RaycastHit.barycentricCoordinate

Description

The barycentric coordinate of the triangle we hit.

This lets you interpolate any of the vertex data along the 3 axes.

// Attach this script to a camera and it will
// draw a debug line pointing outward from the normal
function Update () {
    // Only if we hit something, do we continue
    var hit : RaycastHit;
    if (!Physics.Raycast (Camera.main.ScreenPointToRay(Input.mousePosition), hit))
        return;

    // Just in case, also make sure the collider also has a renderer
    // material and texture
    var meshCollider = hit.collider as MeshCollider;
    if (meshCollider == null || meshCollider.sharedMesh == null)
        return;

    var mesh : Mesh = meshCollider.sharedMesh;
    var normals = mesh.normals;
    var triangles = mesh.triangles;

    // Extract local space normals of the triangle we hit
    var n0 = normals[triangles[hit.triangleIndex * 3 + 0]];
    var n1 = normals[triangles[hit.triangleIndex * 3 + 1]];
    var n2 = normals[triangles[hit.triangleIndex * 3 + 2]];

    // interpolate using the barycentric coordinate of the hitpoint
    var baryCenter = hit.barycentricCoordinate;

    // Use barycentric coordinate to interpolate normal
    var interpolatedNormal = n0 * baryCenter.x + n1 * baryCenter.y + n2 * baryCenter.z;
    // normalize the interpolated normal
    interpolatedNormal =  interpolatedNormal.normalized;

    // Transform local space normals to world space
    var hitTransform : Transform = hit.collider.transform;
    interpolatedNormal = hitTransform.TransformDirection(interpolatedNormal);

    // Display with Debug.DrawLine
    Debug.DrawRay(hit.point, interpolatedNormal);
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Update() {
        RaycastHit hit;
        if (!Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out hit))
            return;
        
        MeshCollider meshCollider = hit.collider as MeshCollider;
        if (meshCollider == null || meshCollider.sharedMesh == null)
            return;
        
        Mesh mesh = meshCollider.sharedMesh;
        Vector3[] normals = mesh.normals;
        int[] triangles = mesh.triangles;
        Vector3 n0 = normals[triangles[hit.triangleIndex * 3 + 0]];
        Vector3 n1 = normals[triangles[hit.triangleIndex * 3 + 1]];
        Vector3 n2 = normals[triangles[hit.triangleIndex * 3 + 2]];
        Vector3 baryCenter = hit.barycentricCoordinate;
        Vector3 interpolatedNormal = n0 * baryCenter.x + n1 * baryCenter.y + n2 * baryCenter.z;
        interpolatedNormal = interpolatedNormal.normalized;
        Transform hitTransform = hit.collider.transform;
        interpolatedNormal = hitTransform.TransformDirection(interpolatedNormal);
        Debug.DrawRay(hit.point, interpolatedNormal);
    }
}