A* Pathfinding Tutorial 02

using UnityEngine;
using System.Collections;

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);
            }
        }
    }

    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];
    }

    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;
                Gizmos.DrawCube(n.worldPosition, Vector3.one * (nodeDiameter-.1f));
            }
        }
    }
}

public class Node {

    public bool walkable;
    public Vector3 worldPosition;

    public Node(bool _walkable, Vector3 _worldPos) {
        walkable = _walkable;
        worldPosition = _worldPos;
    }
}