Lesson 90 +10 XP

Time, Frame Rate and Fixed Updates

Understanding how Unity measures and manages time is fundamental to writing frame-rate-independent gameplay code.

Time.deltaTime

Time.deltaTime is the time in seconds that elapsed since the last Update() call. Multiplying movement values by it makes motion frame-rate independent:

void Update()
{
    // Without deltaTime: faster on high-end machines
    // transform.position += Vector3.forward * 5f;

    // With deltaTime: always moves 5 units per second
    transform.position += Vector3.forward * 5f * Time.deltaTime;
}

FixedUpdate and Time.fixedDeltaTime

FixedUpdate() is called at a fixed interval, not every rendered frame. This is where physics code should live.

Time.fixedDeltaTime: The interval between FixedUpdate calls (default: 0.02s = 50 Hz).
You can change it in Project Settings > Time > Fixed Timestep.

void FixedUpdate()
{
    // Apply physics forces here, not in Update()
    _rigidbody.AddForce(Vector3.forward * _force);
}

Time.timeScale

Time.timeScale controls how fast game time advances relative to real time:

1.0 = normal speed
0.5 = slow motion (half speed)
0.0 = paused (FixedUpdate stops, Update still runs)
2.0 = double speed

// Pause the game
Time.timeScale = 0f;

// Resume
Time.timeScale = 1f;

// Slow-motion effect
Time.timeScale = 0.3f;

Note: Time.unscaledDeltaTime gives the real elapsed time regardless of timeScale. Use it for UI animations and menus that should not be affected by pausing.

Frame Rate Control

// Target 60 FPS
Application.targetFrameRate = 60;

// Disable VSync (required for targetFrameRate to take full effect)
QualitySettings.vSyncCount = 0;

Time.time and Time.realtimeSinceStartup

Time.time: Total game time elapsed since startup (scaled by timeScale).
Time.realtimeSinceStartup: Real-world seconds since the application started (unaffected by timeScale). Useful for benchmarking.

TL;DR

Multiply all movement by Time.deltaTime to ensure frame-rate independence.
Physics code belongs in FixedUpdate(), which runs at a fixed timestep.
Time.timeScale = 0 pauses physics and scaled time; use unscaledDeltaTime for UI.
Application.targetFrameRate caps the frame rate; disable vSync to use it.

Time, Frame Rate and Fixed Updates