// return the height of this gui area
        public static void OnGUI(Rect headerRect, AXNodeGraphEditorWindow editor)
        {
            Event e = Event.current;

            AXModel model = editor.model;

            // DO HEADER MENU BAR -- MODEL MENU


            GUILayout.BeginArea(headerRect);
            GUILayout.BeginHorizontal();

            GUIStyle labelstyle = new GUIStyle(GUI.skin.label);

            labelstyle.alignment = TextAnchor.LowerLeft;

            labelstyle.fixedWidth = 150;


            GUILayout.Space(5);


            if (GUILayout.Button("2D"))
            {
                ArchimatixEngine.openLibrary2D();
            }
            if (GUILayout.Button("3D"))
            {
                ArchimatixEngine.openLibrary3D();
            }



            // NEW MODEL
            GUILayout.Space(10);



            if (GUILayout.Button("▼"))
            {
                AXModel[] allModels = ArchimatixUtils.getAllModels();


                GenericMenu menu = new GenericMenu();

                //menu.AddSeparator("Library ...");


                if (allModels != null && allModels.Length > 0)
                {
                    for (int i = 0; i < allModels.Length; i++)
                    {
                        AXModel m = allModels [i];
                        menu.AddItem(new GUIContent(m.gameObject.name), false, () => {
                            Selection.activeGameObject    = m.gameObject;
                            ArchimatixEngine.currentModel = m;
                        });
                    }
                }


                menu.AddSeparator("");

                menu.AddItem(new GUIContent("New Model"), false, () => {
                    AXEditorUtilities.createNewModel();
                });

                menu.ShowAsContext();
            }



            Color bgc = GUI.backgroundColor;

            GUI.backgroundColor = Color.clear;



            if (model != null)
            {
                // SELECTED MODEL
                if (GUILayout.Button(model.name))
                {
                    model.currentWorkingGroupPO = null;

                    model.selectAllVisibleInGroup(null);

                    float framePadding = 50;

                    Rect allRect = AXUtilities.getBoundaryRectFromPOs(model.selectedPOs);
                    allRect.x      -= framePadding;
                    allRect.y      -= framePadding;
                    allRect.width  += framePadding * 2;
                    allRect.height += framePadding * 2;



                    AXNodeGraphEditorWindow.zoomToRectIfOpen(allRect);
                }



                if (model.currentWorkingGroupPO != null)
                {
                    if (model.currentWorkingGroupPO.grouper != null)
                    {
                        // Make breadcrumb trail
                        List <AXParametricObject> crumbs = new List <AXParametricObject>();
                        AXParametricObject        cursor = model.currentWorkingGroupPO;


                        while (cursor.grouper != null)
                        {
                            crumbs.Add(cursor.grouper);
                            cursor = cursor.grouper;
                        }
                        crumbs.Reverse();

                        // model button frames



                        for (int i = 0; i < crumbs.Count; i++)
                        {
                            if (GUILayout.Button("> " + crumbs[i].Name))
                            {
                                model.currentWorkingGroupPO = crumbs[i];
                                Rect grouperCanvasRect = model.currentWorkingGroupPO.getBoundsRect();
                                editor.zoomToRect(grouperCanvasRect);
                            }
                        }
                    }
                    GUILayout.Button("> " + model.currentWorkingGroupPO.Name);
                }
            }
            GUILayout.FlexibleSpace();



            if (model != null)
            {
                Color  buildBG    = Color.Lerp(Color.cyan, Color.white, .8f);
                string buildLabel = "Rebuild";



                if (model.buildStatus == AXModel.BuildStatus.Generated)
                {
                    buildBG    = Color.red;
                    buildLabel = "Build";
                }



                GUI.backgroundColor = buildBG;
                if (GUILayout.Button(buildLabel))
                {
                    model.build();
                }

                GUI.backgroundColor = Color.cyan;


                if (model.generatedGameObjects != null && model.generatedGameObjects.transform.childCount == 0)
                {
                    GUI.enabled = false;
                }

                if (GUILayout.Button("Stamp"))
                {
                    model.stamp();
                }

                if (GUILayout.Button("Prefab"))
                {
                    string startDir = Application.dataPath;

                    string path = EditorUtility.SaveFilePanel(
                        "Save Prefab",
                        startDir,
                        ("" + model.name),
                        "prefab");

                    if (!string.IsNullOrEmpty(path))
                    {
                        AXPrefabWindow.makePrefab(model, path, editor);
                    }
                }
                GUI.enabled = true;

                GUILayout.Space(4);
            }


            GUILayout.EndHorizontal();
            GUILayout.EndArea();

            GUI.backgroundColor = bgc;
        }