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, 43 insertions, 0 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_input_position.cc b/source/blender/nodes/geometry/nodes/node_geo_input_position.cc
new file mode 100644
index 00000000000..c6365bf6809
--- /dev/null
+++ b/source/blender/nodes/geometry/nodes/node_geo_input_position.cc
@@ -0,0 +1,43 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include "node_geometry_util.hh"
+
+namespace blender::nodes {
+
+static void geo_node_input_position_declare(NodeDeclarationBuilder &b)
+{
+  b.add_output<decl::Vector>("Position");
+}
+
+static void geo_node_input_position_exec(GeoNodeExecParams params)
+{
+  Field<float3> position_field{
+      std::make_shared<bke::AttributeFieldInput>("position", CPPType::get<float3>())};
+  params.set_output("Position", std::move(position_field));
+}
+
+}  // namespace blender::nodes
+
+void register_node_type_geo_input_position()
+{
+  static bNodeType ntype;
+
+  geo_node_type_base(&ntype, GEO_NODE_INPUT_POSITION, "Position", NODE_CLASS_INPUT, 0);
+  ntype.geometry_node_execute = blender::nodes::geo_node_input_position_exec;
+  ntype.declare = blender::nodes::geo_node_input_position_declare;
+  nodeRegisterType(&ntype);
+}