Add an option to use Qt scale engine (#158)

Telegram/Resources/langs/lang.strings

@@ -2752,6 +2752,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 "ktg_net_speed_boost_big" = "Big";
 
 "ktg_settings_system" = "System";
+"ktg_settings_qt_scale" = "Use Qt scale engine";
 "ktg_settings_gtk_integration" = "GTK integration";
 
 "ktg_settings_file_dialog_type" = "File dialog";

Telegram/Resources/langs/rewrites/en.json

@@ -67,6 +67,7 @@
 	"ktg_net_speed_boost_medium": "Medium",
 	"ktg_net_speed_boost_big": "Big",
 	"ktg_settings_system": "System",
+	"ktg_settings_qt_scale": "Use Qt scale engine",
 	"ktg_settings_gtk_integration": "GTK integration",
 	"ktg_settings_file_dialog_type": "File dialog",
 	"ktg_file_dialog_type_default": "Default",

Telegram/SourceFiles/core/application.cpp

@@ -206,7 +206,10 @@ void Application::run() {
 	startLocalStorage();
 	Lang::GetInstance().fillDefaultJson();
 	Lang::GetInstance().fillFromJson();
+
+	if (!cQtScale()) {
 		ValidateScale();
+	}
 
 	if (Local::oldSettingsVersion() < AppVersion) {
 		psNewVersion();

Telegram/SourceFiles/core/launcher.cpp

@@ -300,7 +300,11 @@ void Launcher::init() {
 	QApplication::setApplicationName(qsl("KotatogramDesktop"));
 
 #ifndef OS_MAC_OLD
+	if (cQtScale()) {
+		QApplication::setAttribute(Qt::AA_EnableHighDpiScaling, true);
+	} else {
 		QApplication::setAttribute(Qt::AA_DisableHighDpiScaling, true);
+	}
 #endif // OS_MAC_OLD
 
 	// fallback session management is useless for tdesktop since it doesn't have
@@ -346,7 +350,10 @@ int Launcher::exec() {
 
 	// Must be started before Sandbox is created.
 	Platform::start();
+
+	if (!cQtScale()) {
 		Ui::DisableCustomScaling();
+	}
 
 	if (cUseEnvApi()
 		&& qEnvironmentVariableIsSet(kApiIdVarName.utf8().constData())

Telegram/SourceFiles/core/sandbox.cpp

@@ -200,7 +200,7 @@ void Sandbox::setupScreenScale() {
 	}
 
 	const auto ratio = devicePixelRatio();
-	if (ratio > 1.) {
+	if (ratio > 1. || cQtScale()) {
 		if (!Platform::IsMac() || (ratio != 2.)) {
 			LOG(("Found non-trivial Device Pixel Ratio: %1").arg(ratio));
 			LOG(("Environmental variables: QT_DEVICE_PIXEL_RATIO='%1'").arg(qEnvironmentVariable("QT_DEVICE_PIXEL_RATIO")));
@@ -209,7 +209,7 @@ void Sandbox::setupScreenScale() {
 			LOG(("Environmental variables: QT_SCREEN_SCALE_FACTORS='%1'").arg(qEnvironmentVariable("QT_SCREEN_SCALE_FACTORS")));
 		}
 		style::SetDevicePixelRatio(int(ratio));
-		if (Platform::IsMac() && ratio == 2.) {
+		if (Platform::IsMac() && ratio == 2. && !cQtScale()) {
 			cSetScreenScale(110); // 110% for Retina screens by default.
 		} else {
 			cSetScreenScale(style::kScaleDefault);

Telegram/SourceFiles/kotato/json_settings.cpp

@@ -369,6 +369,7 @@ QByteArray GenerateSettingsJson(bool areDefault = false) {
 	settings.insert(qsl("recent_stickers_limit"), RecentStickersLimit());
 	settings.insert(qsl("userpic_corner_type"), cUserpicCornersType());
 	settings.insert(qsl("always_show_top_userpic"), cShowTopBarUserpic());
+	settings.insert(qsl("qt_scale"), cQtScale());
 	settings.insert(qsl("gtk_integration"), cGtkIntegration());
 	settings.insert(qsl("file_dialog_type"), int(FileDialogType()));
 	settings.insert(qsl("disable_tray_counter"), cDisableTrayCounter());
@@ -613,6 +614,10 @@ bool Manager::readCustomFile() {
 		cSetShowTopBarUserpic(v);
 	});
 
+	ReadBoolOption(settings, "qt_scale", [&](auto v) {
+		cSetQtScale(v);
+	});
+
 	ReadBoolOption(settings, "gtk_integration", [&](auto v) {
 		cSetGtkIntegration(v);
 	});

Telegram/SourceFiles/kotato/settings.cpp

@@ -147,6 +147,8 @@ rpl::producer<int> RecentStickersLimitChanges() {
 
 int gUserpicCornersType = 3;
 bool gShowTopBarUserpic = false;
+
+bool gQtScale = Platform::IsLinux();
 bool gGtkIntegration = false;
 
 rpl::variable<Platform::FileDialog::ImplementationType> gFileDialogType = Platform::FileDialog::ImplementationType::Default;

Telegram/SourceFiles/kotato/settings.h

@@ -103,6 +103,8 @@ void SetRecentStickersLimit(int limit);
 
 DeclareSetting(int, UserpicCornersType);
 DeclareSetting(bool, ShowTopBarUserpic);
+
+DeclareSetting(bool, QtScale);
 DeclareSetting(bool, GtkIntegration);
 
 void SetFileDialogType(Platform::FileDialog::ImplementationType t);

Telegram/SourceFiles/kotato/settings_menu.cpp

@@ -440,6 +440,33 @@ void SetupKotatoSystem(
 	AddSkip(container);
 	AddSubsectionTitle(container, tr::ktg_settings_system());
 
+	const auto qtScaleToggled = Ui::CreateChild<rpl::event_stream<bool>>(
+		container.get());
+	AddButton(
+		container,
+		tr::ktg_settings_qt_scale(),
+		st::settingsButton
+	)->toggleOn(
+		qtScaleToggled->events_starting_with_copy(cQtScale())
+	)->toggledValue(
+	) | rpl::filter([](bool enabled) {
+		return (enabled != cQtScale());
+	}) | rpl::start_with_next([=](bool enabled) {
+		const auto confirmed = [=] {
+			cSetQtScale(enabled);
+			::Kotato::JsonSettings::Write();
+			App::restart();
+		};
+		const auto cancelled = [=] {
+			qtScaleToggled->fire(cQtScale() == true);
+		};
+		Ui::show(Box<ConfirmBox>(
+			tr::lng_settings_need_restart(tr::now),
+			tr::lng_settings_restart_now(tr::now),
+			confirmed,
+			cancelled));
+	}, container->lifetime());
+
 #ifndef DESKTOP_APP_DISABLE_GTK_INTEGRATION
 	if (Platform::IsLinux()) {
 		const auto gtkIntegrationToggled = Ui::CreateChild<rpl::event_stream<bool>>(

Telegram/SourceFiles/platform/linux/specific_linux.cpp

@@ -955,7 +955,9 @@ void start() {
 		integration->load();
 	}
 
+	if (!cQtScale()) {
 		SetGtkScaleFactor();
+	}
 
 	// wait for interface announce to know if native window frame is supported
 	if (const auto integration = WaylandIntegration::Instance()) {

Telegram/SourceFiles/settings/settings_main.cpp

@@ -173,7 +173,7 @@ void SetupSections(
 }
 
 bool HasInterfaceScale() {
-	return true;
+	return !cQtScale();
 }
 
 void SetupInterfaceScale(