A* Pathfinding Tutorial 03

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

public class Pathfinding : MonoBehaviour {

    public Transform seeker, target;

    Grid grid;

    void Awake() {
        grid = GetComponent<Grid>();
    }

    void Update() {
        FindPath(seeker.position,target.position);
    }

    void FindPath(Vector3 startPos, Vector3 targetPos) {
        Node startNode = grid.NodeFromWorldPoint(startPos);
        Node targetNode = grid.NodeFromWorldPoint(targetPos);

        List<Node> openSet = new List<Node>();
        HashSet<Node> closedSet = new HashSet<Node>();
        openSet.Add(startNode);

        while (openSet.Count > 0) {
            Node currentNode = openSet[0];
            for (int i = 1; i < openSet.Count; i ++) {
                if (openSet[i].fCost < currentNode.fCost || openSet[i].fCost == currentNode.fCost && openSet[i].hCost < currentNode.hCost) {
                    currentNode = openSet[i];
                }
            }

            openSet.Remove(currentNode);
            closedSet.Add(currentNode);

            if (currentNode == targetNode) {
                RetracePath(startNode,targetNode);
                return;
            }

            foreach (Node neighbour in grid.GetNeighbours(currentNode)) {
                if (!neighbour.walkable || closedSet.Contains(neighbour)) {
                    continue;
                }

                int newMovementCostToNeighbour = currentNode.gCost + GetDistance(currentNode, neighbour);
                if (newMovementCostToNeighbour < neighbour.gCost || !openSet.Contains(neighbour)) {
                    neighbour.gCost = newMovementCostToNeighbour;
                    neighbour.hCost = GetDistance(neighbour, targetNode);
                    neighbour.parent = currentNode;

                    if (!openSet.Contains(neighbour))
                        openSet.Add(neighbour);
                }
            }
        }
    }

    void RetracePath(Node startNode, Node endNode) {
        List<Node> path = new List<Node>();
        Node currentNode = endNode;

        while (currentNode != startNode) {
            path.Add(currentNode);
            currentNode = currentNode.parent;
        }
        path.Reverse();

        grid.path = path;

    }

    int GetDistance(Node nodeA, Node nodeB) {
        int dstX = Mathf.Abs(nodeA.gridX - nodeB.gridX);
        int dstY = Mathf.Abs(nodeA.gridY - nodeB.gridY);

        if (dstX > dstY)
            return 14*dstY + 10* (dstX-dstY);
        return 14*dstX + 10 * (dstY-dstX);
    }
}

public class Grid : MonoBehaviour {

    public LayerMask unwalkableMask;
    public Vector2 gridWorldSize;
    public float nodeRadius;
    Node[,] grid;

    float nodeDiameter;
    int gridSizeX, gridSizeY;

    void Start() {
        nodeDiameter = nodeRadius*2;
        gridSizeX = Mathf.RoundToInt(gridWorldSize.x/nodeDiameter);
        gridSizeY = Mathf.RoundToInt(gridWorldSize.y/nodeDiameter);
        CreateGrid();
    }

    void CreateGrid() {
        grid = new Node[gridSizeX,gridSizeY];
        Vector3 worldBottomLeft = transform.position - Vector3.right * gridWorldSize.x/2 - Vector3.forward * gridWorldSize.y/2;

        for (int x = 0; x < gridSizeX; x ++) {
            for (int y = 0; y < gridSizeY; y ++) {
                Vector3 worldPoint = worldBottomLeft + Vector3.right * (x * nodeDiameter + nodeRadius) + Vector3.forward * (y * nodeDiameter + nodeRadius);
                bool walkable = !(Physics.CheckSphere(worldPoint,nodeRadius,unwalkableMask));
                grid[x,y] = new Node(walkable,worldPoint, x,y);
            }
        }
    }

    public List<Node> GetNeighbours(Node node) {
        List<Node> neighbours = new List<Node>();

        for (int x = -1; x <= 1; x++) {
            for (int y = -1; y <= 1; y++) {
                if (x == 0 && y == 0)
                    continue;

                int checkX = node.gridX + x;
                int checkY = node.gridY + y;

                if (checkX >= 0 && checkX < gridSizeX && checkY >= 0 && checkY < gridSizeY) {
                    neighbours.Add(grid[checkX,checkY]);
                }
            }
        }

        return neighbours;
    }


    public Node NodeFromWorldPoint(Vector3 worldPosition) {
        float percentX = (worldPosition.x + gridWorldSize.x/2) / gridWorldSize.x;
        float percentY = (worldPosition.z + gridWorldSize.y/2) / gridWorldSize.y;
        percentX = Mathf.Clamp01(percentX);
        percentY = Mathf.Clamp01(percentY);

        int x = Mathf.RoundToInt((gridSizeX-1) * percentX);
        int y = Mathf.RoundToInt((gridSizeY-1) * percentY);
        return grid[x,y];
    }

    public List<Node> path;
    void OnDrawGizmos() {
        Gizmos.DrawWireCube(transform.position,new Vector3(gridWorldSize.x,1,gridWorldSize.y));

        if (grid != null) {
            foreach (Node n in grid) {
                Gizmos.color = (n.walkable)?Color.white:Color.red;
                if (path != null)
                    if (path.Contains(n))
                        Gizmos.color = Color.black;
                Gizmos.DrawCube(n.worldPosition, Vector3.one * (nodeDiameter-.1f));
            }
        }
    }
}

public class Node {

    public bool walkable;
    public Vector3 worldPosition;
    public int gridX;
    public int gridY;

    public int gCost;
    public int hCost;
    public Node parent;

    public Node(bool _walkable, Vector3 _worldPos, int _gridX, int _gridY) {
        walkable = _walkable;
        worldPosition = _worldPos;
        gridX = _gridX;
        gridY = _gridY;
    }

    public int fCost {
        get {
            return gCost + hCost;
        }
    }
}