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

[rburing]

• Production edit: 3D counterpart of Move Godot Physics 2D into a module; add dummy 2D physics server #95261.

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

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

To try it, compile with the SCons option module_godot_physics_3d_enabled=no.

This is useful for games that want to use a different 3D physics server, especially in web builds where binary size matters.

Linux binary size comparison (scons target=template_release production=yes use_llvm=yes linker=lld):

• Before (with Godot Physics 3D): 70.516 MiB (73941216 bytes)
• After (with only dummy 3D physics server): 69.603 MiB (72983072 bytes), nice.

So the binary size of the Godot Physics 3D module is 935.688 KiB (958144 bytes).

[Calinou]

Is this module already automatically disabled with the disable_3d=yes SCons option?

[rburing]

@Calinou Thanks for the suggestion, the disable_3d option is taken into account now, and some #ifndefs that were made redundant were removed.

[Calinou]

Tested locally, it works as expected.

When compiling the editor with module_godot_physics_3d_enabled=no, the project settings dialog is correctly updated to remove the mention of the GodotPhysics server:

All 3D demo projects run when no physics server is enabled (with correct visuals), although you can't move, which is expected.

Some remarks (which also apply to the 2D counterpart of this PR, I assume):

• A warning is also printed on startup of an empty project with just a Node, both in the editor stdout (not visible in the Output panel as it's too early) and in the running project:

WARNING: No PhysicsServer3D implementation was found; 3D physics functionality will be disabled.
     at: initialize_physics (main/main.cpp:326)

• There should probably be a Dummy option you can select in the project settings for two reasons:
  • Silence the warning when you don't compile any physics engines. This is useful when compiling a binary with no physics engines to reduce the binary size of non-game applications, or games that write their own physics without using PhysicsServer.
  • Simulate what happens when physics are disabled at build-time, without needing to compile a separate binary.

[rburing]

Great idea @Calinou. I added the option, and now a warning only appears when the dummy server is used as a fallback:

WARNING: Falling back to dummy PhysicsServer3D; 3D physics functionality will be disabled. If this is intended, set the physics/3d/physics_engine project setting to Dummy.

When the Dummy setting is chosen explicitly, there is no warning.

The fallback warning is still not printed in the editor Output panel when the editor starts, but I guess that's fine.

[akien-mga]

Tested a build of a web template_release template, with the module:

-rwxr-xr-x. 1 akien akien  33838516 Sep 17 17:35 godot.web.template_release.wasm32.wasm
-rw-r--r--. 1 akien akien   8040612 Sep 17 17:35 godot.web.template_release.wasm32.zip

Without:

-rwxr-xr-x. 1 akien akien  33339961 Sep 17 17:31 godot.web.template_release.wasm32.wasm
-rw-r--r--. 1 akien akien   7889273 Sep 17 17:31 godot.web.template_release.wasm32.zip

So a 1.47% size reduction on the wasm (487 KiB), and 1.88% on the zip (148 KiB).

Tested with scons p=web target=template_release module_godot_physics_3d_enabled=yes|no

[akien-mga]

Thanks!