text: // ----------------------------------------------------------------------------
  // -                        Open3D: www.open3d.org                            -
  // ----------------------------------------------------------------------------
  // The MIT License (MIT)
  //
  // Copyright (c) 2018 www.open3d.org
  //
  // Permission is hereby granted, free of charge, to any person obtaining a copy
  // of this software and associated documentation files (the "Software"), to deal
  // in the Software without restriction, including without limitation the rights
  // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  // copies of the Software, and to permit persons to whom the Software is
  // furnished to do so, subject to the following conditions:
  //
  // The above copyright notice and this permission notice shall be included in
  // all copies or substantial portions of the Software.
  //
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  // FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  // IN THE SOFTWARE.
  // ----------------------------------------------------------------------------
  
  #pragma once
  
  #include <memory>
  
  #include "open3d/visualization/gui/Events.h"
  
  namespace open3d {
  namespace visualization {
  namespace gui {
  
  struct DrawContext;
  struct Theme;
  
  /// The menu item action is handled by Window, rather than by registering a
  /// a callback function with (non-existent) Menu::SetOnClicked(). This is
  /// because on macOS the menubar is global over all application windows, so any
  /// callback would need to go find the data object corresponding to the active
  /// window.
  class MenuBase {
  public:
      using ItemId = int;
      static constexpr ItemId NO_ITEM = -1;
  
      MenuBase() {}
      virtual ~MenuBase() {}
  
      virtual void AddItem(const char* name,
                           ItemId item_id = NO_ITEM,
                           KeyName key = KEY_NONE) = 0;
      virtual void AddMenu(const char* name,
                           std::shared_ptr<MenuBase> submenu) = 0;
      virtual void AddSeparator() = 0;
  
      virtual void InsertItem(int index,
                              const char* name,
                              ItemId item_id = NO_ITEM,
                              KeyName key = KEY_NONE) = 0;
      virtual void InsertMenu(int index,
                              const char* name,
                              std::shared_ptr<MenuBase> submenu) = 0;
      virtual void InsertSeparator(int index) = 0;
  
      virtual int GetNumberOfItems() const = 0;
  
      /// Searches the menu hierarchy down from this menu to find the item
      /// and returns true if the item is enabled.
      virtual bool IsEnabled(ItemId item_id) const = 0;
      /// Searches the menu hierarchy down from this menu to find the item
      /// and set it enabled according to \p enabled.
      virtual void SetEnabled(ItemId item_id, bool enabled) = 0;
  
      virtual bool IsChecked(ItemId item_id) const = 0;
      virtual void SetChecked(ItemId item_id, bool checked) = 0;
  
      virtual int CalcHeight(const Theme& theme) const = 0;
  
      /// Returns true if submenu visibility changed on last call to DrawMenuBar
      virtual bool CheckVisibilityChange() const = 0;
  
      virtual ItemId DrawMenuBar(const DrawContext& context, bool is_enabled) = 0;
      virtual ItemId Draw(const DrawContext& context,
                          const char* name,
                          bool is_enabled) = 0;
  
      virtual void* GetNativePointer() = 0;  // nullptr if not using native menus
  };
  
  }  // namespace gui
  }  // namespace visualization
  }  // namespace open3d
  