DolphinQt: Switch dark/light theme when Windows theme changes.

Source/Core/DolphinQt/Main.cpp

@@ -7,8 +7,6 @@
 #include <vector>
 
 #include <Windows.h>
-
-#include <winrt/Windows.UI.ViewManagement.h>
 #endif
 
 #ifdef __linux__
@@ -248,20 +246,7 @@ int main(int argc, char* argv[])
     DolphinAnalytics::Instance().ReportDolphinStart("qt");
 
     MainWindow win{std::move(boot), static_cast<const char*>(options.get("movie"))};
-
-#ifdef _WIN32
-    // Check if the system is set to dark mode so we can set the default theme and window
-    // decorations accordingly.
-    {
-      using namespace winrt::Windows::UI::ViewManagement;
-      const UISettings settings;
-      const auto& color = settings.GetColorValue(UIColorType::Foreground);
-
-      const bool is_system_dark = 5 * color.G + 2 * color.R + color.B > 8 * 128;
-      Settings::Instance().SetSystemDark(is_system_dark);
-    }
-#endif
-
+    Settings::Instance().UpdateSystemDark();
     Settings::Instance().SetCurrentUserStyle(Settings::Instance().GetCurrentUserStyle());
     win.Show();
 

Source/Core/DolphinQt/MainWindow.cpp

@@ -1715,6 +1715,30 @@ QSize MainWindow::sizeHint() const
   return QSize(800, 600);
 }
 
+#ifdef _WIN32
+bool MainWindow::nativeEvent(const QByteArray& eventType, void* message, qintptr* result)
+{
+  auto* msg = reinterpret_cast<MSG*>(message);
+  if (msg && msg->message == WM_SETTINGCHANGE && msg->lParam != NULL &&
+      std::wstring_view(L"ImmersiveColorSet")
+              .compare(reinterpret_cast<const wchar_t*>(msg->lParam)) == 0)
+  {
+    // Windows light/dark theme has changed. Update our flag and refresh the theme.
+    auto& settings = Settings::Instance();
+    const bool was_dark_before = settings.IsSystemDark();
+    settings.UpdateSystemDark();
+    if (settings.IsSystemDark() != was_dark_before)
+      settings.SetCurrentUserStyle(settings.GetCurrentUserStyle());
+
+    // TODO: When switching from light to dark, the window decorations remain light. Qt seems very
+    // convinced that it needs to change these in response to this message, so even if we set them
+    // to dark here, Qt sets them back to light afterwards.
+  }
+
+  return false;
+}
+#endif
+
 void MainWindow::OnBootGameCubeIPL(DiscIO::Region region)
 {
   StartGame(std::make_unique<BootParameters>(BootParameters::IPL{region}));

Source/Core/DolphinQt/MainWindow.h

@@ -210,6 +210,11 @@ private:
   void dropEvent(QDropEvent* event) override;
   QSize sizeHint() const override;
 
+#ifdef _WIN32
+  // This gets called for each event from the Windows message queue.
+  bool nativeEvent(const QByteArray& eventType, void* message, qintptr* result) override;
+#endif
+
 #ifdef HAVE_XRANDR
   std::unique_ptr<X11Utils::XRRConfiguration> m_xrr_config;
 #endif

Source/Core/DolphinQt/Settings.cpp

@@ -19,6 +19,8 @@
 
 #include <fmt/format.h>
 
+#include <winrt/Windows.UI.ViewManagement.h>
+
 #include <QTabBar>
 #include <QToolButton>
 #endif
@@ -127,6 +129,22 @@ QString Settings::GetCurrentUserStyle() const
   return QFileInfo(GetQSettings().value(QStringLiteral("userstyle/path")).toString()).fileName();
 }
 
+void Settings::UpdateSystemDark()
+{
+#ifdef _WIN32
+  // Check if the system is set to dark mode so we can set the default theme and window
+  // decorations accordingly.
+  {
+    using namespace winrt::Windows::UI::ViewManagement;
+    const UISettings settings;
+    const auto& color = settings.GetColorValue(UIColorType::Foreground);
+
+    const bool is_system_dark = 5 * color.G + 2 * color.R + color.B > 8 * 128;
+    Settings::Instance().SetSystemDark(is_system_dark);
+  }
+#endif
+}
+
 void Settings::SetSystemDark(bool dark)
 {
   s_system_dark = dark;

Source/Core/DolphinQt/Settings.h

@@ -52,6 +52,7 @@ public:
 
   // UI
   void SetThemeName(const QString& theme_name);
+  void UpdateSystemDark();
   void SetSystemDark(bool dark);
   bool IsSystemDark();
   void SetCurrentUserStyle(const QString& stylesheet_name);