Geometry Nodes: Do not realize instances in the material assign node

Only run the node once for every unique geometry set in the input's
instance heirarchy. This can massively improve performance when
there are many instances, but it will mean that the result is the same
for every instance. For the previous behavior, a "Realize Instances"
node can be used before this one.

This node can be changed without versioning since the old material
assign node was already deprecated and replaced.

1 files changed, 15 insertions, 16 deletions

diff --git a/source/blender/nodes/geometry/nodes/node_geo_material_assign.cc b/source/blender/nodes/geometry/nodes/node_geo_material_assign.cc
index 2a4481d5404..780994996ae 100644
--- a/source/blender/nodes/geometry/nodes/node_geo_material_assign.cc
+++ b/source/blender/nodes/geometry/nodes/node_geo_material_assign.cc
@@ -64,23 +64,22 @@ static void geo_node_material_assign_exec(GeoNodeExecParams params)
 
   GeometrySet geometry_set = params.extract_input<GeometrySet>("Geometry");
 
-  geometry_set = geometry_set_realize_instances(geometry_set);
-
-  if (geometry_set.has<MeshComponent>()) {
-    MeshComponent &mesh_component = geometry_set.get_component_for_write<MeshComponent>();
-    Mesh *mesh = mesh_component.get_for_write();
-    if (mesh != nullptr) {
-
-      GeometryComponentFieldContext field_context{mesh_component, ATTR_DOMAIN_FACE};
-
-      fn::FieldEvaluator selection_evaluator{field_context, mesh->totpoly};
-      selection_evaluator.add(selection_field);
-      selection_evaluator.evaluate();
-      const IndexMask selection = selection_evaluator.get_evaluated_as_mask(0);
-
-      assign_material_to_faces(*mesh, selection, material);
+  geometry_set.modify_geometry_sets([&](GeometrySet &geometry_set) {
+    if (geometry_set.has<MeshComponent>()) {
+      MeshComponent &mesh_component = geometry_set.get_component_for_write<MeshComponent>();
+      Mesh *mesh = mesh_component.get_for_write();
+      if (mesh != nullptr) {
+        GeometryComponentFieldContext field_context{mesh_component, ATTR_DOMAIN_FACE};
+
+        fn::FieldEvaluator selection_evaluator{field_context, mesh->totpoly};
+        selection_evaluator.add(selection_field);
+        selection_evaluator.evaluate();
+        const IndexMask selection = selection_evaluator.get_evaluated_as_mask(0);
+
+        assign_material_to_faces(*mesh, selection, material);
+      }
     }
-  }
+  });
 
   params.set_output("Geometry", std::move(geometry_set));
 }