Curves: Port subdivide node to the new data-block

This commit moves the subdivide curve node implementation to the
geometry module, changes it to work on the new curves data-block,
and adds support for Catmull Rom curves. Internally I also added
support for a curve domain selection. That isn't used, but it's
nice to have the option anyway.

Users should notice better performance as well, since we can avoid
many small allocations, and there is no conversion to and from the
old curve type.

The code uses a similar structure to the resample node (60a6fbf5b599)
and the set type node (9e393fc2f125). The resample curves node can be
restructured to be more similar to this soon though.

Differential Revision: https://developer.blender.org/D15334

3 files changed, 514 insertions, 0 deletions

diff --git a/source/blender/geometry/CMakeLists.txt b/source/blender/geometry/CMakeLists.txt
index 21b2071d0e6..df66a806c16 100644
--- a/source/blender/geometry/CMakeLists.txt
+++ b/source/blender/geometry/CMakeLists.txt
@@ -25,6 +25,7 @@ set(SRC
   intern/resample_curves.cc
   intern/reverse_uv_sampler.cc
   intern/set_curve_type.cc
+  intern/subdivide_curves.cc
   intern/uv_parametrizer.c
 
   GEO_add_curves_on_mesh.hh
@@ -37,6 +38,7 @@ set(SRC
   GEO_resample_curves.hh
   GEO_reverse_uv_sampler.hh
   GEO_set_curve_type.hh
+  GEO_subdivide_curves.hh
   GEO_uv_parametrizer.h
 )
 
diff --git a/source/blender/geometry/GEO_subdivide_curves.hh b/source/blender/geometry/GEO_subdivide_curves.hh
new file mode 100644
index 00000000000..4f671467b24
--- /dev/null
+++ b/source/blender/geometry/GEO_subdivide_curves.hh
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#pragma once
+
+#include "BLI_function_ref.hh"
+#include "BLI_index_mask.hh"
+
+#include "BKE_curves.hh"
+
+struct CurveComponent;
+
+namespace blender::geometry {
+
+/**
+ * Add more points along each segment, with the amount of points to add in each segment described
+ * by the #cuts input. The new points are equidistant in parameter space, but not in the actual
+ * distances.
+ *
+ * \param selection: A selection of curves to consider when subdividing.
+ */
+Curves *subdivide_curves(const CurveComponent &src_component,
+                         const bke::CurvesGeometry &src_curves,
+                         IndexMask selection,
+                         const VArray<int> &cuts);
+
+}  // namespace blender::geometry
diff --git a/source/blender/geometry/intern/subdivide_curves.cc b/source/blender/geometry/intern/subdivide_curves.cc
new file mode 100644
index 00000000000..4fb21e53013
--- /dev/null
+++ b/source/blender/geometry/intern/subdivide_curves.cc
@@ -0,0 +1,486 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include "BKE_attribute_math.hh"
+#include "BKE_curves.hh"
+#include "BKE_curves_utils.hh"
+#include "BKE_geometry_set.hh"
+
+#include "BLI_task.hh"
+
+#include "GEO_subdivide_curves.hh"
+
+namespace blender::geometry {
+
+/**
+ * \warning Only the curve domain of the input is copied, so the result is invalid!
+ */
+static Curves *create_result_curves(const bke::CurvesGeometry &src_curves)
+{
+  Curves *dst_curves_id = bke::curves_new_nomain(0, src_curves.curves_num());
+  bke::CurvesGeometry &dst_curves = bke::CurvesGeometry::wrap(dst_curves_id->geometry);
+  CurveComponent dst_component;
+  dst_component.replace(dst_curves_id, GeometryOwnershipType::Editable);
+  /* Directly copy curve attributes, since they stay the same. */
+  CustomData_copy(&src_curves.curve_data,
+                  &dst_curves.curve_data,
+                  CD_MASK_ALL,
+                  CD_DUPLICATE,
+                  src_curves.curves_num());
+  dst_curves.runtime->type_counts = src_curves.runtime->type_counts;
+
+  return dst_curves_id;
+}
+
+/**
+ * Return a range used to retrieve values from an array of values stored per point, but with an
+ * extra element at the end of each curve. This is useful for offsets within curves, where it is
+ * convenient to store the first 0 and have the last offset be the total result curve size.
+ */
+static IndexRange curve_dst_offsets(const IndexRange points, const int curve_index)
+{
+  return {curve_index + points.start(), points.size() + 1};
+}
+
+static void calculate_result_offsets(const bke::CurvesGeometry &src_curves,
+                                     const IndexMask selection,
+                                     const Span<IndexRange> unselected_ranges,
+                                     const VArray<int> &cuts,
+                                     const Span<bool> cyclic,
+                                     MutableSpan<int> dst_curve_offsets,
+                                     MutableSpan<int> dst_point_offsets)
+{
+  /* Fill the array with each curve's point count, then accumulate them to the offsets. */
+  bke::curves::fill_curve_counts(src_curves, unselected_ranges, dst_curve_offsets);
+  threading::parallel_for(selection.index_range(), 1024, [&](IndexRange range) {
+    for (const int curve_i : selection.slice(range)) {
+      const IndexRange src_points = src_curves.points_for_curve(curve_i);
+      const IndexRange src_segments = curve_dst_offsets(src_points, curve_i);
+
+      MutableSpan<int> point_offsets = dst_point_offsets.slice(src_segments);
+
+      MutableSpan<int> point_counts = point_offsets.drop_back(1);
+      cuts.materialize_compressed(src_points, point_counts);
+      for (int &count : point_counts) {
+        /* Make sure the number of cuts is greater than zero and add one for the existing point. */
+        count = std::max(count, 0) + 1;
+      }
+      if (!cyclic[curve_i]) {
+        /* The last point only has a segment to be subdivided if the curve isn't cyclic. */
+        point_counts.last() = 1;
+      }
+
+      bke::curves::accumulate_counts_to_offsets(point_offsets);
+      dst_curve_offsets[curve_i] = point_offsets.last();
+    }
+  });
+  bke::curves::accumulate_counts_to_offsets(dst_curve_offsets);
+}
+
+struct AttributeTransferData {
+  /* Expect that if an attribute exists, it is stored as a contiguous array internally anyway. */
+  GVArraySpan src;
+  bke::OutputAttribute dst;
+};
+
+static Vector<AttributeTransferData> retrieve_point_attributes(const CurveComponent &src_component,
+                                                               CurveComponent &dst_component,
+                                                               const Set<std::string> &skip = {})
+{
+  Vector<AttributeTransferData> attributes;
+  src_component.attribute_foreach(
+      [&](const bke::AttributeIDRef &id, const AttributeMetaData meta_data) {
+        if (meta_data.domain != ATTR_DOMAIN_POINT) {
+          /* Curve domain attributes are all copied directly to the result in one step. */
+          return true;
+        }
+        if (id.is_named() && skip.contains(id.name())) {
+          return true;
+        }
+
+        GVArray src = src_component.attribute_try_get_for_read(id, ATTR_DOMAIN_POINT);
+        BLI_assert(src);
+        bke::OutputAttribute dst = dst_component.attribute_try_get_for_output_only(
+            id, ATTR_DOMAIN_POINT, meta_data.data_type);
+        BLI_assert(dst);
+        attributes.append({std::move(src), std::move(dst)});
+
+        return true;
+      });
+  return attributes;
+}
+
+template<typename T>
+static inline void linear_interpolation(const T &a, const T &b, MutableSpan<T> dst)
+{
+  dst.first() = a;
+  const float step = 1.0f / dst.size();
+  for (const int i : dst.index_range().drop_front(1)) {
+    dst[i] = attribute_math::mix2(i * step, a, b);
+  }
+}
+
+template<typename T>
+static void subdivide_attribute_linear(const bke::CurvesGeometry &src_curves,
+                                       const bke::CurvesGeometry &dst_curves,
+                                       const IndexMask selection,
+                                       const Span<int> point_offsets,
+                                       const Span<T> src,
+                                       MutableSpan<T> dst)
+{
+  threading::parallel_for(selection.index_range(), 512, [&](IndexRange selection_range) {
+    for (const int curve_i : selection.slice(selection_range)) {
+      const IndexRange src_points = src_curves.points_for_curve(curve_i);
+      const IndexRange src_segments = curve_dst_offsets(src_points, curve_i);
+      const Span<int> offsets = point_offsets.slice(src_segments);
+
+      const IndexRange dst_points = dst_curves.points_for_curve(curve_i);
+      const Span<T> curve_src = src.slice(src_points);
+      MutableSpan<T> curve_dst = dst.slice(dst_points);
+
+      threading::parallel_for(curve_src.index_range().drop_back(1), 1024, [&](IndexRange range) {
+        for (const int i : range) {
+          const IndexRange segment_points = bke::offsets_to_range(offsets, i);
+          linear_interpolation(curve_src[i], curve_src[i + 1], curve_dst.slice(segment_points));
+        }
+      });
+
+      const IndexRange dst_last_segment = bke::offsets_to_range(offsets, src_points.size() - 1);
+      linear_interpolation(curve_src.last(), curve_src.first(), dst.slice(dst_last_segment));
+    }
+  });
+}
+
+static void subdivide_attribute_linear(const bke::CurvesGeometry &src_curves,
+                                       const bke::CurvesGeometry &dst_curves,
+                                       const IndexMask selection,
+                                       const Span<int> point_offsets,
+                                       const GSpan src,
+                                       GMutableSpan dst)
+{
+  attribute_math::convert_to_static_type(dst.type(), [&](auto dummy) {
+    using T = decltype(dummy);
+    subdivide_attribute_linear(
+        src_curves, dst_curves, selection, point_offsets, src.typed<T>(), dst.typed<T>());
+  });
+}
+
+template<typename T>
+static void subdivide_attribute_catmull_rom(const bke::CurvesGeometry &src_curves,
+                                            const bke::CurvesGeometry &dst_curves,
+                                            const IndexMask selection,
+                                            const Span<int> point_offsets,
+                                            const Span<bool> cyclic,
+                                            const Span<T> src,
+                                            MutableSpan<T> dst)
+{
+  threading::parallel_for(selection.index_range(), 512, [&](IndexRange selection_range) {
+    for (const int curve_i : selection.slice(selection_range)) {
+      const IndexRange src_points = src_curves.points_for_curve(curve_i);
+      const IndexRange src_segments = curve_dst_offsets(src_points, curve_i);
+      const IndexRange dst_points = dst_curves.points_for_curve(curve_i);
+
+      bke::curves::catmull_rom::interpolate_to_evaluated(src.slice(src_points),
+                                                         cyclic[curve_i],
+                                                         point_offsets.slice(src_segments),
+                                                         dst.slice(dst_points));
+    }
+  });
+}
+
+static void subdivide_attribute_catmull_rom(const bke::CurvesGeometry &src_curves,
+                                            const bke::CurvesGeometry &dst_curves,
+                                            const IndexMask selection,
+                                            const Span<int> point_offsets,
+                                            const Span<bool> cyclic,
+                                            const GSpan src,
+                                            GMutableSpan dst)
+{
+  attribute_math::convert_to_static_type(dst.type(), [&](auto dummy) {
+    using T = decltype(dummy);
+    subdivide_attribute_catmull_rom(
+        src_curves, dst_curves, selection, point_offsets, cyclic, src.typed<T>(), dst.typed<T>());
+  });
+}
+
+static void subdivide_bezier_segment(const float3 &position_prev,
+                                     const float3 &handle_prev,
+                                     const float3 &handle_next,
+                                     const float3 &position_next,
+                                     const HandleType type_prev,
+                                     const HandleType type_next,
+                                     const IndexRange segment_points,
+                                     MutableSpan<float3> dst_positions,
+                                     MutableSpan<float3> dst_handles_l,
+                                     MutableSpan<float3> dst_handles_r,
+                                     MutableSpan<int8_t> dst_types_l,
+                                     MutableSpan<int8_t> dst_types_r,
+                                     const bool is_last_cyclic_segment)
+{
+  auto fill_segment_handle_types = [&](const HandleType type) {
+    /* Also change the left handle of the control point following the segment's points. And don't
+     * change the left handle of the first point, since that is part of the previous segment. */
+    dst_types_l.slice(segment_points.shift(1)).fill(type);
+    dst_types_r.slice(segment_points).fill(type);
+  };
+
+  if (bke::curves::bezier::segment_is_vector(type_prev, type_next)) {
+    linear_interpolation(position_prev, position_next, dst_positions.slice(segment_points));
+    fill_segment_handle_types(BEZIER_HANDLE_VECTOR);
+  }
+  else {
+    /* The first point in the segment is always copied. */
+    dst_positions[segment_points.first()] = position_prev;
+
+    /* Non-vector segments in the result curve are given free handles. This could possibly be
+     * improved with another pass that sets handles to aligned where possible, but currently that
+     * does not provide much benefit for the increased complexity. */
+    fill_segment_handle_types(BEZIER_HANDLE_FREE);
+
+    /* In order to generate a Bezier curve with the same shape as the input curve, apply the
+     * De Casteljau algorithm iteratively for the provided number of cuts, constantly updating the
+     * previous result point's right handle and the left handle at the end of the segment. */
+    float3 segment_start = position_prev;
+    float3 segment_handle_prev = handle_prev;
+    float3 segment_handle_next = handle_next;
+    const float3 segment_end = position_next;
+
+    for (const int i : IndexRange(segment_points.size() - 1)) {
+      const float parameter = 1.0f / (segment_points.size() - i);
+      const int point_i = segment_points[i];
+      bke::curves::bezier::Insertion insert = bke::curves::bezier::insert(
+          segment_start, segment_handle_prev, segment_handle_next, segment_end, parameter);
+
+      /* Copy relevant temporary data to the result. */
+      dst_handles_r[point_i] = insert.handle_prev;
+      dst_handles_l[point_i + 1] = insert.left_handle;
+      dst_positions[point_i + 1] = insert.position;
+
+      /* Update the segment to prepare it for the next subdivision. */
+      segment_start = insert.position;
+      segment_handle_prev = insert.right_handle;
+      segment_handle_next = insert.handle_next;
+    }
+
+    /* Copy the handles for the last segment from the working variables. */
+    const int i_segment_last = is_last_cyclic_segment ? 0 : segment_points.one_after_last();
+    dst_handles_r[segment_points.last()] = segment_handle_prev;
+    dst_handles_l[i_segment_last] = segment_handle_next;
+  }
+}
+
+static void subdivide_bezier_positions(const Span<float3> src_positions,
+                                       const Span<int8_t> src_types_l,
+                                       const Span<int8_t> src_types_r,
+                                       const Span<float3> src_handles_l,
+                                       const Span<float3> src_handles_r,
+                                       const Span<int> evaluated_offsets,
+                                       const bool cyclic,
+                                       MutableSpan<float3> dst_positions,
+                                       MutableSpan<int8_t> dst_types_l,
+                                       MutableSpan<int8_t> dst_types_r,
+                                       MutableSpan<float3> dst_handles_l,
+                                       MutableSpan<float3> dst_handles_r)
+{
+  threading::parallel_for(src_positions.index_range().drop_back(1), 512, [&](IndexRange range) {
+    for (const int segment_i : range) {
+      const IndexRange segment = bke::offsets_to_range(evaluated_offsets, segment_i);
+      subdivide_bezier_segment(src_positions[segment_i],
+                               src_handles_r[segment_i],
+                               src_handles_l[segment_i + 1],
+                               src_positions[segment_i + 1],
+                               HandleType(src_types_r[segment_i]),
+                               HandleType(src_types_l[segment_i + 1]),
+                               segment,
+                               dst_positions,
+                               dst_handles_l,
+                               dst_handles_r,
+                               dst_types_l,
+                               dst_types_r,
+                               false);
+    }
+  });
+
+  if (cyclic) {
+    const int last_index = src_positions.index_range().last();
+    const IndexRange segment = bke::offsets_to_range(evaluated_offsets, last_index);
+    const HandleType type_prev = HandleType(src_types_r.last());
+    const HandleType type_next = HandleType(src_types_l.first());
+    subdivide_bezier_segment(src_positions.last(),
+                             src_handles_r.last(),
+                             src_handles_l.first(),
+                             src_positions.first(),
+                             type_prev,
+                             type_next,
+                             segment,
+                             dst_positions,
+                             dst_handles_l,
+                             dst_handles_r,
+                             dst_types_l,
+                             dst_types_r,
+                             true);
+
+    if (bke::curves::bezier::segment_is_vector(type_prev, type_next)) {
+      dst_types_l.first() = BEZIER_HANDLE_VECTOR;
+      dst_types_r.last() = BEZIER_HANDLE_VECTOR;
+    }
+    else {
+      dst_types_l.first() = BEZIER_HANDLE_FREE;
+      dst_types_r.last() = BEZIER_HANDLE_FREE;
+    }
+  }
+  else {
+    dst_positions.last() = src_positions.last();
+    dst_types_l.first() = src_types_l.first();
+    dst_types_r.last() = src_types_r.last();
+    dst_handles_l.first() = src_handles_l.first();
+    dst_handles_r.last() = src_handles_r.last();
+  }
+
+  /* TODO: It would be possible to avoid calling this for all segments besides vector segments. */
+  bke::curves::bezier::calculate_auto_handles(
+      cyclic, dst_types_l, dst_types_r, dst_positions, dst_handles_l, dst_handles_r);
+}
+
+Curves *subdivide_curves(const CurveComponent &src_component,
+                         const bke::CurvesGeometry &src_curves,
+                         const IndexMask selection,
+                         const VArray<int> &cuts)
+{
+  const Vector<IndexRange> unselected_ranges = selection.extract_ranges_invert(
+      src_curves.curves_range());
+
+  /* Cyclic is accessed a lot, it's probably worth it to make sure it's a span. */
+  const VArraySpan<bool> cyclic{src_curves.cyclic()};
+
+  Curves *dst_curves_id = create_result_curves(src_curves);
+  bke::CurvesGeometry &dst_curves = bke::CurvesGeometry::wrap(dst_curves_id->geometry);
+  CurveComponent dst_component;
+  dst_component.replace(dst_curves_id, GeometryOwnershipType::Editable);
+
+  /* For each point, this contains the point offset in the corresponding result curve,
+   * starting at zero. For example for two curves with four points each, the values might
+   * look like this:
+   *
+   * |                     | Curve 0           | Curve 1            |
+   * | ------------------- |---|---|---|---|---|---|---|---|---|----|
+   * | Cuts                | 0 | 3 | 0 | 0 | - | 2 | 0 | 0 | 4 | -  |
+   * | New Point Count     | 1 | 4 | 1 | 1 | - | 3 | 1 | 1 | 5 | -  |
+   * | Accumulated Offsets | 0 | 1 | 5 | 6 | 7 | 0 | 3 | 4 | 5 | 10 |
+   *
+   * Storing the leading zero is unnecessary but makes the array a bit simpler to use by avoiding
+   * a check for the first segment, and because some existing utilities also use leading zeros. */
+  Array<int> dst_point_offsets(src_curves.points_num() + src_curves.curves_num());
+#ifdef DEBUG
+  dst_point_offsets.fill(-1);
+#endif
+  calculate_result_offsets(src_curves,
+                           selection,
+                           unselected_ranges,
+                           cuts,
+                           cyclic,
+                           dst_curves.offsets_for_write(),
+                           dst_point_offsets);
+  const Span<int> point_offsets = dst_point_offsets.as_span();
+
+  dst_curves.resize(dst_curves.offsets().last(), dst_curves.curves_num());
+
+  auto subdivide_catmull_rom = [&](IndexMask selection) {
+    for (auto &attribute : retrieve_point_attributes(src_component, dst_component)) {
+      subdivide_attribute_catmull_rom(src_curves,
+                                      dst_curves,
+                                      selection,
+                                      point_offsets,
+                                      cyclic,
+                                      attribute.src,
+                                      attribute.dst.as_span());
+      attribute.dst.save();
+    }
+  };
+
+  auto subdivide_poly = [&](IndexMask selection) {
+    for (auto &attribute : retrieve_point_attributes(src_component, dst_component)) {
+      subdivide_attribute_linear(src_curves,
+                                 dst_curves,
+                                 selection,
+                                 point_offsets,
+                                 attribute.src,
+                                 attribute.dst.as_span());
+      attribute.dst.save();
+    }
+  };
+
+  auto subdivide_bezier = [&](IndexMask selection) {
+    const Span<float3> src_positions = src_curves.positions();
+    const VArraySpan<int8_t> src_types_l{src_curves.handle_types_left()};
+    const VArraySpan<int8_t> src_types_r{src_curves.handle_types_right()};
+    const Span<float3> src_handles_l = src_curves.handle_positions_left();
+    const Span<float3> src_handles_r = src_curves.handle_positions_right();
+
+    MutableSpan<float3> dst_positions = dst_curves.positions_for_write();
+    MutableSpan<int8_t> dst_types_l = dst_curves.handle_types_left_for_write();
+    MutableSpan<int8_t> dst_types_r = dst_curves.handle_types_right_for_write();
+    MutableSpan<float3> dst_handles_l = dst_curves.handle_positions_left_for_write();
+    MutableSpan<float3> dst_handles_r = dst_curves.handle_positions_right_for_write();
+
+    threading::parallel_for(selection.index_range(), 512, [&](IndexRange range) {
+      for (const int curve_i : selection.slice(range)) {
+        const IndexRange src_points = src_curves.points_for_curve(curve_i);
+        const IndexRange src_segments = curve_dst_offsets(src_points, curve_i);
+
+        const IndexRange dst_points = dst_curves.points_for_curve(curve_i);
+        subdivide_bezier_positions(src_positions.slice(src_points),
+                                   src_types_l.slice(src_points),
+                                   src_types_r.slice(src_points),
+                                   src_handles_l.slice(src_points),
+                                   src_handles_r.slice(src_points),
+                                   point_offsets.slice(src_segments),
+                                   cyclic[curve_i],
+                                   dst_positions.slice(dst_points),
+                                   dst_types_l.slice(dst_points),
+                                   dst_types_r.slice(dst_points),
+                                   dst_handles_l.slice(dst_points),
+                                   dst_handles_r.slice(dst_points));
+      }
+    });
+
+    for (auto &attribute : retrieve_point_attributes(src_component,
+                                                     dst_component,
+                                                     {"position",
+                                                      "handle_type_left",
+                                                      "handle_type_right",
+                                                      "handle_right",
+                                                      "handle_left"})) {
+      subdivide_attribute_linear(src_curves,
+                                 dst_curves,
+                                 selection,
+                                 point_offsets,
+                                 attribute.src,
+                                 attribute.dst.as_span());
+      attribute.dst.save();
+    }
+  };
+
+  /* NURBS curves are just treated as poly curves. NURBS subdivision that maintains
+   * their shape may be possible, but probably wouldn't work with the "cuts" input. */
+  auto subdivide_nurbs = subdivide_poly;
+
+  bke::curves::foreach_curve_by_type(src_curves.curve_types(),
+                                     src_curves.curve_type_counts(),
+                                     selection,
+                                     subdivide_catmull_rom,
+                                     subdivide_poly,
+                                     subdivide_bezier,
+                                     subdivide_nurbs);
+
+  if (!unselected_ranges.is_empty()) {
+    for (auto &attribute : retrieve_point_attributes(src_component, dst_component)) {
+      bke::curves::copy_point_data(
+          src_curves, dst_curves, unselected_ranges, attribute.src, attribute.dst.as_span());
+      attribute.dst.save();
+    }
+  }
+
+  return dst_curves_id;
+}
+
+}  // namespace blender::geometry