PerlinGridPlacer

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

public class PerlinGridPlacer : EditorWindow
{
    private const string RootObjectName = "PerlinGridPlacerRESULT";

    [MenuItem("Window/Tools/PerlinGridPlacer")]
    public static void ShowWindow()
    {
        EditorWindow.GetWindow(typeof(PerlinGridPlacer));
    }

    private GameObject prefab;
    private Transform origin;

    private int cellsX = 50;
    private int cellsY = 50;
    private float cellStepDist = 5f;

    private float perlinScale = 0.15f;
    private float perlinTreshold = 0.1f;

    void OnGUI()
    {
        prefab = EditorGUILayout.ObjectField("Prefab:", prefab, typeof(GameObject), false) as GameObject;
        origin = EditorGUILayout.ObjectField("Origin:", origin, typeof(Transform), true) as Transform;

        cellsX = EditorGUILayout.IntField("CellsX", cellsX);
        cellsY = EditorGUILayout.IntField("CellsY", cellsY);

        cellStepDist = EditorGUILayout.FloatField("cellStepDist", cellStepDist);

        perlinScale = EditorGUILayout.FloatField("PerlinScale", perlinScale);
        perlinTreshold = EditorGUILayout.FloatField("PerlinTreshold", perlinTreshold);

        if (GUILayout.Button("Place!")) DoMagic();
    }

    public void DoMagic()
    {
        Clear();

        GameObject root = new GameObject(RootObjectName);

        float xOff = cellsX * cellStepDist * 0.5f;
        float zOff = cellsY * cellStepDist * 0.5f;

        float scaler = Random.value * perlinScale;

        for (int x = 0; x < cellsX; x++)
        {
            for (int z = 0; z < cellsY; z++)
            {
                if (Mathf.PerlinNoise(x * scaler, z * scaler) < perlinTreshold)
                {
                    Vector3 pos = new Vector3(cellStepDist * x - xOff, 0, cellStepDist * z - zOff);
                    AddObject(pos, root.transform);
                }
            }
        }
    }

    private void AddObject(Vector3 offset, Transform parent)
    {
        GameObject obj = PrefabUtility.InstantiatePrefab(prefab) as GameObject;
        
        obj.transform.position = origin.position + offset;
        obj.transform.parent = parent;
    }

    public void Clear()
    {
        GameObject root = GameObject.Find(RootObjectName);
        if (root) DestroyImmediate(root);
    }
}