Geometry Nodes: Initial basic curve data support

This patch adds initial curve support to geometry nodes. Currently
there is only one node available, the "Curve to Mesh" node, T87428.

However, the aim of the changes here is larger than just supporting
curve data in nodes-- it also uses the opportunity to add better spline
data structures, intended to replace the existing curve evaluation code.
The curve code in Blender is quite old, and it's generally regarded as
some of the messiest, hardest-to-understand code as well. The classes
in `BKE_spline.hh` aim to be faster, more extensible, and much more
easily understandable. Further explanation can be found in comments in
that file.

Initial builtin spline attributes are supported-- reading and writing
from the `cyclic` and `resolution` attributes works with any of the
attribute nodes. Also, only Z-up normal calculation is implemented
at the moment, and tilts do not apply yet.

**Limitations**
 - For now, you must bring curves into the node tree with an "Object
   Info" node. Changes to the curve modifier stack will come later.
 - Converting to a mesh is necessary to visualize the curve data.

Further progress can be tracked in: T87245
Higher level design document: https://wiki.blender.org/wiki/Modules/Physics_Nodes/Projects/EverythingNodes/CurveNodes

Differential Revision: https://developer.blender.org/D11091

1 files changed, 42 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_geometry_set.hh b/source/blender/blenkernel/BKE_geometry_set.hh
index 89cdef34297..2d0f099e5ce 100644
--- a/source/blender/blenkernel/BKE_geometry_set.hh
+++ b/source/blender/blenkernel/BKE_geometry_set.hh
@@ -39,6 +39,7 @@ struct Mesh;
 struct Object;
 struct PointCloud;
 struct Volume;
+class CurveEval;
 
 enum class GeometryOwnershipType {
   /* The geometry is owned. This implies that it can be changed. */
@@ -363,18 +364,25 @@ struct GeometrySet {
       Mesh *mesh, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
   static GeometrySet create_with_pointcloud(
       PointCloud *pointcloud, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
+  static GeometrySet create_with_curve(
+      CurveEval *curve, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
 
   /* Utility methods for access. */
   bool has_mesh() const;
   bool has_pointcloud() const;
   bool has_instances() const;
   bool has_volume() const;
+  bool has_curve() const;
+
   const Mesh *get_mesh_for_read() const;
   const PointCloud *get_pointcloud_for_read() const;
   const Volume *get_volume_for_read() const;
+  const CurveEval *get_curve_for_read() const;
+
   Mesh *get_mesh_for_write();
   PointCloud *get_pointcloud_for_write();
   Volume *get_volume_for_write();
+  CurveEval *get_curve_for_write();
 
   /* Utility methods for replacement. */
   void replace_mesh(Mesh *mesh, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
@@ -382,6 +390,8 @@ struct GeometrySet {
                           GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
   void replace_volume(Volume *volume,
                       GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
+  void replace_curve(CurveEval *curve,
+                     GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
 };
 
 /** A geometry component that can store a mesh. */
@@ -463,6 +473,38 @@ class PointCloudComponent : public GeometryComponent {
   const blender::bke::ComponentAttributeProviders *get_attribute_providers() const final;
 };
 
+/** A geometry component that stores curve data, in other words, a group of splines. */
+class CurveComponent : public GeometryComponent {
+ private:
+  CurveEval *curve_ = nullptr;
+  GeometryOwnershipType ownership_ = GeometryOwnershipType::Owned;
+
+ public:
+  CurveComponent();
+  ~CurveComponent();
+  GeometryComponent *copy() const override;
+
+  void clear();
+  bool has_curve() const;
+  void replace(CurveEval *curve, GeometryOwnershipType ownership = GeometryOwnershipType::Owned);
+  CurveEval *release();
+
+  const CurveEval *get_for_read() const;
+  CurveEval *get_for_write();
+
+  int attribute_domain_size(const AttributeDomain domain) const final;
+
+  bool is_empty() const final;
+
+  bool owns_direct_data() const override;
+  void ensure_owns_direct_data() override;
+
+  static constexpr inline GeometryComponentType static_type = GEO_COMPONENT_TYPE_CURVE;
+
+ private:
+  const blender::bke::ComponentAttributeProviders *get_attribute_providers() const final;
+};
+
 /** A geometry component that stores instances. */
 class InstancesComponent : public GeometryComponent {
  private: