CollisionScript

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

// To be used with Melting Shader: https://pastebin.com/f6nKeerE
// Created by Erika Moya, in collaboration with Gijs Richard Kaerts

public class CollisionScript : MonoBehaviour {

    Mesh mesh;
    public float distance = 0.5f;
    Vector3 lastHit = new Vector3 (0,0,0);
    public float heightOffset = 0.0f;
    float lastHeightOffset = 0.0f;

    private void Start()  {
        mesh = GetComponent<MeshFilter>().mesh;
    }

    void FixedUpdate() {
        RaycastHit hit;
        Ray ray = new Ray (transform.position, Vector3.down);
        Physics.Raycast (ray, out hit);

        if (lastHit == new Vector3(0,0,0) ) {
            if (hit.distance < distance) {
                SendMatrix (hit, lastHit);
                lastHit = hit.point;
            }
        }

        if ((hit.point != new Vector3(0,0,0)) && (lastHeightOffset != heightOffset)) {
            lastHit = hit.point + heightOffset*(hit.normal);
            lastHeightOffset = heightOffset;
            SendMatrix (hit, lastHit);
        }

    }

    void SendMatrix (RaycastHit hit, Vector3 newPoint) {
        //Debug.Log("Collision detected");
        Vector3 normal = hit.normal;
        Vector3 tangent = Vector3.Cross(Vector3.forward, normal);
        if (tangent.magnitude == 0) {
            tangent = Vector3.Cross(Vector3.up, normal); }
        Vector3 bitangent = Vector3.Cross(normal, tangent);

        Vector3 point = hit.point;
        if (newPoint != new Vector3 (0,0,0)) {
            point = newPoint;
        }

        lastHit = point;

        Matrix4x4 colMatrix = new Matrix4x4();

        colMatrix.SetRow(0, new Vector4(tangent.x, tangent.y, tangent.z, 0));
        colMatrix.SetRow(1, new Vector4 (normal.x, normal.y, normal.z, 0));
        colMatrix.SetRow(2, new Vector4(bitangent.x, bitangent.y, bitangent.z, 0));
        colMatrix.SetRow(3, new Vector4(point.x, point.y, point.z, 1));

        GetComponent<Renderer>().material.SetMatrix("collisionMatrix", colMatrix);

        GetComponent<Renderer>().material.SetMatrix("collisionMatrixInverse", colMatrix.inverse);
        //Debug.Log("Matrix sent\n" + colMatrix.GetRow(3));
    }

}