Windows QPA: Add detection of dark mode

Read the dark mode setting and make it accessible
via native interface.
Add a command line option to set the support level.

Task-number: QTBUG-72028
Change-Id: I1e9fe296a6b1bda81512d003183038b866b67545
Reviewed-by: Oliver Wolff <oliver.wolff@qt.io>

src/gui/kernel/qguiapplication.cpp

@@ -592,6 +592,21 @@ static QWindowGeometrySpecification windowGeometrySpecification = Q_WINDOW_GEOME
     \list
         \li \c {altgr}, detect the key \c {AltGr} found on some keyboards as
                Qt::GroupSwitchModifier (since Qt 5.12).
+        \li \c {darkmode=[1|2]} controls how Qt responds to the activation
+               of the \e{Dark Mode for applications} introduced in Windows 10
+               1903 (since Qt 5.15).
+
+               A value of 1 causes Qt to switch the window borders to black
+               when \e{Dark Mode for applications} is activated and no High
+               Contrast Theme is in use. This is intended for applications
+               that implement their own theming.
+
+               A value of 2 will in addition cause the Windows Vista style to
+               be deactivated and switch to the Windows style using a
+               simplified palette in dark mode. This is currently
+               experimental pending the introduction of new style that
+               properly adapts to dark mode.
+
         \li \c {dialogs=[xp|none]}, \c xp uses XP-style native dialogs and
             \c none disables them.
 

src/plugins/platforms/windows/qwindowscontext.cpp

@@ -42,6 +42,7 @@
 #include "qwindowsintegration.h"
 #include "qwindowswindow.h"
 #include "qwindowskeymapper.h"
+#include "qwindowsnativeinterface.h"
 #include "qwindowsmousehandler.h"
 #include "qwindowspointerhandler.h"
 #include "qtwindowsglobal.h"
@@ -277,8 +278,11 @@ struct QWindowsContextPrivate {
     bool m_asyncExpose = false;
     HPOWERNOTIFY m_powerNotification = nullptr;
     HWND m_powerDummyWindow = nullptr;
+    static bool m_darkMode;
 };
 
+bool QWindowsContextPrivate::m_darkMode = false;
+
 QWindowsContextPrivate::QWindowsContextPrivate()
     : m_oleInitializeResult(OleInitialize(nullptr))
 {
@@ -293,6 +297,7 @@ QWindowsContextPrivate::QWindowsContextPrivate()
         m_systemInfo |= QWindowsContext::SI_RTL_Extensions;
         m_keyMapper.setUseRTLExtensions(true);
     }
+    m_darkMode = QWindowsTheme::queryDarkMode();
     if (FAILED(m_oleInitializeResult)) {
        qWarning() << "QWindowsContext: OleInitialize() failed: "
            << QWindowsContext::comErrorString(m_oleInitializeResult);
@@ -485,6 +490,11 @@ void QWindowsContext::setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiA
     }
 }
 
+bool QWindowsContext::isDarkMode()
+{
+    return QWindowsContextPrivate::m_darkMode;
+}
+
 QWindowsContext *QWindowsContext::instance()
 {
     return m_instance;
@@ -1203,9 +1213,17 @@ bool QWindowsContext::windowsProc(HWND hwnd, UINT message,
             t->displayChanged();
         QWindowsWindow::displayChanged();
         return d->m_screenManager.handleDisplayChange(wParam, lParam);
-    case QtWindows::SettingChangedEvent:
+    case QtWindows::SettingChangedEvent: {
         QWindowsWindow::settingsChanged();
+        const bool darkMode = QWindowsTheme::queryDarkMode();
+        if (darkMode != QWindowsContextPrivate::m_darkMode) {
+            QWindowsContextPrivate::m_darkMode = darkMode;
+            auto nativeInterface =
+                static_cast<QWindowsNativeInterface *>(QWindowsIntegration::instance()->nativeInterface());
+            emit nativeInterface->darkModeChanged(darkMode);
+        }
         return d->m_screenManager.handleScreenChanges();
+    }
     default:
         break;
     }

src/plugins/platforms/windows/qwindowscontext.h

@@ -226,6 +226,8 @@ public:
     void setProcessDpiAwareness(QtWindows::ProcessDpiAwareness dpiAwareness);
     static int processDpiAwareness();
 
+    static bool isDarkMode();
+
     void setDetectAltGrModifier(bool a);
 
     // Returns a combination of SystemInfoFlags

src/plugins/platforms/windows/qwindowsintegration.cpp

@@ -219,6 +219,10 @@ static inline unsigned parseOptions(const QStringList &paramList,
             options |= QWindowsIntegration::DontUseWMPointer;
         } else if (param == u"reverse") {
             options |= QWindowsIntegration::RtlEnabled;
+        } else if (param == u"darkmode=1") {
+            options |= QWindowsIntegration::DarkModeWindowFrames;
+        } else if (param == u"darkmode=2") {
+            options |= QWindowsIntegration::DarkModeWindowFrames | QWindowsIntegration::DarkModeStyle;
         } else {
             qWarning() << "Unknown option" << param;
         }

src/plugins/platforms/windows/qwindowsintegration.h

@@ -70,7 +70,9 @@ public:
         NoNativeMenus = 0x200,
         DontUseWMPointer = 0x400,
         DetectAltGrModifier = 0x800,
-        RtlEnabled = 0x1000
+        RtlEnabled = 0x1000,
+        DarkModeWindowFrames = 0x2000,
+        DarkModeStyle = 0x4000
     };
 
     explicit QWindowsIntegration(const QStringList &paramList);

src/plugins/platforms/windows/qwindowsnativeinterface.cpp

@@ -47,6 +47,7 @@
 #include "qwindowsopengltester.h"
 #include "qwindowsintegration.h"
 #include "qwindowsmime.h"
+#include "qwindowstheme.h"
 #include "qwin10helpers.h"
 
 #include <QtGui/qwindow.h>
@@ -316,4 +317,15 @@ QVariant QWindowsNativeInterface::gpuList() const
     return result;
 }
 
+bool QWindowsNativeInterface::isDarkMode() const
+{
+    return QWindowsContext::isDarkMode();
+}
+
+// Dark mode support level 2 (style)
+bool QWindowsNativeInterface::isDarkModeStyle() const
+{
+    return (QWindowsIntegration::instance()->options() & QWindowsIntegration::DarkModeStyle) != 0;
+}
+
 QT_END_NAMESPACE

src/plugins/platforms/windows/qwindowsnativeinterface.h

@@ -65,6 +65,8 @@ class QWindowsNativeInterface : public QPlatformNativeInterface
 {
     Q_OBJECT
     Q_PROPERTY(bool asyncExpose READ asyncExpose WRITE setAsyncExpose)
+    Q_PROPERTY(bool darkMode READ isDarkMode STORED false NOTIFY darkModeChanged)
+    Q_PROPERTY(bool darkModeStyle READ isDarkModeStyle STORED false)
     Q_PROPERTY(QVariant gpu READ gpu STORED false)
     Q_PROPERTY(QVariant gpuList READ gpuList STORED false)
 
@@ -92,6 +94,9 @@ public:
     bool asyncExpose() const;
     void setAsyncExpose(bool value);
 
+    bool isDarkMode() const;
+    bool isDarkModeStyle() const;
+
     QVariant gpu() const;
     QVariant gpuList() const;
 
@@ -109,6 +114,9 @@ public:
 
     QFunctionPointer platformFunction(const QByteArray &function) const override;
 
+Q_SIGNALS:
+    void darkModeChanged(bool);
+
 private:
     static QWindowsWindowFunctions::WindowActivationBehavior m_windowActivationBehavior;
 };

src/plugins/platforms/windows/qwindowstheme.cpp

@@ -63,6 +63,7 @@
 #include <QtCore/qcoreapplication.h>
 #include <QtCore/qdebug.h>
 #include <QtCore/qtextstream.h>
+#include <QtCore/qoperatingsystemversion.h>
 #include <QtCore/qsysinfo.h>
 #include <QtCore/qcache.h>
 #include <QtCore/qthread.h>
@@ -78,6 +79,7 @@
 #include <QtFontDatabaseSupport/private/qwindowsfontdatabase_p.h>
 #include <private/qhighdpiscaling_p.h>
 #include <private/qsystemlibrary_p.h>
+#include <private/qwinregistry_p.h>
 
 #include <algorithm>
 
@@ -946,6 +948,23 @@ bool QWindowsTheme::useNativeMenus()
     return result;
 }
 
+bool QWindowsTheme::queryDarkMode()
+{
+    if (QOperatingSystemVersion::current()
+        < QOperatingSystemVersion(QOperatingSystemVersion::Windows, 10, 0, 17763)
+        || queryHighContrast()) {
+        return false;
+    }
+    const auto setting = QWinRegistryKey(HKEY_CURRENT_USER, LR"(Software\Microsoft\Windows\CurrentVersion\Themes\Personalize)")
+                         .dwordValue(L"AppsUseLightTheme");
+    return setting.second && setting.first == 0;
+}
+
+bool QWindowsTheme::queryHighContrast()
+{
+    return booleanSystemParametersInfo(SPI_GETHIGHCONTRAST, false);
+}
+
 QPlatformMenuItem *QWindowsTheme::createPlatformMenuItem() const
 {
     qCDebug(lcQpaMenus) << __FUNCTION__;

src/plugins/platforms/windows/qwindowstheme.h

@@ -84,6 +84,8 @@ public:
     void showPlatformMenuBar() override;
 
     static bool useNativeMenus();
+    static bool queryDarkMode();
+    static bool queryHighContrast();
 
     void refreshFonts();