changing alpha levels while using color.lerp in unity5

Question

I am using color.lerp on a sprite renderer to interpolate between yellow and red based on values I have in a dataset. I also want the transparency of the sprites to depend on the value so lower values will be more transparent. The color.lerp works fine but I am now having trouble getting the alpha levels of the sprite to depend on the value as well! Here is my code so far:

using UnityEngine;
using System.Collections;

public class Intensity : MonoBehaviour {

public float value;
private float alpha;

void Start() {

    if (GetComponent<SpriteRenderer> ()) {
        SpriteRenderer r = GetComponent<SpriteRenderer> ();
        r.color = new Color32 ();
        r.color = Color.Lerp (Color.yellow, Color.red, value / 100);
        }

    if (GetComponent<MeshRenderer> ()) {
        MeshRenderer r = GetComponent<MeshRenderer> ();
        Material m = r.material;
        Color c = new Color ();
        m.color = c;
        alpha = Mathf.Lerp(0, 1, value/100) ;
        c.a = alpha;
    }
}

}

Any ideas to make this work would be greatly appreciated!

Thank you, Jen

Answer 1

In this code:

    Material m = r.material;
    Color c = new Color ();
    m.color = c;
    alpha = Mathf.Lerp(0, 1, value/100) ;
    c.a = alpha;

Because Color is a struct, any get and set properties such as Material.color will pass by value. This means that c and m.color are separate values that don't affect each other.

You can avoid that by assigning to m.color last:

Color c = Color.Lerp(newYellow, Color.red, value / 100);
c.a = Mathf.Lerp(0, 1, value/100);
m.color = c;

If that doesn't make sense, see if you can understand why this won't work:

m.color.a = 0;

You instead have to get the value, make a change, and assign the new value:

Color c = m.color;
c.a = 0;
m.color = c;