游戏寻路之A*寻路

A*算法

A*算法，A*（A-Star)算法是一种静态路网中求解最短路径最有效的直接搜索方法，也是解决许多搜索问题的有效算法。算法中的距离估算值与实际值越接近，最终搜索速度越快

基础知识直接略过

重温了下服务器的寻路算法，现存代码一共两种，一种是A*方格网格寻路(弃用，原因有遗留bug)，另一种是三角形网格寻路(现用，听师傅这个效率较高，待会研究)。

此文主要是A*寻路的实现。

由于客户端有比较形象的表现方式，笔者就把A*在Unity里做了实现，有时候在想到底是酒不好喝还是游戏不好玩，还是navmesh不好用。ps:一般情况，寻路是放到服务器上的，客户端只要傻傻的当个演员就好了。

码钳约定

1. 基于网格（方格）
2. 方格长度为1，间距为1
3. A*基本函数 F=G+H，估价函数GetCost()使用的欧几里得距离（二维平面真实距离）而非曼哈顿距离，见GetCost()详情，估价函数可以有很多选择视情况而定。

码钳准备

1. 路面方片
2. 人物模型
3. 目标方片
4. 阻挡方片
5. 
   以上除了人物模型（项目里的拿来用了）都是自己手拼的

码

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


/// A*寻路简单实现
/// author by wc 2017/5/25  

//点
public class Point
{
    public int x;
    public int y;
    public Point(int x,int y) {
        this.x = x;
        this.y = y;
    }
    public bool Equals(Point point) {
        return x == point.x && y == point.y;
    }
}

//寻路节点
public class Node :IComparable
{
    public Point point;

    public Node parentNode;
    public int sourceCost
    { 
        get;
        set;
    }
    private Node() { }
    public Node(Point point) { this.point = point; }
    public int destinationCost
    {
        get;
        set;
    }
    public int getH{
        get { return sourceCost + destinationCost; }
    }
    public int CompareTo(object obj)
    {
        Node node = (Node)obj;
        if (getH < node.getH)
        {
            return -1;
        }
        else if (getH == node.getH)
        {
            return 0;
        }else{
            return 1;
        }
    }
    public int GetCost(Node node)
    {
        int m = node.point.x - point.x;
        int n = node.point.y - point.y;
        return (int)Math.Sqrt(m * m + n * n);
    }
    public bool Equals(Node node)
    {
        return point.Equals(node.point);
    }
}
//链表(用于初始化开放and关闭列表)
public class PathList : LinkedList
{
    //开放列表专用Add
    public void Add(Node node){
        Enumerator it = this.GetEnumerator();
        while(it.MoveNext()){
            Node oldNode = it.Current;
            if (node.CompareTo(oldNode) <= 0)
            {
                //链表插入操作
                LinkedListNode priNode = Find(oldNode);
                LinkedListNode curNode = AddBefore(priNode, node);
                return;
            }
        }
        AddLast(node);
    }
    public bool Contains(Node node)
    {
        Enumerator it = this.GetEnumerator();
        while (it.MoveNext())
        {
            Node oldNode = it.Current;
            if (oldNode.Equals(node))
            {
                return true;
            }
        }
        return false;
    }
}
//主类
public class APathFinder : MonoBehaviour
{

    #region 初始化值必填

    public GameObject pathPrefab; //普通路面

    public GameObject playerPrefab;  //玩家模型

    public GameObject obstaclePrefab;  //阻挡模型

    public GameObject aimPrefab;  // 目标模型

    public int[] originPos;   //玩家初始位置

    public int[] destinationPos;  //目标位置

    public bool isMove = false;//为true则开始寻路

    public int hitCount = 5; //碰撞体（模拟）个数

    #endregion

    private static int maxX = 10;   //X最大值

    private static int maxY = 10;   //Y最大值

    private Point[] hitData = null;//碰撞体信息

    private PathList openList = new PathList();  //开放列表

    private PathList closeList = new PathList();  //关闭列表

    private static Quaternion pathRotation = Quaternion.Euler( new Vector3(90, 0, 0)); //路面旋转

    private GameObject player; //玩家对象

    private Vector3 curAimPos = Vector3.zero;//玩家当前寻路的目标点

    private LinkedList path = new LinkedList();//FindPath的结果，路线！！

    private Animator animitor;//状态机

    private LineRenderer line;

    private int lineCount = 0;
    private int lineIndex = 0;

    /// 

    ///  寻路函数
    /// 
    /// 
    /// 
    /// 
    private LinkedList FindPath(Point origination, Point destination)
    {
        try
        {
            Node firstNode = new Node(origination);
            Node destiNode = new Node(destination);
            firstNode.sourceCost = 0;
            firstNode.destinationCost = firstNode.GetCost(destiNode);
            openList.AddFirst(firstNode);
            Node neighborNode = null;
            while (openList.Count > 0)
            {
                LinkedListNode firstLinkedListNode = openList.First;
                Node firstNodeTruth = firstLinkedListNode.Value;
                openList.RemoveFirst();

                if (firstNodeTruth.Equals(destiNode))
                {
                    openList.Clear();
                    closeList.Clear();
                    return makePath(firstNodeTruth);
                }
                else
                {
                    closeList.AddLast(firstNodeTruth);
                    List limitNodes = getLimitNodeList(firstNodeTruth);
                    if (limitNodes.Count > 0)
                    {
                        for (int i = 0; i < limitNodes.Count; i++)
                        {
                            neighborNode = limitNodes[i];
                            if (!openList.Contains(neighborNode) && !closeList.Contains(neighborNode) && !isHit(neighborNode))
                            {
                                neighborNode.sourceCost = firstNodeTruth.sourceCost + 1;
                                neighborNode.destinationCost = neighborNode.GetCost(destiNode);
                                neighborNode.parentNode = firstNodeTruth;
                                openList.Add(neighborNode);
                            }
                        }
                    }
                }
            }

        }
        catch (Exception e)
        {
            LogManager.Log("FindPath Error:" + e.StackTrace, LogType.Error);
        }
        return null;
    }
    /// 

    /// 获得周围点
    /// 
    /// 
    /// 
    public List getLimitNodeList(Node node)
    {

        List limitNode = new List();
        int x = node.point.x;
        int y = node.point.y;


        int prex = 0;
        int prey = 0;

        //1
        prex = x - 1;
        prey = y;
        if (prex < 0 || prex >= maxX)
        {
            prex = x;
        }
        if (prex != x)
        {
            limitNode.Add(new Node(new Point(prex, prey)));
        }

        //2
        prex = x + 1;
        prey = y;
        if (prex < 0 || prex >= maxX)
        {
            prex = x;
        }
        if (prex != x)
        {
            limitNode.Add(new Node(new Point(prex, prey)));
        }
        //3
        prex = x;
        prey = y - 1;
        if (prey < 0 || prey >= maxY)
        {
            prey = y;
        }
        if (prey != y)
        {
            limitNode.Add(new Node(new Point(prex, prey)));
        }
        //4
        prex = x;
        prey = y + 1;
        if (prey < 0 || prey >= maxY)
        {
            prey = y;
        }
        if (prey != y)
        {
            limitNode.Add(new Node(new Point(prex, prey)));
        }
        return limitNode;
    }
    /// 

    /// 检查碰撞，出界
    /// 
    /// 
    /// 
    private bool isHit(Node node)
    {
        if (node.point.x < 0 || node.point.x > maxX || node.point.y < 0 || node.point.y > maxY)
        {
            return false;
        }
        for (int i = 0; i < hitData.Length; i++)
        {
            if (hitData[i] == null)
            {
               continue;
            }
            if (hitData[i].Equals(node.point))
            {
                return true;
            }
        }
        return false;
    }
    /// 

    /// 生成路线
    /// 
    /// 
    /// 
    private LinkedList makePath(Node node)
    {

        LinkedList path = new LinkedList();

        while (node != null && node.parentNode != null)
        {
            path.AddFirst(node);
            node = node.parentNode;
        }
        path.AddFirst(node);
        return path;
    }

    /// 

    /// 以下是行为表现,代码丑陋^_^
    /// 
    void Start() {

        hitData = new Point[hitCount];
        InitMapAndObjs();
        path = FindPath(new Point(originPos[0], originPos[1]), new Point(destinationPos[0], destinationPos[1]));
        line = player.GetComponent();
        lineCount = path.Count;
        line.SetVertexCount(lineCount);
    }
    void Update() {
        if (isMove)
        {
            Move();
        }
    }
    private void InitMapAndObjs() {
        if (pathPrefab == null || playerPrefab == null || obstaclePrefab == null || aimPrefab == null)
        {
            return;
        }
        int hitCountPre = 0;

        for (int i = 0; i < maxX; i++)
        {
            for (int j = 0; j < maxY; j++)
            {
                if (originPos[0] == i && originPos[1] == j)
                {
                    player = Instantiate(playerPrefab, new Vector3(i, 0, j), Quaternion.identity) as GameObject;
                    Instantiate(obstaclePrefab, new Vector3(i, 0, j), pathRotation);
                    animitor = player.GetComponent();
                    animitor.SetBool("run",false);
                }
                else if (destinationPos[0] == i && destinationPos[1] == j)
                {
                    Instantiate(aimPrefab, new Vector3(i, 0, j), pathRotation);
                }
                else if ((i == 5 && j >= 1) || (i == 7 && j >= 3 && j < 7) || (j == 6 && i > 2 && i < 6) || (j == 1 && i >= 7 && i <= 8 ) && hitCountPre < hitCount)
                {
                    Instantiate(obstaclePrefab, new Vector3(i, 0, j), pathRotation);
                    hitData[hitCountPre] = new Point(i,j);
                    hitCountPre++;
                }
                else
                {
                    Instantiate(pathPrefab, new Vector3(i, 0, j), pathRotation);
                }
            }
        }
        curAimPos = player.transform.position;
    }


    private bool isArrive() { 
        if(player == null){
            return false;
        }
        return player.transform.position == curAimPos;
    }
    private void Move() { 
        if(player != null){

            if (!animitor.GetBool("run"))
            {
                animitor.SetBool("run", true);
            }

            if (!isArrive())
            {
                player.transform.LookAt(curAimPos);
                player.transform.position = Vector3.MoveTowards(player.transform.position, curAimPos, Time.deltaTime * 3);
                return;
            }
            if (path.First != null)
            {
                Node node = path.First.Value;
                curAimPos = new Vector3(node.point.x, 0, node.point.y);
                print(curAimPos);
                path.RemoveFirst();
                line.SetPosition(lineIndex, new Vector3(curAimPos.x, 0.5f, curAimPos.z));
                lineIndex++;
            }
            else {
                animitor.SetBool("run", false);
                isMove = false;
            }
        }
    }

}

效果图

完，别忘了听我分享的歌曲