BodiesList

A NativeArray<PhysicsBodyData> on PhysicsStructuresComponent. It is the simulation-side copy of every active physics body — pose, velocity, shape, LOD tier, update cadence, and material data packed for Burst jobs.

Internal systems and custom job interfaces operate on BodiesList instead of querying ECS components during the fixed-step loop.

Allocation and capacity

Bootstrap allocates BodiesList with length MaxEntitiesCount from PhysicsFixedSettingsComponent. The array size is fixed for the session.

Each frame, only the first ActiveBodiesCount entries (from SimulationDataComponent) contain live data. Indices at or above that count are cleared and unused until the next import.

Import (LateSimulation)

ImportPhysicsDataSystem runs in LittlePhysicsInternalImportGroup:

1. Set ActiveBodiesCount from entities with LocalToWorld, PhysicsBodyComponent, and PhysicsBodyUpdateComponent, clamped to MaxEntitiesCount.
2. ClearBodiesJob — zero the full array and clear EntitiesMap.
3. ImportPhysicsDataJob — for each qualifying entity, build a PhysicsBodyData record and write it at the entity’s query index.

Each imported body also registers in EntitiesMap under PhysicsBodyData.Main, and PhysicsBodyUpdateComponent.Index stores the native index for export.

Entities beyond MaxEntitiesCount get PhysicsBodyUpdateComponent.IsEnabled = false and are skipped.

Data copied from ECS

Import merges baked PhysicsBodyComponent data with runtime state:

Source	Copied into PhysicsBodyData
PhysicsBodyComponent + LocalToWorld	Pose, shape, layer, body type, trigger flag, rigidbody coefficients
PhysicsBodyUpdateComponent	TimeElapsed, Interval, LOD index (when camera LOD is active)
PhysicsVelocityComponent (if present)	Linear and angular velocity; rotation block respects ShouldRotateOnCollision

Export (Simulation)

ExportPhysicsDataSystem reads BodiesList[tag.Index] and writes results back to LocalTransform, PhysicsVelocityComponent, and related components using PhysicsBodyUpdateComponent.Index as the lookup key.

Custom jobs — IBodiesJob

Use the package IBodiesJob interface and its nested variants to read or write BodiesList in parallel inside LittlePhysicsUserSystemGroup:

Interface	Access
IBodiesJob.IRead	Read-only per body
IBodiesJob.IWrite	Read-write per body
IBodiesJob.IReadIndex	Read-only; receives body index
IBodiesJob.IWriteIndex	Read-write; receives body index

ScheduleAndChain combines with PhysicsJobHandle and schedules over ActiveBodiesCount automatically.

[BurstCompile]
[UpdateInGroup(typeof(LittlePhysicsUserSystemGroup))]
public partial struct DampVelocitySystem : ISystem
{
    [BurstCompile]
    public void OnCreate(ref SystemState state) =>
        state.RequireForUpdate<PhysicsReadyTag>();

    [BurstCompile]
    public void OnUpdate(ref SystemState state)
    {
        var structures = SystemAPI.GetSingleton<PhysicsStructuresComponent>();
        ref var simulation = ref SystemAPI.GetSingletonRW<SimulationDataComponent>().ValueRW;

        new DampVelocityJob { Factor = 0.99f }
            .ScheduleAndChain(ref state, in structures, ref simulation);
    }

    [BurstCompile]
    private struct DampVelocityJob : IBodiesJob.IWrite
    {
        public float Factor;

        public void Execute(ref PhysicsBodyData body)
        {
            if (!body.IsDynamic)
            {
                return;
            }

            var velocity = body.VelocityData;
            velocity.Linear *= Factor;
            body.VelocityData = velocity;
        }
    }
}

See IBodiesJob for all nested interfaces and scheduling details.

Related

• PhysicsBodyData — struct layout for each slot
• EntitiesMap — entity → index map built during import
• SimulationDataComponent — live body count
• Import workflow — ordering custom work around import