Texture2D Extension: Texture Still Null After Calling It

Questions & Answers
1

I have an extension method for resetting Texture2D:

public static class MyExtensions
{
	public static void Reset(this Texture2D tex)
	{
		if(tex == null) tex = new Texture2D(256,1,TextureFormat.RGBA32,false);
		for(int i=0;i<256;i++)
		{
			tex.SetPixel(i,1,Color.clear);
		}
		tex.Apply();
		tex.wrapMode = TextureWrapMode.Clamp;

	}
}

When i try to call it in another class:

if(ref_tex == null) ref_tex.Reset();
ref_tex.SetPixel(i,1,new Color(r,g,b,1f));

Unity Log always throws an error on the second line: UnassignedReferenceException: The variable ref_tex has not been assigned.

Do I do something wrong?

2

Your best bet is to use a plain old static method with a ref parameter.

public static class ResetTexture {
  public static void Reset(ref Texture2D tex) {
    if(tex == null) tex = new Texture2D(256,1,TextureFormat.RGBA32,false);
    for(int i=0;i<256;i++) {
      tex.SetPixel(i,1,Color.clear);
    }
    tex.Apply();
    tex.wrapMode = TextureWrapMode.Clamp;
  }
}

// Somewhere else
if (ref_tex == null) ResetTexture.Reset(ref ref_tex);
ref_tex.SetPixel(i,1,new Color(r,g,b,1f));

The reason you can’t use an extension method is due to how parameters are passed in C#. Parameters are by default passed by-value. Changing the parameter using = inside the method has no effect on the variable passed to the method.

void Start() {
  var a = "Hi";
  Debug.Log(a);
  Change(a);
  Debug.Log(a);
}

void Change(string b) {
  Debug.Log(b);
  b = "Hello";
  Debug.Log(b);
}

Produces output:
Hi
Hi
Hello
Hi

When you want changes inside a method to propagate back to the caller you use the ref keyword.

void Start() {
  var a = "Hi";
  Debug.Log(a);
  Change(ref a);
  Debug.Log(a);
}

void Change(ref string b) {
  Debug.Log(b);
  b = "Hello";
  Debug.Log(b);
}

Produces output:
Hi
Hi
Hello
Hello

However, the first parameter of an extension method can’t be a ref parameter.

void Change(this ref Texture2D b) {
  // Compile Error: "The parameter modifiers 'this' and 'ref' cannot be used together."
}

This means you can’t use ref to modify the object on which you call an extension method.