[Windows] Add textScaleFactor support (flutter#33316)

Author: moko256

shell/platform/windows/settings_plugin_win32.cc

@@ -12,6 +12,10 @@ namespace {
 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
 
 // static
@@ -26,29 +30,47 @@ SettingsPluginWin32::SettingsPluginWin32(BinaryMessenger* messenger,
     : SettingsPlugin(messenger, task_runner) {
   RegOpenKeyEx(HKEY_CURRENT_USER, kGetPreferredBrightnessRegKey,
                RRF_RT_REG_DWORD, KEY_NOTIFY, &preferred_brightness_reg_hkey_);
+  RegOpenKeyEx(HKEY_CURRENT_USER, kGetTextScaleFactorRegKey, RRF_RT_REG_DWORD,
+               KEY_NOTIFY, &text_scale_factor_reg_hkey_);
 }
 
 SettingsPluginWin32::~SettingsPluginWin32() {
   StopWatching();
   RegCloseKey(preferred_brightness_reg_hkey_);
+  RegCloseKey(text_scale_factor_reg_hkey_);
 }
 
 void SettingsPluginWin32::StartWatching() {
-  if (preferred_brightness_reg_hkey_ != NULL) {
+  if (preferred_brightness_reg_hkey_ != nullptr) {
     WatchPreferredBrightnessChanged();
   }
+  if (text_scale_factor_reg_hkey_ != nullptr) {
+    WatchTextScaleFactorChanged();
+  }
 }
 
 void SettingsPluginWin32::StopWatching() {
   preferred_brightness_changed_watcher_ = nullptr;
+  text_scale_factor_changed_watcher_ = nullptr;
 }
 
 bool SettingsPluginWin32::GetAlwaysUse24HourFormat() {
   return Prefer24HourTime(GetUserTimeFormat());
 }
 
 float SettingsPluginWin32::GetTextScaleFactor() {
-  return 1.0;
+  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
@@ -83,4 +105,18 @@ void SettingsPluginWin32::WatchPreferredBrightnessChanged() {
       preferred_brightness_changed_watcher_->GetHandle(), TRUE);
 }
 
+void SettingsPluginWin32::WatchTextScaleFactorChanged() {
+  text_scale_factor_changed_watcher_ =
+      std::make_unique<EventWatcherWin32>([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_win32.h

@@ -39,11 +39,13 @@ class SettingsPluginWin32 : public SettingsPlugin {
 
  private:
   void WatchPreferredBrightnessChanged();
+  void WatchTextScaleFactorChanged();
 
-  HKEY preferred_brightness_reg_hkey_ = NULL;
+  HKEY preferred_brightness_reg_hkey_ = nullptr;
+  HKEY text_scale_factor_reg_hkey_ = nullptr;
 
-  std::unique_ptr<EventWatcherWin32> preferred_brightness_changed_watcher_{
-      nullptr};
+  std::unique_ptr<EventWatcherWin32> preferred_brightness_changed_watcher_;
+  std::unique_ptr<EventWatcherWin32> text_scale_factor_changed_watcher_;
 
   SettingsPluginWin32(const SettingsPluginWin32&) = delete;
   SettingsPluginWin32& operator=(const SettingsPluginWin32&) = delete;