Digital Speedometer wrong update - Unity

Question

Hi I am making a digital speedometer and I want it to change like a normal meter like: if speed is 10 on meter and the new speed is 50 it does not just show 50 on text instead gradually increase it.

here is what I have done:

    int speed;
    int textSpeed;
    int speedfinal;

    public Text text;

    // Update is called once per frame
    void Update()
    {
        speed = GameObject.Find("gamePlayManager").GetComponent<gamePlayManagerScript>().userSpeed;
        textSpeed = int.Parse(text.text);

        speedfinal = (int)Mathf.Lerp(textSpeed, speed, 0.1f);

        text.text = speedfinal.ToString();
    }

I am not sure if lerp is a good choice here to change text but that is what I know but it is adding 9 less then the orignal speed. Any idea how to do this. thanks.

Answer 1

If you use Lerp with a constant interpolation value of 0.1f, you are reducing the difference between current value and end value in increments of 10% per update, but you will never reach it. Add the precision loss due to rounding it to an integer, and you have no change anymore when you are 9.0 away from the end value.

A simple solution to this problem is to forget about Lerp and simply move the current value one closer to the destination value with each update:

  if (textSpeed < speed) {
       textSpeed++;
  } else if (textSpeed > speed) {
       textSpeed--;
  }

This solution might be sufficient, but has two cosmetic shortcommings:

• It might take a while to process really large changes in speed
• It isn't deltaTime-adjusted

If you want to fix these problems, then integer-arithmetic won't do. Stop keeping track of the currently displayed value by parsing the text. Use a private float variable to keep track of the value you want to display and don't convert it to an integer until you pass it to the text field on the UI.

Instead of adding or subtracting 1 to textSpeed, add or subtract the difference between speed and textSpeed multiplied with Time.deltaTime and a desired speed factor, but if the change is too small, change it by a fixed minimum value instead.

Answer 2

The improvement achieved with the solution below are:

1. You avoid calling GameObject.Find and int.Parse in the Update loop.
2. You use Late Update instead of Update. Not a big deal, but I see this more as a graphical feature, so it's better LateUpdate (it works also if you want to use Update)
3. I see you are trying to Lerp but I do not see this as the best approach, as you need still to have some kind of counter for the interpolation parameter. To make it simple you might just do the counting directly.
4. In the answer I increment it 1 by 1. If you want to see something different (similar to lerp) you may just change the increment to a different formula, to have a different gradual change.
5. With the _changeIntervalInSecond you may directly decide how fast you want the change to happen (_changeIntervalInSecond requires to be > than 0, otherwise you will change it at each loop)

Code solution

public Text text;
//define a speed for the change
public float _changeIntervalInSecond;

//used to store the previous speed instead of taking it from the text
int _speedOnText = 0;
float _lastCountedTime = 0f;

//cache manager at awake
private void Awake()
=> _manager = GameObject.Find("gamePlayManager").GetComponent<gamePlayManagerScript>();

// this is more a graphical feature, so you may use Late Update
void LateUpdate()
{
    //get the current speed
    var currentSpeed = _manager.userSpeed;

    //ignore if we have no changes
    if(_speedOnText == currentSpeed) return;

    _lastCountedTime += Time.deltaTime;
    //if your interval has passed change the speed
    if(_lastCountedTime > _changeIntervalInSecond)
    {
        if(_speedOnText< currentSpeed) _speedOnText++;
        else _speedOnText--;
        text.text = _speedOnText.ToString();
        _lastCountedTime = 0;
    }
}