1Vector3[] myVertices = new Vector3[4];
2
3myVertices[0] = new Vector3(0, 0, 0);
4myVertices[1] = new Vector3(width, 0, 0);
5myVertices[2] = new Vector3(0, hight, 0);
6myVertices[3] = new Vector3(width, hight, 0);
7
8myMesh.SetVertices(myVertices);

1int[] myTriangles = new int[6];
2
3myTriangles[0] = 0;
4myTriangles[1] = 2;
5myTriangles[2] = 1;
6myTriangles[3] = 2;
7myTriangles[4] = 3;
8myTriangles[5] = 1;
9
10myMesh.SetTriangles(myTriangles,0);

1using UnityEngine;
2
3public class MeshManager : MonoBehaviour
4{
5    private MeshFilter meshFilter;
6    private Mesh myMesh;
7    private Vector3[] myVertices = new Vector3[4];
8    private int[] myTriangles = new int[6];
9    private float width = 2;
10    private float hight = 2;
11
12    void Start()
13    {
14        meshFilter = gameObject.GetComponent<MeshFilter>();
15        myMesh = new Mesh();
16
17        myVertices[0] = new Vector3(0, 0, 0);
18        myVertices[1] = new Vector3(width, 0, 0);
19        myVertices[2] = new Vector3(0, hight, 0);
20        myVertices[3] = new Vector3(width, hight, 0);
21
22        myMesh.SetVertices(myVertices);
23
24        myTriangles[0] = 0;
25        myTriangles[1] = 2;
26        myTriangles[2] = 1;
27        myTriangles[3] = 2;
28        myTriangles[4] = 3;
29        myTriangles[5] = 1;
30
31        myMesh.SetTriangles(myTriangles, 0);
32
33        //MeshFilterへの割り当て
34        meshFilter.mesh = myMesh;
35    }
36}

1void Update()
2    {
3        if (Input.GetKey(KeyCode.Space)) //スペースキーの入力
4        {
5            for(int i = 0; i < myVertices.Length; i++)
6            {
7                //頂点をずらす
8                myVertices[i] += new Vector3(Random.Range(-0.05f, 0.05f), Random.Range(-0.05f, 0.05f));
9            }
10            myMesh.SetVertices(myVertices);　//新しい頂点を割り当てる
11
12        }
13        
14    }