Time & RNG

Trecs provides phase-aware time and deterministic random number generation.

Time Properties

Access time values via the World accessor (available in systems as World):

Property	Description
DeltaTime	Time step for the current phase (fixed or variable)
FixedDeltaTime	Fixed timestep (default 1/60s)
VariableDeltaTime	Actual frame delta time
ElapsedTime	Total elapsed time for the current phase
FixedElapsedTime	Total fixed update time
VariableElapsedTime	Total variable update time
Frame	Frame counter for the current phase
FixedFrame	Fixed update frame counter
VariableFrame	Variable update frame counter

Phase-Aware DeltaTime

DeltaTime automatically returns the correct value for the phase your system runs in:

// In a fixed update system: DeltaTime == FixedDeltaTime
public partial class PhysicsSystem : ISystem
{
    [ForEachEntity(MatchByComponents = true)]
    void Execute(ref Position pos, in Velocity vel)
    {
        pos.Value += vel.Value * World.DeltaTime;  // Uses FixedDeltaTime
    }
}

// In a variable update system: DeltaTime == VariableDeltaTime
[VariableUpdate]
public partial class AnimationSystem : ISystem
{
    [ForEachEntity(MatchByComponents = true)]
    void Execute(ref AnimState state)
    {
        state.Time += World.DeltaTime;  // Uses VariableDeltaTime
    }
}

You can also access the fixed time values while in variable update via World.FixedDeltaTime / World.FixedElapsedTime

Deterministic RNG

Trecs provides a deterministic Rng type seeded from WorldSettings.RandomSeed.

Using RNG

// Phase-aware (recommended)
float value = World.Rng.Next();          // [0, 1)
float range = World.Rng.NextFloat(0f, 10f);  // [min, max)

// Phase-specific
float fixedRand = World.FixedRng.Next();
float varRand = World.VariableRng.Next();

Forking RNG

Fork the RNG for sub-sequences that don't affect the parent sequence:

var forked = World.Rng.Fork();
// forked produces independent values without advancing the main RNG

Seeding

Set the seed in world settings for reproducible results:

var settings = new WorldSettings
{
    RandomSeed = 42
};

Warning

For deterministic replay, always use World.Rng — never UnityEngine.Random or System.Random. External RNG sources are not captured in recordings.

Time in Jobs

NativeWorldAccessor provides time values in Burst jobs:

float dt = nativeWorldAccessor.DeltaTime;
float elapsed = nativeWorldAccessor.ElapsedTime;