Move Godot Physics 3D into a module; add dummy 3D physics server

If the module is enabled (default), 3D physics works as it did before.

If the module is disabled and no other 3D physics server is registered
(via a module or GDExtension), then we fall back to a dummy
implementation which effectively disables 3D physics functionality (and
a warning is printed).

The dummy 3D physics server can also be selected explicitly, in which
case no warning is printed.

1 files changed, 10 insertions, 1 deletions

diff --git a/main/main.cpp b/main/main.cpp
index fa50a3039f..439cd385c0 100644
--- a/main/main.cpp
+++ b/main/main.cpp
@@ -83,6 +83,7 @@
 
 #ifndef _3D_DISABLED
 #include "servers/physics_server_3d.h"
+#include "servers/physics_server_3d_dummy.h"
 #include "servers/xr_server.h"
 #endif // _3D_DISABLED
 
@@ -320,7 +321,15 @@ void initialize_physics() {
 		// Physics server not found, Use the default physics
 		physics_server_3d = PhysicsServer3DManager::get_singleton()->new_default_server();
 	}
-	ERR_FAIL_NULL(physics_server_3d);
+
+	// Fall back to dummy if no default server has been registered.
+	if (!physics_server_3d) {
+		WARN_PRINT(vformat("Falling back to dummy PhysicsServer3D; 3D physics functionality will be disabled. If this is intended, set the %s project setting to Dummy.", PhysicsServer3DManager::setting_property_name));
+		physics_server_3d = memnew(PhysicsServer3DDummy);
+	}
+
+	// Should be impossible, but make sure it's not null.
+	ERR_FAIL_NULL_MSG(physics_server_3d, "Failed to initialize PhysicsServer3D.");
 	physics_server_3d->init();
 #endif // _3D_DISABLED