[Net] New replication interface, spawner and synchronizer nodes.

Initial implementation of the MultiplayerReplicationInterface and its
default implementation (SceneReplicationInterface).

New MultiplayerSpawner node helps dealing with instantiation of scenes
on remote peers (e.g. clients).
It supports both custom spawns via a `_spawn_custom` virtual function,
and optional auto-spawn of known scenes via a TypedArray<PackedScenes>
property.

New MultiplayerSynchornizer helps synchronizing states between the local
and remote peers, supports both sync and spawn properties and is
configured via a `SceneReplicationConfig` resource.
It can also sync via path (i.e. without being spawned by a
MultiplayerSpawner if both peers has it in tree, but will not send the
spawn state in that case, only the sync one.

4 files changed, 4 insertions, 12 deletions

diff --git a/scene/main/node.cpp b/scene/main/node.cpp
index 149382bc2a..6b9d8ab211 100644
--- a/scene/main/node.cpp
+++ b/scene/main/node.cpp
@@ -32,6 +32,7 @@
 
 #include "core/core_string_names.h"
 #include "core/io/resource_loader.h"
+#include "core/multiplayer/multiplayer_api.h"
 #include "core/object/message_queue.h"
 #include "core/string/print_string.h"
 #include "instance_placeholder.h"
@@ -110,9 +111,6 @@ void Node::_notification(int p_notification) {
 				memdelete(data.path_cache);
 				data.path_cache = nullptr;
 			}
-			if (data.scene_file_path.length()) {
-				get_multiplayer()->scene_enter_exit_notify(data.scene_file_path, this, false);
-			}
 		} break;
 		case NOTIFICATION_PATH_RENAMED: {
 			if (data.path_cache) {
@@ -141,12 +139,6 @@ void Node::_notification(int p_notification) {
 			}
 
 			GDVIRTUAL_CALL(_ready);
-
-			if (data.scene_file_path.length()) {
-				ERR_FAIL_COND(!is_inside_tree());
-				get_multiplayer()->scene_enter_exit_notify(data.scene_file_path, this, true);
-			}
-
 		} break;
 		case NOTIFICATION_POSTINITIALIZE: {
 			data.in_constructor = false;
diff --git a/scene/main/node.h b/scene/main/node.h
index a1fc672a15..0ac10f4381 100644
--- a/scene/main/node.h
+++ b/scene/main/node.h
@@ -212,7 +212,6 @@ protected:
 	static String _get_name_num_separator();
 
 	friend class SceneState;
-	friend class MultiplayerReplicator;
 
 	void _add_child_nocheck(Node *p_child, const StringName &p_name);
 	void _set_owner_nocheck(Node *p_owner);
@@ -467,7 +466,7 @@ public:
 	bool is_displayed_folded() const;
 	/* NETWORK */
 
-	void set_multiplayer_authority(int p_peer_id, bool p_recursive = true);
+	virtual void set_multiplayer_authority(int p_peer_id, bool p_recursive = true);
 	int get_multiplayer_authority() const;
 	bool is_multiplayer_authority() const;
 
diff --git a/scene/main/scene_tree.cpp b/scene/main/scene_tree.cpp
index 45f04b28b9..0e4a6a4b5c 100644
--- a/scene/main/scene_tree.cpp
+++ b/scene/main/scene_tree.cpp
@@ -36,6 +36,7 @@
 #include "core/io/dir_access.h"
 #include "core/io/marshalls.h"
 #include "core/io/resource_loader.h"
+#include "core/multiplayer/multiplayer_api.h"
 #include "core/object/message_queue.h"
 #include "core/os/keyboard.h"
 #include "core/os/os.h"
diff --git a/scene/main/scene_tree.h b/scene/main/scene_tree.h
index 1dff1dab4f..a5cd52b4ca 100644
--- a/scene/main/scene_tree.h
+++ b/scene/main/scene_tree.h
@@ -31,7 +31,6 @@
 #ifndef SCENE_TREE_H
 #define SCENE_TREE_H
 
-#include "core/multiplayer/multiplayer_api.h"
 #include "core/os/main_loop.h"
 #include "core/os/thread_safe.h"
 #include "core/templates/self_list.h"
@@ -46,6 +45,7 @@ class Node;
 class Window;
 class Material;
 class Mesh;
+class MultiplayerAPI;
 class SceneDebugger;
 class Tween;