'Lerp alpha' not lerping

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1

Trying to lerp the transparency value of a cube’s mesh renderer from 100% to 0%.

The material is a plain green material made in Unity

The script is on a seperate game object, the cube is referenced as a variable in the script

The material is set as a ‘Transparent/Diffuse’

The material’s alpha value begins at 0

When i press ‘l’, the material goes fully (100%) opaque (this is good)

However, it DOESN’T then lerp fully to 0% (this is bad)

When i look at the printed alpha value in the console, it is ‘flicking’ between 0.95 and 0.94

Can anyone tell me why the value isn’t reducing to 0.0?

Here’s the code:

    var damScreen1 : Renderer;
    var lerpDuration : float = 1.0;
    var lerpNow : boolean = false;
    

    function Update () {
    
    //Displays the transparency value
    print (damScreen1.renderer.material.color.a); 
    
    
    if (Input.GetKey ("l"))
       {
       lerpNow = true;
       }
    
    if (lerpNow == true)
       {
       damScreen1.renderer.material.color.a = Mathf.Lerp(1.0, 0.0, lerpDuration * Time.deltaTime);

       }
    }

As always, thank you for your time!

Tom :slight_smile:

3

Mathf.Lerp does not animate the property. It gives you a single value.

Mathf.Lerp(1, 0, 0); // returns 1
Mathf.Lerp(1, 0, 1); // returns 0
Mathf.Lerp(1, 0, 0.5f); // returns 0.5
Mathf.Lerp(2, 0, 0.5f); // returns 1

If you want to use Lerp to animate a value you need to use a variable as the third parameter.

var damScreen1 : Renderer;
var lerpDuration : float = 1.0;
var lerpNow : boolean = false;

private var lerpStart : float = 0;

function Update () {
  //Displays the transparency value
  print (damScreen1.renderer.material.color.a); 
  
  if (Input.GetKey ("l")) {
    lerpNow = true;
    lerpStart = Time.time;
  }
  
  if (lerpNow) {
    var progress = Time.time - lerpStart;
    damScreen1.renderer.material.color.a = Mathf.Lerp(1.0, 0.0, progress / lerpDuration);
    if (lerpDuration < progress) {
      lerpNow = false;
    }
  }
}

See also

2

You either need to lerp from current color, or use Time.time as mentioned in previous comment, in your case you lerp from 1 to 0 by time.delta time which let say is 0.033f in 30FPS. so after 1 frame your alpha is 0.967. Than in next frame you lerp again from 1 to 0 so you alpha will remain at this value.

so you either do like in this unity exampe http://docs.unity3d.com/ScriptReference/Color.Lerp.html

or change your code to something like this :

damScreen1.renderer.material.color.a = Mathf.Lerp(damScreen1.renderer.material.color.a, 0.0, lerpDuration * Time.deltaTime);

its not the best use of lerp but will help you understand issue

//edit almost forgot, if i am correct you cannot change alpha directly (you should get an error)

try This solution