以下.cs需要放置d在名称为 Editor 的文件夹下
EditorFlipMeshNormals.cs

#if UNITY_EDITOR

using UnityEditor;
using UnityEngine;

/// <summary>
/// 在 Hierarchy 视图对象的快捷菜单中增加 Flip Mesh Normals（反转网格法线）项
/// </summary>
public class EditorFlipMeshNormals : Editor {

    /// <summary> 翻转网格的法线 </summary>
    private static void FlipMeshNormals (Mesh mesh) {
        int[] triangles = mesh.triangles;
        for (int i = 0; i < triangles.Length; i += 3) {
            // 交换三角形的首尾索引
            int t = triangles[i];
            triangles[i] = triangles[i + 2];
            triangles[i + 2] = t;
        }
        mesh.triangles = triangles;

    }

    /// <summary> 翻转多个游戏对象网格的法线 </summary>
    private static void FlipMeshNormals (GameObject[] gameObjects) {
        for (int i = 0, len = gameObjects.Length; i < len; i++) {
            GameObject go = gameObjects[i];

            Mesh mesh = null;
            SkinnedMeshRenderer skinnedMeshRenderer = go.GetComponent<SkinnedMeshRenderer>();
            if (skinnedMeshRenderer) {
                mesh = skinnedMeshRenderer.sharedMesh;
            } else {
                MeshFilter meshFilter = go.GetComponent<MeshFilter>();
                if (meshFilter) {
                    mesh = meshFilter.sharedMesh;
                }
            }

            if (mesh) {
                FlipMeshNormals(mesh);
            }
        }
    }

    /// <summary> 验证所选择的游戏对象有网格时菜单才可用(不计算子级) </summary>
    [MenuItem("GameObject/Flip Mesh Normals", true)]
    private static bool ValidateFlipMeshNormalsOnGameObject () {
        bool isHasMesh = false;
        GameObject[] gameObjects = Selection.gameObjects;
        for (int i = 0, len = gameObjects.Length; i < len; i++) {
            GameObject go = gameObjects[i];
            SkinnedMeshRenderer skinnedMeshRenderer = go.GetComponent<SkinnedMeshRenderer>();
            if (skinnedMeshRenderer) {
                isHasMesh = true;
                break;
            }
            MeshFilter meshFilter = go.GetComponent<MeshFilter>();
            if (meshFilter) {
                isHasMesh = true;
                break;
            }
        }
        return isHasMesh;
    }

    [MenuItem("GameObject/Flip Mesh Normals", false, 11)]
    private static void FlipMeshNormalsOnGameObject () {
        FlipMeshNormals(Selection.gameObjects);
    }

}
#endif