LittlePhysicsTimeComponent

A singleton component that tracks physics time scale, substep delta time, and accumulated simulation time. Bootstrap creates it with TimeScale = 1; LittlePhysicsSystemGroup refreshes DeltaTime and ElapsedTime on every inner fixed-step pass.

Use it to pause, slow, or fast-forward the simulation, and to read the scaled timestep inside custom physics systems.

Component fields

Field	Type	Default	Description
TimeScale	int	1	How many full physics loops run per Unity fixed update (0, 1, 2, or 4)
DeltaTime	float	—	Scaled delta for one substep; set by the system group each inner iteration
ElapsedTime	double	0	Accumulated physics time since bootstrap

TimeScale

Valid values are 0, 1, 2, and 4 only:

Value	Effect
0	Pause — the inner physics loop does not run
1	Normal speed
2	Two full physics passes per fixed update
4	Four full physics passes per fixed update

Change TimeScale at runtime with SystemAPI.GetSingletonRW<LittlePhysicsTimeComponent>(). The sample TimeScalePresenter cycles 1 → 2 → 4 and toggles pause by storing the last value and setting TimeScale to 0.

There is no validation in code — assign only 0, 1, 2, or 4. Other values produce undefined loop counts.

DeltaTime and ElapsedTime

These fields are written by LittlePhysicsSystemGroup, not by gameplay code:

float substepDeltaTime = worldTime.DeltaTime / substepsCount;

for (int i = 0; i < timeScale; i++)
{
    for (int substep = 0; substep < substepsCount; substep++)
    {
        timeElapsed += substepDeltaTime;
        // singleton updated with ElapsedTime, DeltaTime = substepDeltaTime, TimeScale
        // ... run full physics pass ...
    }
}

• DeltaTime is Unity fixed delta / SubstepsCount, not multiplied by time scale. Time scale repeats the whole pass instead.
• ElapsedTime advances by DeltaTime on each substep while the simulation is running.

Read DeltaTime inside systems that run in the fixed-step inner loop — especially LittlePhysicsUserSystemGroup and internal systems such as gravity, friction, and velocity integration. Package samples use it for spawn timing and trigger forces.

Outside an active inner iteration (for example while paused), DeltaTime is 0. Do not use UnityEngine.Time.deltaTime for physics integration when a substep-accurate value is required — use this component or chain through the pipeline groups.

Total work per fixed update

Combined cost scales with both time scale and substeps:

passes per fixed update = TimeScale × SubstepsCount

Example: TimeScale = 2 and SubstepsCount = 2 → 4 complete physics passes per Unity fixed tick. See PhysicsVariableSettingsComponent for substep settings.

Runtime example

ref var time = ref SystemAPI.GetSingletonRW<LittlePhysicsTimeComponent>().ValueRW;
time.TimeScale = 0; // pause

// later
time.TimeScale = 2; // 2× speed

For MonoBehaviour UI that runs outside ECS systems, query the singleton from the default world (as TimeScalePresenter does) rather than caching DeltaTime across frames.

What reads TimeScale

Internal systems pass TimeScale into LOD lookups so capacity limits (DynamicsInCells, CellPerEntity, PairPerEntity, and related fields) resolve to the correct tier for the current simulation speed. See Physics settings and LOD.

Related

• PhysicsVariableSettingsComponent — SubstepsCount (1–4) divides DeltaTime
• Pipeline — Fixed update — inner loop driven by this component
• How it works — Fixed step