Geometry Nodes: Support for dynamic attributes on curve splines

With this patch you will be able to add and remove attributes from curve
data inside of geometry nodes. The following is currently implemented:
* Adding attributes with any data type to splines or spline points.
* Support for working with multiple splines at the same time.
* Interaction with the three builtin point attributes.
* Resampling attributes in the resample node.

The following is not implemented in this patch:
* Joining attributes when joining splines with the join geometry node.
* Domain interpolation between spline and point domains.
* More efficient ways to call attribute operations once per spline.

Differential Revision: https://developer.blender.org/D11251

1 files changed, 37 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_attribute_access.hh b/source/blender/blenkernel/BKE_attribute_access.hh
index 358daa40723..d81d66951cc 100644
--- a/source/blender/blenkernel/BKE_attribute_access.hh
+++ b/source/blender/blenkernel/BKE_attribute_access.hh
@@ -37,6 +37,11 @@
 struct AttributeMetaData {
   AttributeDomain domain;
   CustomDataType data_type;
+
+  constexpr friend bool operator==(AttributeMetaData a, AttributeMetaData b)
+  {
+    return (a.domain == b.domain) && (a.data_type == b.data_type);
+  }
 };
 
 /**
@@ -305,4 +310,36 @@ template<typename T> class OutputAttribute_Typed {
   }
 };
 
+/**
+ * A basic container around DNA CustomData so that its users
+ * don't have to implement special copy and move constructors.
+ */
+class CustomDataAttributes {
+  /**
+   * #CustomData needs a size to be freed, and unfortunately it isn't stored in the struct
+   * itself, so keep track of the size here so this class can implement its own destructor.
+   * If the implementation of the attribute storage changes, this could be removed.
+   */
+  int size_;
+
+ public:
+  CustomData data;
+
+  CustomDataAttributes();
+  ~CustomDataAttributes();
+  CustomDataAttributes(const CustomDataAttributes &other);
+  CustomDataAttributes(CustomDataAttributes &&other);
+
+  void reallocate(const int size);
+
+  std::optional<blender::fn::GSpan> get_for_read(const blender::StringRef name) const;
+  std::optional<blender::fn::GMutableSpan> get_for_write(const blender::StringRef name);
+  bool create(const blender::StringRef name, const CustomDataType data_type);
+  bool create_by_move(const blender::StringRef name, const CustomDataType data_type, void *buffer);
+  bool remove(const blender::StringRef name);
+
+  bool foreach_attribute(const AttributeForeachCallback callback,
+                         const AttributeDomain domain) const;
+};
+
 }  // namespace blender::bke