MonoBehaviour.FixedUpdate()

Description

Frame-rate independent MonoBehaviour.FixedUpdate message for physics calculations.

MonoBehaviour.FixedUpdate has the frequency of the physics system; it is called every fixed frame-rate frame. Compute Physics system calculations after FixedUpdate. 0.02 seconds (50 calls per second) is the default time between calls. Use Time.fixedDeltaTime to access this value. Alter it by setting it to your preferred value within a script, or, navigate to Edit > Settings > Time > Fixed Timestep and set it there. The FixedUpdate frequency is more or less than Update. If the application runs at 25 frames per second (fps), Unity calls it approximately twice per frame, Alternatively, 100 fps causes approximately two rendering frames with one FixedUpdate. Control the required frame rate and Fixed Timestep rate from Time settings. Use Application.targetFrameRate to set the frame rate.

Use FixedUpdate when using Rigidbody. Set a force to a Rigidbody and it applies each fixed frame. FixedUpdate occurs at a measured time step that typically does not coincide with MonoBehaviour.Update.

In the following example, the number of Update calls is compared against the number of FixedUpdate calls. FixedUpdate executes 50 times per second. (The game code runs around 200 fps on a test machine.)

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

// GameObject.FixedUpdate example.
//
// Measure frame rate comparing FixedUpdate against Update.
// Show the rates every second.

public class ExampleScript : MonoBehaviour
{
    private float updateCount = 0;
    private float fixedUpdateCount = 0;
    private float updateUpdateCountPerSecond;
    private float updateFixedUpdateCountPerSecond;

    void Awake()
    {
        // Uncommenting this will cause framerate to drop to 10 frames per second.
        // This will mean that FixedUpdate is called more often than Update.
        //Application.targetFrameRate = 10;
        StartCoroutine(Loop());
    }

    // Increase the number of calls to Update.
    void Update()
    {
        updateCount += 1;
    }

    // Increase the number of calls to FixedUpdate.
    void FixedUpdate()
    {
        fixedUpdateCount += 1;
    }

    // Show the number of calls to both messages.
    void OnGUI()
    {
        GUIStyle fontSize = new GUIStyle(GUI.skin.GetStyle("label"));
        fontSize.fontSize = 24;
        GUI.Label(new Rect(100, 100, 200, 50), "Update: " + updateUpdateCountPerSecond.ToString(), fontSize);
        GUI.Label(new Rect(100, 150, 200, 50), "FixedUpdate: " + updateFixedUpdateCountPerSecond.ToString(), fontSize);
    }

    // Update both CountsPerSecond values every second.
    IEnumerator Loop()
    {
        while (true)
        {
            yield return new WaitForSeconds(1);
            updateUpdateCountPerSecond = updateCount;
            updateFixedUpdateCountPerSecond = fixedUpdateCount;

            updateCount = 0;
            fixedUpdateCount = 0;
        }
    }
}