Geometry Nodes: use virtual arrays in internal attribute api

A virtual array is a data structure that is similar to a normal array
in that its elements can be accessed by an index. However, a virtual
array does not have to be a contiguous array internally. Instead, its
elements can be layed out arbitrarily while element access happens
through a virtual function call. However, the virtual array data
structures are designed so that the virtual function call can be avoided
in cases where it could become a bottleneck.

Most commonly, a virtual array is backed by an actual array/span or
is a single value internally, that is the same for every index.
Besides those, there are many more specialized virtual arrays like the
ones that provides vertex positions based on the `MVert` struct or
vertex group weights.

Not all attributes used by geometry nodes are stored in simple contiguous
arrays. To provide uniform access to all kinds of attributes, the attribute
API has to provide virtual array functionality that hides the implementation
details of attributes.

Before this refactor, the attribute API provided its own virtual array
implementation as part of the `ReadAttribute` and `WriteAttribute` types.
That resulted in unnecessary code duplication with the virtual array system.
Even worse, it bound many algorithms used by geometry nodes to the specifics
of the attribute API, even though they could also use different data sources
(such as data from sockets, default values, later results of expressions, ...).

This refactor removes the `ReadAttribute` and `WriteAttribute` types and
replaces them with `GVArray` and `GVMutableArray` respectively. The `GV`
stands for "generic virtual". The "generic" means that the data type contained
in those virtual arrays is only known at run-time. There are the corresponding
statically typed types `VArray<T>` and `VMutableArray<T>` as well.

No regressions are expected from this refactor. It does come with one
improvement for users. The attribute API can convert the data type
on write now. This is especially useful when writing to builtin attributes
like `material_index` with e.g. the Attribute Math node (which usually
just writes to float attributes, while `material_index` is an integer attribute).

Differential Revision: https://developer.blender.org/D10994

1 files changed, 174 insertions, 221 deletions

diff --git a/source/blender/blenkernel/intern/geometry_component_mesh.cc b/source/blender/blenkernel/intern/geometry_component_mesh.cc
index 150cc4589c8..e5accd98952 100644
--- a/source/blender/blenkernel/intern/geometry_component_mesh.cc
+++ b/source/blender/blenkernel/intern/geometry_component_mesh.cc
@@ -32,7 +32,7 @@
 /* Can't include BKE_object_deform.h right now, due to an enum forward declaration.  */
 extern "C" MDeformVert *BKE_object_defgroup_data_create(ID *id);
 
-using blender::bke::ReadAttributePtr;
+using blender::fn::GVArray;
 
 /* -------------------------------------------------------------------- */
 /** \name Geometry Component Implementation
@@ -201,14 +201,14 @@ namespace blender::bke {
 
 template<typename T>
 static void adapt_mesh_domain_corner_to_point_impl(const Mesh &mesh,
-                                                   const TypedReadAttribute<T> &attribute,
+                                                   const VArray<T> &old_values,
                                                    MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totvert);
   attribute_math::DefaultMixer<T> mixer(r_values);
 
   for (const int loop_index : IndexRange(mesh.totloop)) {
-    const T value = attribute[loop_index];
+    const T value = old_values[loop_index];
     const MLoop &loop = mesh.mloop[loop_index];
     const int point_index = loop.v;
     mixer.mix_in(point_index, value);
@@ -216,43 +216,40 @@ static void adapt_mesh_domain_corner_to_point_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_corner_to_point(const Mesh &mesh,
-                                                          ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_corner_to_point(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       /* We compute all interpolated values at once, because for this interpolation, one has to
        * iterate over all loops anyway. */
       Array<T> values(mesh.totvert);
-      adapt_mesh_domain_corner_to_point_impl<T>(mesh, *attribute, values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_corner_to_point_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 static void adapt_mesh_domain_point_to_corner_impl(const Mesh &mesh,
-                                                   const TypedReadAttribute<T> &attribute,
+                                                   const VArray<T> &old_values,
                                                    MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totloop);
 
   for (const int loop_index : IndexRange(mesh.totloop)) {
     const int vertex_index = mesh.mloop[loop_index].v;
-    r_values[loop_index] = attribute[vertex_index];
+    r_values[loop_index] = old_values[vertex_index];
   }
 }
 
-static ReadAttributePtr adapt_mesh_domain_point_to_corner(const Mesh &mesh,
-                                                          ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_point_to_corner(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     /* It is not strictly necessary to compute the value for all corners here. Instead one could
@@ -260,11 +257,10 @@ static ReadAttributePtr adapt_mesh_domain_point_to_corner(const Mesh &mesh,
      * when an algorithm only accesses very few of the corner values. However, for the algorithms
      * we currently have, precomputing the array is fine. Also, it is easier to implement. */
     Array<T> values(mesh.totloop);
-    adapt_mesh_domain_point_to_corner_impl<T>(mesh, *attribute, values);
-    new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_CORNER,
-                                                                 std::move(values));
+    adapt_mesh_domain_point_to_corner_impl<T>(mesh, varray->typed<T>(), values);
+    new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
   });
-  return new_attribute;
+  return new_varray;
 }
 
 /**
@@ -274,7 +270,7 @@ static ReadAttributePtr adapt_mesh_domain_point_to_corner(const Mesh &mesh,
  */
 template<typename T>
 static void adapt_mesh_domain_corner_to_face_impl(const Mesh &mesh,
-                                                  Span<T> old_values,
+                                                  const VArray<T> &old_values,
                                                   MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totpoly);
@@ -291,26 +287,24 @@ static void adapt_mesh_domain_corner_to_face_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_corner_to_face(const Mesh &mesh,
-                                                         ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_corner_to_face(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totpoly);
-      adapt_mesh_domain_corner_to_face_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_corner_to_face_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 static void adapt_mesh_domain_corner_to_edge_impl(const Mesh &mesh,
-                                                  Span<T> old_values,
+                                                  const VArray<T> &old_values,
                                                   MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totedge);
@@ -332,26 +326,24 @@ static void adapt_mesh_domain_corner_to_edge_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_corner_to_edge(const Mesh &mesh,
-                                                         ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_corner_to_edge(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totedge);
-      adapt_mesh_domain_corner_to_edge_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_corner_to_edge_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 void adapt_mesh_domain_face_to_point_impl(const Mesh &mesh,
-                                          Span<T> old_values,
+                                          const VArray<T> &old_values,
                                           MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totvert);
@@ -370,26 +362,24 @@ void adapt_mesh_domain_face_to_point_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_face_to_point(const Mesh &mesh,
-                                                        ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_face_to_point(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totvert);
-      adapt_mesh_domain_face_to_point_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_face_to_point_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 void adapt_mesh_domain_face_to_corner_impl(const Mesh &mesh,
-                                           const Span<T> old_values,
+                                           const VArray<T> &old_values,
                                            MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totloop);
@@ -401,26 +391,24 @@ void adapt_mesh_domain_face_to_corner_impl(const Mesh &mesh,
   }
 }
 
-static ReadAttributePtr adapt_mesh_domain_face_to_corner(const Mesh &mesh,
-                                                         ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_face_to_corner(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totloop);
-      adapt_mesh_domain_face_to_corner_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_face_to_corner_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 void adapt_mesh_domain_face_to_edge_impl(const Mesh &mesh,
-                                         const Span<T> old_values,
+                                         const VArray<T> &old_values,
                                          MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totedge);
@@ -437,21 +425,19 @@ void adapt_mesh_domain_face_to_edge_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_face_to_edge(const Mesh &mesh,
-                                                       ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_face_to_edge(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totedge);
-      adapt_mesh_domain_face_to_edge_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_face_to_edge_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 /**
@@ -461,7 +447,7 @@ static ReadAttributePtr adapt_mesh_domain_face_to_edge(const Mesh &mesh,
  */
 template<typename T>
 static void adapt_mesh_domain_point_to_face_impl(const Mesh &mesh,
-                                                 const Span<T> old_values,
+                                                 const VArray<T> &old_values,
                                                  MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totpoly);
@@ -478,21 +464,19 @@ static void adapt_mesh_domain_point_to_face_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_point_to_face(const Mesh &mesh,
-                                                        ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_point_to_face(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totpoly);
-      adapt_mesh_domain_point_to_face_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_point_to_face_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 /**
@@ -502,7 +486,7 @@ static ReadAttributePtr adapt_mesh_domain_point_to_face(const Mesh &mesh,
  */
 template<typename T>
 static void adapt_mesh_domain_point_to_edge_impl(const Mesh &mesh,
-                                                 const Span<T> old_values,
+                                                 const VArray<T> &old_values,
                                                  MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totedge);
@@ -517,26 +501,24 @@ static void adapt_mesh_domain_point_to_edge_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_point_to_edge(const Mesh &mesh,
-                                                        ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_point_to_edge(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totedge);
-      adapt_mesh_domain_point_to_edge_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_point_to_edge_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 void adapt_mesh_domain_edge_to_corner_impl(const Mesh &mesh,
-                                           const Span<T> old_values,
+                                           const VArray<T> &old_values,
                                            MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totloop);
@@ -558,26 +540,24 @@ void adapt_mesh_domain_edge_to_corner_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_edge_to_corner(const Mesh &mesh,
-                                                         ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_edge_to_corner(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totloop);
-      adapt_mesh_domain_edge_to_corner_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_edge_to_corner_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 template<typename T>
 static void adapt_mesh_domain_edge_to_point_impl(const Mesh &mesh,
-                                                 const Span<T> old_values,
+                                                 const VArray<T> &old_values,
                                                  MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totvert);
@@ -593,21 +573,19 @@ static void adapt_mesh_domain_edge_to_point_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_edge_to_point(const Mesh &mesh,
-                                                        ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_edge_to_point(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totvert);
-      adapt_mesh_domain_edge_to_point_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_edge_to_point_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 /**
@@ -617,7 +595,7 @@ static ReadAttributePtr adapt_mesh_domain_edge_to_point(const Mesh &mesh,
  */
 template<typename T>
 static void adapt_mesh_domain_edge_to_face_impl(const Mesh &mesh,
-                                                const Span<T> old_values,
+                                                const VArray<T> &old_values,
                                                 MutableSpan<T> r_values)
 {
   BLI_assert(r_values.size() == mesh.totpoly);
@@ -634,87 +612,86 @@ static void adapt_mesh_domain_edge_to_face_impl(const Mesh &mesh,
   mixer.finalize();
 }
 
-static ReadAttributePtr adapt_mesh_domain_edge_to_face(const Mesh &mesh,
-                                                       ReadAttributePtr attribute)
+static GVArrayPtr adapt_mesh_domain_edge_to_face(const Mesh &mesh, GVArrayPtr varray)
 {
-  ReadAttributePtr new_attribute;
-  const CustomDataType data_type = attribute->custom_data_type();
+  GVArrayPtr new_varray;
+  const CustomDataType data_type = cpp_type_to_custom_data_type(varray->type());
   attribute_math::convert_to_static_type(data_type, [&](auto dummy) {
     using T = decltype(dummy);
     if constexpr (!std::is_void_v<attribute_math::DefaultMixer<T>>) {
       Array<T> values(mesh.totpoly);
-      adapt_mesh_domain_edge_to_face_impl<T>(mesh, attribute->get_span<T>(), values);
-      new_attribute = std::make_unique<OwnedArrayReadAttribute<T>>(ATTR_DOMAIN_POINT,
-                                                                   std::move(values));
+      adapt_mesh_domain_edge_to_face_impl<T>(mesh, varray->typed<T>(), values);
+      new_varray = std::make_unique<fn::GVArray_For_ArrayContainer<Array<T>>>(std::move(values));
     }
   });
-  return new_attribute;
+  return new_varray;
 }
 
 }  // namespace blender::bke
 
-ReadAttributePtr MeshComponent::attribute_try_adapt_domain(ReadAttributePtr attribute,
-                                                           const AttributeDomain new_domain) const
+blender::fn::GVArrayPtr MeshComponent::attribute_try_adapt_domain(
+    blender::fn::GVArrayPtr varray,
+    const AttributeDomain from_domain,
+    const AttributeDomain to_domain) const
 {
-  if (!attribute) {
+  if (!varray) {
     return {};
   }
-  if (attribute->size() == 0) {
+  if (varray->size() == 0) {
     return {};
   }
-  const AttributeDomain old_domain = attribute->domain();
-  if (old_domain == new_domain) {
-    return attribute;
+  if (from_domain == to_domain) {
+    return varray;
   }
 
-  switch (old_domain) {
+  switch (from_domain) {
     case ATTR_DOMAIN_CORNER: {
-      switch (new_domain) {
+      switch (to_domain) {
         case ATTR_DOMAIN_POINT:
-          return blender::bke::adapt_mesh_domain_corner_to_point(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_corner_to_point(*mesh_, std::move(varray));
         case ATTR_DOMAIN_FACE:
-          return blender::bke::adapt_mesh_domain_corner_to_face(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_corner_to_face(*mesh_, std::move(varray));
         case ATTR_DOMAIN_EDGE:
-          return blender::bke::adapt_mesh_domain_corner_to_edge(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_corner_to_edge(*mesh_, std::move(varray));
         default:
           break;
       }
       break;
     }
     case ATTR_DOMAIN_POINT: {
-      switch (new_domain) {
+      switch (to_domain) {
         case ATTR_DOMAIN_CORNER:
-          return blender::bke::adapt_mesh_domain_point_to_corner(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_point_to_corner(*mesh_, std::move(varray));
         case ATTR_DOMAIN_FACE:
-          return blender::bke::adapt_mesh_domain_point_to_face(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_point_to_face(*mesh_, std::move(varray));
         case ATTR_DOMAIN_EDGE:
-          return blender::bke::adapt_mesh_domain_point_to_edge(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_point_to_edge(*mesh_, std::move(varray));
         default:
           break;
       }
       break;
     }
     case ATTR_DOMAIN_FACE: {
-      switch (new_domain) {
+      switch (to_domain) {
         case ATTR_DOMAIN_POINT:
-          return blender::bke::adapt_mesh_domain_face_to_point(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_face_to_point(*mesh_, std::move(varray));
         case ATTR_DOMAIN_CORNER:
-          return blender::bke::adapt_mesh_domain_face_to_corner(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_face_to_corner(*mesh_, std::move(varray));
         case ATTR_DOMAIN_EDGE:
-          return blender::bke::adapt_mesh_domain_face_to_edge(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_face_to_edge(*mesh_, std::move(varray));
         default:
           break;
       }
       break;
     }
     case ATTR_DOMAIN_EDGE: {
-      switch (new_domain) {
+      switch (to_domain) {
         case ATTR_DOMAIN_CORNER:
-          return blender::bke::adapt_mesh_domain_edge_to_corner(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_edge_to_corner(*mesh_, std::move(varray));
         case ATTR_DOMAIN_POINT:
-          return blender::bke::adapt_mesh_domain_edge_to_point(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_edge_to_point(*mesh_, std::move(varray));
         case ATTR_DOMAIN_FACE:
-          return blender::bke::adapt_mesh_domain_edge_to_face(*mesh_, std::move(attribute));
+          return blender::bke::adapt_mesh_domain_edge_to_face(*mesh_, std::move(varray));
         default:
           break;
       }
@@ -743,25 +720,21 @@ static const Mesh *get_mesh_from_component_for_read(const GeometryComponent &com
 
 namespace blender::bke {
 
-template<typename StructT,
-         typename ElemT,
-         ElemT (*GetFunc)(const StructT &),
-         AttributeDomain Domain>
-static ReadAttributePtr make_derived_read_attribute(const void *data, const int domain_size)
+template<typename StructT, typename ElemT, ElemT (*GetFunc)(const StructT &)>
+static GVArrayPtr make_derived_read_attribute(const void *data, const int domain_size)
 {
-  return std::make_unique<DerivedArrayReadAttribute<StructT, ElemT, GetFunc>>(
-      Domain, Span<StructT>((const StructT *)data, domain_size));
+  return std::make_unique<fn::GVArray_For_DerivedSpan<StructT, ElemT, GetFunc>>(
+      Span<StructT>((const StructT *)data, domain_size));
 }
 
 template<typename StructT,
          typename ElemT,
          ElemT (*GetFunc)(const StructT &),
-         void (*SetFunc)(StructT &, const ElemT &),
-         AttributeDomain Domain>
-static WriteAttributePtr make_derived_write_attribute(void *data, const int domain_size)
+         void (*SetFunc)(StructT &, ElemT)>
+static GVMutableArrayPtr make_derived_write_attribute(void *data, const int domain_size)
 {
-  return std::make_unique<DerivedArrayWriteAttribute<StructT, ElemT, GetFunc, SetFunc>>(
-      Domain, MutableSpan<StructT>((StructT *)data, domain_size));
+  return std::make_unique<fn::GVMutableArray_For_DerivedSpan<StructT, ElemT, GetFunc, SetFunc>>(
+      MutableSpan<StructT>((StructT *)data, domain_size));
 }
 
 static float3 get_vertex_position(const MVert &vert)
@@ -769,7 +742,7 @@ static float3 get_vertex_position(const MVert &vert)
   return float3(vert.co);
 }
 
-static void set_vertex_position(MVert &vert, const float3 &position)
+static void set_vertex_position(MVert &vert, float3 position)
 {
   copy_v3_v3(vert.co, position);
 }
@@ -787,7 +760,7 @@ static int get_material_index(const MPoly &mpoly)
   return static_cast<int>(mpoly.mat_nr);
 }
 
-static void set_material_index(MPoly &mpoly, const int &index)
+static void set_material_index(MPoly &mpoly, int index)
 {
   mpoly.mat_nr = static_cast<short>(std::clamp(index, 0, SHRT_MAX));
 }
@@ -797,7 +770,7 @@ static bool get_shade_smooth(const MPoly &mpoly)
   return mpoly.flag & ME_SMOOTH;
 }
 
-static void set_shade_smooth(MPoly &mpoly, const bool &value)
+static void set_shade_smooth(MPoly &mpoly, bool value)
 {
   SET_FLAG_FROM_TEST(mpoly.flag, value, ME_SMOOTH);
 }
@@ -807,7 +780,7 @@ static float2 get_loop_uv(const MLoopUV &uv)
   return float2(uv.uv);
 }
 
-static void set_loop_uv(MLoopUV &uv, const float2 &co)
+static void set_loop_uv(MLoopUV &uv, float2 co)
 {
   copy_v2_v2(uv.uv, co);
 }
@@ -821,7 +794,7 @@ static Color4f get_loop_color(const MLoopCol &col)
   return linear_color;
 }
 
-static void set_loop_color(MLoopCol &col, const Color4f &linear_color)
+static void set_loop_color(MLoopCol &col, Color4f linear_color)
 {
   linearrgb_to_srgb_uchar4(&col.r, linear_color);
 }
@@ -831,71 +804,62 @@ static float get_crease(const MEdge &edge)
   return edge.crease / 255.0f;
 }
 
-static void set_crease(MEdge &edge, const float &value)
+static void set_crease(MEdge &edge, float value)
 {
   edge.crease = round_fl_to_uchar_clamp(value * 255.0f);
 }
 
-class VertexWeightWriteAttribute final : public WriteAttribute {
+class VMutableArray_For_VertexWeights final : public VMutableArray<float> {
  private:
   MDeformVert *dverts_;
   const int dvert_index_;
 
  public:
-  VertexWeightWriteAttribute(MDeformVert *dverts, const int totvert, const int dvert_index)
-      : WriteAttribute(ATTR_DOMAIN_POINT, CPPType::get<float>(), totvert),
-        dverts_(dverts),
-        dvert_index_(dvert_index)
+  VMutableArray_For_VertexWeights(MDeformVert *dverts, const int totvert, const int dvert_index)
+      : VMutableArray<float>(totvert), dverts_(dverts), dvert_index_(dvert_index)
   {
   }
 
-  void get_internal(const int64_t index, void *r_value) const override
+  float get_impl(const int64_t index) const override
   {
-    get_internal(dverts_, dvert_index_, index, r_value);
+    return get_internal(dverts_, dvert_index_, index);
   }
 
-  void set_internal(const int64_t index, const void *value) override
+  void set_impl(const int64_t index, const float value) override
   {
     MDeformWeight *weight = BKE_defvert_ensure_index(&dverts_[index], dvert_index_);
-    weight->weight = *reinterpret_cast<const float *>(value);
+    weight->weight = value;
   }
 
-  static void get_internal(const MDeformVert *dverts,
-                           const int dvert_index,
-                           const int64_t index,
-                           void *r_value)
+  static float get_internal(const MDeformVert *dverts, const int dvert_index, const int64_t index)
   {
     if (dverts == nullptr) {
-      *(float *)r_value = 0.0f;
-      return;
+      return 0.0f;
     }
     const MDeformVert &dvert = dverts[index];
     for (const MDeformWeight &weight : Span(dvert.dw, dvert.totweight)) {
       if (weight.def_nr == dvert_index) {
-        *(float *)r_value = weight.weight;
-        return;
+        return weight.weight;
       }
     }
-    *(float *)r_value = 0.0f;
+    return 0.0f;
   }
 };
 
-class VertexWeightReadAttribute final : public ReadAttribute {
+class VArray_For_VertexWeights final : public VArray<float> {
  private:
   const MDeformVert *dverts_;
   const int dvert_index_;
 
  public:
-  VertexWeightReadAttribute(const MDeformVert *dverts, const int totvert, const int dvert_index)
-      : ReadAttribute(ATTR_DOMAIN_POINT, CPPType::get<float>(), totvert),
-        dverts_(dverts),
-        dvert_index_(dvert_index)
+  VArray_For_VertexWeights(const MDeformVert *dverts, const int totvert, const int dvert_index)
+      : VArray<float>(totvert), dverts_(dverts), dvert_index_(dvert_index)
   {
   }
 
-  void get_internal(const int64_t index, void *r_value) const override
+  float get_impl(const int64_t index) const override
   {
-    VertexWeightWriteAttribute::get_internal(dverts_, dvert_index_, index, r_value);
+    return VMutableArray_For_VertexWeights::get_internal(dverts_, dvert_index_, index);
   }
 };
 
@@ -904,8 +868,8 @@ class VertexWeightReadAttribute final : public ReadAttribute {
  */
 class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
  public:
-  ReadAttributePtr try_get_for_read(const GeometryComponent &component,
-                                    const StringRef attribute_name) const final
+  ReadAttributeLookup try_get_for_read(const GeometryComponent &component,
+                                       const StringRef attribute_name) const final
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
     const MeshComponent &mesh_component = static_cast<const MeshComponent &>(component);
@@ -917,15 +881,17 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
     }
     if (mesh == nullptr || mesh->dvert == nullptr) {
       static const float default_value = 0.0f;
-      return std::make_unique<ConstantReadAttribute>(
-          ATTR_DOMAIN_POINT, mesh->totvert, CPPType::get<float>(), &default_value);
+      return {std::make_unique<fn::GVArray_For_SingleValueRef>(
+                  CPPType::get<float>(), mesh->totvert, &default_value),
+              ATTR_DOMAIN_POINT};
     }
-    return std::make_unique<VertexWeightReadAttribute>(
-        mesh->dvert, mesh->totvert, vertex_group_index);
+    return {std::make_unique<fn::GVArray_For_EmbeddedVArray<float, VArray_For_VertexWeights>>(
+                mesh->totvert, mesh->dvert, mesh->totvert, vertex_group_index),
+            ATTR_DOMAIN_POINT};
   }
 
-  WriteAttributePtr try_get_for_write(GeometryComponent &component,
-                                      const StringRef attribute_name) const final
+  WriteAttributeLookup try_get_for_write(GeometryComponent &component,
+                                         const StringRef attribute_name) const final
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
     MeshComponent &mesh_component = static_cast<MeshComponent &>(component);
@@ -946,8 +912,11 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
       mesh->dvert = (MDeformVert *)CustomData_duplicate_referenced_layer(
           &mesh->vdata, CD_MDEFORMVERT, mesh->totvert);
     }
-    return std::make_unique<blender::bke::VertexWeightWriteAttribute>(
-        mesh->dvert, mesh->totvert, vertex_group_index);
+    return {
+        std::make_unique<
+            fn::GVMutableArray_For_EmbeddedVMutableArray<float, VMutableArray_For_VertexWeights>>(
+            mesh->totvert, mesh->dvert, mesh->totvert, vertex_group_index),
+        ATTR_DOMAIN_POINT};
   }
 
   bool try_delete(GeometryComponent &component, const StringRef attribute_name) const final
@@ -1009,7 +978,7 @@ class NormalAttributeProvider final : public BuiltinAttributeProvider {
   {
   }
 
-  ReadAttributePtr try_get_for_read(const GeometryComponent &component) const final
+  GVArrayPtr try_get_for_read(const GeometryComponent &component) const final
   {
     const MeshComponent &mesh_component = static_cast<const MeshComponent &>(component);
     const Mesh *mesh = mesh_component.get_for_read();
@@ -1022,8 +991,8 @@ class NormalAttributeProvider final : public BuiltinAttributeProvider {
         CustomData_has_layer(&mesh->pdata, CD_NORMAL)) {
       const void *data = CustomData_get_layer(&mesh->pdata, CD_NORMAL);
 
-      return std::make_unique<ArrayReadAttribute<float3>>(
-          ATTR_DOMAIN_FACE, Span<float3>((const float3 *)data, mesh->totpoly));
+      return std::make_unique<fn::GVArray_For_Span<float3>>(
+          Span<float3>((const float3 *)data, mesh->totpoly));
     }
 
     Array<float3> normals(mesh->totpoly);
@@ -1032,10 +1001,10 @@ class NormalAttributeProvider final : public BuiltinAttributeProvider {
       BKE_mesh_calc_poly_normal(poly, &mesh->mloop[poly->loopstart], mesh->mvert, normals[i]);
     }
 
-    return std::make_unique<OwnedArrayReadAttribute<float3>>(ATTR_DOMAIN_FACE, std::move(normals));
+    return std::make_unique<fn::GVArray_For_ArrayContainer<Array<float3>>>(std::move(normals));
   }
 
-  WriteAttributePtr try_get_for_write(GeometryComponent &UNUSED(component)) const final
+  GVMutableArrayPtr try_get_for_write(GeometryComponent &UNUSED(component)) const final
   {
     return {};
   }
@@ -1105,12 +1074,8 @@ static ComponentAttributeProviders create_attribute_providers_for_mesh()
       BuiltinAttributeProvider::Writable,
       BuiltinAttributeProvider::NonDeletable,
       point_access,
-      make_derived_read_attribute<MVert, float3, get_vertex_position, ATTR_DOMAIN_POINT>,
-      make_derived_write_attribute<MVert,
-                                   float3,
-                                   get_vertex_position,
-                                   set_vertex_position,
-                                   ATTR_DOMAIN_POINT>,
+      make_derived_read_attribute<MVert, float3, get_vertex_position>,
+      make_derived_write_attribute<MVert, float3, get_vertex_position, set_vertex_position>,
       tag_normals_dirty_when_writing_position);
 
   static NormalAttributeProvider normal;
@@ -1124,12 +1089,8 @@ static ComponentAttributeProviders create_attribute_providers_for_mesh()
       BuiltinAttributeProvider::Writable,
       BuiltinAttributeProvider::NonDeletable,
       face_access,
-      make_derived_read_attribute<MPoly, int, get_material_index, ATTR_DOMAIN_FACE>,
-      make_derived_write_attribute<MPoly,
-                                   int,
-                                   get_material_index,
-                                   set_material_index,
-                                   ATTR_DOMAIN_FACE>,
+      make_derived_read_attribute<MPoly, int, get_material_index>,
+      make_derived_write_attribute<MPoly, int, get_material_index, set_material_index>,
       nullptr);
 
   static BuiltinCustomDataLayerProvider shade_smooth(
@@ -1141,12 +1102,8 @@ static ComponentAttributeProviders create_attribute_providers_for_mesh()
       BuiltinAttributeProvider::Writable,
       BuiltinAttributeProvider::NonDeletable,
       face_access,
-      make_derived_read_attribute<MPoly, bool, get_shade_smooth, ATTR_DOMAIN_FACE>,
-      make_derived_write_attribute<MPoly,
-                                   bool,
-                                   get_shade_smooth,
-                                   set_shade_smooth,
-                                   ATTR_DOMAIN_FACE>,
+      make_derived_read_attribute<MPoly, bool, get_shade_smooth>,
+      make_derived_write_attribute<MPoly, bool, get_shade_smooth, set_shade_smooth>,
       nullptr);
 
   static BuiltinCustomDataLayerProvider crease(
@@ -1158,8 +1115,8 @@ static ComponentAttributeProviders create_attribute_providers_for_mesh()
       BuiltinAttributeProvider::Writable,
       BuiltinAttributeProvider::NonDeletable,
       edge_access,
-      make_derived_read_attribute<MEdge, float, get_crease, ATTR_DOMAIN_EDGE>,
-      make_derived_write_attribute<MEdge, float, get_crease, set_crease, ATTR_DOMAIN_EDGE>,
+      make_derived_read_attribute<MEdge, float, get_crease>,
+      make_derived_write_attribute<MEdge, float, get_crease, set_crease>,
       nullptr);
 
   static NamedLegacyCustomDataProvider uvs(
@@ -1167,20 +1124,16 @@ static ComponentAttributeProviders create_attribute_providers_for_mesh()
       CD_PROP_FLOAT2,
       CD_MLOOPUV,
       corner_access,
-      make_derived_read_attribute<MLoopUV, float2, get_loop_uv, ATTR_DOMAIN_CORNER>,
-      make_derived_write_attribute<MLoopUV, float2, get_loop_uv, set_loop_uv, ATTR_DOMAIN_CORNER>);
+      make_derived_read_attribute<MLoopUV, float2, get_loop_uv>,
+      make_derived_write_attribute<MLoopUV, float2, get_loop_uv, set_loop_uv>);
 
   static NamedLegacyCustomDataProvider vertex_colors(
       ATTR_DOMAIN_CORNER,
       CD_PROP_COLOR,
       CD_MLOOPCOL,
       corner_access,
-      make_derived_read_attribute<MLoopCol, Color4f, get_loop_color, ATTR_DOMAIN_CORNER>,
-      make_derived_write_attribute<MLoopCol,
-                                   Color4f,
-                                   get_loop_color,
-                                   set_loop_color,
-                                   ATTR_DOMAIN_CORNER>);
+      make_derived_read_attribute<MLoopCol, Color4f, get_loop_color>,
+      make_derived_write_attribute<MLoopCol, Color4f, get_loop_color, set_loop_color>);
 
   static VertexGroupsAttributeProvider vertex_groups;
   static CustomDataAttributeProvider corner_custom_data(ATTR_DOMAIN_CORNER, corner_access);