text: // ----------------------------------------------------------------------------
  // -                        Open3D: www.open3d.org                            -
  // ----------------------------------------------------------------------------
  // The MIT License (MIT)
  //
  // Copyright (c) 2019 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 <string>
  
  namespace filament {
  class Engine;
  }
  
  namespace open3d {
  namespace visualization {
  namespace rendering {
  
  class FilamentResourceManager;
  
  class EngineInstance {
  public:
      enum class RenderingType { kDefault, kOpenGL, kVulkan, kMetal };
  
      // Selects backend to use.
      // Should be called before instance usage.
      // If not called, platform available default backend will be used.
      static void SelectBackend(RenderingType type);
  
      // Specifies path to load shaders and skyboxes from. Must be called before
      // instance usage, or default path will be used.
      static void SetResourcePath(const std::string& resource_path);
      static const std::string& GetResourcePath();
  
      static filament::Engine& GetInstance();
      static FilamentResourceManager& GetResourceManager();
  
      /// Destroys the singleton instance, to force Filament cleanup at a
      /// specific time. Calling GetInstance() after this will re-create
      /// the instance.
      static void DestroyInstance();
  
      ~EngineInstance();
  
  private:
      static EngineInstance& Get();
  
      EngineInstance();
  
      static RenderingType type_;
      static std::string resource_path_;
      filament::Engine* engine_;
      FilamentResourceManager* resource_manager_;
  };
  
  }  // namespace rendering
  }  // namespace visualization
  }  // namespace open3d
  