Move Godot Physics 2D into a module; add dummy 2D physics server

If the module is enabled (default), 2D physics works as it did before.

If the module is disabled and no other 2D physics server is registered
(via a module or GDExtension), then we fall back to a dummy
implementation which effectively disables 2D physics functionality (and
a warning is printed).

The dummy 2D physics server can also be selected explicitly, in which
case no warning is printed.

COPYRIGHT.txt

@@ -63,6 +63,11 @@ Copyright: 2011, Ole Kniemeyer, MAXON, www.maxon.net
  2007-2014, Juan Linietsky, Ariel Manzur
 License: Expat and Zlib
 
+Files: ./modules/godot_physics_2d/godot_joints_2d.cpp
+Comment: Chipmunk2D Joint Constraints
+Copyright: 2007, Scott Lembcke
+License: Expat
+
 Files: ./modules/lightmapper_rd/lm_compute.glsl
 Comment: Joint Non-Local Means (JNLM) denoiser
 Copyright: 2020, Manuel Prandini
@@ -93,11 +98,6 @@ Copyright: 2001, Robert Penner
  2007-2014, Juan Linietsky, Ariel Manzur
 License: Expat
 
-Files: ./servers/physics_2d/godot_joints_2d.cpp
-Comment: Chipmunk2D Joint Constraints
-Copyright: 2007, Scott Lembcke
-License: Expat
-
 Files: ./servers/physics_3d/collision_solver_3d_sat.cpp
 Comment: Open Dynamics Engine
 Copyright: 2001-2003, Russell L. Smith, Alen Ladavac, Nguyen Binh

doc/classes/ProjectSettings.xml

@@ -2215,6 +2215,7 @@
 		<member name="physics/2d/physics_engine" type="String" setter="" getter="" default="&quot;DEFAULT&quot;">
 			Sets which physics engine to use for 2D physics.
 			"DEFAULT" and "GodotPhysics2D" are the same, as there is currently no alternative 2D physics server implemented.
+			"Dummy" is a 2D physics server that does nothing and returns only dummy values, effectively disabling all 2D physics functionality.
 		</member>
 		<member name="physics/2d/run_on_separate_thread" type="bool" setter="" getter="" default="false">
 			If [code]true[/code], the 2D physics server runs on a separate thread, making better use of multi-core CPUs. If [code]false[/code], the 2D physics server runs on the main thread. Running the physics server on a separate thread can increase performance, but restricts API access to only physics process.

main/main.cpp

@@ -80,6 +80,7 @@
 #include "servers/navigation_server_2d.h"
 #include "servers/navigation_server_2d_dummy.h"
 #include "servers/physics_server_2d.h"
+#include "servers/physics_server_2d_dummy.h"
 
 #ifndef _3D_DISABLED
 #include "servers/physics_server_3d.h"
@@ -331,7 +332,15 @@ void initialize_physics() {
 		// Physics server not found, Use the default physics
 		physics_server_2d = PhysicsServer2DManager::get_singleton()->new_default_server();
 	}
-	ERR_FAIL_NULL(physics_server_2d);
+
+	// Fall back to dummy if no default server has been registered.
+	if (!physics_server_2d) {
+		WARN_PRINT(vformat("Falling back to dummy PhysicsServer2D; 2D physics functionality will be disabled. If this is intended, set the %s project setting to Dummy.", PhysicsServer2DManager::setting_property_name));
+		physics_server_2d = memnew(PhysicsServer2DDummy);
+	}
+
+	// Should be impossible, but make sure it's not null.
+	ERR_FAIL_NULL_MSG(physics_server_2d, "Failed to initialize PhysicsServer2D.");
 	physics_server_2d->init();
 }
 

modules/godot_physics_2d/SCsub

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+
+Import('env')
+
+env.add_source_files(env.modules_sources, "*.cpp")

modules/godot_physics_2d/config.py

@@ -0,0 +1,6 @@
+def can_build(env, platform):
+    return True
+
+
+def configure(env):
+    pass

modules/godot_physics_2d/register_types.cpp

@@ -0,0 +1,61 @@
+/**************************************************************************/
+/*  register_types.cpp                                                    */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* 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.                 */
+/**************************************************************************/
+
+#include "register_types.h"
+
+#include "godot_physics_server_2d.h"
+#include "servers/physics_server_2d.h"
+#include "servers/physics_server_2d_wrap_mt.h"
+
+static PhysicsServer2D *_createGodotPhysics2DCallback() {
+#ifdef THREADS_ENABLED
+	bool using_threads = GLOBAL_GET("physics/2d/run_on_separate_thread");
+#else
+	bool using_threads = false;
+#endif
+
+	PhysicsServer2D *physics_server_2d = memnew(GodotPhysicsServer2D(using_threads));
+
+	return memnew(PhysicsServer2DWrapMT(physics_server_2d, using_threads));
+}
+
+void initialize_godot_physics_2d_module(ModuleInitializationLevel p_level) {
+	if (p_level != MODULE_INITIALIZATION_LEVEL_SERVERS) {
+		return;
+	}
+	PhysicsServer2DManager::get_singleton()->register_server("GodotPhysics2D", callable_mp_static(_createGodotPhysics2DCallback));
+	PhysicsServer2DManager::get_singleton()->set_default_server("GodotPhysics2D");
+}
+
+void uninitialize_godot_physics_2d_module(ModuleInitializationLevel p_level) {
+	if (p_level != MODULE_INITIALIZATION_LEVEL_SERVERS) {
+		return;
+	}
+}

modules/godot_physics_2d/register_types.h

@@ -0,0 +1,39 @@
+/**************************************************************************/
+/*  register_types.h                                                      */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* 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 GODOT_PHYSICS_2D_REGISTER_TYPES_H
+#define GODOT_PHYSICS_2D_REGISTER_TYPES_H
+
+#include "modules/register_module_types.h"
+
+void initialize_godot_physics_2d_module(ModuleInitializationLevel p_level);
+void uninitialize_godot_physics_2d_module(ModuleInitializationLevel p_level);
+
+#endif // GODOT_PHYSICS_2D_REGISTER_TYPES_H

scene/2d/physics/shape_cast_2d.cpp

@@ -34,7 +34,7 @@
 #include "scene/2d/physics/collision_object_2d.h"
 #include "scene/2d/physics/physics_body_2d.h"
 #include "scene/resources/2d/circle_shape_2d.h"
-#include "servers/physics_2d/godot_physics_server_2d.h"
+#include "servers/physics_server_2d.h"
 
 void ShapeCast2D::set_target_position(const Vector2 &p_point) {
 	target_position = p_point;

scu_builders.py

@@ -322,6 +322,7 @@ def generate_scu_files(max_includes_per_scu):
     process_folder(["modules/openxr"], ["register_types"])
     process_folder(["modules/openxr/action_map"])
     process_folder(["modules/openxr/editor"])
+    process_folder(["modules/godot_physics_2d"])
 
     process_folder(["modules/csg"])
     process_folder(["modules/gdscript"])
@@ -348,7 +349,6 @@ def generate_scu_files(max_includes_per_scu):
     process_folder(["servers/rendering/renderer_rd/effects"])
     process_folder(["servers/rendering/renderer_rd/environment"])
     process_folder(["servers/rendering/renderer_rd/storage_rd"])
-    process_folder(["servers/physics_2d"])
     process_folder(["servers/physics_3d"])
     process_folder(["servers/physics_3d/joints"])
     process_folder(["servers/audio"])

servers/SCsub

@@ -25,8 +25,6 @@ SConscript("navigation/SCsub")
 SConscript("rendering/SCsub")
 SConscript("text/SCsub")
 
-SConscript("physics_2d/SCsub")
-
 if not env["disable_3d"]:
     SConscript("physics_3d/SCsub")
     env.add_source_files(env.servers_sources, "physics_server_3d.cpp")

servers/physics_server_2d.cpp

@@ -972,7 +972,9 @@ String PhysicsServer2DManager::get_server_name(int p_id) {
 }
 
 PhysicsServer2D *PhysicsServer2DManager::new_default_server() {
-	ERR_FAIL_COND_V(default_server_id == -1, nullptr);
+	if (default_server_id == -1) {
+		return nullptr;
+	}
 	Variant ret;
 	Callable::CallError ce;
 	physics_2d_servers[default_server_id].create_callback.callp(nullptr, 0, ret, ce);