Only use multi window manager when platform supports

src/anbox/cmds/session_manager.cpp

@@ -186,10 +186,10 @@ anbox::cmds::SessionManager::SessionManager(const BusFactory &bus_factory)
     auto app_db = std::make_shared<application::Database>();
 
     std::shared_ptr<wm::Manager> window_manager;
-    if (single_window_)
-      window_manager = std::make_shared<wm::SingleWindowManager>(platform, display_frame, app_db);
-    else
+    if (platform->supports_multi_window() && !single_window_)
       window_manager = std::make_shared<wm::MultiWindowManager>(platform, android_api_stub, app_db);
+    else
+      window_manager = std::make_shared<wm::SingleWindowManager>(platform, display_frame, app_db);
 
     auto gl_server = std::make_shared<graphics::GLRendererServer>(
           graphics::GLRendererServer::Config{gles_driver_, single_window_}, window_manager);

src/anbox/platform/base_platform.h

@@ -56,6 +56,8 @@ class BasePlatform {
 
   virtual void set_renderer(const std::shared_ptr<Renderer> &renderer) = 0;
   virtual void set_window_manager(const std::shared_ptr<wm::Manager> &window_manager) = 0;
+
+  virtual bool supports_multi_window() const = 0;
 };
 std::shared_ptr<BasePlatform> create(const std::string &name = "",
                                      const std::shared_ptr<input::Manager> &input_manager = nullptr,

src/anbox/platform/null/platform.cpp

@@ -67,5 +67,9 @@ void NullPlatform::set_window_manager(const std::shared_ptr<wm::Manager> &window
   (void) window_manager;
   ERROR("Not implemented");
 }
+
+bool NullPlatform::supports_multi_window() const {
+  return false;
+}
 }  // namespace wm
 }  // namespace anbox

src/anbox/platform/null/platform.h

@@ -35,6 +35,7 @@ class NullPlatform : public BasePlatform {
   std::shared_ptr<audio::Source> create_audio_source() override;
   void set_renderer(const std::shared_ptr<Renderer> &renderer) override;
   void set_window_manager(const std::shared_ptr<wm::Manager> &window_manager) override;
+  bool supports_multi_window() const override;
 };
 }  // namespace wm
 }  // namespace anbox

src/anbox/platform/sdl/platform.cpp

@@ -312,6 +312,10 @@ std::shared_ptr<audio::Source> Platform::create_audio_source() {
   ERROR("Not implemented");
   return nullptr;
 }
+
+bool Platform::supports_multi_window() const {
+  return true;
+}
 } // namespace sdl
 } // namespace platform
 } // namespace anbox

src/anbox/platform/sdl/platform.h

@@ -68,6 +68,8 @@ class Platform : public std::enable_shared_from_this<Platform>,
   std::shared_ptr<audio::Sink> create_audio_sink() override;
   std::shared_ptr<audio::Source> create_audio_source() override;
 
+  bool supports_multi_window() const override;
+
  private:
   void process_events();
   void process_input_event(const SDL_Event &event);