Nodes: move some code from blenkernel directory to nodes

This also introduces the `blender::nodes` namespace. Eventually,
we want to move most/all of the node implementation files into
this namespace.

The reason for this file-move is that the code fits much better
into the `nodes` directory than in the `blenkernel` directory.

4 files changed, 969 insertions, 7 deletions

diff --git a/source/blender/nodes/intern/derived_node_tree.cc b/source/blender/nodes/intern/derived_node_tree.cc
new file mode 100644
index 00000000000..daec67b53a9
--- /dev/null
+++ b/source/blender/nodes/intern/derived_node_tree.cc
@@ -0,0 +1,441 @@
+/*
+ * 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 "NOD_derived_node_tree.hh"
+
+#include "BLI_dot_export.hh"
+
+#define UNINITIALIZED_ID UINT32_MAX
+
+namespace blender::nodes {
+
+static const NodeTreeRef &get_tree_ref(NodeTreeRefMap &node_tree_refs, bNodeTree *btree)
+{
+  return *node_tree_refs.lookup_or_add_cb(btree,
+                                          [&]() { return std::make_unique<NodeTreeRef>(btree); });
+}
+
+DerivedNodeTree::DerivedNodeTree(bNodeTree *btree, NodeTreeRefMap &node_tree_refs) : btree_(btree)
+{
+  const NodeTreeRef &main_tree_ref = get_tree_ref(node_tree_refs, btree);
+
+  Vector<DNode *> all_nodes;
+  Vector<DGroupInput *> all_group_inputs;
+  Vector<DParentNode *> all_parent_nodes;
+
+  this->insert_nodes_and_links_in_id_order(main_tree_ref, nullptr, all_nodes);
+  this->expand_groups(all_nodes, all_group_inputs, all_parent_nodes, node_tree_refs);
+  this->remove_expanded_group_interfaces(all_nodes);
+  this->remove_unused_group_inputs(all_group_inputs);
+  this->store_in_this_and_init_ids(
+      std::move(all_nodes), std::move(all_group_inputs), std::move(all_parent_nodes));
+}
+
+BLI_NOINLINE void DerivedNodeTree::insert_nodes_and_links_in_id_order(const NodeTreeRef &tree_ref,
+                                                                      DParentNode *parent,
+                                                                      Vector<DNode *> &all_nodes)
+{
+  Array<DSocket *, 64> sockets_map(tree_ref.sockets().size());
+
+  /* Insert nodes. */
+  for (const NodeRef *node_ref : tree_ref.nodes()) {
+    DNode &node = this->create_node(*node_ref, parent, sockets_map);
+    all_nodes.append(&node);
+  }
+
+  /* Insert links. */
+  for (const NodeRef *node_ref : tree_ref.nodes()) {
+    for (const InputSocketRef *to_socket_ref : node_ref->inputs()) {
+      DInputSocket *to_socket = (DInputSocket *)sockets_map[to_socket_ref->id()];
+      for (const OutputSocketRef *from_socket_ref : to_socket_ref->linked_sockets()) {
+        DOutputSocket *from_socket = (DOutputSocket *)sockets_map[from_socket_ref->id()];
+        to_socket->linked_sockets_.append(from_socket);
+        from_socket->linked_sockets_.append(to_socket);
+      }
+    }
+  }
+}
+
+DNode &DerivedNodeTree::create_node(const NodeRef &node_ref,
+                                    DParentNode *parent,
+                                    MutableSpan<DSocket *> r_sockets_map)
+{
+  DNode &node = *allocator_.construct<DNode>();
+  node.node_ref_ = &node_ref;
+  node.parent_ = parent;
+  node.id_ = UNINITIALIZED_ID;
+
+  node.inputs_ = allocator_.construct_elements_and_pointer_array<DInputSocket>(
+      node_ref.inputs().size());
+  node.outputs_ = allocator_.construct_elements_and_pointer_array<DOutputSocket>(
+      node_ref.outputs().size());
+
+  for (uint i : node.inputs_.index_range()) {
+    const InputSocketRef &socket_ref = node_ref.input(i);
+    DInputSocket &socket = *node.inputs_[i];
+
+    socket.id_ = UNINITIALIZED_ID;
+    socket.node_ = &node;
+    socket.socket_ref_ = &socket_ref;
+
+    r_sockets_map[socket_ref.id()] = &socket;
+  }
+
+  for (uint i : node.outputs_.index_range()) {
+    const OutputSocketRef &socket_ref = node_ref.output(i);
+    DOutputSocket &socket = *node.outputs_[i];
+
+    socket.id_ = UNINITIALIZED_ID;
+    socket.node_ = &node;
+    socket.socket_ref_ = &socket_ref;
+
+    r_sockets_map[socket_ref.id()] = &socket;
+  }
+
+  return node;
+}
+
+BLI_NOINLINE void DerivedNodeTree::expand_groups(Vector<DNode *> &all_nodes,
+                                                 Vector<DGroupInput *> &all_group_inputs,
+                                                 Vector<DParentNode *> &all_parent_nodes,
+                                                 NodeTreeRefMap &node_tree_refs)
+{
+  for (uint i = 0; i < all_nodes.size(); i++) {
+    DNode &node = *all_nodes[i];
+    if (node.node_ref_->is_group_node()) {
+      this->expand_group_node(node, all_nodes, all_group_inputs, all_parent_nodes, node_tree_refs);
+    }
+  }
+}
+
+BLI_NOINLINE void DerivedNodeTree::expand_group_node(DNode &group_node,
+                                                     Vector<DNode *> &all_nodes,
+                                                     Vector<DGroupInput *> &all_group_inputs,
+                                                     Vector<DParentNode *> &all_parent_nodes,
+                                                     NodeTreeRefMap &node_tree_refs)
+{
+  const NodeRef &group_node_ref = *group_node.node_ref_;
+  BLI_assert(group_node_ref.is_group_node());
+
+  bNodeTree *btree = (bNodeTree *)group_node_ref.bnode()->id;
+  if (btree == nullptr) {
+    return;
+  }
+
+  const NodeTreeRef &group_ref = get_tree_ref(node_tree_refs, btree);
+
+  DParentNode &parent = *allocator_.construct<DParentNode>();
+  parent.id_ = all_parent_nodes.append_and_get_index(&parent);
+  parent.parent_ = group_node.parent_;
+  parent.node_ref_ = &group_node_ref;
+
+  this->insert_nodes_and_links_in_id_order(group_ref, &parent, all_nodes);
+  Span<DNode *> new_nodes_by_id = all_nodes.as_span().take_back(group_ref.nodes().size());
+
+  this->create_group_inputs_for_unlinked_inputs(group_node, all_group_inputs);
+  this->relink_group_inputs(group_ref, new_nodes_by_id, group_node);
+  this->relink_group_outputs(group_ref, new_nodes_by_id, group_node);
+}
+
+BLI_NOINLINE void DerivedNodeTree::create_group_inputs_for_unlinked_inputs(
+    DNode &node, Vector<DGroupInput *> &all_group_inputs)
+{
+  for (DInputSocket *input_socket : node.inputs_) {
+    if (input_socket->is_linked()) {
+      continue;
+    }
+
+    DGroupInput &group_input = *allocator_.construct<DGroupInput>();
+    group_input.id_ = UNINITIALIZED_ID;
+    group_input.socket_ref_ = &input_socket->socket_ref();
+    group_input.parent_ = node.parent_;
+
+    group_input.linked_sockets_.append(input_socket);
+    input_socket->linked_group_inputs_.append(&group_input);
+    all_group_inputs.append(&group_input);
+  }
+}
+
+BLI_NOINLINE void DerivedNodeTree::relink_group_inputs(const NodeTreeRef &group_ref,
+                                                       Span<DNode *> nodes_by_id,
+                                                       DNode &group_node)
+{
+  Span<const NodeRef *> node_refs = group_ref.nodes_by_type("NodeGroupInput");
+  if (node_refs.size() == 0) {
+    return;
+  }
+  /* TODO: Pick correct group input node if there are more than one. */
+  const NodeRef &input_node_ref = *node_refs[0];
+  DNode &input_node = *nodes_by_id[input_node_ref.id()];
+
+  uint input_amount = group_node.inputs().size();
+  BLI_assert(input_amount == input_node_ref.outputs().size() - 1);
+
+  for (uint input_index : IndexRange(input_amount)) {
+    DInputSocket *outside_group = group_node.inputs_[input_index];
+    DOutputSocket *inside_group = input_node.outputs_[input_index];
+
+    for (DOutputSocket *outside_connected : outside_group->linked_sockets_) {
+      outside_connected->linked_sockets_.remove_first_occurrence_and_reorder(outside_group);
+    }
+
+    for (DGroupInput *outside_connected : outside_group->linked_group_inputs_) {
+      outside_connected->linked_sockets_.remove_first_occurrence_and_reorder(outside_group);
+    }
+
+    for (DInputSocket *inside_connected : inside_group->linked_sockets_) {
+      inside_connected->linked_sockets_.remove_first_occurrence_and_reorder(inside_group);
+
+      for (DOutputSocket *outside_connected : outside_group->linked_sockets_) {
+        inside_connected->linked_sockets_.append(outside_connected);
+        outside_connected->linked_sockets_.append(inside_connected);
+      }
+
+      for (DGroupInput *outside_connected : outside_group->linked_group_inputs_) {
+        inside_connected->linked_group_inputs_.append(outside_connected);
+        outside_connected->linked_sockets_.append(inside_connected);
+      }
+    }
+
+    inside_group->linked_sockets_.clear();
+    outside_group->linked_sockets_.clear();
+    outside_group->linked_group_inputs_.clear();
+  }
+}
+
+BLI_NOINLINE void DerivedNodeTree::relink_group_outputs(const NodeTreeRef &group_ref,
+                                                        Span<DNode *> nodes_by_id,
+                                                        DNode &group_node)
+{
+  Span<const NodeRef *> node_refs = group_ref.nodes_by_type("NodeGroupOutput");
+  if (node_refs.size() == 0) {
+    return;
+  }
+  /* TODO: Pick correct group output node if there are more than one. */
+  const NodeRef &output_node_ref = *node_refs[0];
+  DNode &output_node = *nodes_by_id[output_node_ref.id()];
+
+  uint output_amount = group_node.outputs().size();
+  BLI_assert(output_amount == output_node_ref.inputs().size() - 1);
+
+  for (uint output_index : IndexRange(output_amount)) {
+    DOutputSocket *outside_group = group_node.outputs_[output_index];
+    DInputSocket *inside_group = output_node.inputs_[output_index];
+
+    for (DInputSocket *outside_connected : outside_group->linked_sockets_) {
+      outside_connected->linked_sockets_.remove_first_occurrence_and_reorder(outside_group);
+    }
+
+    for (DOutputSocket *inside_connected : inside_group->linked_sockets_) {
+      inside_connected->linked_sockets_.remove_first_occurrence_and_reorder(inside_group);
+
+      for (DInputSocket *outside_connected : outside_group->linked_sockets_) {
+        inside_connected->linked_sockets_.append(outside_connected);
+        outside_connected->linked_sockets_.append(inside_connected);
+      }
+    }
+
+    for (DGroupInput *inside_connected : inside_group->linked_group_inputs_) {
+      inside_connected->linked_sockets_.remove_first_occurrence_and_reorder(inside_group);
+
+      for (DInputSocket *outside_connected : outside_group->linked_sockets_) {
+        inside_connected->linked_sockets_.append(outside_connected);
+        outside_connected->linked_group_inputs_.append(inside_connected);
+      }
+    }
+
+    outside_group->linked_sockets_.clear();
+    inside_group->linked_sockets_.clear();
+  }
+}
+
+BLI_NOINLINE void DerivedNodeTree::remove_expanded_group_interfaces(Vector<DNode *> &all_nodes)
+{
+  int index = 0;
+  while (index < all_nodes.size()) {
+    DNode &node = *all_nodes[index];
+    const NodeRef &node_ref = *node.node_ref_;
+    if (node_ref.is_group_node() ||
+        (node.parent_ != nullptr &&
+         (node_ref.is_group_input_node() || node_ref.is_group_output_node()))) {
+      all_nodes.remove_and_reorder(index);
+      node.destruct_with_sockets();
+    }
+    else {
+      index++;
+    }
+  }
+}
+
+BLI_NOINLINE void DerivedNodeTree::remove_unused_group_inputs(
+    Vector<DGroupInput *> &all_group_inputs)
+{
+  int index = 0;
+  while (index < all_group_inputs.size()) {
+    DGroupInput &group_input = *all_group_inputs[index];
+    if (group_input.linked_sockets_.is_empty()) {
+      all_group_inputs.remove_and_reorder(index);
+      group_input.~DGroupInput();
+    }
+    else {
+      index++;
+    }
+  }
+}
+
+void DNode::destruct_with_sockets()
+{
+  for (DInputSocket *socket : inputs_) {
+    socket->~DInputSocket();
+  }
+  for (DOutputSocket *socket : outputs_) {
+    socket->~DOutputSocket();
+  }
+  this->~DNode();
+}
+
+BLI_NOINLINE void DerivedNodeTree::store_in_this_and_init_ids(
+    Vector<DNode *> &&all_nodes,
+    Vector<DGroupInput *> &&all_group_inputs,
+    Vector<DParentNode *> &&all_parent_nodes)
+{
+  nodes_by_id_ = std::move(all_nodes);
+  group_inputs_ = std::move(all_group_inputs);
+  parent_nodes_ = std::move(all_parent_nodes);
+
+  for (uint node_index : nodes_by_id_.index_range()) {
+    DNode *node = nodes_by_id_[node_index];
+    node->id_ = node_index;
+
+    const bNodeType *nodetype = node->node_ref_->bnode()->typeinfo;
+    nodes_by_type_.lookup_or_add_default(nodetype).append(node);
+
+    for (DInputSocket *socket : node->inputs_) {
+      socket->id_ = sockets_by_id_.append_and_get_index(socket);
+      input_sockets_.append(socket);
+    }
+    for (DOutputSocket *socket : node->outputs_) {
+      socket->id_ = sockets_by_id_.append_and_get_index(socket);
+      output_sockets_.append(socket);
+    }
+  }
+
+  for (uint i : group_inputs_.index_range()) {
+    group_inputs_[i]->id_ = i;
+  }
+}
+
+DerivedNodeTree::~DerivedNodeTree()
+{
+  for (DInputSocket *socket : input_sockets_) {
+    socket->~DInputSocket();
+  }
+  for (DOutputSocket *socket : output_sockets_) {
+    socket->~DOutputSocket();
+  }
+  for (DNode *node : nodes_by_id_) {
+    node->~DNode();
+  }
+  for (DGroupInput *group_input : group_inputs_) {
+    group_input->~DGroupInput();
+  }
+  for (DParentNode *parent : parent_nodes_) {
+    parent->~DParentNode();
+  }
+}
+
+static dot::Cluster *get_cluster_for_parent(dot::DirectedGraph &graph,
+                                            Map<const DParentNode *, dot::Cluster *> &clusters,
+                                            const DParentNode *parent)
+{
+  if (parent == nullptr) {
+    return nullptr;
+  }
+  return clusters.lookup_or_add_cb(parent, [&]() {
+    dot::Cluster *parent_cluster = get_cluster_for_parent(graph, clusters, parent->parent());
+    bNodeTree *btree = (bNodeTree *)parent->node_ref().bnode()->id;
+    dot::Cluster *new_cluster = &graph.new_cluster(parent->node_ref().name() + " / " +
+                                                   StringRef(btree->id.name + 2));
+    new_cluster->set_parent_cluster(parent_cluster);
+    return new_cluster;
+  });
+}
+
+std::string DerivedNodeTree::to_dot() const
+{
+  dot::DirectedGraph digraph;
+  digraph.set_rankdir(dot::Attr_rankdir::LeftToRight);
+
+  Map<const DNode *, dot::NodeWithSocketsRef> dot_nodes;
+  Map<const DGroupInput *, dot::NodeWithSocketsRef> dot_group_inputs;
+  Map<const DParentNode *, dot::Cluster *> dot_clusters;
+
+  for (const DNode *node : nodes_by_id_) {
+    dot::Node &dot_node = digraph.new_node("");
+    dot_node.set_background_color("white");
+
+    Vector<std::string> input_names;
+    for (const DInputSocket *socket : node->inputs()) {
+      input_names.append(socket->name());
+    }
+    Vector<std::string> output_names;
+    for (const DOutputSocket *socket : node->outputs()) {
+      output_names.append(socket->name());
+    }
+
+    dot_nodes.add_new(node,
+                      dot::NodeWithSocketsRef(dot_node, node->name(), input_names, output_names));
+
+    dot::Cluster *cluster = get_cluster_for_parent(digraph, dot_clusters, node->parent());
+    dot_node.set_parent_cluster(cluster);
+  }
+
+  for (const DGroupInput *group_input : group_inputs_) {
+    dot::Node &dot_node = digraph.new_node("");
+    dot_node.set_background_color("white");
+
+    std::string group_input_name = group_input->name();
+    dot_group_inputs.add_new(
+        group_input, dot::NodeWithSocketsRef(dot_node, "Group Input", {}, {group_input_name}));
+
+    dot::Cluster *cluster = get_cluster_for_parent(digraph, dot_clusters, group_input->parent());
+    dot_node.set_parent_cluster(cluster);
+  }
+
+  for (const DNode *to_node : nodes_by_id_) {
+    dot::NodeWithSocketsRef &to_dot_node = dot_nodes.lookup(to_node);
+
+    for (const DInputSocket *to_socket : to_node->inputs()) {
+      for (const DOutputSocket *from_socket : to_socket->linked_sockets()) {
+        const DNode *from_node = &from_socket->node();
+        dot::NodeWithSocketsRef &from_dot_node = dot_nodes.lookup(from_node);
+
+        digraph.new_edge(from_dot_node.output(from_socket->index()),
+                         to_dot_node.input(to_socket->index()));
+      }
+      for (const DGroupInput *group_input : to_socket->linked_group_inputs()) {
+        dot::NodeWithSocketsRef &from_dot_node = dot_group_inputs.lookup(group_input);
+
+        digraph.new_edge(from_dot_node.output(0), to_dot_node.input(to_socket->index()));
+      }
+    }
+  }
+
+  digraph.set_random_cluster_bgcolors();
+  return digraph.to_dot_string();
+}
+
+}  // namespace blender::nodes
diff --git a/source/blender/nodes/intern/node_socket.cc b/source/blender/nodes/intern/node_socket.cc
index 02124465dda..3a82438a211 100644
--- a/source/blender/nodes/intern/node_socket.cc
+++ b/source/blender/nodes/intern/node_socket.cc
@@ -34,13 +34,13 @@
 
 #include "BKE_lib_id.h"
 #include "BKE_node.h"
-#include "BKE_node_tree_multi_function.hh"
 
 #include "RNA_access.h"
 #include "RNA_types.h"
 
 #include "MEM_guardedalloc.h"
 
+#include "NOD_node_tree_multi_function.hh"
 #include "NOD_socket.h"
 
 struct bNodeSocket *node_add_socket_from_template(struct bNodeTree *ntree,
@@ -517,7 +517,7 @@ static bNodeSocketType *make_socket_type_bool()
 {
   bNodeSocketType *socktype = make_standard_socket_type(SOCK_BOOLEAN, PROP_NONE);
   socktype->get_mf_data_type = []() { return blender::fn::MFDataType::ForSingle<bool>(); };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     bool value = builder.socket_default_value<bNodeSocketValueBoolean>()->value;
     builder.set_constant_value(value);
   };
@@ -528,7 +528,7 @@ static bNodeSocketType *make_socket_type_float(PropertySubType subtype)
 {
   bNodeSocketType *socktype = make_standard_socket_type(SOCK_FLOAT, subtype);
   socktype->get_mf_data_type = []() { return blender::fn::MFDataType::ForSingle<float>(); };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     float value = builder.socket_default_value<bNodeSocketValueFloat>()->value;
     builder.set_constant_value(value);
   };
@@ -539,7 +539,7 @@ static bNodeSocketType *make_socket_type_int(PropertySubType subtype)
 {
   bNodeSocketType *socktype = make_standard_socket_type(SOCK_INT, subtype);
   socktype->get_mf_data_type = []() { return blender::fn::MFDataType::ForSingle<int>(); };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     int value = builder.socket_default_value<bNodeSocketValueInt>()->value;
     builder.set_constant_value(value);
   };
@@ -552,7 +552,7 @@ static bNodeSocketType *make_socket_type_vector(PropertySubType subtype)
   socktype->get_mf_data_type = []() {
     return blender::fn::MFDataType::ForSingle<blender::float3>();
   };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     blender::float3 value = builder.socket_default_value<bNodeSocketValueVector>()->value;
     builder.set_constant_value(value);
   };
@@ -565,7 +565,7 @@ static bNodeSocketType *make_socket_type_rgba()
   socktype->get_mf_data_type = []() {
     return blender::fn::MFDataType::ForSingle<blender::Color4f>();
   };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     blender::Color4f value = builder.socket_default_value<bNodeSocketValueRGBA>()->value;
     builder.set_constant_value(value);
   };
@@ -576,7 +576,7 @@ static bNodeSocketType *make_socket_type_string()
 {
   bNodeSocketType *socktype = make_standard_socket_type(SOCK_STRING, PROP_NONE);
   socktype->get_mf_data_type = []() { return blender::fn::MFDataType::ForSingle<std::string>(); };
-  socktype->expand_in_mf_network = [](blender::bke::SocketMFNetworkBuilder &builder) {
+  socktype->expand_in_mf_network = [](blender::nodes::SocketMFNetworkBuilder &builder) {
     std::string value = builder.socket_default_value<bNodeSocketValueString>()->value;
     builder.set_constant_value(value);
   };
diff --git a/source/blender/nodes/intern/node_tree_multi_function.cc b/source/blender/nodes/intern/node_tree_multi_function.cc
new file mode 100644
index 00000000000..f77b19354a4
--- /dev/null
+++ b/source/blender/nodes/intern/node_tree_multi_function.cc
@@ -0,0 +1,344 @@
+/*
+ * 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 "NOD_node_tree_multi_function.hh"
+
+#include "BLI_color.hh"
+#include "BLI_float3.hh"
+
+namespace blender::nodes {
+
+/* Maybe this should be moved to BKE_node.h. */
+static std::optional<fn::MFDataType> try_get_multi_function_data_type_of_socket(
+    const bNodeSocket *bsocket)
+{
+  if (bsocket->typeinfo->get_mf_data_type == nullptr) {
+    return {};
+  }
+  return bsocket->typeinfo->get_mf_data_type();
+}
+
+const fn::MultiFunction &NodeMFNetworkBuilder::get_default_fn(StringRef name)
+{
+  Vector<fn::MFDataType, 10> input_types;
+  Vector<fn::MFDataType, 10> output_types;
+
+  for (const DInputSocket *dsocket : dnode_.inputs()) {
+    if (dsocket->is_available()) {
+      std::optional<fn::MFDataType> data_type = try_get_multi_function_data_type_of_socket(
+          dsocket->bsocket());
+      if (data_type.has_value()) {
+        input_types.append(*data_type);
+      }
+    }
+  }
+  for (const DOutputSocket *dsocket : dnode_.outputs()) {
+    if (dsocket->is_available()) {
+      std::optional<fn::MFDataType> data_type = try_get_multi_function_data_type_of_socket(
+          dsocket->bsocket());
+      if (data_type.has_value()) {
+        output_types.append(*data_type);
+      }
+    }
+  }
+
+  const fn::MultiFunction &fn = this->construct_fn<fn::CustomMF_DefaultOutput>(
+      name, input_types, output_types);
+  return fn;
+}
+
+static void insert_dummy_node(CommonMFNetworkBuilderData &common, const DNode &dnode)
+{
+  constexpr uint stack_capacity = 10;
+
+  Vector<fn::MFDataType, stack_capacity> input_types;
+  Vector<StringRef, stack_capacity> input_names;
+  Vector<const DInputSocket *, stack_capacity> input_dsockets;
+
+  for (const DInputSocket *dsocket : dnode.inputs()) {
+    if (dsocket->is_available()) {
+      std::optional<fn::MFDataType> data_type = try_get_multi_function_data_type_of_socket(
+          dsocket->bsocket());
+      if (data_type.has_value()) {
+        input_types.append(*data_type);
+        input_names.append(dsocket->name());
+        input_dsockets.append(dsocket);
+      }
+    }
+  }
+
+  Vector<fn::MFDataType, stack_capacity> output_types;
+  Vector<StringRef, stack_capacity> output_names;
+  Vector<const DOutputSocket *, stack_capacity> output_dsockets;
+
+  for (const DOutputSocket *dsocket : dnode.outputs()) {
+    if (dsocket->is_available()) {
+      std::optional<fn::MFDataType> data_type = try_get_multi_function_data_type_of_socket(
+          dsocket->bsocket());
+      if (data_type.has_value()) {
+        output_types.append(*data_type);
+        output_names.append(dsocket->name());
+        output_dsockets.append(dsocket);
+      }
+    }
+  }
+
+  fn::MFDummyNode &dummy_node = common.network.add_dummy(
+      dnode.name(), input_types, output_types, input_names, output_names);
+
+  common.network_map.add(input_dsockets, dummy_node.inputs());
+  common.network_map.add(output_dsockets, dummy_node.outputs());
+}
+
+static bool has_data_sockets(const DNode &dnode)
+{
+  for (const DInputSocket *socket : dnode.inputs()) {
+    if (is_multi_function_data_socket(socket->bsocket())) {
+      return true;
+    }
+  }
+  for (const DOutputSocket *socket : dnode.outputs()) {
+    if (is_multi_function_data_socket(socket->bsocket())) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Expands all function nodes in the multi-function network. Nodes that don't have an expand
+ * function, but do have data sockets, will get corresponding dummy nodes.
+ */
+static void insert_nodes(CommonMFNetworkBuilderData &common)
+{
+  for (const DNode *dnode : common.tree.nodes()) {
+    const bNodeType *node_type = dnode->node_ref().bnode()->typeinfo;
+    if (node_type->expand_in_mf_network != nullptr) {
+      NodeMFNetworkBuilder builder{common, *dnode};
+      node_type->expand_in_mf_network(builder);
+    }
+    else if (has_data_sockets(*dnode)) {
+      insert_dummy_node(common, *dnode);
+    }
+  }
+}
+
+static void insert_group_inputs(CommonMFNetworkBuilderData &common)
+{
+  for (const DGroupInput *group_input : common.tree.group_inputs()) {
+    bNodeSocket *bsocket = group_input->bsocket();
+    if (is_multi_function_data_socket(bsocket)) {
+      bNodeSocketType *socktype = bsocket->typeinfo;
+      BLI_assert(socktype->expand_in_mf_network != nullptr);
+
+      SocketMFNetworkBuilder builder{common, *group_input};
+      socktype->expand_in_mf_network(builder);
+
+      fn::MFOutputSocket *from_socket = builder.built_socket();
+      BLI_assert(from_socket != nullptr);
+      common.network_map.add(*group_input, *from_socket);
+    }
+  }
+}
+
+static fn::MFOutputSocket *try_find_origin(CommonMFNetworkBuilderData &common,
+                                           const DInputSocket &to_dsocket)
+{
+  Span<const DOutputSocket *> from_dsockets = to_dsocket.linked_sockets();
+  Span<const DGroupInput *> from_group_inputs = to_dsocket.linked_group_inputs();
+  uint total_linked_amount = from_dsockets.size() + from_group_inputs.size();
+  BLI_assert(total_linked_amount <= 1);
+
+  if (total_linked_amount == 0) {
+    return nullptr;
+  }
+
+  if (from_dsockets.size() == 1) {
+    const DOutputSocket &from_dsocket = *from_dsockets[0];
+    if (!from_dsocket.is_available()) {
+      return nullptr;
+    }
+    if (is_multi_function_data_socket(from_dsocket.bsocket())) {
+      return &common.network_map.lookup(from_dsocket);
+    }
+    return nullptr;
+  }
+  else {
+    const DGroupInput &from_group_input = *from_group_inputs[0];
+    if (is_multi_function_data_socket(from_group_input.bsocket())) {
+      return &common.network_map.lookup(from_group_input);
+    }
+    return nullptr;
+  }
+}
+
+using ImplicitConversionsMap =
+    Map<std::pair<fn::MFDataType, fn::MFDataType>, const fn::MultiFunction *>;
+
+template<typename From, typename To>
+static void add_implicit_conversion(ImplicitConversionsMap &map)
+{
+  static fn::CustomMF_Convert<From, To> function;
+  map.add({fn::MFDataType::ForSingle<From>(), fn::MFDataType::ForSingle<To>()}, &function);
+}
+
+template<typename From, typename To, typename ConversionF>
+static void add_implicit_conversion(ImplicitConversionsMap &map,
+                                    StringRef name,
+                                    ConversionF conversion)
+{
+  static fn::CustomMF_SI_SO<From, To> function{name, conversion};
+  map.add({fn::MFDataType::ForSingle<From>(), fn::MFDataType::ForSingle<To>()}, &function);
+}
+
+static ImplicitConversionsMap get_implicit_conversions()
+{
+  ImplicitConversionsMap conversions;
+  add_implicit_conversion<float, int32_t>(conversions);
+  add_implicit_conversion<float, float3>(conversions);
+  add_implicit_conversion<int32_t, float>(conversions);
+  add_implicit_conversion<float3, float>(
+      conversions, "Vector Length", [](float3 a) { return a.length(); });
+  add_implicit_conversion<int32_t, float3>(
+      conversions, "int32 to float3", [](int32_t a) { return float3((float)a); });
+  add_implicit_conversion<float3, Color4f>(
+      conversions, "float3 to Color4f", [](float3 a) { return Color4f(a.x, a.y, a.z, 1.0f); });
+  add_implicit_conversion<Color4f, float3>(
+      conversions, "Color4f to float3", [](Color4f a) { return float3(a.r, a.g, a.b); });
+  return conversions;
+}
+
+static const fn::MultiFunction *try_get_conversion_function(fn::MFDataType from, fn::MFDataType to)
+{
+  static const ImplicitConversionsMap conversions = get_implicit_conversions();
+  const fn::MultiFunction *function = conversions.lookup_default({from, to}, nullptr);
+  return function;
+}
+
+static fn::MFOutputSocket &insert_default_value_for_type(CommonMFNetworkBuilderData &common,
+                                                         fn::MFDataType type)
+{
+  const fn::MultiFunction *default_fn;
+  if (type.is_single()) {
+    default_fn = &common.resources.construct<fn::CustomMF_GenericConstant>(
+        AT, type.single_type(), type.single_type().default_value());
+  }
+  else {
+    default_fn = &common.resources.construct<fn::CustomMF_GenericConstantArray>(
+        AT, fn::GSpan(type.vector_base_type()));
+  }
+
+  fn::MFNode &node = common.network.add_function(*default_fn);
+  return node.output(0);
+}
+
+static void insert_links(CommonMFNetworkBuilderData &common)
+{
+  for (const DInputSocket *to_dsocket : common.tree.input_sockets()) {
+    if (!to_dsocket->is_available()) {
+      continue;
+    }
+    if (!to_dsocket->is_linked()) {
+      continue;
+    }
+    if (!is_multi_function_data_socket(to_dsocket->bsocket())) {
+      continue;
+    }
+
+    Span<fn::MFInputSocket *> to_sockets = common.network_map.lookup(*to_dsocket);
+    BLI_assert(to_sockets.size() >= 1);
+    fn::MFDataType to_type = to_sockets[0]->data_type();
+
+    fn::MFOutputSocket *from_socket = try_find_origin(common, *to_dsocket);
+    if (from_socket == nullptr) {
+      from_socket = &insert_default_value_for_type(common, to_type);
+    }
+
+    fn::MFDataType from_type = from_socket->data_type();
+
+    if (from_type != to_type) {
+      const fn::MultiFunction *conversion_fn = try_get_conversion_function(from_type, to_type);
+      if (conversion_fn != nullptr) {
+        fn::MFNode &node = common.network.add_function(*conversion_fn);
+        common.network.add_link(*from_socket, node.input(0));
+        from_socket = &node.output(0);
+      }
+      else {
+        from_socket = &insert_default_value_for_type(common, to_type);
+      }
+    }
+
+    for (fn::MFInputSocket *to_socket : to_sockets) {
+      common.network.add_link(*from_socket, *to_socket);
+    }
+  }
+}
+
+static void insert_unlinked_input(CommonMFNetworkBuilderData &common, const DInputSocket &dsocket)
+{
+  bNodeSocket *bsocket = dsocket.bsocket();
+  bNodeSocketType *socktype = bsocket->typeinfo;
+  BLI_assert(socktype->expand_in_mf_network != nullptr);
+
+  SocketMFNetworkBuilder builder{common, dsocket};
+  socktype->expand_in_mf_network(builder);
+
+  fn::MFOutputSocket *from_socket = builder.built_socket();
+  BLI_assert(from_socket != nullptr);
+
+  for (fn::MFInputSocket *to_socket : common.network_map.lookup(dsocket)) {
+    common.network.add_link(*from_socket, *to_socket);
+  }
+}
+
+static void insert_unlinked_inputs(CommonMFNetworkBuilderData &common)
+{
+  Vector<const DInputSocket *> unlinked_data_inputs;
+  for (const DInputSocket *dsocket : common.tree.input_sockets()) {
+    if (dsocket->is_available()) {
+      if (is_multi_function_data_socket(dsocket->bsocket())) {
+        if (!dsocket->is_linked()) {
+          insert_unlinked_input(common, *dsocket);
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Expands all function nodes contained in the given node tree within the given multi-function
+ * network.
+ *
+ * Returns a mapping between the original node tree and the generated nodes/sockets for further
+ * processing.
+ */
+MFNetworkTreeMap insert_node_tree_into_mf_network(fn::MFNetwork &network,
+                                                  const DerivedNodeTree &tree,
+                                                  ResourceCollector &resources)
+{
+  MFNetworkTreeMap network_map{tree, network};
+
+  CommonMFNetworkBuilderData common{resources, network, network_map, tree};
+
+  insert_nodes(common);
+  insert_group_inputs(common);
+  insert_links(common);
+  insert_unlinked_inputs(common);
+
+  return network_map;
+}
+
+}  // namespace blender::nodes
diff --git a/source/blender/nodes/intern/node_tree_ref.cc b/source/blender/nodes/intern/node_tree_ref.cc
new file mode 100644
index 00000000000..186ca750f10
--- /dev/null
+++ b/source/blender/nodes/intern/node_tree_ref.cc
@@ -0,0 +1,177 @@
+/*
+ * 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 "NOD_node_tree_ref.hh"
+
+#include "BLI_dot_export.hh"
+
+namespace blender::nodes {
+
+NodeTreeRef::NodeTreeRef(bNodeTree *btree) : btree_(btree)
+{
+  Map<bNode *, NodeRef *> node_mapping;
+
+  LISTBASE_FOREACH (bNode *, bnode, &btree->nodes) {
+    NodeRef &node = *allocator_.construct<NodeRef>();
+
+    node.tree_ = this;
+    node.bnode_ = bnode;
+    node.id_ = nodes_by_id_.append_and_get_index(&node);
+    RNA_pointer_create(&btree->id, &RNA_Node, bnode, &node.rna_);
+
+    LISTBASE_FOREACH (bNodeSocket *, bsocket, &bnode->inputs) {
+      InputSocketRef &socket = *allocator_.construct<InputSocketRef>();
+      socket.node_ = &node;
+      socket.index_ = node.inputs_.append_and_get_index(&socket);
+      socket.is_input_ = true;
+      socket.bsocket_ = bsocket;
+      socket.id_ = sockets_by_id_.append_and_get_index(&socket);
+      RNA_pointer_create(&btree->id, &RNA_NodeSocket, bsocket, &socket.rna_);
+    }
+
+    LISTBASE_FOREACH (bNodeSocket *, bsocket, &bnode->outputs) {
+      OutputSocketRef &socket = *allocator_.construct<OutputSocketRef>();
+      socket.node_ = &node;
+      socket.index_ = node.outputs_.append_and_get_index(&socket);
+      socket.is_input_ = false;
+      socket.bsocket_ = bsocket;
+      socket.id_ = sockets_by_id_.append_and_get_index(&socket);
+      RNA_pointer_create(&btree->id, &RNA_NodeSocket, bsocket, &socket.rna_);
+    }
+
+    input_sockets_.extend(node.inputs_.as_span());
+    output_sockets_.extend(node.outputs_.as_span());
+
+    node_mapping.add_new(bnode, &node);
+  }
+
+  LISTBASE_FOREACH (bNodeLink *, blink, &btree->links) {
+    OutputSocketRef &from_socket = this->find_output_socket(
+        node_mapping, blink->fromnode, blink->fromsock);
+    InputSocketRef &to_socket = this->find_input_socket(
+        node_mapping, blink->tonode, blink->tosock);
+
+    from_socket.directly_linked_sockets_.append(&to_socket);
+    to_socket.directly_linked_sockets_.append(&from_socket);
+  }
+
+  for (OutputSocketRef *socket : output_sockets_) {
+    if (!socket->node_->is_reroute_node()) {
+      this->find_targets_skipping_reroutes(*socket, socket->linked_sockets_);
+      for (SocketRef *target : socket->linked_sockets_) {
+        target->linked_sockets_.append(socket);
+      }
+    }
+  }
+
+  for (NodeRef *node : nodes_by_id_) {
+    const bNodeType *nodetype = node->bnode_->typeinfo;
+    nodes_by_type_.lookup_or_add_default(nodetype).append(node);
+  }
+}
+
+NodeTreeRef::~NodeTreeRef()
+{
+  for (NodeRef *node : nodes_by_id_) {
+    node->~NodeRef();
+  }
+  for (InputSocketRef *socket : input_sockets_) {
+    socket->~InputSocketRef();
+  }
+  for (OutputSocketRef *socket : output_sockets_) {
+    socket->~OutputSocketRef();
+  }
+}
+
+InputSocketRef &NodeTreeRef::find_input_socket(Map<bNode *, NodeRef *> &node_mapping,
+                                               bNode *bnode,
+                                               bNodeSocket *bsocket)
+{
+  NodeRef *node = node_mapping.lookup(bnode);
+  for (SocketRef *socket : node->inputs_) {
+    if (socket->bsocket_ == bsocket) {
+      return *(InputSocketRef *)socket;
+    }
+  }
+  BLI_assert(false);
+  return *node->inputs_[0];
+}
+
+OutputSocketRef &NodeTreeRef::find_output_socket(Map<bNode *, NodeRef *> &node_mapping,
+                                                 bNode *bnode,
+                                                 bNodeSocket *bsocket)
+{
+  NodeRef *node = node_mapping.lookup(bnode);
+  for (SocketRef *socket : node->outputs_) {
+    if (socket->bsocket_ == bsocket) {
+      return *(OutputSocketRef *)socket;
+    }
+  }
+  BLI_assert(false);
+  return *node->outputs_[0];
+}
+
+void NodeTreeRef::find_targets_skipping_reroutes(OutputSocketRef &socket,
+                                                 Vector<SocketRef *> &r_targets)
+{
+  for (SocketRef *direct_target : socket.directly_linked_sockets_) {
+    if (direct_target->node_->is_reroute_node()) {
+      this->find_targets_skipping_reroutes(*direct_target->node_->outputs_[0], r_targets);
+    }
+    else {
+      r_targets.append_non_duplicates(direct_target);
+    }
+  }
+}
+
+std::string NodeTreeRef::to_dot() const
+{
+  dot::DirectedGraph digraph;
+  digraph.set_rankdir(dot::Attr_rankdir::LeftToRight);
+
+  Map<const NodeRef *, dot::NodeWithSocketsRef> dot_nodes;
+
+  for (const NodeRef *node : nodes_by_id_) {
+    dot::Node &dot_node = digraph.new_node("");
+    dot_node.set_background_color("white");
+
+    Vector<std::string> input_names;
+    Vector<std::string> output_names;
+    for (const InputSocketRef *socket : node->inputs()) {
+      input_names.append(socket->name());
+    }
+    for (const OutputSocketRef *socket : node->outputs()) {
+      output_names.append(socket->name());
+    }
+
+    dot_nodes.add_new(node,
+                      dot::NodeWithSocketsRef(dot_node, node->name(), input_names, output_names));
+  }
+
+  for (const OutputSocketRef *from_socket : output_sockets_) {
+    for (const InputSocketRef *to_socket : from_socket->directly_linked_sockets()) {
+      dot::NodeWithSocketsRef &from_dot_node = dot_nodes.lookup(&from_socket->node());
+      dot::NodeWithSocketsRef &to_dot_node = dot_nodes.lookup(&to_socket->node());
+
+      digraph.new_edge(from_dot_node.output(from_socket->index()),
+                       to_dot_node.input(to_socket->index()));
+    }
+  }
+
+  return digraph.to_dot_string();
+}
+
+}  // namespace blender::nodes