Geometry Nodes: refactor virtual array system

Goals of this refactor:
* Simplify creating virtual arrays.
* Simplify passing virtual arrays around.
* Simplify converting between typed and generic virtual arrays.
* Reduce memory allocations.

As a quick reminder, a virtual arrays is a data structure that behaves like an
array (i.e. it can be accessed using an index). However, it may not actually
be stored as array internally. The two most important implementations
of virtual arrays are those that correspond to an actual plain array and those
that have the same value for every index. However, many more
implementations exist for various reasons (interfacing with legacy attributes,
unified iterator over all points in multiple splines, ...).

With this refactor the core types (`VArray`, `GVArray`, `VMutableArray` and
`GVMutableArray`) can be used like "normal values". They typically live
on the stack. Before, they were usually inside a `std::unique_ptr`. This makes
passing them around much easier. Creation of new virtual arrays is also
much simpler now due to some constructors. Memory allocations are
reduced by making use of small object optimization inside the core types.

Previously, `VArray` was a class with virtual methods that had to be overridden
to change the behavior of a the virtual array. Now,`VArray` has a fixed size
and has no virtual methods. Instead it contains a `VArrayImpl` that is
similar to the old `VArray`. `VArrayImpl` should rarely ever be used directly,
unless a new virtual array implementation is added.

To support the small object optimization for many `VArrayImpl` classes,
a new `blender::Any` type is added. It is similar to `std::any` with two
additional features. It has an adjustable inline buffer size and alignment.
The inline buffer size of `std::any` can't be relied on and is usually too
small for our use case here. Furthermore, `blender::Any` can store
additional user-defined type information without increasing the
stack size.

Differential Revision: https://developer.blender.org/D12986

1 files changed, 53 insertions, 39 deletions

diff --git a/source/blender/blenkernel/BKE_geometry_set.hh b/source/blender/blenkernel/BKE_geometry_set.hh
index 58a89d0207a..63ada807c55 100644
--- a/source/blender/blenkernel/BKE_geometry_set.hh
+++ b/source/blender/blenkernel/BKE_geometry_set.hh
@@ -119,10 +119,21 @@ class GeometryComponent {
   /* Get a read-only attribute for the domain based on the given attribute. This can be used to
    * interpolate from one domain to another.
    * Returns null if the interpolation is not implemented. */
-  virtual std::unique_ptr<blender::fn::GVArray> attribute_try_adapt_domain(
-      std::unique_ptr<blender::fn::GVArray> varray,
-      const AttributeDomain from_domain,
-      const AttributeDomain to_domain) const;
+  blender::fn::GVArray attribute_try_adapt_domain(const blender::fn::GVArray &varray,
+                                                  const AttributeDomain from_domain,
+                                                  const AttributeDomain to_domain) const
+  {
+    return this->attribute_try_adapt_domain_impl(varray, from_domain, to_domain);
+  }
+
+  template<typename T>
+  blender::VArray<T> attribute_try_adapt_domain(const blender::VArray<T> &varray,
+                                                const AttributeDomain from_domain,
+                                                const AttributeDomain to_domain) const
+  {
+    return this->attribute_try_adapt_domain_impl(varray, from_domain, to_domain)
+        .template typed<T>();
+  }
 
   /* Returns true when the attribute has been deleted. */
   bool attribute_try_delete(const blender::bke::AttributeIDRef &attribute_id);
@@ -146,16 +157,15 @@ class GeometryComponent {
   /* Get a virtual array to read the data of an attribute on the given domain and data type.
    * Returns null when the attribute does not exist or cannot be converted to the requested domain
    * and data type. */
-  std::unique_ptr<blender::fn::GVArray> attribute_try_get_for_read(
-      const blender::bke::AttributeIDRef &attribute_id,
-      const AttributeDomain domain,
-      const CustomDataType data_type) const;
+  blender::fn::GVArray attribute_try_get_for_read(const blender::bke::AttributeIDRef &attribute_id,
+                                                  const AttributeDomain domain,
+                                                  const CustomDataType data_type) const;
 
   /* Get a virtual array to read the data of an attribute on the given domain. The data type is
    * left unchanged. Returns null when the attribute does not exist or cannot be adapted to the
    * requested domain. */
-  std::unique_ptr<blender::fn::GVArray> attribute_try_get_for_read(
-      const blender::bke::AttributeIDRef &attribute_id, const AttributeDomain domain) const;
+  blender::fn::GVArray attribute_try_get_for_read(const blender::bke::AttributeIDRef &attribute_id,
+                                                  const AttributeDomain domain) const;
 
   /* Get a virtual array to read data of an attribute with the given data type. The domain is
    * left unchanged. Returns null when the attribute does not exist or cannot be converted to the
@@ -165,25 +175,22 @@ class GeometryComponent {
 
   /* Get a virtual array to read the data of an attribute. If that is not possible, the returned
    * virtual array will contain a default value. This never returns null. */
-  std::unique_ptr<blender::fn::GVArray> attribute_get_for_read(
-      const blender::bke::AttributeIDRef &attribute_id,
-      const AttributeDomain domain,
-      const CustomDataType data_type,
-      const void *default_value = nullptr) const;
+  blender::fn::GVArray attribute_get_for_read(const blender::bke::AttributeIDRef &attribute_id,
+                                              const AttributeDomain domain,
+                                              const CustomDataType data_type,
+                                              const void *default_value = nullptr) const;
 
   /* Should be used instead of the method above when the requested data type is known at compile
    * time for better type safety. */
   template<typename T>
-  blender::fn::GVArray_Typed<T> attribute_get_for_read(
-      const blender::bke::AttributeIDRef &attribute_id,
-      const AttributeDomain domain,
-      const T &default_value) const
+  blender::VArray<T> attribute_get_for_read(const blender::bke::AttributeIDRef &attribute_id,
+                                            const AttributeDomain domain,
+                                            const T &default_value) const
   {
     const blender::fn::CPPType &cpp_type = blender::fn::CPPType::get<T>();
     const CustomDataType type = blender::bke::cpp_type_to_custom_data_type(cpp_type);
-    std::unique_ptr varray = this->attribute_get_for_read(
-        attribute_id, domain, type, &default_value);
-    return blender::fn::GVArray_Typed<T>(std::move(varray));
+    return this->attribute_get_for_read(attribute_id, domain, type, &default_value)
+        .template typed<T>();
   }
 
   /**
@@ -234,6 +241,11 @@ class GeometryComponent {
 
  private:
   virtual const blender::bke::ComponentAttributeProviders *get_attribute_providers() const;
+
+  virtual blender::fn::GVArray attribute_try_adapt_domain_impl(
+      const blender::fn::GVArray &varray,
+      const AttributeDomain from_domain,
+      const AttributeDomain to_domain) const;
 };
 
 template<typename T>
@@ -391,10 +403,6 @@ class MeshComponent : public GeometryComponent {
   Mesh *get_for_write();
 
   int attribute_domain_size(const AttributeDomain domain) const final;
-  std::unique_ptr<blender::fn::GVArray> attribute_try_adapt_domain(
-      std::unique_ptr<blender::fn::GVArray> varray,
-      const AttributeDomain from_domain,
-      const AttributeDomain to_domain) const final;
 
   bool is_empty() const final;
 
@@ -405,6 +413,11 @@ class MeshComponent : public GeometryComponent {
 
  private:
   const blender::bke::ComponentAttributeProviders *get_attribute_providers() const final;
+
+  blender::fn::GVArray attribute_try_adapt_domain_impl(
+      const blender::fn::GVArray &varray,
+      const AttributeDomain from_domain,
+      const AttributeDomain to_domain) const final;
 };
 
 /** A geometry component that stores a point cloud. */
@@ -469,10 +482,6 @@ class CurveComponent : public GeometryComponent {
   CurveEval *get_for_write();
 
   int attribute_domain_size(const AttributeDomain domain) const final;
-  std::unique_ptr<blender::fn::GVArray> attribute_try_adapt_domain(
-      std::unique_ptr<blender::fn::GVArray> varray,
-      const AttributeDomain from_domain,
-      const AttributeDomain to_domain) const final;
 
   bool is_empty() const final;
 
@@ -485,6 +494,11 @@ class CurveComponent : public GeometryComponent {
 
  private:
   const blender::bke::ComponentAttributeProviders *get_attribute_providers() const final;
+
+  blender::fn::GVArray attribute_try_adapt_domain_impl(
+      const blender::fn::GVArray &varray,
+      const AttributeDomain from_domain,
+      const AttributeDomain to_domain) const final;
 };
 
 class InstanceReference {
@@ -759,9 +773,9 @@ class AttributeFieldInput : public fn::FieldInput {
     return name_;
   }
 
-  const GVArray *get_varray_for_context(const fn::FieldContext &context,
-                                        IndexMask mask,
-                                        ResourceScope &scope) const override;
+  GVArray get_varray_for_context(const fn::FieldContext &context,
+                                 IndexMask mask,
+                                 ResourceScope &scope) const override;
 
   std::string socket_inspection_name() const override;
 
@@ -776,9 +790,9 @@ class IDAttributeFieldInput : public fn::FieldInput {
     category_ = Category::Generated;
   }
 
-  const GVArray *get_varray_for_context(const fn::FieldContext &context,
-                                        IndexMask mask,
-                                        ResourceScope &scope) const override;
+  GVArray get_varray_for_context(const fn::FieldContext &context,
+                                 IndexMask mask,
+                                 ResourceScope &scope) const override;
 
   std::string socket_inspection_name() const override;
 
@@ -815,9 +829,9 @@ class AnonymousAttributeFieldInput : public fn::FieldInput {
     return fn::Field<T>{field_input};
   }
 
-  const GVArray *get_varray_for_context(const fn::FieldContext &context,
-                                        IndexMask mask,
-                                        ResourceScope &scope) const override;
+  GVArray get_varray_for_context(const fn::FieldContext &context,
+                                 IndexMask mask,
+                                 ResourceScope &scope) const override;
 
   std::string socket_inspection_name() const override;