Combine Meshes for Unity (Editor)

//this is the editor script of the mesh combiner, put this script in a Editor folder, the combiner will not work if this script is missing
using UnityEditor;
using UnityEngine;

[CustomEditor(typeof(MeshMerge))]
[CanEditMultipleObjects]
public class MeshMergeEditor : Editor
{
    SerializedProperty material;
    SerializedProperty combineType;
    SerializedProperty subMeshesType;
    SerializedProperty use32BitsBuffer;
    SerializedProperty mesh;
    SerializedProperty colors;
    SerializedProperty range;
    SerializedProperty gridOffset;
    SerializedProperty gridMaxSize;
    SerializedProperty groupedItems;
    SerializedProperty items;
    SerializedProperty atlasTexture;
    SerializedProperty path;
    SerializedProperty newMat;

    bool showCombiner = false;
    bool showAtlas = false;
    bool showItems = false;
    bool showAtlasAndCombine = false;

    void OnEnable()
    {
        // Setup the SerializedProperties.
        material = serializedObject.FindProperty("material");
        combineType = serializedObject.FindProperty("combineType");
        subMeshesType = serializedObject.FindProperty("subMeshesType");
        use32BitsBuffer = serializedObject.FindProperty("use32BitsBuffer");
        mesh = serializedObject.FindProperty("mesh");
        colors = serializedObject.FindProperty("colors");
        range = serializedObject.FindProperty("range");
        gridOffset = serializedObject.FindProperty("gridOffset");
        gridMaxSize = serializedObject.FindProperty("gridMaxSize");
        groupedItems = serializedObject.FindProperty("groupedItems");
        items = serializedObject.FindProperty("items");
        atlasTexture = serializedObject.FindProperty("atlasTexture");
        path = serializedObject.FindProperty("path");
        newMat = serializedObject.FindProperty("newMat");
    }
    public override void OnInspectorGUI()
    {
        serializedObject.Update();
        MeshMerge meshMerge = (MeshMerge)target;

        GUILayout.Space(10);
        showCombiner = EditorGUILayout.Foldout(showCombiner, "COMBINER SETTINGS", true, new GUIStyle(EditorStyles.foldout) { fontStyle = FontStyle.Bold });
        if (showCombiner)
        {
            EditorGUILayout.BeginHorizontal();
            EditorGUILayout.PropertyField(material, new GUIContent("Material"));
            if (GUILayout.Button("Set with first mat."))
                material.objectReferenceValue = meshMerge.items[0].GetComponent<MeshRenderer>().sharedMaterial;
            if (GUILayout.Button("X")) material.objectReferenceValue = null;
            EditorGUILayout.EndHorizontal();

            EditorGUILayout.PropertyField(combineType, new GUIContent("Combine Type"));
            EditorGUILayout.PropertyField(subMeshesType, new GUIContent("SubMeshes Type"));
            EditorGUILayout.PropertyField(use32BitsBuffer, new GUIContent("Use 32 bits Buffer ?"));
            if (combineType.enumValueIndex == 1)
                EditorGUILayout.PropertyField(mesh, new GUIContent("Hexagon Mesh"));
            if (combineType.enumValueIndex == 0 || combineType.enumValueIndex == 1)
            {
                EditorGUILayout.PropertyField(colors, new GUIContent("Colors"));
                EditorGUILayout.BeginHorizontal();
                EditorGUILayout.PropertyField(range, new GUIContent("Range"));
                if (GUILayout.Button("Calculate perfect cell size")) meshMerge.CalculatePerfectCellSize();
                EditorGUILayout.EndHorizontal();

                EditorGUILayout.PropertyField(gridOffset, new GUIContent("Grid Offset"));
                if (GUILayout.Button("Set offset"))
                {
                    gridOffset.vector3Value = new Vector3(range.intValue / 2, 0, range.intValue / 2);
                    SceneView.RepaintAll();
                }
                EditorGUILayout.PropertyField(gridMaxSize, new GUIContent("Grid Max Size"));
                EditorGUILayout.PropertyField(groupedItems, new GUIContent("Items Into Cells"), true);
                if (GUILayout.Button("Group items to grid"))
                {
                    meshMerge.SetGroupedList();
                    meshMerge.GroupItems();
                }
            }
            GUILayout.Space(5);
            if (GUILayout.Button("Merge meshes")) meshMerge.CombineMeshes();
        }

        GUILayout.Space(10);
        showAtlas = EditorGUILayout.Foldout(showAtlas, "ATLAS SETTINGS", true, new GUIStyle(EditorStyles.foldout) { fontStyle = FontStyle.Bold });
        if (showAtlas)
        {
            EditorGUILayout.PropertyField(atlasTexture, new GUIContent("Final Atlas Texture"));
            path.stringValue = EditorGUILayout.TextField("Save Path", path.stringValue);
            EditorGUILayout.PropertyField(newMat, new GUIContent("Final Atlas Material"));

            EditorGUILayout.HelpBox("Warning, Atlas will not work correctly if one of the 3d objects have several submeshes/materials.\n Consider using \"Atlas & Combine\" property in this case.", MessageType.Warning);
            if (GUILayout.Button("Atlas")) meshMerge.AtlasUVS();
        }

        GUILayout.Space(10);
        EditorGUILayout.PropertyField(items, new GUIContent("Items"), true);
        EditorGUILayout.BeginHorizontal();
        if (GUILayout.Button("Get children"))
            for (int i = 0; i < meshMerge.transform.childCount; i++)
                meshMerge.items.Add(meshMerge.transform.GetChild(i).gameObject);
        if (GUILayout.Button("Clear list")) meshMerge.items.Clear();
        EditorGUILayout.EndHorizontal();

        GUILayout.Space(10);
        EditorGUILayout.BeginHorizontal();
        EditorGUILayout.LabelField("Atlas & Combine", EditorStyles.boldLabel);
        if (GUILayout.Button("Atlas & Combine")) meshMerge.AtlasAndCombine();
        EditorGUILayout.EndHorizontal();
        if (GUILayout.Button("Undo all")) meshMerge.Undo();

        serializedObject.ApplyModifiedProperties();
    }
}