Serialization

When the serde-serialize feature of Rapier is enabled, most data structures of Rapier become serializable using serde. Serialization can be useful to save the complete state of the simulation, e.g., to send it over the network, or to restore this state later. In order to fully serialize the simulation state, it is necessary to serialize every structure described in the simulation structures page, except for the PhysicsPipeline and the CollisionPipeline which don't hold any useful state. The following shows an example of serialization of the complete physics state. For convenience, the example defines a PhysicsState serializable struct that wraps every relevant serializable state. It uses bincode as the serialization format:

use serde::{Deserialize, Serialize};

// Use serde derives for our wrapper struct.
#[derive(Serialize, Deserialize)]
struct PhysicsState {
    pub islands: IslandManager,
    pub broad_phase: DefaultBroadPhase,
    pub narrow_phase: NarrowPhase,
    pub bodies: RigidBodySet,
    pub colliders: ColliderSet,
    pub impulse_joints: ImpulseJointSet,
    pub multibody_joints: MultibodyJointSet,
    pub ccd_solver: CCDSolver,
    pub query_pipeline: QueryPipeline,
    pub integration_parameters: IntegrationParameters,
    pub gravity: Vector<f32>,
}

fn main() {
    let physics_state = setup_physics_scene();
    // Serialize everything.
    let serialized = bincode::serialize(&physics_state).unwrap();
    // Deserialize everything.
    let deserialized = bincode::deserialize::<PhysicsState>(&serialized).unwrap();
    // The simulation can continue using the deserialized state.
}

info

If the enhanced-determinism feature of Rapier is enabled, and if your platform fulfills the required determinism requirements, then you have the guarantee that running the exact same simulation on two different machine will result in the exact same byte vectors if the physics state is serialized on both machines after the same number of timesteps.