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, 27 insertions, 26 deletions

diff --git a/source/blender/blenkernel/intern/geometry_set_instances.cc b/source/blender/blenkernel/intern/geometry_set_instances.cc
index 376792b9b96..0e19324a3c1 100644
--- a/source/blender/blenkernel/intern/geometry_set_instances.cc
+++ b/source/blender/blenkernel/intern/geometry_set_instances.cc
@@ -331,7 +331,7 @@ void geometry_set_instances_attribute_foreach(const GeometrySet &geometry_set,
 void geometry_set_gather_instances_attribute_info(Span<GeometryInstanceGroup> set_groups,
                                                   Span<GeometryComponentType> component_types,
                                                   const Set<std::string> &ignored_attributes,
-                                                  Map<std::string, AttributeKind> &r_attributes)
+                                                  Map<AttributeIDRef, AttributeKind> &r_attributes)
 {
   for (const GeometryInstanceGroup &set_group : set_groups) {
     const GeometrySet &set = set_group.geometry_set;
@@ -341,23 +341,24 @@ void geometry_set_gather_instances_attribute_info(Span<GeometryInstanceGroup> se
       }
       const GeometryComponent &component = *set.get_component_for_read(component_type);
 
-      component.attribute_foreach([&](StringRefNull name, const AttributeMetaData &meta_data) {
-        if (ignored_attributes.contains(name)) {
-          return true;
-        }
-        auto add_info = [&](AttributeKind *attribute_kind) {
-          attribute_kind->domain = meta_data.domain;
-          attribute_kind->data_type = meta_data.data_type;
-        };
-        auto modify_info = [&](AttributeKind *attribute_kind) {
-          attribute_kind->domain = meta_data.domain; /* TODO: Use highest priority domain. */
-          attribute_kind->data_type = bke::attribute_data_type_highest_complexity(
-              {attribute_kind->data_type, meta_data.data_type});
-        };
-
-        r_attributes.add_or_modify(name, add_info, modify_info);
-        return true;
-      });
+      component.attribute_foreach(
+          [&](const AttributeIDRef &attribute_id, const AttributeMetaData &meta_data) {
+            if (attribute_id.is_named() && ignored_attributes.contains(attribute_id.name())) {
+              return true;
+            }
+            auto add_info = [&](AttributeKind *attribute_kind) {
+              attribute_kind->domain = meta_data.domain;
+              attribute_kind->data_type = meta_data.data_type;
+            };
+            auto modify_info = [&](AttributeKind *attribute_kind) {
+              attribute_kind->domain = meta_data.domain; /* TODO: Use highest priority domain. */
+              attribute_kind->data_type = bke::attribute_data_type_highest_complexity(
+                  {attribute_kind->data_type, meta_data.data_type});
+            };
+
+            r_attributes.add_or_modify(attribute_id, add_info, modify_info);
+            return true;
+          });
     }
   }
 }
@@ -512,11 +513,11 @@ static Mesh *join_mesh_topology_and_builtin_attributes(Span<GeometryInstanceGrou
 
 static void join_attributes(Span<GeometryInstanceGroup> set_groups,
                             Span<GeometryComponentType> component_types,
-                            const Map<std::string, AttributeKind> &attribute_info,
+                            const Map<AttributeIDRef, AttributeKind> &attribute_info,
                             GeometryComponent &result)
 {
-  for (Map<std::string, AttributeKind>::Item entry : attribute_info.items()) {
-    StringRef name = entry.key;
+  for (Map<AttributeIDRef, AttributeKind>::Item entry : attribute_info.items()) {
+    const AttributeIDRef attribute_id = entry.key;
     const AttributeDomain domain_output = entry.value.domain;
     const CustomDataType data_type_output = entry.value.data_type;
     const CPPType *cpp_type = bke::custom_data_type_to_cpp_type(data_type_output);
@@ -524,7 +525,7 @@ static void join_attributes(Span<GeometryInstanceGroup> set_groups,
 
     result.attribute_try_create(
         entry.key, domain_output, data_type_output, AttributeInitDefault());
-    WriteAttributeLookup write_attribute = result.attribute_try_get_for_write(name);
+    WriteAttributeLookup write_attribute = result.attribute_try_get_for_write(attribute_id);
     if (!write_attribute || &write_attribute.varray->type() != cpp_type ||
         write_attribute.domain != domain_output) {
       continue;
@@ -543,7 +544,7 @@ static void join_attributes(Span<GeometryInstanceGroup> set_groups,
             continue; /* Domain size is 0, so no need to increment the offset. */
           }
           GVArrayPtr source_attribute = component.attribute_try_get_for_read(
-              name, domain_output, data_type_output);
+              attribute_id, domain_output, data_type_output);
 
           if (source_attribute) {
             fn::GVArray_GSpan src_span{*source_attribute};
@@ -653,7 +654,7 @@ static void join_instance_groups_mesh(Span<GeometryInstanceGroup> set_groups,
   }
 
   /* Don't copy attributes that are stored directly in the mesh data structs. */
-  Map<std::string, AttributeKind> attributes;
+  Map<AttributeIDRef, AttributeKind> attributes;
   geometry_set_gather_instances_attribute_info(
       set_groups,
       component_types,
@@ -674,7 +675,7 @@ static void join_instance_groups_pointcloud(Span<GeometryInstanceGroup> set_grou
   PointCloudComponent &dst_component = result.get_component_for_write<PointCloudComponent>();
   dst_component.replace(new_pointcloud);
 
-  Map<std::string, AttributeKind> attributes;
+  Map<AttributeIDRef, AttributeKind> attributes;
   geometry_set_gather_instances_attribute_info(
       set_groups, {GEO_COMPONENT_TYPE_POINT_CLOUD}, {"position"}, attributes);
   join_attributes(set_groups,
@@ -708,7 +709,7 @@ static void join_instance_groups_curve(Span<GeometryInstanceGroup> set_groups, G
   CurveComponent &dst_component = result.get_component_for_write<CurveComponent>();
   dst_component.replace(curve);
 
-  Map<std::string, AttributeKind> attributes;
+  Map<AttributeIDRef, AttributeKind> attributes;
   geometry_set_gather_instances_attribute_info(
       set_groups,
       {GEO_COMPONENT_TYPE_CURVE},