[Windows] Merge SettingsPluginWin32 and superclass (flutter#35019)

This merges SettingsPluginWin32 into SettingsPlugin.

With the removal of the UWP embedder, we can merge Win32-specific
implementation classes with their abstract superclasses where those
superclasses existed only to support both UWP and Win32.

No new tests since this is purely a restructuring of existing code
within the Win32 embedder, with no expected change in behaviour.

Issue: flutter#108386

ci/licenses_golden/licenses_flutter

@@ -2422,8 +2422,6 @@ FILE: ../../../flutter/shell/platform/windows/sequential_id_generator_unittests.
 FILE: ../../../flutter/shell/platform/windows/settings_plugin.cc
 FILE: ../../../flutter/shell/platform/windows/settings_plugin.h
 FILE: ../../../flutter/shell/platform/windows/settings_plugin_unittests.cc
-FILE: ../../../flutter/shell/platform/windows/settings_plugin_win32.cc
-FILE: ../../../flutter/shell/platform/windows/settings_plugin_win32.h
 FILE: ../../../flutter/shell/platform/windows/system_utils.cc
 FILE: ../../../flutter/shell/platform/windows/system_utils.h
 FILE: ../../../flutter/shell/platform/windows/system_utils_unittests.cc

shell/platform/windows/BUILD.gn

@@ -88,8 +88,6 @@ source_set("flutter_windows_source") {
     "sequential_id_generator.h",
     "settings_plugin.cc",
     "settings_plugin.h",
-    "settings_plugin_win32.cc",
-    "settings_plugin_win32.h",
     "system_utils.cc",
     "system_utils.h",
     "task_runner.cc",

shell/platform/windows/flutter_windows_engine.cc

@@ -187,8 +187,8 @@ FlutterWindowsEngine::FlutterWindowsEngine(const FlutterProjectBundle& project)
   // Set up internal channels.
   // TODO: Replace this with an embedder.h API. See
   // https://github.com/flutter/flutter/issues/71099
-  settings_plugin_ =
-      SettingsPlugin::Create(messenger_wrapper_.get(), task_runner_.get());
+  settings_plugin_ = std::make_unique<SettingsPlugin>(messenger_wrapper_.get(),
+                                                      task_runner_.get());
 }
 
 FlutterWindowsEngine::~FlutterWindowsEngine() {

shell/platform/windows/settings_plugin.cc

@@ -5,6 +5,7 @@
 #include "flutter/shell/platform/windows/settings_plugin.h"
 
 #include "flutter/shell/platform/common/json_message_codec.h"
+#include "flutter/shell/platform/windows/system_utils.h"
 
 namespace flutter {
 
@@ -17,6 +18,14 @@ constexpr char kPlatformBrightness[] = "platformBrightness";
 
 constexpr char kPlatformBrightnessDark[] = "dark";
 constexpr char kPlatformBrightnessLight[] = "light";
+
+constexpr wchar_t kGetPreferredBrightnessRegKey[] =
+    L"Software\\Microsoft\\Windows\\CurrentVersion\\Themes\\Personalize";
+constexpr wchar_t kGetPreferredBrightnessRegValue[] = L"AppsUseLightTheme";
+
+constexpr wchar_t kGetTextScaleFactorRegKey[] =
+    L"Software\\Microsoft\\Accessibility";
+constexpr wchar_t kGetTextScaleFactorRegValue[] = L"TextScaleFactor";
 }  // namespace
 
 SettingsPlugin::SettingsPlugin(BinaryMessenger* messenger,
@@ -45,4 +54,81 @@ void SettingsPlugin::SendSettings() {
   channel_->Send(settings);
 }
 
+void SettingsPlugin::StartWatching() {
+  if (preferred_brightness_reg_hkey_ != nullptr) {
+    WatchPreferredBrightnessChanged();
+  }
+  if (text_scale_factor_reg_hkey_ != nullptr) {
+    WatchTextScaleFactorChanged();
+  }
+}
+
+void SettingsPlugin::StopWatching() {
+  preferred_brightness_changed_watcher_ = nullptr;
+  text_scale_factor_changed_watcher_ = nullptr;
+}
+
+bool SettingsPlugin::GetAlwaysUse24HourFormat() {
+  return Prefer24HourTime(GetUserTimeFormat());
+}
+
+float SettingsPlugin::GetTextScaleFactor() {
+  DWORD text_scale_factor;
+  DWORD text_scale_factor_size = sizeof(text_scale_factor);
+  LONG result = RegGetValue(
+      HKEY_CURRENT_USER, kGetTextScaleFactorRegKey, kGetTextScaleFactorRegValue,
+      RRF_RT_REG_DWORD, nullptr, &text_scale_factor, &text_scale_factor_size);
+
+  if (result == 0) {
+    return text_scale_factor / 100.0;
+  } else {
+    // The current OS does not have text scale factor.
+    return 1.0;
+  }
+}
+
+SettingsPlugin::PlatformBrightness SettingsPlugin::GetPreferredBrightness() {
+  DWORD use_light_theme;
+  DWORD use_light_theme_size = sizeof(use_light_theme);
+  LONG result = RegGetValue(HKEY_CURRENT_USER, kGetPreferredBrightnessRegKey,
+                            kGetPreferredBrightnessRegValue, RRF_RT_REG_DWORD,
+                            nullptr, &use_light_theme, &use_light_theme_size);
+
+  if (result == 0) {
+    return use_light_theme ? SettingsPlugin::PlatformBrightness::kLight
+                           : SettingsPlugin::PlatformBrightness::kDark;
+  } else {
+    // The current OS does not support dark mode. (Older Windows 10 or before
+    // Windows 10)
+    return SettingsPlugin::PlatformBrightness::kLight;
+  }
+}
+
+void SettingsPlugin::WatchPreferredBrightnessChanged() {
+  preferred_brightness_changed_watcher_ =
+      std::make_unique<EventWatcher>([this]() {
+        task_runner_->PostTask([this]() {
+          SendSettings();
+          WatchPreferredBrightnessChanged();
+        });
+      });
+
+  RegNotifyChangeKeyValue(
+      preferred_brightness_reg_hkey_, FALSE, REG_NOTIFY_CHANGE_LAST_SET,
+      preferred_brightness_changed_watcher_->GetHandle(), TRUE);
+}
+
+void SettingsPlugin::WatchTextScaleFactorChanged() {
+  text_scale_factor_changed_watcher_ = std::make_unique<EventWatcher>([this]() {
+    task_runner_->PostTask([this]() {
+      SendSettings();
+      WatchTextScaleFactorChanged();
+    });
+  });
+
+  RegNotifyChangeKeyValue(
+      text_scale_factor_reg_hkey_, FALSE, REG_NOTIFY_CHANGE_LAST_SET,
+      text_scale_factor_changed_watcher_->GetHandle(), TRUE);
+}
+
 }  // namespace flutter

shell/platform/windows/settings_plugin.h

@@ -5,10 +5,13 @@
 #ifndef FLUTTER_SHELL_PLATFORM_WINDOWS_SETTINGS_PLUGIN_H_
 #define FLUTTER_SHELL_PLATFORM_WINDOWS_SETTINGS_PLUGIN_H_
 
+#include <Windows.h>
+
 #include <memory>
 
 #include "flutter/shell/platform/common/client_wrapper/include/flutter/basic_message_channel.h"
 #include "flutter/shell/platform/common/client_wrapper/include/flutter/binary_messenger.h"
+#include "flutter/shell/platform/windows/event_watcher.h"
 #include "flutter/shell/platform/windows/task_runner.h"
 #include "rapidjson/document.h"
 
@@ -24,36 +27,42 @@ class SettingsPlugin {
 
   virtual ~SettingsPlugin();
 
-  static std::unique_ptr<SettingsPlugin> Create(BinaryMessenger* messenger,
-                                                TaskRunner* task_runner);
-
   // Sends settings (e.g., platform brightness) to the engine.
   void SendSettings();
 
   // Start watching settings changes and notify the engine of the update.
-  virtual void StartWatching() = 0;
+  virtual void StartWatching();
 
   // Stop watching settings change. The `SettingsPlugin` destructor will call
   // this automatically.
-  virtual void StopWatching() = 0;
+  virtual void StopWatching();
 
  protected:
   enum struct PlatformBrightness { kDark, kLight };
 
   // Returns `true` if the user uses 24 hour time.
-  virtual bool GetAlwaysUse24HourFormat() = 0;
+  virtual bool GetAlwaysUse24HourFormat();
 
   // Returns the user-preferred text scale factor.
-  virtual float GetTextScaleFactor() = 0;
+  virtual float GetTextScaleFactor();
 
   // Returns the user-preferred brightness.
-  virtual PlatformBrightness GetPreferredBrightness() = 0;
-
-  TaskRunner* task_runner_;
+  virtual PlatformBrightness GetPreferredBrightness();
 
  private:
   std::unique_ptr<BasicMessageChannel<rapidjson::Document>> channel_;
 
+  void WatchPreferredBrightnessChanged();
+  void WatchTextScaleFactorChanged();
+
+  HKEY preferred_brightness_reg_hkey_ = nullptr;
+  HKEY text_scale_factor_reg_hkey_ = nullptr;
+
+  std::unique_ptr<EventWatcher> preferred_brightness_changed_watcher_;
+  std::unique_ptr<EventWatcher> text_scale_factor_changed_watcher_;
+
+  TaskRunner* task_runner_;
+
   SettingsPlugin(const SettingsPlugin&) = delete;
   SettingsPlugin& operator=(const SettingsPlugin&) = delete;
 };