[游戏开发]Unity 程序化网格几何体之矩形

最近在做编辑器的功能，碰到一个需求是创建任意长度的墙体。思路是点击鼠标，然后拖动鼠标，墙体长度随着鼠标的拖动而增加。
通过实现此功能，感觉其中有几个关键点：
1.绘制矩形顶点
2.绘制矩形三角面
3.绘制矩形纹理
4.绘制矩形法线
5.矩形始终指向鼠标位置
6.在结束绘制矩形时，调用Mesh.Clear()，然后重新给矩形顶点赋值，否则会出现拉近视角，模型消失的情况

目前发现的问题：
在绘制斜着的矩形时，发现贴图会有重影。

实现代码如下：

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

public class CreateMesh : MonoBehaviour
{

    [SerializeField]
    private Material wallMat = null;

    [SerializeField]
    private float width = 1;

    [SerializeField]
    private float height = 3.4f;

    private float length = 0;

    private float halfWidth = 0;

    private Mesh mesh = null;

    private MeshRenderer meshRender = null;

    private Vector3[] vertics = new Vector3[24];

    private int[] triangles = new int[36];

    private Vector2[] UVs = new Vector2[24];

    private int clickCount = 0;

    private RaycastHit hit;

    private bool isStartCreate = false;

    private Vector3 originPos = Vector3.zero;

    private GameObject curObj = null;

    private void Start()
    {
        halfWidth = width / 2f;
    }

    private void Update()
    {
        if (Input.GetMouseButtonDown(0))
        {
            if (clickCount == 0)
            {
                StartCreateCustomObject();
                clickCount = 1;
            }
            else if (clickCount == 1)
            {
                EndCreateCustomObject();
                clickCount = 0;
            }
        }

        CreatingCustomObject();
    }

    private void StartCreateCustomObject()
    {
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        if (Physics.Raycast(ray, out hit))
        {
            curObj = new GameObject();
            meshRender = curObj.AddComponent<MeshRenderer>();
            meshRender.sharedMaterial = wallMat;
            var vmf = curObj.AddComponent<MeshFilter>();
            mesh = vmf.mesh;

            curObj.transform.position = hit.point;
            originPos = hit.point;
            length = 0;

            vertics = new Vector3[] {
                //left
                new Vector3(0,0,halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,height,-halfWidth),
                new Vector3(0,0,-halfWidth),

                //front
                new Vector3(0,0,-halfWidth),
                new Vector3(0,height,-halfWidth),
                new Vector3(0,height,-halfWidth),
                new Vector3(0,0,-halfWidth),

                //right
                new Vector3(0,0,-halfWidth),
                new Vector3(0,height,-halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,0,halfWidth),

                //back
                new Vector3(0,0,halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,0,halfWidth),

                //up
                new Vector3(0,height,-halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,height,halfWidth),
                new Vector3(0,height,-halfWidth),

                //down
                new Vector3(0,0,halfWidth),
                new Vector3(0,0,-halfWidth),
                new Vector3(0,0,-halfWidth),
                new Vector3(0,0,halfWidth)

         };
            //绘制顶点
            mesh.vertices = vertics;

            triangles = new int[] {
            //left
            0,1,2,
            2,3,0,

            //front
            4,5,6,
            6,7,4,

            //right
            8,9,10,
            10,11,8,

            //back
            12,13,14,
            14,15,12,

            //up
            16,17,18,
            18,19,16,

            //down
            20,21,22,
            22,23,20
            };
            //绘制三角面
            mesh.triangles = triangles;

            UVs = new Vector2[] {
            //left
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),

            //front
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),

            //right
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),

            //back
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),

            //up
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),

            //down
            new Vector2(0,0),
            new Vector2(0,1),
            new Vector2(1,1),
            new Vector2(1,0),
            };
            //绘制纹理
            mesh.uv = UVs;

            //计算法线
            mesh.RecalculateNormals();

            isStartCreate = true;

        }
    }

    private void CreatingCustomObject()
    {
        if (isStartCreate)
        {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit))
            {
                vertics = mesh.vertices;

                var vEndCenterX = hit.point.x - originPos.x;
                var vEndCenterZ = hit.point.z - originPos.z;
                length = Mathf.Sqrt(vEndCenterX * vEndCenterX + vEndCenterZ * vEndCenterZ);

                var vros = hit.point - originPos;
                curObj.transform.rotation = Quaternion.FromToRotation(Vector3.right, vros);

                vertics[6] = new Vector3(length, height, -halfWidth);
                vertics[7] = new Vector3(length, 0, -halfWidth);
                vertics[8] = new Vector3(length, 0, -halfWidth);
                vertics[9] = new Vector3(length, height, -halfWidth);
                vertics[10] = new Vector3(length, height, halfWidth);
                vertics[11] = new Vector3(length, 0, halfWidth);
                vertics[12] = new Vector3(length, 0, halfWidth);
                vertics[13] = new Vector3(length, height, halfWidth);
                vertics[18] = new Vector3(length, height, halfWidth);
                vertics[19] = new Vector3(length, height, -halfWidth);
                vertics[22] = new Vector3(length, 0, -halfWidth);
                vertics[23] = new Vector3(length, 0, halfWidth);

                mesh.vertices = vertics;

                //如果不实时计算法线的话，在创建过程中模型无法正常接收光照和着色
                mesh.RecalculateNormals();

            }

        }
    }

    private void EndCreateCustomObject()
    {
        Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
        if (Physics.Raycast(ray, out hit))
        {
            //最后结束创建的时候重新赋值一下顶点，否则会出现Bound跟Mesh尺寸不一致的情况
            //如果Bound和Mesh尺寸不一致，拉近视角模型则会消失
            mesh.Clear();

            var vEndCenterX = hit.point.x - originPos.x;
            var vEndCenterZ = hit.point.z - originPos.z;
            length = Mathf.Sqrt(vEndCenterX * vEndCenterX + vEndCenterZ * vEndCenterZ);

            var vros = hit.point - originPos;
            curObj.transform.rotation = Quaternion.FromToRotation(Vector3.right, vros);

            vertics[6] = new Vector3(length, height, -halfWidth);
            vertics[7] = new Vector3(length, 0, -halfWidth);
            vertics[8] = new Vector3(length, 0, -halfWidth);
            vertics[9] = new Vector3(length, height, -halfWidth);
            vertics[10] = new Vector3(length, height, halfWidth);
            vertics[11] = new Vector3(length, 0, halfWidth);
            vertics[12] = new Vector3(length, 0, halfWidth);
            vertics[13] = new Vector3(length, height, halfWidth);
            vertics[18] = new Vector3(length, height, halfWidth);
            vertics[19] = new Vector3(length, height, -halfWidth);
            vertics[22] = new Vector3(length, 0, -halfWidth);
            vertics[23] = new Vector3(length, 0, halfWidth);

            mesh.vertices = vertics;

            mesh.triangles = triangles;

            mesh.uv = UVs;

            mesh.RecalculateNormals();

            curObj.AddComponent<BoxCollider>();

            curObj = null;

            isStartCreate = false;
        }
    }
}

墙体Shader：https://download.csdn.net/download/qq_39353597/52010659
参考资料：https://docs.unity.cn/cn/2019.4/Manual/UsingtheMeshClass.html