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);
    }
}