Add an explicit API for font change notification (#21164)

Originally font change notification was handled by forwarding
WM_FONTCHANGE to the Flutter HWND, to avoid adding new API surface, but
that's not a good solution in a multi-window scenario, and it would
require a completely different solution for UWP. It also requires
non-obvious plumbing in the runner.

This replaces that with an explicit API, so that there's a clean and
obvious way for the runner to trigger this event.

shell/platform/windows/client_wrapper/flutter_engine.cc

@@ -64,6 +64,10 @@ std::chrono::nanoseconds FlutterEngine::ProcessMessages() {
   return std::chrono::nanoseconds(FlutterDesktopEngineProcessMessages(engine_));
 }
 
+void FlutterEngine::ReloadSystemFonts() {
+  FlutterDesktopEngineReloadSystemFonts(engine_);
+}
+
 FlutterDesktopPluginRegistrarRef FlutterEngine::GetRegistrarForPlugin(
     const std::string& plugin_name) {
   if (!engine_) {

shell/platform/windows/client_wrapper/flutter_engine_unittests.cc

@@ -38,16 +38,22 @@ class TestFlutterWindowsApi : public testing::StubFlutterWindowsApi {
   // |flutter::testing::StubFlutterWindowsApi|
   uint64_t EngineProcessMessages() override { return 99; }
 
+  // |flutter::testing::StubFlutterWindowsApi|
+  void EngineReloadSystemFonts() override { reload_fonts_called_ = true; }
+
   bool create_called() { return create_called_; }
 
   bool run_called() { return run_called_; }
 
   bool destroy_called() { return destroy_called_; }
 
+  bool reload_fonts_called() { return reload_fonts_called_; }
+
  private:
   bool create_called_ = false;
   bool run_called_ = false;
   bool destroy_called_ = false;
+  bool reload_fonts_called_ = false;
 };
 
 }  // namespace
@@ -93,6 +99,18 @@ TEST(FlutterEngineTest, ProcessMessages) {
   EXPECT_EQ(next_event_time.count(), 99);
 }
 
+TEST(FlutterEngineTest, ReloadFonts) {
+  testing::ScopedStubFlutterWindowsApi scoped_api_stub(
+      std::make_unique<TestFlutterWindowsApi>());
+  auto test_api = static_cast<TestFlutterWindowsApi*>(scoped_api_stub.stub());
+
+  FlutterEngine engine(DartProject(L"fake/project/path"));
+  engine.Run();
+
+  engine.ReloadSystemFonts();
+  EXPECT_TRUE(test_api->reload_fonts_called());
+}
+
 TEST(FlutterEngineTest, GetMessenger) {
   DartProject project(L"data");
   testing::ScopedStubFlutterWindowsApi scoped_api_stub(

shell/platform/windows/client_wrapper/include/flutter/flutter_engine.h

@@ -53,6 +53,11 @@ class FlutterEngine : public PluginRegistry {
   // last return value from this function.
   std::chrono::nanoseconds ProcessMessages();
 
+  // Tells the engine that the system font list has changed. Should be called
+  // by clients when OS-level font changes happen (e.g., WM_FONTCHANGE in a
+  // Win32 application).
+  void ReloadSystemFonts();
+
   // flutter::PluginRegistry:
   FlutterDesktopPluginRegistrarRef GetRegistrarForPlugin(
       const std::string& plugin_name) override;

shell/platform/windows/client_wrapper/testing/stub_flutter_windows_api.cc

@@ -108,6 +108,12 @@ uint64_t FlutterDesktopEngineProcessMessages(FlutterDesktopEngineRef engine) {
   return 0;
 }
 
+void FlutterDesktopEngineReloadSystemFonts(FlutterDesktopEngineRef engine) {
+  if (s_stub_implementation) {
+    s_stub_implementation->EngineReloadSystemFonts();
+  }
+}
+
 FlutterDesktopPluginRegistrarRef FlutterDesktopEngineGetPluginRegistrar(
     FlutterDesktopEngineRef engine,
     const char* plugin_name) {

shell/platform/windows/client_wrapper/testing/stub_flutter_windows_api.h

@@ -62,6 +62,9 @@ class StubFlutterWindowsApi {
   // Called for FlutterDesktopEngineProcessMessages.
   virtual uint64_t EngineProcessMessages() { return 0; }
 
+  // Called for FlutterDesktopEngineReloadSystemFonts.
+  virtual void EngineReloadSystemFonts() {}
+
   // Called for FlutterDesktopViewGetHWND.
   virtual HWND ViewGetHWND() { return reinterpret_cast<HWND>(1); }
 

shell/platform/windows/flutter_windows.cc

@@ -136,6 +136,10 @@ uint64_t FlutterDesktopEngineProcessMessages(FlutterDesktopEngineRef engine) {
   return EngineFromHandle(engine)->task_runner()->ProcessTasks().count();
 }
 
+void FlutterDesktopEngineReloadSystemFonts(FlutterDesktopEngineRef engine) {
+  FlutterEngineReloadSystemFonts(EngineFromHandle(engine)->engine());
+}
+
 FlutterDesktopPluginRegistrarRef FlutterDesktopEngineGetPluginRegistrar(
     FlutterDesktopEngineRef engine,
     const char* plugin_name) {

shell/platform/windows/flutter_windows_view.cc

@@ -105,13 +105,6 @@ void FlutterWindowsView::OnScroll(double x,
   SendScroll(x, y, delta_x, delta_y, scroll_offset_multiplier);
 }
 
-void FlutterWindowsView::OnFontChange() {
-  if (engine_->engine() == nullptr) {
-    return;
-  }
-  FlutterEngineReloadSystemFonts(engine_->engine());
-}
-
 // Sends new size  information to FlutterEngine.
 void FlutterWindowsView::SendWindowMetrics(size_t width,
                                            size_t height,

shell/platform/windows/flutter_windows_view.h

@@ -98,9 +98,6 @@ class FlutterWindowsView : public WindowBindingHandlerDelegate {
                 double delta_y,
                 int scroll_offset_multiplier) override;
 
-  // |WindowBindingHandlerDelegate|
-  void OnFontChange() override;
-
  private:
   // Struct holding the mouse state. The engine doesn't keep track of which
   // mouse buttons have been pressed, so it's the embedding's responsibility.

shell/platform/windows/public/flutter_windows.h

@@ -143,6 +143,9 @@ FLUTTER_EXPORT bool FlutterDesktopEngineRun(FlutterDesktopEngineRef engine,
 FLUTTER_EXPORT uint64_t
 FlutterDesktopEngineProcessMessages(FlutterDesktopEngineRef engine);
 
+FLUTTER_EXPORT void FlutterDesktopEngineReloadSystemFonts(
+    FlutterDesktopEngineRef engine);
+
 // Returns the plugin registrar handle for the plugin with the given name.
 //
 // The name must be unique across the application.

shell/platform/windows/testing/mock_win32_window.h

@@ -38,7 +38,6 @@ class MockWin32Window : public Win32Window {
   MOCK_METHOD1(OnText, void(const std::u16string&));
   MOCK_METHOD4(OnKey, void(int, int, int, char32_t));
   MOCK_METHOD2(OnScroll, void(double, double));
-  MOCK_METHOD0(OnFontChange, void());
 };
 
 }  // namespace testing

shell/platform/windows/testing/win32_flutter_window_test.cc

@@ -12,12 +12,5 @@ Win32FlutterWindowTest::Win32FlutterWindowTest(int width, int height)
 
 Win32FlutterWindowTest::~Win32FlutterWindowTest() = default;
 
-void Win32FlutterWindowTest::OnFontChange() {
-  on_font_change_called_ = true;
-}
-
-bool Win32FlutterWindowTest::OnFontChangeWasCalled() {
-  return on_font_change_called_;
-}
 }  // namespace testing
 }  // namespace flutter

shell/platform/windows/testing/win32_flutter_window_test.h

@@ -19,11 +19,6 @@ class Win32FlutterWindowTest : public Win32FlutterWindow {
   Win32FlutterWindowTest(Win32FlutterWindowTest const&) = delete;
   Win32FlutterWindowTest& operator=(Win32FlutterWindowTest const&) = delete;
 
-  // |Win32Window|
-  void OnFontChange() override;
-
-  bool OnFontChangeWasCalled();
-
  private:
   bool on_font_change_called_ = false;
 };

shell/platform/windows/win32_flutter_window.cc

@@ -171,8 +171,4 @@ void Win32FlutterWindow::OnScroll(double delta_x, double delta_y) {
                                       kScrollOffsetMultiplier);
 }
 
-void Win32FlutterWindow::OnFontChange() {
-  binding_handler_delegate_->OnFontChange();
-}
-
 }  // namespace flutter

shell/platform/windows/win32_flutter_window.h

@@ -59,9 +59,6 @@ class Win32FlutterWindow : public Win32Window, public WindowBindingHandler {
   // |Win32Window|
   void OnScroll(double delta_x, double delta_y) override;
 
-  // |Win32Window|
-  void OnFontChange() override;
-
   // |FlutterWindowBindingHandler|
   void SetView(WindowBindingHandlerDelegate* view) override;
 

shell/platform/windows/win32_flutter_window_unittests.cc

@@ -13,13 +13,5 @@ TEST(Win32FlutterWindowTest, CreateDestroy) {
   ASSERT_TRUE(TRUE);
 }
 
-TEST(Win32FlutterWindowTest, CanFontChange) {
-  Win32FlutterWindowTest window(800, 600);
-  HWND hwnd = window.GetWindowHandle();
-  LRESULT result = SendMessage(hwnd, WM_FONTCHANGE, NULL, NULL);
-  ASSERT_EQ(result, 0);
-  ASSERT_TRUE(window.OnFontChangeWasCalled());
-}
-
 }  // namespace testing
 }  // namespace flutter

shell/platform/windows/win32_window.cc

@@ -130,9 +130,6 @@ Win32Window::HandleMessage(UINT const message,
       current_height_ = height;
       HandleResize(width, height);
       break;
-    case WM_FONTCHANGE:
-      OnFontChange();
-      break;
     case WM_MOUSEMOVE:
       TrackMouseLeaveEvent(window_handle_);
 

shell/platform/windows/win32_window.h

@@ -97,9 +97,6 @@ class Win32Window {
   // Called when mouse scrollwheel input occurs.
   virtual void OnScroll(double delta_x, double delta_y) = 0;
 
-  // Called when the system font change.
-  virtual void OnFontChange() = 0;
-
   UINT GetCurrentDPI();
 
   UINT GetCurrentWidth();

shell/platform/windows/window_binding_handler_delegate.h

@@ -50,10 +50,6 @@ class WindowBindingHandlerDelegate {
                         double delta_x,
                         double delta_y,
                         int scroll_offset_multiplier) = 0;
-
-  // Notifies delegate that backing window size has had system font change.
-  // Typically called by currently configured WindowBindingHandler
-  virtual void OnFontChange() = 0;
 };
 
 }  // namespace flutter