Make NavigationServer backend engine selectable

Adds engine backend selection for NavigationServers, aka allows to swap navigation module for other backend implementations.

Author: smix8

doc/classes/@GlobalScope.xml

@@ -1608,9 +1608,15 @@
 		<member name="NavigationServer2D" type="NavigationServer2D" setter="" getter="">
 			The [NavigationServer2D] singleton.
 		</member>
+		<member name="NavigationServer2DManager" type="NavigationServer2DManager" setter="" getter="">
+			The [NavigationServer2DManager] singleton.
+		</member>
 		<member name="NavigationServer3D" type="NavigationServer3D" setter="" getter="">
 			The [NavigationServer3D] singleton.
 		</member>
+		<member name="NavigationServer3DManager" type="NavigationServer3DManager" setter="" getter="">
+			The [NavigationServer3DManager] singleton.
+		</member>
 		<member name="OS" type="OS" setter="" getter="">
 			The [OS] singleton.
 		</member>

doc/classes/NavigationServer2DManager.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="NavigationServer2DManager" inherits="Object" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		A singleton for managing [NavigationServer2D] implementations.
+	</brief_description>
+	<description>
+		[NavigationServer2DManager] is the API for registering [NavigationServer2D] implementations and setting the default implementation.
+		[b]Note:[/b] It is not possible to switch servers at runtime. This class is only used on startup at the server initialization level.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="register_server">
+			<return type="void" />
+			<param index="0" name="name" type="String" />
+			<param index="1" name="create_callback" type="Callable" />
+			<description>
+				Registers a [NavigationServer2D] implementation by passing a [param name] and a [Callable] that returns a [NavigationServer2D] object.
+			</description>
+		</method>
+		<method name="set_default_server">
+			<return type="void" />
+			<param index="0" name="name" type="String" />
+			<param index="1" name="priority" type="int" />
+			<description>
+				Sets the default [NavigationServer2D] implementation to the one identified by [param name], if [param priority] is greater than the priority of the current default implementation.
+			</description>
+		</method>
+	</methods>
+</class>

doc/classes/NavigationServer3DManager.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<class name="NavigationServer3DManager" inherits="Object" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
+	<brief_description>
+		A singleton for managing [NavigationServer3D] implementations.
+	</brief_description>
+	<description>
+		[NavigationServer3DManager] is the API for registering [NavigationServer3D] implementations and setting the default implementation.
+		[b]Note:[/b] It is not possible to switch servers at runtime. This class is only used on startup at the server initialization level.
+	</description>
+	<tutorials>
+	</tutorials>
+	<methods>
+		<method name="register_server">
+			<return type="void" />
+			<param index="0" name="name" type="String" />
+			<param index="1" name="create_callback" type="Callable" />
+			<description>
+				Registers a [NavigationServer3D] implementation by passing a [param name] and a [Callable] that returns a [NavigationServer3D] object.
+			</description>
+		</method>
+		<method name="set_default_server">
+			<return type="void" />
+			<param index="0" name="name" type="String" />
+			<param index="1" name="priority" type="int" />
+			<description>
+				Sets the default [NavigationServer3D] implementation to the one identified by [param name], if [param priority] is greater than the priority of the current default implementation.
+			</description>
+		</method>
+	</methods>
+</class>

doc/classes/ProjectSettings.xml

@@ -2348,6 +2348,13 @@
 		<member name="navigation/2d/merge_rasterizer_cell_scale" type="float" setter="" getter="" default="1.0">
 			Default merge rasterizer cell scale for 2D navigation maps. See [method NavigationServer2D.map_set_merge_rasterizer_cell_scale].
 		</member>
+		<member name="navigation/2d/navigation_engine" type="String" setter="" getter="" default="&quot;DEFAULT&quot;">
+			Sets which navigation engine to use for 2D navigation.
+			[b]DEFAULT[/b] is equivalent to [b]GodotNavigation2D[/b], but may change in future releases. Select an explicit implementation if you want to ensure that your project stays on the same engine.
+			[b]GodotNavigation2D[/b] is Godot's internal 2D navigation engine.
+			[b]Dummy[/b] is a 2D navigation server that does nothing and returns only dummy values, effectively disabling all 2D navigation functionality.
+			Third-party modules can add other navigation engines to select with this setting.
+		</member>
 		<member name="navigation/2d/use_edge_connections" type="bool" setter="" getter="" default="true">
 			If enabled 2D navigation regions will use edge connections to connect with other navigation regions within proximity of the navigation map edge connection margin. This setting only affects World2D default navigation maps.
 		</member>
@@ -2375,6 +2382,13 @@
 		<member name="navigation/3d/merge_rasterizer_cell_scale" type="float" setter="" getter="" default="1.0">
 			Default merge rasterizer cell scale for 3D navigation maps. See [method NavigationServer3D.map_set_merge_rasterizer_cell_scale].
 		</member>
+		<member name="navigation/3d/navigation_engine" type="String" setter="" getter="" default="&quot;DEFAULT&quot;">
+			Sets which navigation engine to use for 3D navigation.
+			[b]DEFAULT[/b] is equivalent to [b]GodotNavigation3D[/b], but may change in future releases. Select an explicit implementation if you want to ensure that your project stays on the same engine.
+			[b]GodotNavigation3D[/b] is Godot's internal 3D navigation engine.
+			[b]Dummy[/b] is a 3D navigation server that does nothing and returns only dummy values, effectively disabling all 3D navigation functionality.
+			Third-party modules can add other navigation engines to select with this setting.
+		</member>
 		<member name="navigation/3d/use_edge_connections" type="bool" setter="" getter="" default="true">
 			If enabled 3D navigation regions will use edge connections to connect with other navigation regions within proximity of the navigation map edge connection margin. This setting only affects World3D default navigation maps.
 		</member>

main/main.cpp

@@ -746,6 +746,13 @@ Error Main::test_setup() {
 	physics_server_2d_manager = memnew(PhysicsServer2DManager);
 #endif // PHYSICS_2D_DISABLED
 
+#ifndef NAVIGATION_2D_DISABLED
+	NavigationServer2DManager::initialize_server_manager();
+#endif // NAVIGATION_2D_DISABLED
+#ifndef NAVIGATION_3D_DISABLED
+	NavigationServer3DManager::initialize_server_manager();
+#endif // NAVIGATION_3D_DISABLED
+
 	// From `Main::setup2()`.
 	register_early_core_singletons();
 	initialize_modules(MODULE_INITIALIZATION_LEVEL_CORE);
@@ -863,9 +870,11 @@ void Main::test_cleanup() {
 
 #ifndef NAVIGATION_2D_DISABLED
 	NavigationServer2DManager::finalize_server();
+	NavigationServer2DManager::finalize_server_manager();
 #endif // NAVIGATION_2D_DISABLED
 #ifndef NAVIGATION_3D_DISABLED
 	NavigationServer3DManager::finalize_server();
+	NavigationServer3DManager::finalize_server_manager();
 #endif // NAVIGATION_3D_DISABLED
 
 	GDExtensionManager::get_singleton()->deinitialize_extensions(GDExtension::INITIALIZATION_LEVEL_SERVERS);
@@ -3018,6 +3027,13 @@ Error Main::setup2(bool p_show_boot_logo) {
 	physics_server_2d_manager = memnew(PhysicsServer2DManager);
 #endif // PHYSICS_2D_DISABLED
 
+#ifndef NAVIGATION_2D_DISABLED
+	NavigationServer2DManager::initialize_server_manager();
+#endif // NAVIGATION_2D_DISABLED
+#ifndef NAVIGATION_3D_DISABLED
+	NavigationServer3DManager::initialize_server_manager();
+#endif // NAVIGATION_3D_DISABLED
+
 	register_server_types();
 	{
 		OS::get_singleton()->benchmark_begin_measure("Servers", "Modules and Extensions");
@@ -4979,9 +4995,11 @@ void Main::cleanup(bool p_force) {
 // Before deinitializing server extensions, finalize servers which may be loaded as extensions.
 #ifndef NAVIGATION_2D_DISABLED
 	NavigationServer2DManager::finalize_server();
+	NavigationServer2DManager::finalize_server_manager();
 #endif // NAVIGATION_2D_DISABLED
 #ifndef NAVIGATION_3D_DISABLED
 	NavigationServer3DManager::finalize_server();
+	NavigationServer3DManager::finalize_server_manager();
 #endif // NAVIGATION_3D_DISABLED
 	finalize_physics();
 

modules/navigation_2d/register_types.cpp

@@ -41,13 +41,14 @@
 #include "editor/navigation_region_2d_editor_plugin.h"
 #endif
 
-NavigationServer2D *new_navigation_server_2d() {
+static NavigationServer2D *_createGodotNavigation2DCallback() {
 	return memnew(GodotNavigationServer2D);
 }
 
 void initialize_navigation_2d_module(ModuleInitializationLevel p_level) {
 	if (p_level == MODULE_INITIALIZATION_LEVEL_SERVERS) {
-		NavigationServer2DManager::set_default_server(new_navigation_server_2d);
+		NavigationServer2DManager::get_singleton()->register_server("GodotNavigation2D", callable_mp_static(_createGodotNavigation2DCallback));
+		NavigationServer2DManager::get_singleton()->set_default_server("GodotNavigation2D");
 	}
 
 #ifdef TOOLS_ENABLED

modules/navigation_3d/register_types.cpp

@@ -49,13 +49,14 @@
 NavigationMeshGenerator *_nav_mesh_generator = nullptr;
 #endif // DISABLE_DEPRECATED
 
-NavigationServer3D *new_navigation_server_3d() {
+static NavigationServer3D *_createGodotNavigation3DCallback() {
 	return memnew(GodotNavigationServer3D);
 }
 
 void initialize_navigation_3d_module(ModuleInitializationLevel p_level) {
 	if (p_level == MODULE_INITIALIZATION_LEVEL_SERVERS) {
-		NavigationServer3DManager::set_default_server(new_navigation_server_3d);
+		NavigationServer3DManager::get_singleton()->register_server("GodotNavigation3D", callable_mp_static(_createGodotNavigation3DCallback));
+		NavigationServer3DManager::get_singleton()->set_default_server("GodotNavigation3D");
 
 #ifndef DISABLE_DEPRECATED
 		_nav_mesh_generator = memnew(NavigationMeshGenerator);

servers/navigation_2d/navigation_server_2d.cpp

@@ -256,8 +256,8 @@ NavigationServer2D::NavigationServer2D() {
 	debug_navigation_avoidance_enable_obstacles_static = GLOBAL_DEF("debug/shapes/avoidance/2d/enable_obstacles_static", true);
 
 	if (Engine::get_singleton()->is_editor_hint()) {
-		// enable NavigationServer3D when in Editor or else navigation mesh edge connections are invisible
-		// on runtime tests SceneTree has "Visible Navigation" set and main iteration takes care of this.
+		// Enable NavigationServer2D when in Editor or navigation mesh edge connections are invisible.
+		// On runtime tests SceneTree has "Visible Navigation" set and main iteration takes care of this.
 		set_debug_enabled(true);
 		set_debug_navigation_enabled(true);
 		set_debug_avoidance_enabled(true);
@@ -550,30 +550,24 @@ bool NavigationServer2D::get_debug_navigation_avoidance_enable_obstacles_static(
 
 static NavigationServer2D *navigation_server_2d = nullptr;
 
-NavigationServer2DCallback NavigationServer2DManager::create_callback = nullptr;
-
-void NavigationServer2DManager::set_default_server(NavigationServer2DCallback p_callback) {
-	create_callback = p_callback;
-}
-
-NavigationServer2D *NavigationServer2DManager::new_default_server() {
-	if (create_callback == nullptr) {
-		return nullptr;
-	}
-
-	return create_callback();
-}
-
 void NavigationServer2DManager::initialize_server() {
 	ERR_FAIL_COND(navigation_server_2d != nullptr);
 
-	// Init 2D Navigation Server
-	navigation_server_2d = NavigationServer2DManager::new_default_server();
+	// Init 2D Navigation Server.
+	navigation_server_2d = NavigationServer2DManager::get_singleton()->new_server(
+			GLOBAL_GET(NavigationServer2DManager::setting_property_name));
+	if (!navigation_server_2d) {
+		// Navigation server not found, use the default.
+		navigation_server_2d = NavigationServer2DManager::get_singleton()->new_default_server();
+	}
+
+	// Fall back to dummy if no default server has been registered.
 	if (!navigation_server_2d) {
 		WARN_VERBOSE("Failed to initialize NavigationServer2D. Fall back to dummy server.");
 		navigation_server_2d = memnew(NavigationServer2DDummy);
 	}
 
+	// Should be impossible, but make sure it's not null.
 	ERR_FAIL_NULL_MSG(navigation_server_2d, "Failed to initialize NavigationServer2D.");
 	navigation_server_2d->init();
 }
@@ -584,3 +578,101 @@ void NavigationServer2DManager::finalize_server() {
 	memdelete(navigation_server_2d);
 	navigation_server_2d = nullptr;
 }
+
+const String NavigationServer2DManager::setting_property_name(PNAME("navigation/2d/navigation_engine"));
+
+void NavigationServer2DManager::on_servers_changed() {
+	String navigation_servers_enum_str("DEFAULT");
+	for (int i = get_servers_count() - 1; 0 <= i; --i) {
+		navigation_servers_enum_str += "," + get_server_name(i);
+	}
+	ProjectSettings::get_singleton()->set_custom_property_info(PropertyInfo(Variant::STRING, setting_property_name, PROPERTY_HINT_ENUM, navigation_servers_enum_str));
+	ProjectSettings::get_singleton()->set_restart_if_changed(setting_property_name, true);
+	ProjectSettings::get_singleton()->set_as_basic(setting_property_name, true);
+}
+
+void NavigationServer2DManager::_bind_methods() {
+	ClassDB::bind_method(D_METHOD("register_server", "name", "create_callback"), &NavigationServer2DManager::register_server);
+	ClassDB::bind_method(D_METHOD("set_default_server", "name", "priority"), &NavigationServer2DManager::set_default_server);
+}
+
+NavigationServer2DManager *NavigationServer2DManager::get_singleton() {
+	return singleton;
+}
+
+void NavigationServer2DManager::register_server(const String &p_name, const Callable &p_create_callback) {
+	ERR_FAIL_COND(find_server_id(p_name) != -1);
+	navigation_servers.push_back(ClassInfo(p_name, p_create_callback));
+	on_servers_changed();
+}
+
+void NavigationServer2DManager::set_default_server(const String &p_name, int p_priority) {
+	const int id = find_server_id(p_name);
+	ERR_FAIL_COND(id == -1); // Not found
+	if (default_server_priority < p_priority) {
+		default_server_id = id;
+		default_server_priority = p_priority;
+	}
+}
+
+int NavigationServer2DManager::find_server_id(const String &p_name) {
+	for (int i = navigation_servers.size() - 1; 0 <= i; --i) {
+		if (p_name == navigation_servers[i].name) {
+			return i;
+		}
+	}
+	return -1;
+}
+
+int NavigationServer2DManager::get_servers_count() {
+	return navigation_servers.size();
+}
+
+String NavigationServer2DManager::get_server_name(int p_id) {
+	ERR_FAIL_INDEX_V(p_id, get_servers_count(), "");
+	return navigation_servers[p_id].name;
+}
+
+NavigationServer2D *NavigationServer2DManager::new_default_server() {
+	if (default_server_id == -1) {
+		return nullptr;
+	}
+	Variant ret;
+	Callable::CallError ce;
+	navigation_servers[default_server_id].create_callback.callp(nullptr, 0, ret, ce);
+	ERR_FAIL_COND_V(ce.error != Callable::CallError::CALL_OK, nullptr);
+	return Object::cast_to<NavigationServer2D>(ret.get_validated_object());
+}
+
+NavigationServer2D *NavigationServer2DManager::new_server(const String &p_name) {
+	int id = find_server_id(p_name);
+	if (id == -1) {
+		return nullptr;
+	} else {
+		Variant ret;
+		Callable::CallError ce;
+		navigation_servers[id].create_callback.callp(nullptr, 0, ret, ce);
+		ERR_FAIL_COND_V(ce.error != Callable::CallError::CALL_OK, nullptr);
+		return Object::cast_to<NavigationServer2D>(ret.get_validated_object());
+	}
+}
+
+NavigationServer2D *NavigationServer2DManager::create_dummy_server_callback() {
+	return memnew(NavigationServer2DDummy);
+}
+
+NavigationServer2DManager::NavigationServer2DManager() {
+}
+
+NavigationServer2DManager::~NavigationServer2DManager() {
+}
+
+void NavigationServer2DManager::initialize_server_manager() {
+	ERR_FAIL_COND(singleton != nullptr);
+	singleton = memnew(NavigationServer2DManager);
+}
+
+void NavigationServer2DManager::finalize_server_manager() {
+	ERR_FAIL_NULL(singleton);
+	memdelete(singleton);
+}