[Net] MultiplayerReplicator with initial state.

Move the former "spawnables" functions to a dedicated
MultiplayerReplicator class.
Support custom overrides in replicator.
Spawn/despawn messages can now contain a state.
The state can be automatically encoded/decoded by passing the desired
object properties to `spawnable_config`.
You can use script properties to optimize the state representation.
2 Callables can be also specified to completely override the default
implementation for sending and receiving the spawn/despawn event.
(9 bytes overhead, and there's room for improvement here).
When using a custom implementation `spawn` and `despawn` can be called
with any Object, `send_spawn`/`send_despawn` can receive any Variant as
a state, and the path is not required.

Two new functions, `spawn` and `despawn`, convey the implementation
independent method for requesting a spawn/despawn of an Object, while
`send_spawn` and `send_despawn` represent the more low-level send event
for a Variant to be used by the custom implementations.

1 files changed, 99 insertions, 0 deletions

diff --git a/core/io/multiplayer_replicator.h b/core/io/multiplayer_replicator.h
new file mode 100644
index 0000000000..e19dd80602
--- /dev/null
+++ b/core/io/multiplayer_replicator.h
@@ -0,0 +1,99 @@
+/*************************************************************************/
+/*  multiplayer_replicator.h                                             */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef MULTIPLAYER_REPLICATOR_H
+#define MULTIPLAYER_REPLICATOR_H
+
+#include "core/io/multiplayer_api.h"
+#include "core/variant/typed_array.h"
+
+class MultiplayerReplicator : public Object {
+	GDCLASS(MultiplayerReplicator, Object);
+
+public:
+	enum {
+		SPAWN_CMD_OFFSET = 9,
+	};
+
+	enum ReplicationMode {
+		REPLICATION_MODE_NONE,
+		REPLICATION_MODE_SERVER,
+		REPLICATION_MODE_CUSTOM,
+	};
+
+	struct SceneConfig {
+		ReplicationMode mode;
+		List<StringName> properties;
+		Callable on_spawn_despawn_send;
+		Callable on_spawn_despawn_receive;
+	};
+
+protected:
+	static void _bind_methods();
+
+private:
+	MultiplayerAPI *multiplayer = nullptr;
+	Vector<uint8_t> packet_cache;
+	Map<ResourceUID::ID, SceneConfig> replications;
+	Map<ObjectID, ResourceUID::ID> replicated_nodes;
+
+	Error _encode_state(const List<Variant> &p_variants, uint8_t *p_buffer, int &r_len, bool *r_raw = nullptr);
+	Error _decode_state(const List<StringName> &p_cfg, Object *p_obj, const uint8_t *p_buffer, int p_len, int &r_len, bool p_raw = false);
+	Error _get_state(const List<StringName> &p_properties, const Object *p_obj, List<Variant> &r_variant);
+	Error _spawn_despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer, bool p_spawn);
+	Error _send_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data, bool p_spawn);
+	void _process_default_spawn_despawn(int p_from, const ResourceUID::ID &p_scene_id, const uint8_t *p_packet, int p_packet_len, bool p_spawn);
+	Error _send_default_spawn_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, Object *p_obj, const NodePath &p_path, bool p_spawn);
+
+public:
+	void clear();
+
+	Error spawn_config(const ResourceUID::ID &p_id, ReplicationMode p_mode, const TypedArray<StringName> &p_props = TypedArray<StringName>(), const Callable &p_on_send = Callable(), const Callable &p_on_recv = Callable());
+	Error spawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer = 0);
+	Error despawn(ResourceUID::ID p_scene_id, Object *p_obj, int p_peer = 0);
+
+	Error send_despawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data = Variant(), const NodePath &p_path = NodePath());
+	Error send_spawn(int p_peer_id, const ResourceUID::ID &p_scene_id, const Variant &p_data = Variant(), const NodePath &p_path = NodePath());
+	PackedByteArray encode_state(const ResourceUID::ID &p_scene_id, const Object *p_node);
+	Error decode_state(const ResourceUID::ID &p_scene_id, Object *p_node, PackedByteArray p_data);
+
+	// Used by MultiplayerAPI
+	void spawn_all(int p_peer);
+	void process_spawn_despawn(int p_from, const uint8_t *p_packet, int p_packet_len, bool p_spawn);
+	void scene_enter_exit_notify(const String &p_scene, Node *p_node, bool p_enter);
+
+	MultiplayerReplicator(MultiplayerAPI *p_multiplayer) {
+		multiplayer = p_multiplayer;
+	}
+};
+
+VARIANT_ENUM_CAST(MultiplayerReplicator::ReplicationMode);
+
+#endif // MULTIPLAYER_REPLICATOR_H