A simple Unity Editor tool that converts trees in a Terrain into GameObjects

TreeToGameObjectConverter.cs

// This is a simple Unity Editor tool that converts trees in a Terrain (with multi-terrain support) into GameObjects.
// It should be placed in the Assets/Editor directory. Do not use it without any VCS!
// Copyright (c) 2023 Michał Biernat @m-biernat, licensed under the MIT License.

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

public class TreeToGameObjectConverter : EditorWindow
{
    readonly string _rootName = "CONVERTED TREES";
    GameObject _root;

    List<Terrain> _terrainList; 

    [MenuItem("Tools/Tree to GameObject Converter")]
    public static void ShowEditorWindow()
    {
        EditorWindow window = GetWindow<TreeToGameObjectConverter>();
        window.titleContent = new GUIContent("Tree to GameObject Converter");
    }

    void OnGUI()
    {
        if (GUILayout.Button("Add Selected Terrain Objects", GUILayout.Height(40)))
            AddSelectedTerrainObjects();

        GUILayout.Space(10);

        GUILayout.BeginHorizontal();
        GUILayout.FlexibleSpace();
        
        if (_terrainList == null || _terrainList.Count == 0)
            GUILayout.Label("No Terrain Objects Selected");
        else
            GUILayout.Label($"Currently Selected {_terrainList.Count} Terrain Objects");
        
        GUILayout.FlexibleSpace();
        GUILayout.EndHorizontal();

        GUILayout.Space(10);

        if (GUILayout.Button($"Convert Trees into GameObjects", GUILayout.Height(40)))
            ConvertTreesToGameObjects();

        if (GUILayout.Button($"Remove \"{_rootName}\"", GUILayout.Height(40)))
            RemoveConverted();

        GUILayout.Space(10);

        GUI.color = Color.red;
        if (GUILayout.Button($"Remove Trees from Terrain Objects", GUILayout.Height(40)))
            RemoveTrees();
    }

    void AddSelectedTerrainObjects()
    {
        _terrainList = new List<Terrain>();

        foreach (var selectedGO in Selection.gameObjects)
        {
            Terrain terrain;

            if (selectedGO.TryGetComponent(out terrain))
                _terrainList.Add(terrain);
        }
    }

    void ConvertTreesToGameObjects()
    {
        if (GetRoot() == null)
            _root = new GameObject(_rootName);
        else
        {
            Debug.LogError($"Object with the name \"{_rootName}\" already exists");
            return;
        }

        int numOfTrees = 0;

        foreach (var terrain in _terrainList)
        {
            numOfTrees += ConvertTrees(terrain);
        }
       
        Debug.Log($"Converted {numOfTrees} Trees into GameObjects");
    }

    GameObject GetRoot()
        => GameObject.Find(_rootName);

    int ConvertTrees(Terrain terrain)
    {
        var treeInstances = terrain.terrainData.treeInstances;
        var treePrototypes = terrain.terrainData.treePrototypes;
        
        if (treeInstances.Length == 0 && treePrototypes.Length == 0)
            return 0;

        var parent = new GameObject(terrain.name);
        parent.transform.position = terrain.transform.position;
        parent.transform.SetParent(_root.transform);

        foreach (var treeInstance in treeInstances)
        {
            var treePrototype = treePrototypes[treeInstance.prototypeIndex];

            var go = Instantiate(treePrototype.prefab, parent.transform);

            go.transform.localPosition = Vector3.Scale(treeInstance.position,
                                                       terrain.terrainData.size);
            
            go.transform.localScale = new Vector3(treeInstance.widthScale,
                                                  treeInstance.widthScale,
                                                  treeInstance.heightScale);

            go.transform.Rotate(0, treeInstance.rotation * Mathf.Rad2Deg, 0);
        }

        return treeInstances.Length;
    }

    void RemoveTrees()
    {
        foreach (var terrain in _terrainList)
        {
            terrain.terrainData.treeInstances = new TreeInstance[0];
            terrain.terrainData.treePrototypes = new TreePrototype[0];
        }
    }

    void RemoveConverted()
        => DestroyImmediate(GetRoot());
}