Stepping Physics with Rollback

[albertok]

Helper classes for supporting physics stepping and rollback.

Auto-stepping is disabled and taken over by the netfox loop.

Physics implementations supported:

• Godot Rapier Physics addon.
• Custom Godot Builds with the stepping PR

Progress

• bass classes
• docs
• disable physics drivers on build

Closes #265

[elementbound]

Added a PhysicsDriverToggle implementation - they show up in the editor under Project > Tools, and they can check whether the toggled physics driver is even available:

[albertok]

Nice work on the toggles @elementbound

I havent forgottten about this PR, just that time of year where I'm traveling a bit and don't get as much time to work on things.

Working on a RollbackSynchronizer Player driven RigidBody at the moment. It's a bit tricky as the pattern is a little different to what you would do with a CharacterBody.

Generally movement is all self contained in rollback_tick. When dealing with RigidBodies we need to let all RigidBodies take in what forces they will have, run the physics simulation for a step and then save the snapshots.

[kumpmati]

Noticed that a CharacterBody's collider transform doesn't ever update unless force_update_transform is called, resulting in 'ghost' colliders. Not sure if there's a more elegant solution, but this works.

From my testing all the relevant CharacterBody transforms need to be updated on both _snapshot_space and _rollback_space, otherwise the collider might skip an update occasionally when the game window loses focus 🤷

[kumpmati]

Rapier seems to have a bunch of collision issues for me, but these might not be fixable in the rollback code:

1. With rollback_space enabled in the driver, CharacterBody no longer collides with Areas or other CharacterBodies at all
2. RigidBodies go through the floor in 3D

Here's the project I used to test these out: https://github.com/kumpmati/netfox-physics-rollback-test

[albertok]

@kumpmati Thanks for picking up on the 2D and CharacterBody issues.

Still looking into all its variations. Its mentioned here also:
godotengine/godot#76462 (comment)

Rapier seems to have a bunch of collision issues for me, but these might not be fixable in the rollback code:

Yeah, Rapier has its own issues. Collision seems to be spotty unless the surface is really thick.

[kumpmati]

get_tree().get_nodes_in_group(...) crashes the game if the scene with the driver is reloaded, since the driver is removed from the tree momentarily.

[elementbound]

Made sure that the signal handlers are disconnected if the node is not in the tree