頂点数と長さを変えられるPlaneを生成する

CustomPlane.cs

using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(MeshRenderer))]
[ExecuteInEditMode]
public class CustomPlane : MonoBehaviour
{
    [Range(1, 1000)]
    public   int cols = 1,  rows = 1;
    [Range(0.01f, 100.0f)]
    public float width = 1.0f, height = 1.0f;

#if UNITY_EDITOR
    void Start()
    {
        MeshFilter meshFilter;
        meshFilter = gameObject.AddComponent<MeshFilter>();
        if (meshFilter == null) return;
        Mesh mesh  = CreateCustomPlane(cols, rows, width, height);
        meshFilter.mesh = mesh;

    }

    void Update()
    {
        MeshFilter meshFilter = GetComponent<MeshFilter>();
        if (meshFilter == null) return;
        Mesh mesh  = CreateCustomPlane(cols, rows, width, height);
        meshFilter.mesh = mesh;
    }
#endif

    private Mesh CreateCustomPlane(int cols, int rows, float width, float height)
    {
        if (cols <= 0 || rows <= 0 || width <= 0 || height <= 0) return new Mesh(); 
        Mesh mesh = new Mesh();
        mesh.name = "CustomPlane";
        mesh.vertices = CreateCustomVertices(cols, rows, width, height);
        mesh.triangles =  CreateCustomTriangles(cols, rows);
        mesh.uv         = CreateCustomUv(cols, rows);

        mesh.RecalculateNormals();
        mesh.RecalculateBounds();

        return mesh;
    }

    Vector3[] CreateCustomVertices(int cols, int rows, float width, float height)
    {
        var vertices = new Vector3[(cols + 1) * (rows + 1)];

        int length = vertices.Length;
        for (int i = 0; i < length; i++) {
            int x = i % (cols + 1);
            int z = i / (cols + 1);
            vertices[i] = new Vector3(
                width / 2 - (width / cols) * x,
                0,
                height / 2 - (height / rows) * z
            );
        }
        /*
        foreach(var v in vertices) {
            print("vertex : " + v.ToString("F3"));
        }
        */
        return vertices;
    }

    int[] CreateCustomTriangles(int cols, int rows)
    {
        var listTriangles   = new List<int>();
        int verticesLength  = (cols + 1) * (rows + 1);

        //頂点を順になぞる、最後の行はやらない
        for (int i = 0; i < verticesLength - (cols + 1); i++) {
            //左端を飛ばす
            if ((i % (cols + 1)) == cols) continue;

            //四角1ずつ(三角2つずつ)
            listTriangles.Add(i);
            listTriangles.Add(i + cols + 1);
            listTriangles.Add(i + cols + 2);
            listTriangles.Add(i);
            listTriangles.Add(i + cols + 2);
            listTriangles.Add(i + 1);
        }
        /*
        foreach(var t in listTriangles.ToArray()) {
            print("triangle : " + t);
        }
        */

        return listTriangles.ToArray();
    }

    Vector2[] CreateCustomUv(int cols, int rows)
    {
        var uv     = new Vector2[(cols + 1) * (rows + 1)];
        int length  = uv.Length;

        for (int i = 0; i < length; i++) {
            int u = i % (cols + 1);
            int v = i / (cols + 1);
            uv[i] = new Vector2(
                1.0f - (1.0f / cols) * u,
                1.0f - (1.0f / rows) * v
            );
        }
        /*
        foreach(var u in uv) {
            print("uv : " + u.ToString("F3"));
        }
        */

        return uv;
    }

}