Transform Textures in Unity

TextureTransformation.shader

// TextureTransformation.shader
// A simple shader that allows us to transition between two textures from a script.
//
// Author: Nathan Campos <nathan@innoveworkshop.com>

Shader "Custom/TextureTransformation" {
    Properties {
        _Color ("Color", Color) = (1,1,1,1)
        _MainTex ("Original Texture", 2D) = "white" {}
        _TransTex("Transformed Texture", 2D) = "gray" {}
        _Glossiness ("Smoothness", Range(0,1)) = 0.0
        _Metallic ("Metallic", Range(0,1)) = 0.0
        _Transformation("Transformation", Range(0,1)) = 0.0
    }

    SubShader {
        // Make sure we can do transparency.
        Tags { "RenderType" = "Transparent" "Queue" = "Transparent" }
        LOD 300
        Blend SrcAlpha OneMinusSrcAlpha  // Use blend for alpha values.

        CGPROGRAM
        // Physically based Standard lighting model, and enable shadows on all light types.
        #pragma surface surf Standard fullforwardshadows
        // Use shader model 3.0 target, to get nicer looking lighting.
        #pragma target 3.0

        struct Input {
            float2 uv_MainTex;
            float2 uv_TransTex;
        };

        // Turn our properties into variables.
        sampler2D _MainTex;
        sampler2D _TransTex;
        half _Glossiness;
        half _Metallic;
        fixed4 _Color;
        half _Transformation;

        // Add instancing support for this shader. You need to check 'Enable Instancing' on materials that use the shader.
        // See https://docs.unity3d.com/Manual/GPUInstancing.html for more information about instancing.
        // #pragma instancing_options assumeuniformscaling
        UNITY_INSTANCING_BUFFER_START(Props)
            // put more per-instance properties here
        UNITY_INSTANCING_BUFFER_END(Props)

        // Calculate the surface properties.
        void surf (Input IN, inout SurfaceOutputStandard o) {
            // Get textures.
            fixed4 colMain = tex2D (_MainTex, IN.uv_MainTex) * _Color;
            fixed4 colTrans = tex2D(_TransTex, IN.uv_TransTex) * _Color;

            // Calculate how much each texture will weigh in the transformation.
            o.Albedo = (colMain.rgb * (1 - _Transformation)) + (colTrans.rgb * _Transformation);

            // Apply all the other "standard" effects.
            o.Metallic = _Metallic;
            o.Smoothness = _Glossiness;
            o.Alpha = _Color.a;
        }
        ENDCG
    }
    FallBack "Diffuse"
}

TransformShader.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

/// <summary>
/// Transforms a <see cref="GameObject"/> when the fog touches it using our
/// custom shader.
/// </summary>
[RequireComponent(typeof(Renderer))]
public class TransformShader : MonoBehaviour, ITransformation {
	public GameObject fog;
	public float transformationAmount = 0.0f;
	private Renderer objectRenderer;
	private float insideDistance = 33.0f;

	// Start is called before the first frame update
	void Start() {
		objectRenderer = gameObject.GetComponent<Renderer>();
	}

	// Update is called once per frame
	void Update() {
		// Do nothing if we've already transformed.
		if (transformationAmount == 1.0f)
			return;

		// Check if we are inside the fog.
		if (InsideFog())
			StartTransformation();

		// Apply transformation to the shader.
		objectRenderer.material.SetFloat("_Transformation", transformationAmount);
	}

	public void StartTransformation() {
		transformationAmount = 1;
	}

	/// <summary>
	/// Check if our <see cref="GameObject"/> is inside the fog.
	/// </summary>
	/// <returns>True if we are inside the fog.</returns>
	private bool InsideFog() {
		// Check if the distance from the fog is less than its radius.
		return Vector3.Distance(transform.position, fog.transform.position) < insideDistance;
	}
}