Geometry Nodes: reduce overhead when processing single values

Currently the geometry nodes evaluator always stores a field for every
type that supports it, even if it is just a single value. This results in a lot
of overhead when there are many sockets that just contain a single
value, which is often the case.

This introduces a new `ValueOrField<T>` type that is used by the geometry
nodes evaluator. Now a field will only be created when it is actually
necessary. See D13307 for more details. In extrem cases this can speed
up the evaluation 2-3x (those cases are probably never hit in practice
though, but it's good to get rid of unnecessary overhead nevertheless).

Differential Revision: https://developer.blender.org/D13307

1 files changed, 8 insertions, 2 deletions

diff --git a/source/blender/functions/intern/field.cc b/source/blender/functions/intern/field.cc
index 91b1bdfd8f0..7934490a6d9 100644
--- a/source/blender/functions/intern/field.cc
+++ b/source/blender/functions/intern/field.cc
@@ -511,10 +511,16 @@ GField make_field_constant_if_possible(GField field)
   const CPPType &type = field.cpp_type();
   BUFFER_FOR_CPP_TYPE_VALUE(type, buffer);
   evaluate_constant_field(field, buffer);
-  auto constant_fn = std::make_unique<CustomMF_GenericConstant>(type, buffer, true);
+  GField new_field = make_constant_field(type, buffer);
   type.destruct(buffer);
+  return new_field;
+}
+
+GField make_constant_field(const CPPType &type, const void *value)
+{
+  auto constant_fn = std::make_unique<CustomMF_GenericConstant>(type, value, true);
   auto operation = std::make_shared<FieldOperation>(std::move(constant_fn));
-  return GField{operation, 0};
+  return GField{std::move(operation), 0};
 }
 
 GVArray FieldContext::get_varray_for_input(const FieldInput &field_input,