How to get a precise time measurement for a stop watch function (race game)?

Questions & Answers
1

Hello everyone,

I am working at my first Unity project which is a simple race game.
Now I encountered that my time measurement is not very exact and varies from run to run. Even though only within the milliseconds, but if I want to create a highscore list, that can make a relevant difference.

My test track is the following:

  • A short straight track

  • “car” accelerates on its own, so no user interaction which might cause a delay

  • the time measurement starts after a 3 seconds count down (after the car starts the acceleration).

  • the time is stopped after hitting (collision) the finishing line (which is an obstacle in my case).

The observed time span with this setting is between 2:50 sec and 2:80 sec, so quite huge.

With my little knowledge about Unity I assume that it could have to do something with how and especially when unity calls the different methodes, in my case the time span between 2 update() calls. Am I on the right track?

Anyhow, how can I get a precise time measurement?

Here is my stopwatch script:

public class Stopwatch : MonoBehaviour
{
    float timer;
    float msec;
    float sec;
    float min;
    [SerializeField] Text txt_stopWatch;
    bool doCalculation;


    // Start is called before the first frame update
    void Start()
    {
        doCalculation = false;
        timer = 0;
    }

    // Update is called once per frame
    void Update()
    {
        if (doCalculation)
        {
            StopWatchCalculation();
        }
    }

    void StopWatchCalculation()
    {
        timer += Time.deltaTime;
        //example: timer = 1.3375 | int(timer) = 1 | (int)((timer - (int)timer) * 1000) = 337
        msec = (int)((timer - (int)timer) * 1000);
        sec = (int)(timer % 60);
        min = (int)(timer / 60 % 60);

        txt_stopWatch.text = string.Format("{0:00}:{1:00}:{2:00}", min, sec, msec);
    }

    public static string GimmeTimeFormat(float time)
    {
        float tmpMsec = (int)((time - (int)time) * 1000);
        float tmpSec = (int)(time % 60);
        float tmpMin = (int)(time / 60 % 60);

        return string.Format("{0:00}:{1:00}:{2:00}", tmpMin, tmpSec, tmpMsec);
    }

    public void StartStopwatch()
    {
        doCalculation = true;
    }
    public void StopStopwatch()
    {
        doCalculation = false;
    }
2

Something like this? :

public class Player : MonoBehaviour
{
    bool bTimeCounting = false;
    internal float fTotalTime = 0.0f;
    
    //I use FixedUpdate() since I think it is most fair to players
	// but may be done in Update also using Time.deltaTime
    void FixedUpdate()
    {
        if (bTimeCounting) fTotalTime += Time.fixedDeltaTime;
    }
    
    void Update()
    {
	    if(...) bTimeCounting = true; //set bTimeCounting to true only after all init/loading is
        // done, so any hickups won't be part of the time. Perhaps have a start-line needed to
	    // be crossed to begin time counting
	
        //finished?
        /*if (iCurLap == iTotalLaps)
        {
            bTimeCounting = false;
        }*/
    }
    
    public static string GimmeTimeFormat(float time)
    {
        //...
    }
}
3

Anyone else any idea how to get a precise time measurement as possible?

4

Look into System.Diagnostics.Stopwatch class. Bear in mind reading will be different between the two different object Update calls (in the same frame), so you probably want to read it once every frame anyway? It doesn’t get more precise that though.