FlipNormals on mesh (FlipNormals.cs in Editor Folder)

gistfile1.txt

using UnityEngine;
using System.Collections;
using UnityEditor;


public class FlipNormals 
{
    [MenuItem("Tools/Flip Normals")]
    static void FlipMeshNormals()
    { // Flip Mesh Normals on selected mesh(es)
        FlipInit();
    }

    private static void FlipInit()
    {
        foreach (GameObject go in Selection.gameObjects)
        {
            MeshFilter filter = go.GetComponent(typeof(MeshFilter)) as MeshFilter;

            FlipNormalMethod(ref filter);

        }
    }



    private static void FlipNormalMethod(ref MeshFilter filter)
    {
      
        if (filter != null)
        {
            Mesh mesh = filter.sharedMesh;

            Vector3[] normals = mesh.normals;
            for (int i = 0; i < normals.Length; i++)
                normals[i] = -normals[i];
            mesh.normals = normals;

            for (int m = 0; m < mesh.subMeshCount; m++)
            {
                int[] triangles = mesh.GetTriangles(m);
                for (int i = 0; i < triangles.Length; i += 3)
                {
                    int temp = triangles[i + 0];
                    triangles[i + 0] = triangles[i + 1];
                    triangles[i + 1] = temp;
                }
                mesh.SetTriangles(triangles, m);
            }
        }
    }
}