Provide access to GLFW window in plugins (#8806)

Plugins may need to be able to access functions affecting the GLFW
window (e.g., a plugin to resize the window). This restructures the API
to create a distinction at both the C and C++ level between the window
controller, which provides access to high-level behaviors driving the
Flutter application, and the window, which provides access to functions
to affect the UI state of the window (i.e., wrapped GLFWwindow
functions).

Also provides a PluginRegistrar extension for plugins that need access
to GLFW-specific functionality.

ci/licenses_golden/licenses_flutter

@@ -717,7 +717,9 @@ FILE: ../../../flutter/shell/platform/embedder/vsync_waiter_embedder.cc
 FILE: ../../../flutter/shell/platform/embedder/vsync_waiter_embedder.h
 FILE: ../../../flutter/shell/platform/glfw/client_wrapper/flutter_window_controller.cc
 FILE: ../../../flutter/shell/platform/glfw/client_wrapper/flutter_window_controller_unittests.cc
+FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/flutter_window.h
 FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/flutter_window_controller.h
+FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/plugin_registrar_glfw.h
 FILE: ../../../flutter/shell/platform/glfw/flutter_glfw.cc
 FILE: ../../../flutter/shell/platform/glfw/key_event_handler.cc
 FILE: ../../../flutter/shell/platform/glfw/key_event_handler.h

shell/platform/common/cpp/client_wrapper/include/flutter/plugin_registrar.h

@@ -28,7 +28,7 @@ class PluginRegistrar {
   // provides must remain valid as long as this object exists.
   explicit PluginRegistrar(FlutterDesktopPluginRegistrarRef core_registrar);
 
-  ~PluginRegistrar();
+  virtual ~PluginRegistrar();
 
   // Prevent copying.
   PluginRegistrar(PluginRegistrar const&) = delete;

shell/platform/glfw/client_wrapper/BUILD.gn

@@ -4,7 +4,11 @@
 
 import("$flutter_root/shell/platform/common/cpp/client_wrapper/publish.gni")
 
-_wrapper_includes = [ "include/flutter/flutter_window_controller.h" ]
+_wrapper_includes = [
+  "include/flutter/flutter_window.h",
+  "include/flutter/flutter_window_controller.h",
+  "include/flutter/plugin_registrar_glfw.h",
+]
 
 _wrapper_sources = [ "flutter_window_controller.cc" ]
 

shell/platform/glfw/client_wrapper/flutter_window_controller.cc

@@ -16,6 +16,9 @@ FlutterWindowController::FlutterWindowController(
 }
 
 FlutterWindowController::~FlutterWindowController() {
+  if (controller_) {
+    FlutterDesktopDestroyWindow(controller_);
+  }
   if (init_succeeded_) {
     FlutterDesktopTerminate();
   }
@@ -33,7 +36,7 @@ bool FlutterWindowController::CreateWindow(
     return false;
   }
 
-  if (window_) {
+  if (controller_) {
     std::cerr << "Only one Flutter window can exist at a time." << std::endl;
     return false;
   }
@@ -44,45 +47,35 @@ bool FlutterWindowController::CreateWindow(
       [](const std::string& arg) -> const char* { return arg.c_str(); });
   size_t arg_count = engine_arguments.size();
 
-  window_ = FlutterDesktopCreateWindow(
+  controller_ = FlutterDesktopCreateWindow(
       width, height, title.c_str(), assets_path.c_str(), icu_data_path_.c_str(),
       arg_count > 0 ? &engine_arguments[0] : nullptr, arg_count);
-  if (!window_) {
+  if (!controller_) {
     std::cerr << "Failed to create window." << std::endl;
     return false;
   }
+  window_ =
+      std::make_unique<FlutterWindow>(FlutterDesktopGetWindow(controller_));
   return true;
 }
 
 FlutterDesktopPluginRegistrarRef FlutterWindowController::GetRegistrarForPlugin(
     const std::string& plugin_name) {
-  if (!window_) {
+  if (!controller_) {
     std::cerr << "Cannot get plugin registrar without a window; call "
                  "CreateWindow first."
               << std::endl;
     return nullptr;
   }
-  return FlutterDesktopGetPluginRegistrar(window_, plugin_name.c_str());
-}
-
-void FlutterWindowController::SetHoverEnabled(bool enabled) {
-  FlutterDesktopSetHoverEnabled(window_, enabled);
-}
-
-void FlutterWindowController::SetTitle(const std::string& title) {
-  FlutterDesktopSetWindowTitle(window_, title.c_str());
-}
-
-void FlutterWindowController::SetIcon(uint8_t* pixel_data,
-                                      int width,
-                                      int height) {
-  FlutterDesktopSetWindowIcon(window_, pixel_data, width, height);
+  return FlutterDesktopGetPluginRegistrar(controller_, plugin_name.c_str());
 }
 
 void FlutterWindowController::RunEventLoop() {
-  if (window_) {
-    FlutterDesktopRunWindowLoop(window_);
+  if (controller_) {
+    FlutterDesktopRunWindowLoop(controller_);
   }
+  window_ = nullptr;
+  controller_ = nullptr;
 }
 
 }  // namespace flutter

shell/platform/glfw/client_wrapper/include/flutter/flutter_window.h

+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_FLUTTER_WINDOW_H_
+#define FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_FLUTTER_WINDOW_H_
+
+#include <string>
+#include <vector>
+
+#include <flutter_glfw.h>
+
+#include "plugin_registrar.h"
+
+namespace flutter {
+
+// A window displaying Flutter content.
+class FlutterWindow {
+ public:
+  explicit FlutterWindow(FlutterDesktopWindowRef window) : window_(window) {}
+
+  ~FlutterWindow() = default;
+
+  // Prevent copying.
+  FlutterWindow(FlutterWindow const&) = delete;
+  FlutterWindow& operator=(FlutterWindow const&) = delete;
+
+  // Enables or disables hover tracking.
+  //
+  // If hover is enabled, mouse movement will send hover events to the Flutter
+  // engine, rather than only tracking the mouse while the button is pressed.
+  // Defaults to off.
+  void SetHoverEnabled(bool enabled) {
+    FlutterDesktopWindowSetHoverEnabled(window_, enabled);
+  }
+
+  // Sets the displayed title of the window.
+  void SetTitle(const std::string& title) {
+    FlutterDesktopWindowSetTitle(window_, title.c_str());
+  }
+
+  // Sets the displayed icon for the window.
+  //
+  // The pixel format is 32-bit RGBA. The provided image data only needs to be
+  // valid for the duration of the call to this method. Pass a nullptr to revert
+  // to the default icon.
+  void SetIcon(uint8_t* pixel_data, int width, int height) {
+    FlutterDesktopWindowSetIcon(window_, pixel_data, width, height);
+  }
+
+ private:
+  // Handle for interacting with the C API's window.
+  //
+  // Note: window_ is conceptually owned by the controller, not this object.
+  FlutterDesktopWindowRef window_;
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_FLUTTER_WINDOW_H_

shell/platform/glfw/client_wrapper/include/flutter/flutter_window_controller.h

@@ -5,11 +5,13 @@
 #ifndef FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_FLUTTER_WINDOW_CONTROLLER_H_
 #define FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_FLUTTER_WINDOW_CONTROLLER_H_
 
+#include <memory>
 #include <string>
 #include <vector>
 
 #include <flutter_glfw.h>
 
+#include "flutter_window.h"
 #include "plugin_registrar.h"
 
 namespace flutter {
@@ -33,6 +35,10 @@ class FlutterWindowController {
 
   ~FlutterWindowController();
 
+  // Prevent copying.
+  FlutterWindowController(FlutterWindowController const&) = delete;
+  FlutterWindowController& operator=(FlutterWindowController const&) = delete;
+
   // Creates and displays a window for displaying Flutter content.
   //
   // The |assets_path| is the path to the flutter_assets folder for the Flutter
@@ -57,22 +63,9 @@ class FlutterWindowController {
   FlutterDesktopPluginRegistrarRef GetRegistrarForPlugin(
       const std::string& plugin_name);
 
-  // Enables or disables hover tracking.
-  //
-  // If hover is enabled, mouse movement will send hover events to the Flutter
-  // engine, rather than only tracking the mouse while the button is pressed.
-  // Defaults to off.
-  void SetHoverEnabled(bool enabled);
-
-  // Sets the displayed title of the window.
-  void SetTitle(const std::string& title);
-
-  // Sets the displayed icon for the window.
-  //
-  // The pixel format is 32-bit RGBA. The provided image data only needs to be
-  // valid for the duration of the call to this method. Pass a nullptr to revert
-  // to the default icon.
-  void SetIcon(uint8_t* pixel_data, int width, int height);
+  // The FlutterWindow managed by this controller, if any. Returns nullptr
+  // before CreateWindow is called, and after RunEventLoop returns;
+  FlutterWindow* window() { return window_.get(); }
 
   // Loops on Flutter window events until the window closes.
   void RunEventLoop();
@@ -85,8 +78,11 @@ class FlutterWindowController {
   // Whether or not FlutterDesktopInit succeeded at creation time.
   bool init_succeeded_ = false;
 
-  // The curent Flutter window, if any.
-  FlutterDesktopWindowRef window_ = nullptr;
+  // The owned FlutterWindow, if any.
+  std::unique_ptr<FlutterWindow> window_;
+
+  // Handle for interacting with the C API's window controller, if any.
+  FlutterDesktopWindowControllerRef controller_ = nullptr;
 };
 
 }  // namespace flutter

shell/platform/glfw/client_wrapper/include/flutter/plugin_registrar_glfw.h

+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_PLUGIN_REGISTRAR_GLFW_H_
+#define FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_PLUGIN_REGISTRAR_GLFW_H_
+
+#include <memory>
+
+#include <flutter_glfw.h>
+
+#include "flutter_window.h"
+#include "plugin_registrar.h"
+
+namespace flutter {
+
+// An extension to PluginRegistrar providing access to GLFW-shell-specific
+// functionality.
+class PluginRegistrarGlfw : public PluginRegistrar {
+ public:
+  // Creates a new PluginRegistrar. |core_registrar| and the messenger it
+  // provides must remain valid as long as this object exists.
+  explicit PluginRegistrarGlfw(FlutterDesktopPluginRegistrarRef core_registrar)
+      : PluginRegistrar(core_registrar) {
+    window_ = std::make_unique<FlutterWindow>(
+        FlutterDesktopRegistrarGetWindow(core_registrar));
+  }
+
+  virtual ~PluginRegistrarGlfw() = default;
+
+  // Prevent copying.
+  PluginRegistrarGlfw(PluginRegistrarGlfw const&) = delete;
+  PluginRegistrarGlfw& operator=(PluginRegistrarGlfw const&) = delete;
+
+  FlutterWindow* window() { return window_.get(); }
+
+ private:
+  // The owned FlutterWindow, if any.
+  std::unique_ptr<FlutterWindow> window_;
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_GLFW_CLIENT_WRAPPER_INCLUDE_FLUTTER_PLUGIN_REGISTRAR_GLFW_H_

shell/platform/glfw/client_wrapper/testing/stub_flutter_glfw_api.cc

@@ -48,13 +48,14 @@ void FlutterDesktopTerminate() {
   }
 }
 
-FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
-                                                   int initial_height,
-                                                   const char* title,
-                                                   const char* assets_path,
-                                                   const char* icu_data_path,
-                                                   const char** arguments,
-                                                   size_t argument_count) {
+FlutterDesktopWindowControllerRef FlutterDesktopCreateWindow(
+    int initial_width,
+    int initial_height,
+    const char* title,
+    const char* assets_path,
+    const char* icu_data_path,
+    const char** arguments,
+    size_t argument_count) {
   if (s_stub_implementation) {
     return s_stub_implementation->CreateWindow(
         initial_width, initial_height, title, assets_path, icu_data_path,
@@ -63,21 +64,27 @@ FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
   return nullptr;
 }
 
-void FlutterDesktopSetHoverEnabled(FlutterDesktopWindowRef flutter_window,
-                                   bool enabled) {
+void FlutterDesktopDestroyWindow(FlutterDesktopWindowControllerRef controller) {
+  if (s_stub_implementation) {
+    s_stub_implementation->DestroyWindow();
+  }
+}
+
+void FlutterDesktopWindowSetHoverEnabled(FlutterDesktopWindowRef flutter_window,
+                                         bool enabled) {
   if (s_stub_implementation) {
     s_stub_implementation->SetHoverEnabled(enabled);
   }
 }
 
-void FlutterDesktopSetWindowTitle(FlutterDesktopWindowRef flutter_window,
+void FlutterDesktopWindowSetTitle(FlutterDesktopWindowRef flutter_window,
                                   const char* title) {
   if (s_stub_implementation) {
     s_stub_implementation->SetWindowTitle(title);
   }
 }
 
-void FlutterDesktopSetWindowIcon(FlutterDesktopWindowRef flutter_window,
+void FlutterDesktopWindowSetIcon(FlutterDesktopWindowRef flutter_window,
                                  uint8_t* pixel_data,
                                  int width,
                                  int height) {
@@ -86,7 +93,7 @@ void FlutterDesktopSetWindowIcon(FlutterDesktopWindowRef flutter_window,
   }
 }
 
-void FlutterDesktopRunWindowLoop(FlutterDesktopWindowRef flutter_window) {
+void FlutterDesktopRunWindowLoop(FlutterDesktopWindowControllerRef controller) {
   if (s_stub_implementation) {
     s_stub_implementation->RunWindowLoop();
   }
@@ -110,9 +117,15 @@ bool FlutterDesktopShutDownEngine(FlutterDesktopEngineRef engine_ref) {
   return true;
 }
 
+FlutterDesktopWindowRef FlutterDesktopGetWindow(
+    FlutterDesktopWindowControllerRef controller) {
+  // The stub ignores this, so just return an arbitrary non-zero value.
+  return reinterpret_cast<FlutterDesktopWindowRef>(1);
+}
+
 FlutterDesktopPluginRegistrarRef FlutterDesktopGetPluginRegistrar(
-    FlutterDesktopWindowRef flutter_window,
+    FlutterDesktopWindowControllerRef controller,
     const char* plugin_name) {
   // The stub ignores this, so just return an arbitrary non-zero value.
-  return reinterpret_cast<FlutterDesktopPluginRegistrarRef>(1);
+  return reinterpret_cast<FlutterDesktopPluginRegistrarRef>(2);
 }

shell/platform/glfw/client_wrapper/testing/stub_flutter_glfw_api.h

@@ -36,23 +36,27 @@ class StubFlutterGlfwApi {
   virtual void Terminate() {}
 
   // Called for FlutterDesktopCreateWindow.
-  virtual FlutterDesktopWindowRef CreateWindow(int initial_width,
-                                               int initial_height,
-                                               const char* title,
-                                               const char* assets_path,
-                                               const char* icu_data_path,
-                                               const char** arguments,
-                                               size_t argument_count) {
+  virtual FlutterDesktopWindowControllerRef CreateWindow(
+      int initial_width,
+      int initial_height,
+      const char* title,
+      const char* assets_path,
+      const char* icu_data_path,
+      const char** arguments,
+      size_t argument_count) {
     return nullptr;
   }
 
-  // Called for FlutterDesktopSetHoverEnabled.
+  // Called for FlutterDesktopDestroyWindow
+  virtual void DestroyWindow() {}
+
+  // Called for FlutterDesktopWindowSetHoverEnabled.
   virtual void SetHoverEnabled(bool enabled) {}
 
-  // Called for FlutterDesktopSetWindowTitle.
+  // Called for FlutterDesktopWindowSetTitle.
   virtual void SetWindowTitle(const char* title) {}
 
-  //  Called for FlutterDesktopSetWindowIcon.
+  //  Called for FlutterDesktopWindowSetIcon.
   virtual void SetWindowIcon(uint8_t* pixel_data, int width, int height) {}
 
   // Called for FlutterDesktopRunWindowLoop.

shell/platform/glfw/flutter_glfw.cc

@@ -39,13 +39,16 @@ static_assert(FLUTTER_ENGINE_VERSION == 1, "");
 static constexpr double kDpPerInch = 160.0;
 
 // Struct for storing state within an instance of the GLFW Window.
-struct FlutterDesktopWindowState {
+struct FlutterDesktopWindowControllerState {
   // The GLFW window that owns this state object.
   GLFWwindow* window;
 
   // The handle to the Flutter engine instance.
   FlutterEngine engine;
 
+  // The window handle given to API clients.
+  std::unique_ptr<FlutterDesktopWindow> window_wrapper;
+
   // The plugin registrar handle given to API clients.
   std::unique_ptr<FlutterDesktopPluginRegistrar> plugin_registrar;
 
@@ -59,9 +62,6 @@ struct FlutterDesktopWindowState {
   std::vector<std::unique_ptr<flutter::KeyboardHookHandler>>
       keyboard_hook_handlers;
 
-  // Whether or not to track mouse movements to send kHover events.
-  bool hover_tracking_enabled = false;
-
   // Whether or not the pointer has been added (or if tracking is enabled, has
   // been added since it was last removed).
   bool pointer_currently_added = false;
@@ -73,6 +73,17 @@ struct FlutterDesktopWindowState {
   double window_pixels_per_screen_coordinate = 1.0;
 };
 
+// Opaque reference for the GLFW window itself. This is separate from the
+// controller so that it can be provided to plugins without giving them access
+// to all of the controller-based functionality.
+struct FlutterDesktopWindow {
+  // The GLFW window that (indirectly) owns this state object.
+  GLFWwindow* window;
+
+  // Whether or not to track mouse movements to send kHover events.
+  bool hover_tracking_enabled = false;
+};
+
 // Struct for storing state of a Flutter engine instance.
 struct FlutterDesktopEngineState {
   // The handle to the Flutter engine instance.
@@ -83,6 +94,9 @@ struct FlutterDesktopEngineState {
 struct FlutterDesktopPluginRegistrar {
   // The plugin messenger handle given to API clients.
   std::unique_ptr<FlutterDesktopMessenger> messenger;
+
+  // The handle for the window associated with this registrar.
+  FlutterDesktopWindow* window;
 };
 
 // State associated with the messenger used to communicate with the engine.
@@ -95,8 +109,9 @@ struct FlutterDesktopMessenger {
 };
 
 // Retrieves state bag for the window in question from the GLFWWindow.
-static FlutterDesktopWindowState* GetSavedWindowState(GLFWwindow* window) {
-  return reinterpret_cast<FlutterDesktopWindowState*>(
+static FlutterDesktopWindowControllerState* GetSavedWindowState(
+    GLFWwindow* window) {
+  return reinterpret_cast<FlutterDesktopWindowControllerState*>(
       glfwGetWindowUserPointer(window));
 }
 
@@ -254,7 +269,8 @@ static void GLFWMouseButtonCallback(GLFWwindow* window,
 
   // If mouse tracking isn't already enabled, turn it on for the duration of
   // the drag to generate kMove events.
-  bool hover_enabled = GetSavedWindowState(window)->hover_tracking_enabled;
+  bool hover_enabled =
+      GetSavedWindowState(window)->window_wrapper->hover_tracking_enabled;
   if (!hover_enabled) {
     glfwSetCursorPosCallback(
         window, (action == GLFW_PRESS) ? GLFWCursorPositionCallback : nullptr);
@@ -319,7 +335,7 @@ static void GLFWAssignEventCallbacks(GLFWwindow* window) {
   glfwSetCharCallback(window, GLFWCharCallback);
   glfwSetMouseButtonCallback(window, GLFWMouseButtonCallback);
   glfwSetScrollCallback(window, GLFWScrollCallback);
-  if (GetSavedWindowState(window)->hover_tracking_enabled) {
+  if (GetSavedWindowState(window)->window_wrapper->hover_tracking_enabled) {
     SetHoverCallbacksEnabled(window, true);
   }
 }
@@ -469,18 +485,19 @@ void FlutterDesktopTerminate() {
   glfwTerminate();
 }
 
-FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
-                                                   int initial_height,
-                                                   const char* title,
-                                                   const char* assets_path,
-                                                   const char* icu_data_path,
-                                                   const char** arguments,
-                                                   size_t argument_count) {
+FlutterDesktopWindowControllerRef FlutterDesktopCreateWindow(
+    int initial_width,
+    int initial_height,
+    const char* title,
+    const char* assets_path,
+    const char* icu_data_path,
+    const char** arguments,
+    size_t argument_count) {
 #ifdef __linux__
   gtk_init(0, nullptr);
 #endif
   // Create the window.
-  auto window =
+  auto* window =
       glfwCreateWindow(initial_width, initial_height, title, NULL, NULL);
   if (window == nullptr) {
     return nullptr;
@@ -496,7 +513,7 @@ FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
   }
 
   // Create a state object attached to the window.
-  FlutterDesktopWindowState* state = new FlutterDesktopWindowState();
+  auto* state = new FlutterDesktopWindowControllerState();
   state->window = window;
   glfwSetWindowUserPointer(window, state);
   state->engine = engine;
@@ -509,8 +526,12 @@ FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
   messenger->engine = engine;
   messenger->dispatcher = state->message_dispatcher.get();
 
+  state->window_wrapper = std::make_unique<FlutterDesktopWindow>();
+  state->window_wrapper->window = window;
+
   state->plugin_registrar = std::make_unique<FlutterDesktopPluginRegistrar>();
   state->plugin_registrar->messenger = std::move(messenger);
+  state->plugin_registrar->window = state->window_wrapper.get();
 
   state->internal_plugin_registrar =
       std::make_unique<flutter::PluginRegistrar>(state->plugin_registrar.get());
@@ -536,19 +557,25 @@ FlutterDesktopWindowRef FlutterDesktopCreateWindow(int initial_width,
   return state;
 }
 
-void FlutterDesktopSetHoverEnabled(FlutterDesktopWindowRef flutter_window,
-                                   bool enabled) {
+void FlutterDesktopDestroyWindow(FlutterDesktopWindowControllerRef controller) {
+  FlutterEngineShutdown(controller->engine);
+  glfwDestroyWindow(controller->window);
+  delete controller;
+}
+
+void FlutterDesktopWindowSetHoverEnabled(FlutterDesktopWindowRef flutter_window,
+                                         bool enabled) {
   flutter_window->hover_tracking_enabled = enabled;
   SetHoverCallbacksEnabled(flutter_window->window, enabled);
 }
 
-void FlutterDesktopSetWindowTitle(FlutterDesktopWindowRef flutter_window,
+void FlutterDesktopWindowSetTitle(FlutterDesktopWindowRef flutter_window,
                                   const char* title) {
   GLFWwindow* window = flutter_window->window;
   glfwSetWindowTitle(window, title);
 }
 
-void FlutterDesktopSetWindowIcon(FlutterDesktopWindowRef flutter_window,
+void FlutterDesktopWindowSetIcon(FlutterDesktopWindowRef flutter_window,
                                  uint8_t* pixel_data,
                                  int width,
                                  int height) {
@@ -557,8 +584,8 @@ void FlutterDesktopSetWindowIcon(FlutterDesktopWindowRef flutter_window,
   glfwSetWindowIcon(window, pixel_data ? 1 : 0, &image);
 }
 
-void FlutterDesktopRunWindowLoop(FlutterDesktopWindowRef flutter_window) {
-  GLFWwindow* window = flutter_window->window;
+void FlutterDesktopRunWindowLoop(FlutterDesktopWindowControllerRef controller) {
+  GLFWwindow* window = controller->window;
 #ifdef __linux__
   // Necessary for GTK thread safety.
   XInitThreads();
@@ -573,9 +600,24 @@ void FlutterDesktopRunWindowLoop(FlutterDesktopWindowRef flutter_window) {
     // TODO(awdavies): This will be deprecated soon.
     __FlutterEngineFlushPendingTasksNow();
   }
-  FlutterEngineShutdown(flutter_window->engine);
-  delete flutter_window;
-  glfwDestroyWindow(window);
+  FlutterDesktopDestroyWindow(controller);
+}
+
+FlutterDesktopWindowRef FlutterDesktopGetWindow(
+    FlutterDesktopWindowControllerRef controller) {
+  // Currently, one registrar acts as the registrar for all plugins, so the
+  // name is ignored. It is part of the API to reduce churn in the future when
+  // aligning more closely with the Flutter registrar system.
+  return controller->window_wrapper.get();
+}
+
+FlutterDesktopPluginRegistrarRef FlutterDesktopGetPluginRegistrar(
+    FlutterDesktopWindowControllerRef controller,
+    const char* plugin_name) {
+  // Currently, one registrar acts as the registrar for all plugins, so the
+  // name is ignored. It is part of the API to reduce churn in the future when
+  // aligning more closely with the Flutter registrar system.
+  return controller->plugin_registrar.get();
 }
 
 FlutterDesktopEngineRef FlutterDesktopRunEngine(const char* assets_path,
@@ -599,15 +641,6 @@ bool FlutterDesktopShutDownEngine(FlutterDesktopEngineRef engine_ref) {
   return (result == kSuccess);
 }
 
-FlutterDesktopPluginRegistrarRef FlutterDesktopGetPluginRegistrar(
-    FlutterDesktopWindowRef flutter_window,
-    const char* plugin_name) {
-  // Currently, one registrar acts as the registrar for all plugins, so the
-  // name is ignored. It is part of the API to reduce churn in the future when
-  // aligning more closely with the Flutter registrar system.
-  return flutter_window->plugin_registrar.get();
-}
-
 void FlutterDesktopRegistrarEnableInputBlocking(
     FlutterDesktopPluginRegistrarRef registrar,
     const char* channel) {
@@ -619,6 +652,11 @@ FlutterDesktopMessengerRef FlutterDesktopRegistrarGetMessenger(
   return registrar->messenger.get();
 }
 
+FlutterDesktopWindowRef FlutterDesktopRegistrarGetWindow(
+    FlutterDesktopPluginRegistrarRef registrar) {
+  return registrar->window;
+}
+
 void FlutterDesktopMessengerSend(FlutterDesktopMessengerRef messenger,
                                  const char* channel,
                                  const uint8_t* message,

shell/platform/glfw/public/flutter_glfw.h

@@ -16,8 +16,12 @@
 extern "C" {
 #endif
 
+// Opaque reference to a Flutter window controller.
+typedef struct FlutterDesktopWindowControllerState*
+    FlutterDesktopWindowControllerRef;
+
 // Opaque reference to a Flutter window.
-typedef struct FlutterDesktopWindowState* FlutterDesktopWindowRef;
+typedef struct FlutterDesktopWindow* FlutterDesktopWindowRef;
 
 // Opaque reference to a Flutter engine instance.
 typedef struct FlutterDesktopEngineState* FlutterDesktopEngineRef;
@@ -46,10 +50,11 @@ FLUTTER_EXPORT void FlutterDesktopTerminate();
 // for details. Not all arguments will apply to desktop.
 //
 // Returns a null pointer in the event of an error. Otherwise, the pointer is
-// valid until FlutterDesktopRunWindowLoop has been called and returned.
+// valid until FlutterDesktopRunWindowLoop has been called and returned, or
+// FlutterDesktopDestroyWindow is called.
 // Note that calling FlutterDesktopCreateWindow without later calling
-// FlutterDesktopRunWindowLoop on the returned reference is a memory leak.
-FLUTTER_EXPORT FlutterDesktopWindowRef
+// one of those two methods on the returned reference is a memory leak.
+FLUTTER_EXPORT FlutterDesktopWindowControllerRef
 FlutterDesktopCreateWindow(int initial_width,
                            int initial_height,
                            const char* title,
@@ -58,17 +63,48 @@ FlutterDesktopCreateWindow(int initial_width,
                            const char** arguments,
                            size_t argument_count);
 
+// Shuts down the engine instance associated with |controller|, and cleans up
+// associated state.
+//
+// |controller| is no longer valid after this call.
+FLUTTER_EXPORT void FlutterDesktopDestroyWindow(
+    FlutterDesktopWindowControllerRef controller);
+
+// Loops on Flutter window events until the window is closed.
+//
+// Once this function returns, |controller| is no longer valid, and must not be
+// be used again, as it calls FlutterDesktopDestroyWindow internally.
+//
+// TODO: Replace this with a method that allows running the runloop
+// incrementally.
+FLUTTER_EXPORT void FlutterDesktopRunWindowLoop(
+    FlutterDesktopWindowControllerRef controller);
+
+// Returns the window handle for the window associated with
+// FlutterDesktopWindowControllerRef.
+//
+// Its lifetime is the same as the |controller|'s.
+FLUTTER_EXPORT FlutterDesktopWindowRef
+FlutterDesktopGetWindow(FlutterDesktopWindowControllerRef controller);
+
+// Returns the plugin registrar handle for the plugin with the given name.
+//
+// The name must be unique across the application.
+FLUTTER_EXPORT FlutterDesktopPluginRegistrarRef
+FlutterDesktopGetPluginRegistrar(FlutterDesktopWindowControllerRef controller,
+                                 const char* plugin_name);
+
 // Enables or disables hover tracking.
 //
 // If hover is enabled, mouse movement will send hover events to the Flutter
 // engine, rather than only tracking the mouse while the button is pressed.
 // Defaults to off.
-FLUTTER_EXPORT void FlutterDesktopSetHoverEnabled(
+FLUTTER_EXPORT void FlutterDesktopWindowSetHoverEnabled(
     FlutterDesktopWindowRef flutter_window,
     bool enabled);
 
 // Sets the displayed title for |flutter_window|.
-FLUTTER_EXPORT void FlutterDesktopSetWindowTitle(
+FLUTTER_EXPORT void FlutterDesktopWindowSetTitle(
     FlutterDesktopWindowRef flutter_window,
     const char* title);
 
@@ -77,19 +113,12 @@ FLUTTER_EXPORT void FlutterDesktopSetWindowTitle(
 // The pixel format is 32-bit RGBA. The provided image data only needs to be
 // valid for the duration of the call to this method. Pass a nullptr to revert
 // to the default icon.
-FLUTTER_EXPORT void FlutterDesktopSetWindowIcon(
+FLUTTER_EXPORT void FlutterDesktopWindowSetIcon(
     FlutterDesktopWindowRef flutter_window,
     uint8_t* pixel_data,
     int width,
     int height);
 
-// Loops on Flutter window events until the window is closed.
-//
-// Once this function returns, FlutterDesktopWindowRef is no longer valid, and
-// must not be used again.
-FLUTTER_EXPORT void FlutterDesktopRunWindowLoop(
-    FlutterDesktopWindowRef flutter_window);
-
 // Runs an instance of a headless Flutter engine.
 //
 // The |assets_path| is the path to the flutter_assets folder for the Flutter
@@ -112,12 +141,10 @@ FlutterDesktopRunEngine(const char* assets_path,
 FLUTTER_EXPORT bool FlutterDesktopShutDownEngine(
     FlutterDesktopEngineRef engine_ref);
 
-// Returns the plugin registrar handle for the plugin with the given name.
-//
-// The name must be unique across the application.
-FLUTTER_EXPORT FlutterDesktopPluginRegistrarRef
-FlutterDesktopGetPluginRegistrar(FlutterDesktopWindowRef flutter_window,
-                                 const char* plugin_name);
+// Returns the window associated with this registrar's engine instance.
+// This is a GLFW shell-specific extension to flutter_plugin_registrar.h
+FLUTTER_EXPORT FlutterDesktopWindowRef
+FlutterDesktopRegistrarGetWindow(FlutterDesktopPluginRegistrarRef registrar);
 
 #if defined(__cplusplus)
 }  // extern "C"