Struct DeterministicSimulation 

pub struct DeterministicSimulation {
    pub world: PhysicsWorld,
    /* private fields */
}

Frame-based deterministic simulation wrapper.

Wraps PhysicsWorld with:

• Frame counter
• Input application pipeline
• State checksum computation
• Snapshot save/restore for rollback

Determinism Guarantee

Given identical NetcodeConfig, identical add_body() calls, and identical advance_frame() input sequences, two DeterministicSimulation instances will produce bit-exact identical states on any platform.

Fields

world: PhysicsWorld

The underlying physics world

Implementations

impl DeterministicSimulation

pub fn new(config: NetcodeConfig) -> Self

Create a new deterministic simulation

pub fn add_body(&mut self, body: RigidBody) -> usize

Add a rigid body to the simulation. Returns the body index.

pub fn assign_player_body(&mut self, player_id: u8, body_index: usize)

Assign a player to control a specific body.

pub fn advance_frame(&mut self, inputs: &[FrameInput]) -> SimulationChecksum

Advance one frame with the given player inputs.

1. Apply inputs to player-controlled bodies
2. Step physics
3. Compute and record checksum

Returns the checksum for this frame.

pub fn advance_frame_with_applicator( &mut self, inputs: &[FrameInput], applicator: &dyn InputApplicator, ) -> SimulationChecksum

Advance one frame with a custom input applicator.

pub fn save_snapshot(&mut self) -> &SimulationSnapshot

Save a snapshot of the current state for rollback.

Panics

Panics if the snapshot deque is empty after push (should never happen).

pub fn load_snapshot(&mut self, frame: u64) -> bool

Restore state from a snapshot (for rollback).

Returns true if the snapshot was found and loaded. Rotations are restored as stored (PhysicsWorld::deserialize_state) and brought to unit length by the next step.

pub fn get_snapshot(&self, frame: u64) -> Option<&SimulationSnapshot>

Get a snapshot for a specific frame (if available).

pub fn checksum(&self) -> SimulationChecksum

Compute the current state checksum.

pub const fn frame(&self) -> u64

Current frame number.

pub fn checksum_at(&self, frame: u64) -> Option<SimulationChecksum>

Get checksum for a specific frame from history.

pub fn verify_checksum( &self, frame: u64, remote: SimulationChecksum, ) -> Option<bool>

Verify a remote checksum against local history.

Returns:

• None if the frame is not in local history (too old or future)
• Some(true) if checksums match (clients in sync)
• Some(false) if checksums differ (DESYNC detected!)

pub const fn dt(&self) -> Fix128

Get the fixed timestep.

pub fn snapshot_count(&self) -> usize

Number of snapshots currently stored.