由于MeshCollider组件可以挂载多个，所以不需要Mesh重新合并了。

除了反转法线还需要反转所有三角面的顺序

 

脚本如下：

using System.Collections;using System.Collections.Generic;using UnityEngine;public class DoubleSideMeshCollider : MonoBehaviour{    public MeshCollider meshCollider;    void Start()    {        var mesh1 = meshCollider.sharedMesh;        var mesh2 = Instantiate(mesh1);        var normals = mesh2.normals;        for (int i = 0; i < normals.Length; ++i)        {            normals[i] = -normals[i];        }        mesh2.normals = normals;        for (int i = 0; i < mesh2.subMeshCount; ++i)        {            int[] triangles = mesh2.GetTriangles(i);            for (int j = 0; j < triangles.Length; j += 3)            {                int temp = triangles[j];                triangles[j] = triangles[j + 1];                triangles[j + 1] = temp;            }            mesh2.SetTriangles(triangles, i);        }        gameObject.AddComponent
     
      ().sharedMesh = mesh2;    }}