Curves: Port curve to mesh node to the new data-block

This commit changes the Curve to Mesh node to work with `Curves`
instead of `CurveEval`. The change ends up basically completely
rewriting the node, since the different attribute storage means that
the decisions made previously don't make much sense anymore.

The main loops are now "for each attribute: for each curve combination"
rather than the other way around, with the goal of taking advantage
of the locality of curve attributes. This improvement is quite
noticeable with many small curves; I measured a 4-5x improvement
(around 4-5s to <1s) when converting millions of curves to tens of
millions of faces. I didn't obverse any change in performance compared
to 3.1 with fewer curves though.

The changes also solve an algorithmic flaw where any interpolated
attributes would be evaluated for every curve combination instead
of just once per curve. This can be a large improvement when there
are many profile curves.

The code relies heavily on a function `foreach_curve_combination`
which calculates some basic information about each combination and
calls a templated function. I made assumptions about unnecessary reads
being removed by compiler optimizations. For further performance
improvements in the future that might be an area to investigate.
Another might be using a "for a group of curves: for each attribute:
for each curve" pattern to increase the locality of memory access.

Differential Revision: https://developer.blender.org/D14642

1 files changed, 29 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_curves.hh b/source/blender/blenkernel/BKE_curves.hh
index 3d912e10fb2..282e2a40bd0 100644
--- a/source/blender/blenkernel/BKE_curves.hh
+++ b/source/blender/blenkernel/BKE_curves.hh
@@ -328,6 +328,10 @@ class CurvesGeometry : public ::CurvesGeometry {
    * calculated. That can be ensured with #ensure_evaluated_offsets.
    */
   void interpolate_to_evaluated(int curve_index, GSpan src, GMutableSpan dst) const;
+  /**
+   * Evaluate generic data for curve control points to the standard evaluated points of the curves.
+   */
+  void interpolate_to_evaluated(GSpan src, GMutableSpan dst) const;
 
  private:
   /**
@@ -446,6 +450,13 @@ bool segment_is_vector(Span<int8_t> handle_types_left,
 bool last_cylic_segment_is_vector(Span<int8_t> handle_types_left, Span<int8_t> handle_types_right);
 
 /**
+ * Return true if the handle types at the index are free (#BEZIER_HANDLE_FREE) or vector
+ * (#BEZIER_HANDLE_VECTOR). In these cases, directional continuitity from the previous and next
+ * evaluated segments is assumed not to be desired.
+ */
+bool point_is_sharp(Span<int8_t> handle_types_left, Span<int8_t> handle_types_right, int index);
+
+/**
  * Calculate offsets into the curve's evaluated points for each control point. While most control
  * point edges generate the number of edges specified by the resolution, vector segments only
  * generate one edge.
@@ -715,4 +726,22 @@ inline float CurvesGeometry::evaluated_length_total_for_curve(const int curve_in
 
 /** \} */
 
+/* -------------------------------------------------------------------- */
+/** \name Bezier Inline Methods
+ * \{ */
+
+namespace curves::bezier {
+
+inline bool point_is_sharp(const Span<int8_t> handle_types_left,
+                           const Span<int8_t> handle_types_right,
+                           const int index)
+{
+  return ELEM(handle_types_left[index], BEZIER_HANDLE_VECTOR, BEZIER_HANDLE_FREE) ||
+         ELEM(handle_types_right[index], BEZIER_HANDLE_VECTOR, BEZIER_HANDLE_FREE);
+}
+
+}  // namespace curves::bezier
+
+/** \} */
+
 }  // namespace blender::bke