mesh就是组成3d物体的三角形们。

mesh由顶点组成的三角形组成，三角形的大小 并不 需要一样，由顶点之间的位置决定。

mesh可以是一个或者多个面。

贴图的原点在左下角，uv是贴图的坐标，数量和顶点数一样（不是100%确定，比如前后左右4个面，贴图最终如何封闭，我还不知道），是贴图和顶点的对应关系。

新建空场景，把一下代码放到main camera：

using System;
using System.Collections;
using System.Collections.Generic;

using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

public class codeMesh2 : MonoBehaviour
{
	GUIStyle fontStyle = new GUIStyle();
	string msg = " - - ";
	// Start is called before the first frame update
	Vector3 center = new Vector3();
	GameObject o;
	bool ready = false;
	//int startCalled = 0;
	Camera c;
	string err = "";
	int moveRage = 25; 
	int moveRage2 = 0;
	int moveRage2_1 = 0;
	Mesh mesh = null;

	public int width = 10;
	public int height = 10;
	public Texture aText = null;

	/// <summary>
	/// 上一次更新帧率的时间
	/// </summary>
	private float m_lastUpdateShowTime = 0f;
	/// <summary>
	/// 更新显示帧率的时间间隔
	/// </summary>
	private readonly float m_updateTime = 0.05f;
	/// <summary>
	/// 帧数
	/// </summary>
	private int m_frames = 0;
	/// <summary>
	/// 帧间间隔
	/// </summary>
	//private float m_frameDeltaTime = 0;
	private float m_FPS = 0;
	//private Rect m_fps, m_dtime;

	//顶点数组
	private Vector3[] vertices;
	//顶点法线
	private Vector3[] normals;
	private MeshFilter meshFilter;

	private int i = 0;
	private bool f = false;
	private string test2 = "";
	private int waitCount = 0;
	private void Awake()
	{
		Application.targetFrameRate = 30;
		moveRage2 = moveRage * 2;
		moveRage2_1 = moveRage * 2 - 1;

		fontStyle.normal.background = null;    //设置背景填充
		fontStyle.normal.textColor = Color.red;   //设置字体颜色
		fontStyle.fontSize = 40;
		fontStyle.wordWrap = true;
		c = GetComponent<Camera>();
		msg += " Waiting ";

		Vector3 v1 = new Vector3(5, 5, 5);
		Vector3 v2 = new Vector3(5, 5, 3);

		test2 = (v2 - v1).normalized.ToString();
	}

	void Start()
	{
		try
		{
			o = GenerateMeshTest1();
			center = c.transform.position;
			o.name = "d mesh";
			o.transform.position = new Vector3(-5, -5, 20);
			o.transform.localScale = new Vector3(10.0f, 10.0f, 10.0f);
			o.transform.rotation = Quaternion.Euler(new Vector3(0, 45, 45));
			m_lastUpdateShowTime = Time.realtimeSinceStartup;
			ready = true;
		}
		catch (Exception e)
		{
			err = printException(e);
		}

		aText = Resources.Load("type/two_sizes") as Texture;

		o.GetComponent<MeshRenderer>().material.mainTexture = aText;

#if UNITY_EDITOR
		showNormals();
#endif

	}
	private void OnGUI()
	{
		GUI.color = Color.red;
		msg = "fps=" + m_FPS + "/"+ Application.targetFrameRate +(err.Length>1?(", err=" + err):"")  + " waitCount = " + (ready? waitCount : (waitCount++));

		GUI.Label(new Rect(50, 10, 900, 100), "" + test2, fontStyle);
		GUI.Label(new Rect(100, 100, 900, 100), "[V07]：" + msg, fontStyle);
	}

	// Update is called once per frame
	void Update()
	{
		if (!ready) return;
		int ri = i % (moveRage2);

		float x = ri - moveRage;

		if (!f)
		{
			x = moveRage - ri;
		}

		if (ri == moveRage2_1)
		{
			f = !f;
		}
		//o.transform.position = new Vector3(x, x, 20);
		//Debug.Log(x);
		//o.transform.rotation = Quaternion.Euler(new Vector3(0, 0, 0));

		/*
		Mesh mesh = o.GetComponent<MeshFilter>().mesh;
		//mesh.Clear();
		Vector3[] vertices = mesh.vertices;
		Vector3[] normals = mesh.normals;

		for (var i = 0; i < vertices.Length; i++)
		{
			vertices[i] += normals[i] * Mathf.Sin(Time.time);
		}

		mesh.vertices = vertices;
		*/


		m_frames++;
		if (Time.realtimeSinceStartup - m_lastUpdateShowTime >= m_updateTime)
		{
			m_FPS = m_frames / (Time.realtimeSinceStartup - m_lastUpdateShowTime);
			//m_frameDeltaTime = (Time.realtimeSinceStartup - m_lastUpdateShowTime) / m_frames;
			m_frames = 0;
			m_lastUpdateShowTime = Time.realtimeSinceStartup;
			//Debug.Log("FPS: " + m_FPS + "，间隔: " + m_FrameDeltaTime);
		}
		i++;
	}


	private GameObject GenerateMeshTest1()
	{
		GameObject obj = new GameObject();
		meshFilter = obj.AddComponent<MeshFilter>();
		//创建mesh
		mesh = new Mesh();
		meshFilter.mesh = mesh;
		MeshRenderer renderer = obj.AddComponent<MeshRenderer>();
		//标准材质
		Material mat = new Material(Shader.Find("Legacy Shaders/Transparent/Diffuse"));
		mat.color = Color.white;
		renderer.material = mat;
		
		//创建顶点和UV
		vertices = new Vector3[6];
		Vector2[] uv = new Vector2[6];

		vertices[0] = new Vector3(0, 1, 0);//0
		vertices[1] = new Vector3(1, 1, 0);//1
		vertices[2] = new Vector3(1, 0, 0);//2
		vertices[3] = new Vector3(0, 0, 0);//3
		vertices[4] = new Vector3(0, 0, 1);//4
		vertices[5] = new Vector3(1, 0, 1);//5-
		int k = 0;
		uv[k++%6] = new Vector2(0, 1);
		uv[k++ % 6] = new Vector2(1, 1);
		uv[k++ % 6] = new Vector2(1, 0.5f);
		uv[k++ % 6] = new Vector2(0,0.5f);
		uv[k++ % 6] = new Vector2(0, 0);
		uv[k++ % 6] = new Vector2(1, 0);

		mesh.vertices = vertices;
		mesh.uv = uv;
		//mat.mainTexture = aText;

		int[] triangles = new int[12];
		k = 0;
		triangles[k++] = 3;
		triangles[k++] = 2;
		triangles[k++] = 5;

		triangles[k++] = 3;
		triangles[k++] = 5;
		triangles[k++] = 4; 
		
		triangles[k++] = 0;
		triangles[k++] = 1;
		triangles[k++] = 2;

		triangles[k++] = 0;
		triangles[k++] = 2;
		triangles[k++] = 3;




		mesh.triangles = triangles; //三角面
		mesh.RecalculateNormals();  //计算法线



		/*Vector3[] normals = new Vector3[4];
		normals[0] = Vector3.back;
		normals[1] = Vector3.back;
		normals[2] = Vector3.back;
		normals[3] = Vector3.back;
		mesh.normals = normals;*/



		//mesh.SetIndices
		//mat.SetTexture()

		return obj;
	}

	public static string printException(Exception e)
	{
		return "\n\trs=" + e.HResult + ",\n\tmsg=" + e.Message + ",\n\tstack=" + e.StackTrace + "\n------------------------------------\n";
	}


#if UNITY_EDITOR
	private void showNormals()
	{
		if (mesh != null)
		{
			//当前对象的操做从局部空间转换到世界空间 这样在下面的操作位置即可同步 否则位置是不会同步的
			Handles.matrix = meshFilter.transform.localToWorldMatrix;
			Handles.color = Color.green;

			int vertextCount = mesh.vertices.Length;
			//采用从顶点的位置[法线的起点】到法线的终点位置，既可以显示出当前顶点的法线
			for (int index = 0; index < vertextCount; index++)
			{
				Handles.DrawLine(vertices[index], vertices[index] + normals[index]);
			}
		}
	}
#endif
}

two_sizes.png是一张 宽高比为1：2的图片。

三角形之间的定义顺序不会影响贴图。但单个三角形三个顶点是逆时针，则从外部可以看到贴图，从内部看不到。反之亦然：

（顺时针之后，从内部可见）

如果把图片直接放到场景，则两面都可见。