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, 42 insertions, 40 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_curve_to_points.cc b/source/blender/nodes/geometry/nodes/node_geo_curve_to_points.cc
index 17cd8e987a7..74740ba244f 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_curve_to_points.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_curve_to_points.cc
@@ -115,21 +115,21 @@ static Array<int> calculate_spline_point_offsets(GeoNodeExecParams &params,
 }
 
 static GMutableSpan create_attribute_and_retrieve_span(PointCloudComponent &points,
-                                                       const StringRef name,
+                                                       const AttributeIDRef &attribute_id,
                                                        const CustomDataType data_type)
 {
-  points.attribute_try_create(name, ATTR_DOMAIN_POINT, data_type, AttributeInitDefault());
-  WriteAttributeLookup attribute = points.attribute_try_get_for_write(name);
+  points.attribute_try_create(attribute_id, ATTR_DOMAIN_POINT, data_type, AttributeInitDefault());
+  WriteAttributeLookup attribute = points.attribute_try_get_for_write(attribute_id);
   BLI_assert(attribute);
   return attribute.varray->get_internal_span();
 }
 
 template<typename T>
 static MutableSpan<T> create_attribute_and_retrieve_span(PointCloudComponent &points,
-                                                         const StringRef name)
+                                                         const AttributeIDRef &attribute_id)
 {
   GMutableSpan attribute = create_attribute_and_retrieve_span(
-      points, name, bke::cpp_type_to_custom_data_type(CPPType::get<T>()));
+      points, attribute_id, bke::cpp_type_to_custom_data_type(CPPType::get<T>()));
   return attribute.typed<T>();
 }
 
@@ -147,9 +147,10 @@ CurveToPointsResults curve_to_points_create_result_attributes(PointCloudComponen
   /* Because of the invariants of the curve component, we use the attributes of the
    * first spline as a representative for the attribute meta data all splines. */
   curve.splines().first()->attributes.foreach_attribute(
-      [&](StringRefNull name, const AttributeMetaData &meta_data) {
+      [&](const AttributeIDRef &attribute_id, const AttributeMetaData &meta_data) {
         attributes.point_attributes.add_new(
-            name, create_attribute_and_retrieve_span(points, name, meta_data.data_type));
+            attribute_id,
+            create_attribute_and_retrieve_span(points, attribute_id, meta_data.data_type));
         return true;
       },
       ATTR_DOMAIN_POINT);
@@ -179,12 +180,12 @@ static void copy_evaluated_point_attributes(Span<SplinePtr> splines,
       spline.interpolate_to_evaluated(spline.radii())->materialize(data.radii.slice(offset, size));
       spline.interpolate_to_evaluated(spline.tilts())->materialize(data.tilts.slice(offset, size));
 
-      for (const Map<std::string, GMutableSpan>::Item &item : data.point_attributes.items()) {
-        const StringRef name = item.key;
+      for (const Map<AttributeIDRef, GMutableSpan>::Item &item : data.point_attributes.items()) {
+        const AttributeIDRef attribute_id = item.key;
         GMutableSpan point_span = item.value;
 
-        BLI_assert(spline.attributes.get_for_read(name));
-        GSpan spline_span = *spline.attributes.get_for_read(name);
+        BLI_assert(spline.attributes.get_for_read(attribute_id));
+        GSpan spline_span = *spline.attributes.get_for_read(attribute_id);
 
         spline.interpolate_to_evaluated(spline_span)
             ->materialize(point_span.slice(offset, size).data());
@@ -222,12 +223,12 @@ static void copy_uniform_sample_point_attributes(Span<SplinePtr> splines,
                                               uniform_samples,
                                               data.tilts.slice(offset, size));
 
-      for (const Map<std::string, GMutableSpan>::Item &item : data.point_attributes.items()) {
-        const StringRef name = item.key;
+      for (const Map<AttributeIDRef, GMutableSpan>::Item &item : data.point_attributes.items()) {
+        const AttributeIDRef attribute_id = item.key;
         GMutableSpan point_span = item.value;
 
-        BLI_assert(spline.attributes.get_for_read(name));
-        GSpan spline_span = *spline.attributes.get_for_read(name);
+        BLI_assert(spline.attributes.get_for_read(attribute_id));
+        GSpan spline_span = *spline.attributes.get_for_read(attribute_id);
 
         spline.sample_with_index_factors(*spline.interpolate_to_evaluated(spline_span),
                                          uniform_samples,
@@ -257,31 +258,32 @@ static void copy_spline_domain_attributes(const CurveComponent &curve_component,
                                           Span<int> offsets,
                                           PointCloudComponent &points)
 {
-  curve_component.attribute_foreach([&](StringRefNull name, const AttributeMetaData &meta_data) {
-    if (meta_data.domain != ATTR_DOMAIN_CURVE) {
-      return true;
-    }
-    GVArrayPtr spline_attribute = curve_component.attribute_get_for_read(
-        name, ATTR_DOMAIN_CURVE, meta_data.data_type);
-    const CPPType &type = spline_attribute->type();
-
-    OutputAttribute result_attribute = points.attribute_try_get_for_output_only(
-        name, ATTR_DOMAIN_POINT, meta_data.data_type);
-    GMutableSpan result = result_attribute.as_span();
-
-    for (const int i : IndexRange(spline_attribute->size())) {
-      const int offset = offsets[i];
-      const int size = offsets[i + 1] - offsets[i];
-      if (size != 0) {
-        BUFFER_FOR_CPP_TYPE_VALUE(type, buffer);
-        spline_attribute->get(i, buffer);
-        type.fill_assign_n(buffer, result[offset], size);
-      }
-    }
-
-    result_attribute.save();
-    return true;
-  });
+  curve_component.attribute_foreach(
+      [&](const AttributeIDRef &attribute_id, const AttributeMetaData &meta_data) {
+        if (meta_data.domain != ATTR_DOMAIN_CURVE) {
+          return true;
+        }
+        GVArrayPtr spline_attribute = curve_component.attribute_get_for_read(
+            attribute_id, ATTR_DOMAIN_CURVE, meta_data.data_type);
+        const CPPType &type = spline_attribute->type();
+
+        OutputAttribute result_attribute = points.attribute_try_get_for_output_only(
+            attribute_id, ATTR_DOMAIN_POINT, meta_data.data_type);
+        GMutableSpan result = result_attribute.as_span();
+
+        for (const int i : IndexRange(spline_attribute->size())) {
+          const int offset = offsets[i];
+          const int size = offsets[i + 1] - offsets[i];
+          if (size != 0) {
+            BUFFER_FOR_CPP_TYPE_VALUE(type, buffer);
+            spline_attribute->get(i, buffer);
+            type.fill_assign_n(buffer, result[offset], size);
+          }
+        }
+
+        result_attribute.save();
+        return true;
+      });
 }
 
 void curve_create_default_rotation_attribute(Span<float3> tangents,