Combined grid tracking, can handle particle list, terrain trees, GO colliders. Places collider / NavMeshObstacles. Uses trigger value to Invoke

GridTracking.cs

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


public class GridValue
{
    public enum EntityType
    {
        None,
        Tree,
        Rock
    }

    public string id;
    public Vector3 position;
    public EntityType entityType;
    public GameObject go;
}

public class Grid
{
    public static Dictionary<string, Grid> grids = new Dictionary<string, Grid>();
    private Dictionary<int, Dictionary<string, GridValue>> cells = new Dictionary<int, Dictionary<string, GridValue>>();
    private Dictionary<string, GridValue> objectIndex = new Dictionary<string, GridValue>();
    private Dictionary<string, int> cellsIndex = new Dictionary<string, int>();

    public static float coordOffset = 5000f;

    private int max;
    private int cellSize = 0;
    private float convFactor;
    private int width;
    private int cellCount;

    private List<GridValue> result;

    public Grid(int max, int cellSize)
    {
        this.max = max;
        this.cellSize = cellSize;
        this.convFactor = 1.0f / this.cellSize;
        this.width = (int)(this.max / this.cellSize);
        this.cellCount = this.width * this.width;
    }

    public int Count()
    {
        return objectIndex.Count;
    }

    public static Grid FindOrCreate(string id, int max, int cellSize)
    {
        if (!grids.ContainsKey(id))
        {
            grids[id] = new Grid(max, cellSize);
        }
        return grids[id];
    }

   private HashSet<int> __mcells;
    public HashSet<int> CellsWithinBounds(float x, float z)
    {
        x += coordOffset;
        z += coordOffset;

        //HashSet<int> 
            __mcells = new HashSet<int>();

        int offset = this.cellSize;

        int startX = (int)(x - offset);
        int startZ = (int)(z - offset);

        int endX = (int)(x + offset);
        int endZ = (int)(z + offset);

        for (int rowNum = startX; rowNum <= endX; rowNum += offset)
        {
            for (int colNum = startZ; colNum <= endZ; colNum += offset)
            {
                if (rowNum >= 0 && colNum >= 0)
                {
                    __mcells.Add(Hash(rowNum, colNum));
                }
            }
        }
        return __mcells;
    }

    private HashSet<int> __cells;
    private ICollection<GridValue> __gridValues;

    public List<GridValue> Neighbors(float x, float z, GridValue.EntityType entityType)
    {
        result = new List<GridValue>();
       // ICollection<GridValue> gridValues;
        __gridValues = null;
      

        //HashSet<int> 
            __cells = CellsWithinBounds(x, z);

            foreach (int cell in __cells)
        {
            __gridValues = GridValuesInCell(cell);
            if (__gridValues == null)
            {
                continue;
            }
            foreach (GridValue gridValue in __gridValues)
            {
                if (gridValue != null)
                {
                    if (entityType == GridValue.EntityType.None)
                    {
                        result.Add(gridValue);
                    }
                    else if (gridValue.entityType == entityType)
                    {
                        result.Add(gridValue);
                    }
                }
            }
        }
        return result;
    }

    public ICollection<GridValue> GridValuesInCell(int cell)
    {
        if (cells.ContainsKey(cell))
        {
            return cells[cell].Values;
        }
        else
        {
            return null;
        }
    }

    public void Set(GridValue gridValue)
    {
        bool hasExisting = false;
        int oldCellValue = -1;
        string id = gridValue.id;

        if (objectIndex.ContainsKey(id))
        {
            hasExisting = true;
            oldCellValue = cellsIndex[id];
        }

        int cell = Hash(gridValue.position.x + coordOffset, gridValue.position.z + coordOffset);

        Dictionary<string, GridValue> cellGridValues;

        if (hasExisting && oldCellValue != cell)
        {
            if (cells.ContainsKey(oldCellValue))
            {
                cellGridValues = cells[oldCellValue];
                if (cellGridValues.ContainsKey(id))
                {
                    cellGridValues.Remove(id);
                }
                if (cellGridValues.Count == 0)
                {
                    cells.Remove(oldCellValue);
                }
            }
        }
        cellsIndex[id] = cell;
        objectIndex[id] = gridValue;



        if (cells.ContainsKey(cell))
        {
            cellGridValues = cells[cell];
            cellGridValues[id] = gridValue;
        }
        else
        {
            cellGridValues = new Dictionary<string, GridValue>();
            cellGridValues[id] = gridValue;
            cells[cell] = cellGridValues;
        }
    }

    public int Hash(float x, float z)
    {
        return (int)((x * this.convFactor)) + (int)((z * this.convFactor)) * this.width;
    }
}

    public sealed class Objectpool2<T>
      where T : new()
    {
        private readonly int size;
        private readonly Queue<T> queue;
        private int count = 0;

        /// <summary>
        /// Initializes a new instance of the ObjectPool class.
        /// </summary>
        /// <param name="size">The size of the object pool.</param>
        public Objectpool2(int size)
        {
            this.size = size;
            queue = new Queue<T>();
        }

        public int Count()
        {
            return queue.Count;
        }

        /// <summary>
        /// Retrieves an item from the pool. 
        /// </summary>
        /// <returns>The item retrieved from the pool.</returns>
        public T Get()
        {
            if (queue.Count > 0)
            {
                T item = queue.Dequeue();
                count--;
                return item;
            }
            else
            {
                Debug.Log("Queue is empty count=" + count + " size=" + size);
                return default(T);
            }
        }

        /// <summary>
        /// Places an item in the pool.
        /// </summary>
        /// <param name="item">The item to place to the pool.</param>
        public void Put(T item)
        {
            queue.Enqueue(item);
            count++;
        }
    }

    public class GridTracking : MonoBehaviour
    {
        public int MaxCapacity = 5000;
        public int ObjectPoolSize = 200;
        public int SearchDistance = 20;

        public static int __MaxCapacity;
        public static int __ObjectPoolSize = 200;
        public static int __SearchDistance = 20;

        private Grid grid;
        private Dictionary<string, GridValue> objectIndex = new Dictionary<string, GridValue>(5000 * 4);
        private Objectpool2<GameObject> objectPool = new Objectpool2<GameObject>(200);
        private int removeCheckCount;
        Transform player;

        void Start()
        {
            objectIndex = new Dictionary<string, GridValue>(MaxCapacity * 4);
            objectPool = new Objectpool2<GameObject>(ObjectPoolSize);

            __MaxCapacity = MaxCapacity;
            __ObjectPoolSize = ObjectPoolSize;
            __SearchDistance = SearchDistance;

            if (GameManager.playerEntity == null)
            {
                player = GameObject.Find("TestController").transform; // or w/e
            }
            else
            {
                player = GameManager.playerEntity.transform;  // I created a placeholder static GameManager Class
            }
            grid = Grid.FindOrCreate("terrain", MaxCapacity, SearchDistance);

            StartRepeatingCheckForParticleCount();

        }

        private void StartRepeatingCheckForParticleCount()
        {
            InvokeRepeating("CreateGridsWhenParticlesPlaced", 0, 0.05F); // skim edges
        }

        private void CreateGridsWhenParticlesPlaced()
        {

            // Now actually create some stuff. 
            // Once the value is indicated in the manager class that we are ready.

            if (!GameManager.TreesPlaced)
            {
                return;
            }
            CreateGrid();
            CreatePool();
            InvokeRepeating("UpdateGrid", 0.005f, 2f);

            CancelInvoke("CreateGridsWhenParticlesPlaced");
            Debug.Log("Cancelled CreateGridsWhenParticlesPlaced as complete ");
        }

        public static void SetMeshColliders(GameObject go, bool enabled)
        {
            MeshCollider col;

            col = go.GetComponent<MeshCollider>() as MeshCollider;
            if (col == null)
            {
                foreach (Transform s in go.transform)
                {
                    col = s.GetComponent<MeshCollider>() as MeshCollider;
                    if (col != null)
                    {
                        col.enabled = enabled;
                    }
                }
            }
            else
            {
                col.enabled = enabled;
            }
        }

        public static void CreateGrid()
        {
            Grid grid = Grid.FindOrCreate("terrain", __MaxCapacity, __SearchDistance);

            // GAMEOBJECT IN A PARENT VERSION

            foreach (Transform t in GameObject.Find("Items").transform)
            {
                foreach (Transform s in t.gameObject.transform)
                {
                    GridValue gridValue = new GridValue();
                    gridValue.position = s.position;
                    gridValue.id = "rock+" + s.name;
                    gridValue.go = s.gameObject;
                    gridValue.entityType = GridValue.EntityType.Rock;
                    grid.Set(gridValue);
                }
            }

            // TERRAIN TREE VERSION

            //int treecount = 0;
            //foreach (Transform t in GameObject.Find("Terrains").transform)
            //{
            //    Terrain terrain = t.GetComponent<Terrain>() as Terrain;
            //    foreach (TreeInstance ti in terrain.terrainData.treeInstances)
            //    {
            //        Vector3 tpos = (Vector3.Scale(terrain.terrainData.size, ti.position) + t.position);
            //        GridValue gridValue = new GridValue();
            //        gridValue.position = tpos;
            //        gridValue.id = "tree_" + treecount;
            //        gridValue.entityType = GridValue.EntityType.Tree;
            //        grid.Set(gridValue);
            //        treecount++;
            //    }
            //}

            // PARTICLE TREE VERSION

            int treecount = 0;
            ParticleSystem.Particle p;

            for (int i = 0; i < PlaceParticles.ParticleList.Length; i++)
            {
                p = PlaceParticles.ParticleList[i];
                Vector3 tpos = p.position;

                GridValue gridValue = new GridValue();
                gridValue.position = tpos;
                gridValue.id = "tree_" + treecount;
                gridValue.entityType = GridValue.EntityType.Tree;
                grid.Set(gridValue);
                treecount++;

            }


//            Debug.Log("Grid size " + grid.Count());
        }

        void CreatePool()
        {
            GameObject trees = new GameObject();
            trees.name = "trees";
            for (int i = 0; i < __ObjectPoolSize; i++)
            {
                GameObject go = new GameObject();
                go.transform.parent = trees.transform;
                go.tag = "harvestable";
                go.name = "Tree";
                go.transform.position = Vector3.zero;
                Rigidbody rigid = go.AddComponent<Rigidbody>();
                rigid.isKinematic = true;
                CapsuleCollider col = go.AddComponent<CapsuleCollider>() as CapsuleCollider;
                col.center = Vector3.zero;
                col.height = 10f;
                col.radius = 0.4f;
                col.direction = 1;
                col.enabled = false;
                NavMeshObstacle nmo = go.AddComponent<NavMeshObstacle>() as NavMeshObstacle;
                nmo.center = Vector3.zero;
                nmo.shape = NavMeshObstacleShape.Capsule;
                nmo.height = 10f;
                nmo.radius = 0.4f;
                nmo.enabled = false;


                objectPool.Put(go);
            }

        }
        // Update is called once per frame
        void UpdateGrid()
        {
            List<GridValue> gridValues = grid.Neighbors(player.position.x, player.position.z, 0);
            if (gridValues.Count > 0)
            {
                AddNew(gridValues);

                if (removeCheckCount >= 1)
                {
                    removeCheckCount = 0;
                    RemoveOld(gridValues);
                    //Debug.Log ("Gridvalues count " + gridValues.Count + " indexcount " + objectIndex.Count + " queuecount " + objectPool.Count ());
                }
                else
                {
                    removeCheckCount++;
                }
            }
        }

        void AddNew(List<GridValue> gridValues)
        {
            int addCount = 0;
            foreach (GridValue gridValue in gridValues)
            {
                if (AddCollider(gridValue))
                {
                    addCount++;
                }

                if (addCount > 10)
                {
                    return;
                }
            }
        }

        private GridValue _tempGridValueReference;

        void RemoveOld(List<GridValue> gridValues)
        {
            HashSet<GridValue> toCheck = new HashSet<GridValue>(gridValues);

            List<string> idsToRemove = new List<string>();


            foreach (GridValue old in objectIndex.Values)
            {
                if (!toCheck.Contains(old))
                {
                    idsToRemove.Add(old.id);
                }
            }

            int removeCount = 0;

            for (int i = 0; i < idsToRemove.Count; i++)
            {          
                GridValue gridValue = objectIndex[idsToRemove[i]];
                RemoveCollider(gridValue);
                objectIndex.Remove(idsToRemove[i]);
                removeCount++;

                if (removeCount > 20)
                {
                    break;
                }
            }

            //if (removeCount > 0)
            //{
            //    Debug.Log(removeCount);  // unelide to get a readout
            //}
        }

        void RemoveCollider(GridValue gridValue)
        {
            if (gridValue.entityType == GridValue.EntityType.Rock)
            {
                SetMeshColliders(gridValue.go, false);
            }
            else if (gridValue.entityType == GridValue.EntityType.Tree)
            {
                GameObject go = gridValue.go;
                go.transform.position = Vector3.zero;
                go.GetComponent<CapsuleCollider>().enabled = false;
                go.GetComponent<NavMeshObstacle>().enabled = false;
                objectPool.Put(go);
                gridValue.go = null;
            }
        }

        bool AddCollider(GridValue gridValue)
        {

            if (objectIndex.ContainsKey(gridValue.id))
            {
                return false;
            }

            if (gridValue.entityType == GridValue.EntityType.Rock)
            {
                SetMeshColliders(gridValue.go, true);
            }
            else if (gridValue.entityType == GridValue.EntityType.Tree)
            {
                GameObject go = objectPool.Get();
                go.transform.position = gridValue.position;
                go.GetComponent<CapsuleCollider>().enabled = true;
                go.GetComponent<NavMeshObstacle>().enabled = true;
                gridValue.go = go;
            }
            objectIndex[gridValue.id] = gridValue;
            return true;
        }
    }

I've added a Remove(id) method to the Grid, and it seems to work, but I'm not sure if there are any side effects I'm not noticing with it:

    public void Remove(int id)
    {
        var cellValue = cellsIndex[id];
        cells.Remove(cellValue);
        objectIndex.Remove(id);
        cellsIndex.Remove(id);
    }

Do you think I should add anything to it?

Btw, I changed the ids to integers instead of strings.

Err. Looks okay.

I would be very happy to see a gist of it :)