[ta-edu-course-survival-game] Chapter 2 — Coroutines (2)

_Instructions.md

• Implement IEnumerator FadeOut()
  • Coroutines must have a return value of IEnumerator
  • This is because they're based on iterator methods
  • You can use iterator methods to create a source for enumeration
  • Every value that you yield return from an iterator method is essentially a part of a collection that the method represents
  • Unity treats the collection that coroutines return as instructions for when to continue exectution, if ever
• Make FadeOut() yield return to null
  • yield return null instructs to skip one frame before contining execution
  • In this case, there's nothing else to execute so nothing else will happen
• Declare a local variable named "elapsed" with a value of 0
  • FadeOut() will be responsible for the fade state now
• Wrap yield return null with a while statement for elapsed < duration
• In the while loop, incremenet elapsed by Time.deltaTime
  • Now this function will continue to execute once every frame until elapsed is greater than duration
• Copy the fading logic (lines 26-28) and paste it into FadeOut()
• Delete Update() and _elapsed
  • We no longer need to keep track of state or manage the fade using update
• Remove call to _isFading from Interact() and delete _isFading
• Add a call to StartCoroutine(FadeOut) to Interact()
  • Now we can simply start our coroutine when the interaction occurs

FadingInteractable.cs

public class FadingInteractable : Interactable
{
  [SerializeField] private float duration = 3;
  
  private Renderer _renderer;
  
  public void Interact()
  {
     StartCoroutine(FadeOut);
  }
  
  private void Awake()
  {
    if (!TryGetComponent(out Renderer renderer))
    {
      this.enabled = false;
      return;
    }
  }
  
  private IEnumerator FadeOut()
  {
    var elapsed = 0;
    while (elapsed <= duraion)
    {
      var color = _renderer.material.color;
      color.a = Mathf.Lerp(1, 0, elapsed / duration);
      _renderer.material.color = color;
      
      elapsed += Time.deltaTime;
      yield return null;
    }
  }
}