Add Windows dark mode detection and automatic GTK theme switching (#111)

Author: Claude

src/gui/gsc_init.cpp

@@ -505,6 +505,32 @@ bool app_init_and_loop(int& argc, char**& argv)
 	}
 */
 
+	// Detect Windows dark mode and set GTK theme preference accordingly
+	if constexpr(BuildEnv::is_kernel_family_windows()) {
+		Glib::RefPtr<Gtk::Settings> gtk_settings = Gtk::Settings::get_default();
+		if (gtk_settings) {
+			bool use_dark_theme = false;
+		#ifdef _WIN32
+			// Check Windows registry for dark mode preference
+			// HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize
+			// AppsUseLightTheme = 0 means dark mode, 1 means light mode
+			DWORD apps_use_light_theme = 1;  // Default to light mode
+			if (hz::win32_get_registry_value_dword(HKEY_CURRENT_USER,
+					R"(Software\Microsoft\Windows\CurrentVersion\Themes\Personalize)",
+					"AppsUseLightTheme", apps_use_light_theme)) {
+				use_dark_theme = (apps_use_light_theme == 0);
+				debug_out_dump("app", "Windows theme detected: " << (use_dark_theme ? "dark" : "light") << "\n");
+			} else {
+				debug_out_dump("app", "Could not read Windows theme preference, defaulting to light mode.\n");
+			}
+		#endif
+			// Apply the dark theme preference to GTK
+			gtk_settings->property_gtk_application_prefer_dark_theme().set_value(use_dark_theme);
+			debug_out_dump("app", "GTK dark theme preference set to: " << (use_dark_theme ? "dark" : "light") << "\n");
+		}
+	}
+
+
 	// The application is dpi-aware in Windows.
 	// However, Gtk3 does not support fractional scaling, so at 250% scaling in system settings, the UI will use 200%.
 	//

src/gui/gsc_main_window_iconview.cpp

@@ -120,7 +120,7 @@ bool GscMainWindowIconView::on_draw(const Cairo::RefPtr<Cairo::Context>& cr)
 		return true;
 	}
 	if (empty_view_message_ != Message::None && this->num_icons_ == 0) {  // no icons
-		Glib::RefPtr<Pango::Layout> layout = this->create_pango_layout("");
+		const Glib::RefPtr<Pango::Layout> layout = this->create_pango_layout("");
 		layout->set_alignment(Pango::ALIGN_CENTER);
 		layout->set_markup(get_message_string(empty_view_message_));
 
@@ -131,6 +131,12 @@ bool GscMainWindowIconView::on_draw(const Cairo::RefPtr<Cairo::Context>& cr)
 		const int pos_y = (get_allocation().get_height() - layout_h) / 2;
 		cr->move_to(pos_x, pos_y);
 
+		// Use the foreground color from the widget's style context so
+		// the text is visible in both light and dark themes.
+		const auto style_context = get_style_context();
+		const Gdk::RGBA fg_color = style_context->get_color(style_context->get_state());
+		cr->set_source_rgba(fg_color.get_red(), fg_color.get_green(), fg_color.get_blue(), fg_color.get_alpha());
+
 		layout->show_in_cairo_context(cr);
 
 		return true;

src/hz/win32_tools.h

@@ -79,6 +79,14 @@ inline bool win32_set_registry_value_string(HKEY base,
 		const std::string& keydir, const std::string& key, const std::string& value);
 
 
+/// Get registry value as a DWORD.
+/// Base may be e.g. HKEY_CURRENT_USER.
+/// Note that this works only with REG_DWORD types.
+/// False is returned for all other types.
+inline bool win32_get_registry_value_dword(HKEY base,
+		const std::string& keydir, const std::string& key, DWORD& put_here);
+
+
 /// Redirect stdout and stderr to console window (if open). Requires winxp (at compile-time).
 /// \param create_if_none if true, create a new console if none was found and attach to it.
 /// \return false if failed or unsupported.
@@ -340,6 +348,49 @@ inline bool win32_set_registry_value_string(HKEY base,
 
 
 
+// Get registry value as a DWORD.
+// Note that this works only with REG_DWORD types.
+inline bool win32_get_registry_value_dword(HKEY base,
+		const std::string& keydir, const std::string& key, DWORD& put_here)
+{
+	std::wstring wkeydir = win32_utf8_to_utf16(keydir);
+	if (wkeydir.empty())
+		return false;
+
+	HKEY reg_key = nullptr;
+	bool open_status = (RegOpenKeyExW(base, wkeydir.c_str(), 0, KEY_QUERY_VALUE, &reg_key) == ERROR_SUCCESS);
+
+	if (!open_status)
+		return false;
+
+	bool ok = false;
+	std::wstring wkey = win32_utf8_to_utf16(key, &ok);
+	if (!ok) {  // conversion error. Note that an empty string is not an error.
+		if (reg_key)
+			RegCloseKey(reg_key);
+		return false;
+	}
+
+	DWORD type = 0;
+	DWORD value = 0;
+	DWORD nbytes = sizeof(DWORD);
+	bool status = (RegQueryValueExW(reg_key, wkey.c_str(), nullptr, &type,
+			reinterpret_cast<BYTE*>(&value), &nbytes) == ERROR_SUCCESS);
+
+	if (status && type == REG_DWORD) {
+		put_here = value;
+	} else {
+		status = false;
+	}
+
+	if (reg_key)
+		RegCloseKey(reg_key);
+
+	return status;
+}
+
+
+
 // Redirect stdout and stderr to console window (if open).
 inline bool win32_redirect_stdio_to_console(bool create_if_none)
 {