Geometry Nodes: add field support for socket inspection

Since fields were committed to master, socket inspection did
not work correctly for all socket types anymore. Now the same
functionality as before is back. Furthermore, fields that depend
on some input will now show the inputs in the socket inspection.

I added support for evaluating constant fields more immediately.
This has the benefit that the same constant field is not evaluated
more than once. It also helps with making the field independent
of the multi-functions that it uses. We might still want to change
the ownership handling for the multi-functions of nodes a bit,
but that can be done separately.

Differential Revision: https://developer.blender.org/D12444

2 files changed, 91 insertions, 2 deletions

diff --git a/source/blender/functions/intern/field.cc b/source/blender/functions/intern/field.cc
index fa7dea97b7f..6133658d8e3 100644
--- a/source/blender/functions/intern/field.cc
+++ b/source/blender/functions/intern/field.cc
@@ -462,6 +462,29 @@ void evaluate_constant_field(const GField &field, void *r_value)
   varrays[0]->get_to_uninitialized(0, r_value);
 }
 
+/**
+ * If the field depends on some input, the same field is returned.
+ * Otherwise the field is evaluated and a new field is created that just computes this constant.
+ *
+ * Making the field constant has two benefits:
+ * - The field-tree becomes a single node, which is more efficient when the field is evaluated many
+ *   times.
+ * - Memory of the input fields may be freed.
+ */
+GField make_field_constant_if_possible(GField field)
+{
+  if (field.node().depends_on_input()) {
+    return 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);
+  type.destruct(buffer);
+  auto operation = std::make_shared<FieldOperation>(std::move(constant_fn));
+  return GField{operation, 0};
+}
+
 const GVArray *FieldContext::get_varray_for_input(const FieldInput &field_input,
                                                   IndexMask mask,
                                                   ResourceScope &scope) const
@@ -472,6 +495,55 @@ const GVArray *FieldContext::get_varray_for_input(const FieldInput &field_input,
 }
 
 /* --------------------------------------------------------------------
+ * FieldOperation.
+ */
+
+FieldOperation::FieldOperation(std::unique_ptr<const MultiFunction> function,
+                               Vector<GField> inputs)
+    : FieldOperation(*function, std::move(inputs))
+{
+  owned_function_ = std::move(function);
+}
+
+static bool any_field_depends_on_input(Span<GField> fields)
+{
+  for (const GField &field : fields) {
+    if (field.node().depends_on_input()) {
+      return true;
+    }
+  }
+  return false;
+}
+
+FieldOperation::FieldOperation(const MultiFunction &function, Vector<GField> inputs)
+    : FieldNode(false, any_field_depends_on_input(inputs)),
+      function_(&function),
+      inputs_(std::move(inputs))
+{
+}
+
+void FieldOperation::foreach_field_input(FunctionRef<void(const FieldInput &)> foreach_fn) const
+{
+  for (const GField &field : inputs_) {
+    field.node().foreach_field_input(foreach_fn);
+  }
+}
+
+/* --------------------------------------------------------------------
+ * FieldInput.
+ */
+
+FieldInput::FieldInput(const CPPType &type, std::string debug_name)
+    : FieldNode(true, true), type_(&type), debug_name_(std::move(debug_name))
+{
+}
+
+void FieldInput::foreach_field_input(FunctionRef<void(const FieldInput &)> foreach_fn) const
+{
+  foreach_fn(*this);
+}
+
+/* --------------------------------------------------------------------
  * FieldEvaluator.
  */
 
diff --git a/source/blender/functions/intern/multi_function_builder.cc b/source/blender/functions/intern/multi_function_builder.cc
index 180d1f17a54..f891f162820 100644
--- a/source/blender/functions/intern/multi_function_builder.cc
+++ b/source/blender/functions/intern/multi_function_builder.cc
@@ -20,9 +20,18 @@
 
 namespace blender::fn {
 
-CustomMF_GenericConstant::CustomMF_GenericConstant(const CPPType &type, const void *value)
-    : type_(type), value_(value)
+CustomMF_GenericConstant::CustomMF_GenericConstant(const CPPType &type,
+                                                   const void *value,
+                                                   bool make_value_copy)
+    : type_(type), owns_value_(make_value_copy)
 {
+  if (make_value_copy) {
+    void *copied_value = MEM_mallocN_aligned(type.size(), type.alignment(), __func__);
+    type.copy_construct(value, copied_value);
+    value = copied_value;
+  }
+  value_ = value;
+
   MFSignatureBuilder signature{"Constant " + type.name()};
   std::stringstream ss;
   type.print_or_default(value, ss, type.name());
@@ -31,6 +40,14 @@ CustomMF_GenericConstant::CustomMF_GenericConstant(const CPPType &type, const vo
   this->set_signature(&signature_);
 }
 
+CustomMF_GenericConstant::~CustomMF_GenericConstant()
+{
+  if (owns_value_) {
+    signature_.param_types[0].data_type().single_type().destruct((void *)value_);
+    MEM_freeN((void *)value_);
+  }
+}
+
 void CustomMF_GenericConstant::call(IndexMask mask,
                                     MFParams params,
                                     MFContext UNUSED(context)) const