Coroutine stops when Time.timeScale = 0

Question

I have a coroutine that smoothly changes a variable in my UI, but when I pause the game, the coroutine pauses too. How can I fix that?

Code:

using UnityEngine;
using System.Collections;

public class HUDController : MonoBehaviour {
    public void PauseGame() {
        FreezeTime();
        StartCoroutine(ShowPauseMenu());
    }

    private void FreezeTime() {
        Time.timeScale = 0;
    }

    private IEnumerator ShowPauseMenu() {
        var pauseMenuCanvasGroup = GameObject.FindWithTag("PauseMenu").GetComponent<CanvasGroup>();
        var alphaValue = 1f;
        var velocity = 0f;
        var time = 0.15f;

        while (!Mathf.Approximately(pauseMenuCanvasGroup.alpha, alphaValue)) {
            pauseMenuCanvasGroup.alpha = Mathf.SmoothDamp(pauseMenuCanvasGroup.alpha, alphaValue, ref velocity, time);
            yield return null;
        }

        pauseMenuCanvasGroup.alpha = 1; // Since float is not accurate, manually set the alpha to 1
        pauseMenuCanvasGroup.interactable = true;
    }
}

Answer 1

This is sure to happened because Mathf.SmoothDamp uses Time.deltaTime in default calculation. When you set Time.timeScale = 0 then Mathf.SmoothDamp won't give the expected value but only first value, repeatedly.

You can further verify by printing alpha value to console, print it in your while loop so that you can confirm it by the unlimited logs of same value.

Here is the Documentation on Mathf.SmoothDamp.

You can fix this by passing your own deltaTime to keep it from using its default Time.deltaTime. Just add one more parameter to the end of the call:

pauseMenuCanvasGroup.alpha = Mathf.SmoothDamp(
  pauseMenuCanvasGroup.alpha, 
  alphaValue, 
  ref velocity, 
  time,
  1000,          // <-- Fifth parameter Optionally allows you to clamp the maximum speed.
  1.0f/30.0f);   // <-- Add a sixth parameter representing your framerate.

You can use a function that measures realtime elapsed instead of a constant, if your rendering framerate is variable.

Answer 2

I had this problem and the situation was like this, and I SOLVED IT. User presses the pause button then some objects goes off (these objects has couroutine(s) ). THIS IS THE PROBLEM. I must not turn off those game objects. The coroutines working fine while the game object is on and when you turn them off every thing is going to be mess.