使用Unity实现A*寻路算法

在寻路过程中有许多的影响因素，例如时间，能量，金钱，地形，距离的美好。对于起始节点与目标节点之间的每一条可行路径，都可以用代价的大小来描述。而A*算法的任务就是选取代价最小的那条路径

先介绍导航图(参考于Unity3D 人工智能编程精粹一书)：

1.基于单元的导航图，寻路使以网格为单位进行的。如果单个正方形过大，网格很粗糙，那么很难得到好的路径，如果网格很精细，那么虽然会寻找到很好的路径，但这时需要存储和搜索大量的节点，对内存要求高，而且也很影响效率。

2.基于可视点导航图，一般由场景设计者在场景中手工放置一些路径点，然后由设计人员测试这些“路径点”之间的可视性

3.创建导航网格：导航网格将游戏场景中的可行走区域划分成凸多边形。导航网格表示出了可行走区域的真实几何关系，使一个非均匀网格。Unity3D自带的寻路系统就建立在导航网格的基础上。利用A*算法，可以找到路径所经过的那么多边形。如果直接把这些多边形的中心连接起来，就会得到从起始点到目标点的一条路径。下面用Unity3D来实现。

首先介绍A*寻路算法：

点击打开链接

下面是在Unity中实现的效果

绿色部分代表初始点，红色部分代表目标点，蓝色部分代表障碍物，灰色部分代表路径，白色部分代表整个虚拟网格

再给出他们的实现代码：

Ponit.cpp

using System.Collections;using System.Collections.Generic;using UnityEngine;public class Point {    public Point Parent { get; set; } //父节点    //F=G+H    public int F { get; set; }    public int G { get; set; }    public int H { get; set; }    //Position    public int X { get; set; }    public int Y { get; set; }    //障碍物    public bool IsWall { get; set; }    //非路径非障碍物，渲染成白色    public bool IsWhite { get; set; }    public Point(int x,int y , Point parent = null)    {        this.X = x;        this.Y = y;        this.Parent = parent;        IsWall = false;        IsWhite = true;    }    //更新父节点    public void UpdateParent(Point parent,int g)    {        this.Parent = parent;        this.G = g;        F = G + H;    }}

AStar.cpp

using System.Collections;using System.Collections.Generic;using UnityEngine;public class AStar : MonoBehaviour {    private const int mapWith = 8;    private const int mapHeight = 8;    private Point[,] map = new Point[mapWith, mapHeight];// Use this for initializationvoid Start () {        InitMap();  //虚拟化地图        //定义初试点和目的点        Point start = map[2,3];        Point end = map[7, 4];        //寻找路径        FindPath(start, end);        //显示路径        ShowPath(start,end);        //List<Point> l= GetSurroundPoints(map[0, 0]);        //foreach(Point p in l)        //{        //    Debug.Log(p.X + "-" + p.Y);        //}}    private void ShowPath(Point start,Point end)    {        Point temp = end;        //从目的点倒回出发点来显示路径        while (true)        {            //Debug.Log(temp.X + "," + temp.Y);            Color c = Color.gray;            if (temp == start)            {                c = Color.green;            }else if (temp == end)            {                c = Color.red;            }            CreateCube(temp.X, temp.Y, c);            temp.IsWhite = false;            if (temp.Parent == null)                break;            temp = temp.Parent;                    }        for (int x = 0; x < mapWith; x++)        {            for (int y = 0; y < mapHeight; y++)            {                if (map[x, y].IsWall)                {                    CreateCube(x, y, Color.blue);                }                if (map[x, y].IsWhite==true )                {                    CreateCube(x, y, Color.white);                }            }        }    }               private void CreateCube(int x,int y,Color color)    {        GameObject go =  GameObject.CreatePrimitive(PrimitiveType.Cube);        go.transform.position = new Vector3(x, y, 0);        go.GetComponent<Renderer>().material.color = color;    }    private void InitMap()    {        for(int x = 0; x < mapWith; x++)        {            for(int y = 0; y < mapHeight; y++)            {                map[x, y] = new Point(x,y);            }        }        map[4, 2].IsWall = true;        map[4, 3].IsWall = true;        map[4, 4].IsWall = true;        map[4, 5].IsWall = true;        map[4, 6].IsWall = true;        map[4, 2].IsWhite = false;        map[4, 3].IsWhite = false;        map[4, 4].IsWhite = false;        map[4, 5].IsWhite = false;        map[4, 6].IsWhite = false;    }    private void FindPath(Point start,Point end)    {        List<Point> openList = new List<Point>();//openList表，等待考察的节点的优先级队列        List<Point> closeList = new List<Point>();//已经考察过，无须再考察的节点列表        openList.Add(start);        while (openList.Count > 0)        {            Point point = FindMinFOfPoint(openList); //在openList表中选择F最小的值加入closeList表中            openList.Remove(point);            closeList.Add(point);            List<Point> surroundPoints = GetSurroundPoints(point); //寻找周围点            PointsFilter(surroundPoints, closeList); //过滤掉close表中已有的节点            foreach(Point surroundPoint in surroundPoints)            {                if (openList.IndexOf(surroundPoint) > -1) //如果在openList已经存在，比较                {                    int nowG =(int) CalcG(surroundPoint, point);                    if(nowG< surroundPoint.G)                    {                        surroundPoint.UpdateParent(point,nowG);                    }                }                else                {                    surroundPoint.Parent = point;                    CalcF(surroundPoint, end);                    openList.Add(surroundPoint);                }            }            //判断一下            if (openList.IndexOf(end) > -1) //如果到达了目的地，break            {                break;            }        }    }    private void PointsFilter(List<Point> src,List<Point> closeList)    {        foreach(Point p in closeList)        {            if (src.IndexOf(p) > -1)            {                src.Remove(p);            }        }    }    private List<Point> GetSurroundPoints(Point point)    {        Point up = null, down = null, left = null, right = null;        Point lu = null, ru = null, ld = null, rd = null;        if (point.Y < mapHeight- 1)        {            up = map[point.X, point.Y + 1];        }        if (point.Y > 0)        {            down = map[point.X, point.Y - 1];        }        if (point.X > 0)        {            left = map[point.X - 1, point.Y];        }        if(point.X <mapWith-1)        {            right = map[point.X + 1, point.Y];        }        if (up != null && left != null)        {            lu = map[point.X - 1, point.Y + 1];        }        if (up != null && right != null)        {            ru = map[point.X + 1, point.Y + 1];        }        if (down != null && left != null)        {            ld = map[point.X - 1, point.Y - 1];        }        if (down != null && right != null)        {            rd = map[point.X + 1, point.Y - 1];        }        List<Point> list = new List<Point>();        if (down != null && down.IsWall == false)        {            list.Add(down);        }        if (up != null && up.IsWall == false)        {            list.Add(up);        }        if (left != null && left.IsWall == false)        {            list.Add(left);        }        if (right != null && right.IsWall == false)        {            list.Add(right);        }        if (lu != null && lu.IsWall == false && left.IsWall == false && up.IsWall == false)        {            list.Add(lu);        }        if (ld != null && ld.IsWall == false && left.IsWall == false && down.IsWall == false)        {            list.Add(ld);        }        if (ru != null && ru.IsWall == false && right.IsWall == false && up.IsWall == false)        {            list.Add(ru);        }        if (rd != null && rd.IsWall == false && right.IsWall == false && down.IsWall == false)        {            list.Add(rd);        }        return list;    }    private Point FindMinFOfPoint(List<Point> openList)    {        int f = int.MaxValue;        Point temp = null;        foreach(Point p in openList)        {            if (p.F < f)            {                temp = p;                f = p.F;            }        }        return temp;    }    private float CalcG(Point now,Point parent)    {        return  Vector2.Distance(new Vector2(now.X, now.Y), new Vector2(parent.X, parent.Y)) + parent.G;    }    private void CalcF(Point now,Point end)    {        //F = G + H        int h = Mathf.Abs(end.X - now.X) + Mathf.Abs(end.Y - now.Y);        int g = 0;        if (now.Parent == null)        {            g = 0;        }        else        {            g=(int)Vector2.Distance(new Vector2(now.X, now.Y), new Vector2(now.Parent.X, now.Parent.Y)) + now.Parent.G;        }        int f = g + h;        now.F = f;        now.G = g;        now.H = h;    }}