Geometry Nodes: fields and anonymous attributes

This implements the initial core framework for fields and anonymous
attributes (also see T91274).

The new functionality is hidden behind the "Geometry Nodes Fields"
feature flag. When enabled in the user preferences, the following
new nodes become available: `Position`, `Index`, `Normal`,
`Set Position` and `Attribute Capture`.

Socket inspection has not been updated to work with fields yet.

Besides these changes at the user level, this patch contains the
ground work for:
* building and evaluating fields at run-time (`FN_fields.hh`) and
* creating and accessing anonymous attributes on geometry
  (`BKE_anonymous_attribute.h`).

For evaluating fields we use a new so called multi-function procedure
(`FN_multi_function_procedure.hh`). It allows composing multi-functions
in arbitrary ways and supports efficient evaluation as is required by
fields. See `FN_multi_function_procedure.hh` for more details on how
this evaluation mechanism can be used.

A new `AttributeIDRef` has been added which allows handling named
and anonymous attributes in the same way in many places.

Hans and I worked on this patch together.

Differential Revision: https://developer.blender.org/D12414

1 files changed, 18 insertions, 6 deletions

diff --git a/source/blender/blenkernel/intern/geometry_component_mesh.cc b/source/blender/blenkernel/intern/geometry_component_mesh.cc
index ef93a3f9b3f..9a4b8f4eb92 100644
--- a/source/blender/blenkernel/intern/geometry_component_mesh.cc
+++ b/source/blender/blenkernel/intern/geometry_component_mesh.cc
@@ -818,16 +818,20 @@ class VArray_For_VertexWeights final : public VArray<float> {
 class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
  public:
   ReadAttributeLookup try_get_for_read(const GeometryComponent &component,
-                                       const StringRef attribute_name) const final
+                                       const AttributeIDRef &attribute_id) const final
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
+    if (!attribute_id.is_named()) {
+      return {};
+    }
     const MeshComponent &mesh_component = static_cast<const MeshComponent &>(component);
     const Mesh *mesh = mesh_component.get_for_read();
     if (mesh == nullptr) {
       return {};
     }
+    const std::string name = attribute_id.name();
     const int vertex_group_index = BLI_findstringindex(
-        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
+        &mesh->vertex_group_names, name.c_str(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return {};
     }
@@ -843,17 +847,21 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
   }
 
   WriteAttributeLookup try_get_for_write(GeometryComponent &component,
-                                         const StringRef attribute_name) const final
+                                         const AttributeIDRef &attribute_id) const final
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
+    if (!attribute_id.is_named()) {
+      return {};
+    }
     MeshComponent &mesh_component = static_cast<MeshComponent &>(component);
     Mesh *mesh = mesh_component.get_for_write();
     if (mesh == nullptr) {
       return {};
     }
 
+    const std::string name = attribute_id.name();
     const int vertex_group_index = BLI_findstringindex(
-        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
+        &mesh->vertex_group_names, name.c_str(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return {};
     }
@@ -872,17 +880,21 @@ class VertexGroupsAttributeProvider final : public DynamicAttributesProvider {
         ATTR_DOMAIN_POINT};
   }
 
-  bool try_delete(GeometryComponent &component, const StringRef attribute_name) const final
+  bool try_delete(GeometryComponent &component, const AttributeIDRef &attribute_id) const final
   {
     BLI_assert(component.type() == GEO_COMPONENT_TYPE_MESH);
+    if (!attribute_id.is_named()) {
+      return false;
+    }
     MeshComponent &mesh_component = static_cast<MeshComponent &>(component);
     Mesh *mesh = mesh_component.get_for_write();
     if (mesh == nullptr) {
       return true;
     }
 
+    const std::string name = attribute_id.name();
     const int vertex_group_index = BLI_findstringindex(
-        &mesh->vertex_group_names, attribute_name.data(), offsetof(bDeformGroup, name));
+        &mesh->vertex_group_names, name.c_str(), offsetof(bDeformGroup, name));
     if (vertex_group_index < 0) {
       return false;
     }