Add experimental option for QT_WIDGETS_HIGHDPI_DOWNSCALE

Author: ilya-fedin

Telegram/SourceFiles/core/launcher.cpp

@@ -21,12 +21,25 @@ For license and copyright information please follow this link:
 
 #include <QtCore/QLoggingCategory>
 #include <QtCore/QStandardPaths>
+#include <QtCore/QLibraryInfo>
 
 namespace Core {
 namespace {
 
 uint64 InstallationTag = 0;
 
+base::options::toggle OptionHighDpiDownscale({
+	.id = kOptionHighDpiDownscale,
+	.name = "High DPI downscale",
+	.description = "Follow system interface scale settings exactly"
+		" (another approach, likely better quality).",
+	.scope = [] {
+		return !Platform::IsMac()
+			&& QLibraryInfo::version() >= QVersionNumber(6, 4);
+	},
+	.restartRequired = true,
+});
+
 base::options::toggle OptionFreeType({
 	.id = kOptionFreeType,
 	.name = "FreeType font engine",
@@ -62,7 +75,7 @@ FilteredCommandLineArguments::FilteredCommandLineArguments(
 	}
 
 #if defined Q_OS_WIN || defined Q_OS_MAC
-	if (OptionFreeType.value()) {
+	if (OptionFreeType.value() || OptionHighDpiDownscale.value()) {
 		pushArgument("-platform");
 #ifdef Q_OS_WIN
 		pushArgument("windows:fontengine=freetype");
@@ -294,6 +307,7 @@ base::options::toggle OptionFractionalScalingEnabled({
 } // namespace
 
 const char kOptionFractionalScalingEnabled[] = "fractional-scaling-enabled";
+const char kOptionHighDpiDownscale[] = "high-dpi-downscale";
 const char kOptionFreeType[] = "freetype";
 
 Launcher *Launcher::InstanceSetter::Instance = nullptr;
@@ -345,7 +359,14 @@ void Launcher::initHighDpi() {
 	QApplication::setAttribute(Qt::AA_EnableHighDpiScaling, true);
 #endif // Qt < 6.0.0
 
-	if (OptionFractionalScalingEnabled.value()) {
+	if (OptionHighDpiDownscale.value()) {
+		qputenv("QT_WIDGETS_HIGHDPI_DOWNSCALE", "1");
+		qputenv("QT_WIDGETS_RHI", "1");
+		qputenv("QT_WIDGETS_RHI_BACKEND", "opengl");
+	}
+
+	if (OptionFractionalScalingEnabled.value()
+			|| OptionHighDpiDownscale.value()) {
 		QApplication::setHighDpiScaleFactorRoundingPolicy(
 			Qt::HighDpiScaleFactorRoundingPolicy::PassThrough);
 	} else {

Telegram/SourceFiles/core/launcher.h

@@ -12,6 +12,7 @@ For license and copyright information please follow this link:
 namespace Core {
 
 extern const char kOptionFractionalScalingEnabled[];
+extern const char kOptionHighDpiDownscale[];
 extern const char kOptionFreeType[];
 
 class Launcher {

Telegram/SourceFiles/settings/settings_experimental.cpp

@@ -150,6 +150,7 @@ void SetupExperimental(
 	addToggle(ChatHelpers::kOptionTabbedPanelShowOnClick);
 	addToggle(Dialogs::kOptionForumHideChatsList);
 	addToggle(Core::kOptionFractionalScalingEnabled);
+	addToggle(Core::kOptionHighDpiDownscale);
 	addToggle(Window::kOptionViewProfileInChatsListContextMenu);
 	addToggle(Info::Profile::kOptionShowPeerIdBelowAbout);
 	addToggle(Info::Profile::kOptionShowChannelJoinedBelowAbout);