Add virtual member QPlatformTheme::contrastPreference()

This function can be overridden by individual platform themes, in order
to read contrast settings from the platform's system settings, and
report the result back to Qt.

This information is relevant for our styles, and can be used to
determine color palette values, and additional elements like outline
thickness for controls/widgets.

Currently only the Windows, macOS, Gnome and Flatpak themes support this
feature.

Task-number: QTBUG-133595
Change-Id: I3aff519aa7f07c8b2fdcc1e7fb35ec719ab8efcc
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/corelib/global/qnamespace.h

@@ -54,6 +54,11 @@ namespace Qt {
         Dark,
     };
 
+    enum class ContrastPreference {
+        NoPreference,
+        HighContrast,
+    };
+
     enum MouseButton {
         NoButton         = 0x00000000,
         LeftButton       = 0x00000001,
@@ -1786,6 +1791,7 @@ namespace Qt {
     Q_ENUM_NS(CursorShape)
     Q_ENUM_NS(GlobalColor)
     Q_ENUM_NS(ColorScheme)
+    Q_ENUM_NS(ContrastPreference)
     Q_ENUM_NS(AspectRatioMode)
     Q_ENUM_NS(TransformationMode)
     Q_FLAG_NS(ImageConversionFlags)

src/gui/kernel/qplatformtheme.cpp

@@ -484,6 +484,11 @@ void QPlatformTheme::requestColorScheme(Qt::ColorScheme scheme)
     }
 }
 
+Qt::ContrastPreference QPlatformTheme::contrastPreference() const
+{
+    return Qt::ContrastPreference::NoPreference;
+}
+
 /*!
     \internal
     \brief Return a color palette for type \a type.

src/gui/kernel/qplatformtheme.h

@@ -319,6 +319,7 @@ public:
     virtual QKeySequence standardButtonShortcut(int button) const;
 #endif
     virtual void requestColorScheme(Qt::ColorScheme scheme);
+    virtual Qt::ContrastPreference contrastPreference() const;
 
     static QVariant defaultThemeHint(ThemeHint hint);
     static QString defaultStandardButtonText(int button);

src/gui/platform/unix/qdbuslistener.cpp

@@ -209,6 +209,9 @@ void QDBusListener::populateSignalMap()
     m_signalMap.insert(DBusKey("org.freedesktop.appearance"_L1, "color-scheme"_L1),
                        ChangeSignal(Provider::Gnome, Setting::ColorScheme));
 
+    m_signalMap.insert(DBusKey("org.freedesktop.appearance"_L1, "contrast"_L1),
+                       ChangeSignal(Provider::Gnome, Setting::Contrast));
+
     const QString &saveJsonFile = qEnvironmentVariable("QT_QPA_DBUS_SIGNALS_SAVE");
     if (!saveJsonFile.isEmpty())
         saveJson(saveJsonFile);
@@ -232,6 +235,6 @@ void QDBusListener::onSettingChanged(const QString &location, const QString &key
     if (!sig.has_value())
         return;
 
-    emit settingChanged(sig.value().provider, sig.value().setting, value.variant().toString());
+    emit settingChanged(sig.value().provider, sig.value().setting, value.variant());
 }
 QT_END_NAMESPACE

src/gui/platform/unix/qdbuslistener_p.h

@@ -38,6 +38,7 @@ public:
         Theme,
         ApplicationStyle,
         ColorScheme,
+        Contrast,
     };
     Q_ENUM(Setting)
 
@@ -51,7 +52,7 @@ private Q_SLOTS:
 Q_SIGNALS:
     void settingChanged(QDBusListener::Provider provider,
                         QDBusListener::Setting setting,
-                        const QString &value);
+                        const QVariant &value);
 
 private:
     struct DBusKey

src/gui/platform/unix/qgnometheme.cpp

@@ -15,6 +15,10 @@
 
 QT_BEGIN_NAMESPACE
 
+#ifndef QT_NO_DBUS
+Q_STATIC_LOGGING_CATEGORY(lcQpaThemeGnome, "qt.qpa.theme.gnome")
+#endif // QT_NO_DBUS
+
 /*!
     \class QGnomeTheme
     \brief QGnomeTheme is a theme implementation for the Gnome desktop.
@@ -27,7 +31,30 @@ const char *QGnomeTheme::name = "gnome";
 QGnomeThemePrivate::QGnomeThemePrivate()
 {
 #ifndef QT_NO_DBUS
-    initDbus();
+    QDBusMessage message = QDBusMessage::createMethodCall(QLatin1String("org.freedesktop.portal.Desktop"),
+                                             QLatin1String("/org/freedesktop/portal/desktop"),
+                                             QLatin1String("org.freedesktop.portal.Settings"),
+                                             QLatin1String("ReadOne"));
+    static constexpr QLatin1String appearanceNamespace("org.freedesktop.appearance");
+    static constexpr QLatin1String contrastKey("contrast");
+
+    message << appearanceNamespace << contrastKey;
+
+    QDBusConnection dbus = QDBusConnection::sessionBus();
+    if (!dbus.isConnected())
+        qCWarning(lcQpaThemeGnome) << "dbus connection failed. Last error: " << dbus.lastError();
+
+    QDBusPendingCall pendingCall = dbus.asyncCall(message);
+    QDBusPendingCallWatcher *watcher = new QDBusPendingCallWatcher(pendingCall);
+    QObject::connect(watcher, &QDBusPendingCallWatcher::finished, watcher, [this](QDBusPendingCallWatcher *watcher) {
+        if (!watcher->isError()) {
+            QDBusPendingReply<QVariant> reply = *watcher;
+            if (Q_LIKELY(reply.isValid()))
+                m_contrast = static_cast<Qt::ContrastPreference>(reply.value().toUInt());
+        }
+        watcher->deleteLater();
+        initDbus();
+    });
 #endif // QT_NO_DBUS
 }
 QGnomeThemePrivate::~QGnomeThemePrivate()
@@ -60,14 +87,22 @@ bool QGnomeThemePrivate::initDbus()
     // Wrap slot in a lambda to avoid inheriting QGnomeThemePrivate from QObject
     auto wrapper = [this](QDBusListener::Provider provider,
                           QDBusListener::Setting setting,
-                          const QString &value) {
+                          const QVariant &value) {
         if (provider != QDBusListener::Provider::Gnome
             && provider != QDBusListener::Provider::Gtk) {
             return;
         }
 
-        if (setting == QDBusListener::Setting::Theme)
+        switch (setting) {
-            updateColorScheme(value);
+        case QDBusListener::Setting::Theme:
+            updateColorScheme(value.toString());
+            break;
+        case QDBusListener::Setting::Contrast:
+            updateHighContrast(static_cast<Qt::ContrastPreference>(value.toUInt()));
+            break;
+        default:
+            break;
+        }
     };
 
     return QObject::connect(dbus.get(), &QDBusListener::settingChanged, dbus.get(), wrapper);
@@ -87,6 +122,15 @@ void QGnomeThemePrivate::updateColorScheme(const QString &themeName)
     if (oldColorScheme != m_colorScheme)
         QWindowSystemInterface::handleThemeChange();
 }
+
+void QGnomeThemePrivate::updateHighContrast(Qt::ContrastPreference contrast)
+{
+    if (m_contrast == contrast)
+        return;
+    m_contrast = contrast;
+    QWindowSystemInterface::handleThemeChange();
+}
+
 #endif // QT_NO_DBUS
 
 QGnomeTheme::QGnomeTheme()
@@ -181,6 +225,11 @@ Qt::ColorScheme QGnomeTheme::colorScheme() const
     return d_func()->m_colorScheme;
 }
 
+Qt::ContrastPreference QGnomeTheme::contrastPreference() const
+{
+    return d_func()->m_contrast;
+}
+
 #endif
 
 #if !defined(QT_NO_DBUS) && !defined(QT_NO_SYSTEMTRAYICON)

src/gui/platform/unix/qgnometheme_p.h

@@ -41,6 +41,7 @@ public:
 #ifndef QT_NO_DBUS
     QPlatformMenuBar *createPlatformMenuBar() const override;
     Qt::ColorScheme colorScheme() const override;
+    Qt::ContrastPreference contrastPreference() const override;
 #endif
 #if !defined(QT_NO_DBUS) && !defined(QT_NO_SYSTEMTRAYICON)
     QPlatformSystemTrayIcon *createPlatformSystemTrayIcon() const override;
@@ -62,10 +63,12 @@ public:
 
 #ifndef QT_NO_DBUS
     Qt::ColorScheme m_colorScheme = Qt::ColorScheme::Unknown;
+    Qt::ContrastPreference m_contrast = Qt::ContrastPreference::NoPreference;
 private:
     std::unique_ptr<QDBusListener> dbus;
     bool initDbus();
     void updateColorScheme(const QString &themeName);
+    void updateHighContrast(Qt::ContrastPreference contrast);
 #endif // QT_NO_DBUS
 };
 

src/gui/platform/unix/qkdetheme.cpp

@@ -114,7 +114,7 @@ private:
     bool initDbus();
     void settingChangedHandler(QDBusListener::Provider provider,
                                QDBusListener::Setting setting,
-                               const QString &value);
+                               const QVariant &value);
     Qt::ColorScheme colorSchemeFromPalette() const;
 #endif // QT_NO_DBUS
     void clearResources();
@@ -123,21 +123,23 @@ private:
 #ifndef QT_NO_DBUS
 void QKdeThemePrivate::settingChangedHandler(QDBusListener::Provider provider,
                                              QDBusListener::Setting setting,
-                                             const QString &value)
+                                             const QVariant &value)
 {
     if (provider != QDBusListener::Provider::Kde)
         return;
 
     switch (setting) {
     case QDBusListener::Setting::ColorScheme:
-        qCDebug(lcQpaThemeKde) << "KDE color theme changed to:" << value;
+        qCDebug(lcQpaThemeKde) << "KDE color theme changed to:" << value.toUInt();
         break;
     case QDBusListener::Setting::Theme:
-        qCDebug(lcQpaThemeKde) << "KDE global theme changed to:" << value;
+        qCDebug(lcQpaThemeKde) << "KDE global theme changed to:" << value.toString();
         break;
     case QDBusListener::Setting::ApplicationStyle:
-        qCDebug(lcQpaThemeKde) << "KDE application style changed to:" << value;
+        qCDebug(lcQpaThemeKde) << "KDE application style changed to:" << value.toString();
         break;
+    case QDBusListener::Setting::Contrast:
+        qCDebug(lcQpaThemeKde) << "KDE contrast setting changed to: " << static_cast<Qt::ContrastPreference>(value.toUInt());
     }
 
     refresh();
@@ -158,7 +160,7 @@ bool QKdeThemePrivate::initDbus()
     // Wrap slot in a lambda to avoid inheriting QKdeThemePrivate from QObject
     auto wrapper = [this](QDBusListener::Provider provider,
                           QDBusListener::Setting setting,
-                          const QString &value) {
+                          const QVariant &value) {
         settingChangedHandler(provider, setting, value);
     };
 

src/plugins/platforms/cocoa/qcocoatheme.h

@@ -39,6 +39,7 @@ public:
 
     QVariant themeHint(ThemeHint hint) const override;
     Qt::ColorScheme colorScheme() const override;
+    Qt::ContrastPreference contrastPreference() const override;
     QString standardButtonText(int button) const override;
     QKeySequence standardButtonShortcut(int button) const override;
 

src/plugins/platforms/cocoa/qcocoatheme.mm

@@ -508,6 +508,12 @@ void QCocoaTheme::updateColorScheme()
     m_colorScheme = qt_mac_applicationIsInDarkMode() ? Qt::ColorScheme::Dark : Qt::ColorScheme::Light;
 }
 
+Qt::ContrastPreference QCocoaTheme::contrastPreference() const
+{
+    return NSWorkspace.sharedWorkspace.accessibilityDisplayShouldIncreaseContrast ? Qt::ContrastPreference::HighContrast
+                                                                                  : Qt::ContrastPreference::NoPreference;
+}
+
 QString QCocoaTheme::standardButtonText(int button) const
 {
     return button == QPlatformDialogHelper::Discard ?

src/plugins/platforms/windows/qwindowstheme.cpp

@@ -597,6 +597,12 @@ void QWindowsTheme::requestColorScheme(Qt::ColorScheme scheme)
     handleSettingsChanged();
 }
 
+Qt::ContrastPreference QWindowsTheme::contrastPreference() const
+{
+    return queryHighContrast() ? Qt::ContrastPreference::HighContrast
+                               : Qt::ContrastPreference::NoPreference;
+}
+
 void QWindowsTheme::handleSettingsChanged()
 {
     const auto oldColorScheme = s_colorScheme;

src/plugins/platforms/windows/qwindowstheme.h

@@ -33,6 +33,7 @@ public:
 
     Qt::ColorScheme colorScheme() const override;
     void requestColorScheme(Qt::ColorScheme scheme) override;
+    Qt::ContrastPreference contrastPreference() const override;
 
     static void handleSettingsChanged();
 

src/plugins/platformthemes/gtk3/qgtk3theme.cpp

@@ -233,7 +233,7 @@ const QPalette *QGtk3Theme::palette(Palette type) const
 #ifdef QT_DEBUG
     if (m_requestedColorScheme != Qt::ColorScheme::Unknown
         && m_requestedColorScheme != m_storage->colorScheme()) {
-        qCDebug(lcQGtk3Interface) << "Current KDE theme doesn't support reuqested color scheme"
+        qCDebug(lcQGtk3Interface) << "Current KDE theme doesn't support requested color scheme"
                                   << m_requestedColorScheme << "Falling back to fusion palette.";
         return QPlatformTheme::palette(type);
     }

src/plugins/platformthemes/xdgdesktopportal/qxdgdesktopportaltheme.cpp

@@ -20,6 +20,10 @@ QT_BEGIN_NAMESPACE
 
 using namespace Qt::StringLiterals;
 
+static constexpr QLatin1StringView appearanceInterface("org.freedesktop.appearance");
+static constexpr QLatin1StringView colorSchemeKey("color-scheme");
+static constexpr QLatin1StringView contrastKey("contrast");
+
 class QXdgDesktopPortalThemePrivate : public QObject
     {
     Q_OBJECT
@@ -67,9 +71,14 @@ public Q_SLOTS:
     void settingChanged(const QString &group, const QString &key,
                         const QDBusVariant &value)
     {
-        if (group == "org.freedesktop.appearance"_L1 && key == "color-scheme"_L1) {
+        if (group == appearanceInterface) {
-            colorScheme = colorSchemeFromXdgPref(static_cast<XdgColorschemePref>(value.variant().toUInt()));
+            if (key == colorSchemeKey) {
-            QWindowSystemInterface::handleThemeChange();
+                colorScheme = colorSchemeFromXdgPref(static_cast<XdgColorschemePref>(value.variant().toUInt()));
+                QWindowSystemInterface::handleThemeChange();
+            } else if (key == contrastKey) {
+                contrast = static_cast<Qt::ContrastPreference>(value.variant().toUInt());
+                QWindowSystemInterface::handleThemeChange();
+            }
         }
     }
 
@@ -77,6 +86,7 @@ public:
     QPlatformTheme *baseTheme = nullptr;
     uint fileChooserPortalVersion = 0;
     Qt::ColorScheme colorScheme = Qt::ColorScheme::Unknown;
+    Qt::ContrastPreference contrast = Qt::ContrastPreference::NoPreference;
 };
 
 QXdgDesktopPortalTheme::QXdgDesktopPortalTheme()
@@ -123,15 +133,18 @@ QXdgDesktopPortalTheme::QXdgDesktopPortalTheme()
     message = QDBusMessage::createMethodCall("org.freedesktop.portal.Desktop"_L1,
                                              "/org/freedesktop/portal/desktop"_L1,
                                              "org.freedesktop.portal.Settings"_L1,
-                                             "Read"_L1);
+                                             "ReadAll"_L1);
-    message << "org.freedesktop.appearance"_L1 << "color-scheme"_L1;
+    message << appearanceInterface;
 
     // this must not be asyncCall() because we have to set appearance now
     QDBusReply<QVariant> reply = QDBusConnection::sessionBus().call(message);
     if (reply.isValid()) {
-        const QDBusVariant dbusVariant = qvariant_cast<QDBusVariant>(reply.value());
+        const QMap<QString, QVariantMap> settingsMap = qvariant_cast<QMap<QString, QVariantMap>>(reply.value());
-        const QXdgDesktopPortalThemePrivate::XdgColorschemePref xdgPref = static_cast<QXdgDesktopPortalThemePrivate::XdgColorschemePref>(dbusVariant.variant().toUInt());
+        if (!settingsMap.isEmpty()) {
-        d->colorScheme = QXdgDesktopPortalThemePrivate::colorSchemeFromXdgPref(xdgPref);
+            const auto xdgColorSchemePref = static_cast<QXdgDesktopPortalThemePrivate::XdgColorschemePref>(settingsMap.value(appearanceInterface).value(colorSchemeKey).toUInt());
+            d->colorScheme = QXdgDesktopPortalThemePrivate::colorSchemeFromXdgPref(xdgColorSchemePref);
+            d->contrast = static_cast<Qt::ContrastPreference>(settingsMap.value(appearanceInterface).value(contrastKey).toUInt());
+        }
     }
 
     QDBusConnection::sessionBus().connect(
@@ -225,6 +238,12 @@ Qt::ColorScheme QXdgDesktopPortalTheme::colorScheme() const
     return d->colorScheme;
 }
 
+Qt::ContrastPreference QXdgDesktopPortalTheme::contrastPreference() const
+{
+    Q_D(const QXdgDesktopPortalTheme);
+    return d->contrast;
+}
+
 QPixmap QXdgDesktopPortalTheme::standardPixmap(StandardPixmap sp, const QSizeF &size) const
 {
     Q_D(const QXdgDesktopPortalTheme);

src/plugins/platformthemes/xdgdesktopportal/qxdgdesktopportaltheme.h

@@ -35,6 +35,7 @@ public:
     QVariant themeHint(ThemeHint hint) const override;
 
     Qt::ColorScheme colorScheme() const override;
+    Qt::ContrastPreference contrastPreference() const override;
 
     QPixmap standardPixmap(StandardPixmap sp, const QSizeF &size) const override;
     QIcon fileIcon(const QFileInfo &fileInfo,