Mesh.RecalculateTangents

Description

Recalculates the tangents of the Mesh from the normals and texture coordinates.

After modifying the vertices and the normals of the Mesh, tangents need to be updated if the Mesh is rendered using Shaders that reference normal maps. Tangents are calculated using the vertices, normals and texture coordinates of the Mesh.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Start() {
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        mesh.RecalculateTangents();
    }
}