Add API in QWindowsPrivate to provide window palette

The window uses default palette (QPalette()) to determine frame
color (either light or dark). This doesn't work for quickcontrols
as they depend quicktheme palettes and they don't overwrite default
palettes.

This patch add API in QWindowPrivate to provide palette for window
and this can be overridden by quickcontrol windows to provide
their corresponding palette.

Fixes: QTBUG-111491
Pick-to: 6.5
Change-Id: I39eea20ee7c61ecf0279143c9784da35be15edd3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

2 files changed, 8 insertions, 4 deletions

diff --git a/src/gui/kernel/qwindow_p.h b/src/gui/kernel/qwindow_p.h
index cf6a6934eb..ef633d093a 100644
--- a/src/gui/kernel/qwindow_p.h
+++ b/src/gui/kernel/qwindow_p.h
@@ -23,7 +23,8 @@
 #include <QtCore/private/qobject_p.h>
 #include <QtCore/qelapsedtimer.h>
 #include <QtCore/qxpfunctional.h>
-#include <QtGui/QIcon>
+#include <QtGui/qicon.h>
+#include <QtGui/qpalette.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -53,6 +54,7 @@ public:
     QWindow *topLevelWindow(QWindow::AncestorMode mode = QWindow::IncludeTransients) const;
 
     virtual QWindow *eventReceiver() { Q_Q(QWindow); return q; }
+    virtual QPalette windowPalette() const { return QPalette(); }
 
     virtual void setVisible(bool visible);
     void updateVisibility();
diff --git a/src/plugins/platforms/windows/qwindowswindow.cpp b/src/plugins/platforms/windows/qwindowswindow.cpp
index 7dec51c4cc..6fcc226abc 100644
--- a/src/plugins/platforms/windows/qwindowswindow.cpp
+++ b/src/plugins/platforms/windows/qwindowswindow.cpp
@@ -845,11 +845,13 @@ static inline bool shouldApplyDarkFrame(const QWindow *w)
     // the application has explicitly opted out of dark frames
     if (!QWindowsIntegration::instance()->darkModeHandling().testFlag(QWindowsApplication::DarkModeWindowFrames))
         return false;
+
     // if the application supports a dark border, and the palette is dark (window background color
     // is darker than the text), then turn dark-border support on, otherwise use a light border.
-    const QPalette defaultPalette;
-    return defaultPalette.color(QPalette::WindowText).lightness()
-         > defaultPalette.color(QPalette::Window).lightness();
+    auto *dWindow = QWindowPrivate::get(const_cast<QWindow*>(w));
+    const QPalette windowPal = dWindow->windowPalette();
+    return windowPal.color(QPalette::WindowText).lightness()
+         > windowPal.color(QPalette::Window).lightness();
 }
 
 QWindowsWindowData