          O
+ *       point_prev                  point_next
+ * </pre>
+ */
+BezierSpline::InsertResult BezierSpline::calculate_segment_insertion(const int index,
+                                                                     const int next_index,
+                                                                     const float parameter)
+{
+  BLI_assert(parameter <= 1.0f && parameter >= 0.0f);
+  BLI_assert(next_index == 0 || next_index == index + 1);
+  const float3 &point_prev = positions_[index];
+  const float3 &handle_prev = handle_positions_right_[index];
+  const float3 &handle_next = handle_positions_left_[next_index];
+  const float3 &point_next = positions_[next_index];
+  const float3 center_point = float3::interpolate(handle_prev, handle_next, parameter);
+
+  BezierSpline::InsertResult result;
+  result.handle_prev = float3::interpolate(point_prev, handle_prev, parameter);
+  result.handle_next = float3::interpolate(handle_next, point_next, parameter);
+  result.left_handle = float3::interpolate(result.handle_prev, center_point, parameter);
+  result.right_handle = float3::interpolate(center_point, result.handle_next, parameter);
+  result.position = float3::interpolate(result.left_handle, result.right_handle, parameter);
+  return result;
+}
+
 static void bezier_forward_difference_3d(const float3 &point_0,
                                          const float3 &point_1,
                                          const float3 &point_2,