一、创建空游戏对象

二、创建绘制脚本，并附给新建游戏对象

using System.Collections;
using System.Collections.Generic;
using UnityEngine;public class NewBehaviourScript : MonoBehaviour
{//记录顶点数组private Vector3[] vertices;//三角形索引private int[] triangles;//记录顶点数private int count;private Mesh mesh;private List<Vector3> list;// Start is called before the first frame updatevoid Start(){//添加MeshFiltergameObject.AddComponent<MeshFilter>();//添加MeshRenderergameObject.AddComponent<MeshRenderer>();//new一个链表list = new List<Vector3>();//获得Meshmesh = GetComponent<MeshFilter>().mesh;//修改Material的颜色GetComponent<MeshRenderer>().material.color = Color.green;//选择材质的shader//  GetComponent<MeshRenderer>().material.shader = Shander.Find("Transparent/Diffuse");//清空所有点用于初始化mesh.Clear();}// Update is called once per framevoid Update(){//点击鼠标左键if (Input.GetMouseButton(0)){//顶点数+1count++;//将鼠标点击的屏幕坐标转换为世界坐标，添加到list链表中list.Add(Camera.main.ScreenToWorldPoint(new Vector3(Input.mousePosition.x, Input.mousePosition.y, 0.8f)));}//如果顶点数>=3 开始渲染if(count >= 3){//初始化顶点数组vertices = new Vector3[count];//将list坐标赋值给顶点坐标数组for(int i = 0; i < count; i++){vertices[i] = list[i];}//三角形网格数int trangle_count = count - 2;//三角形索引triangles = new int[3 * trangle_count];for(int i =0;i< trangle_count; i++){triangles[3 * i] = 0;triangles[3 * i + 1] = i + 2;triangles[3 * i + 2] = i + 1;}//设置顶点坐标mesh.vertices = vertices;mesh.triangles = triangles;}}
}

效果如下：