From 738c180c4f03bf82efce04dc4c751cd6eb0043c7 Mon Sep 17 00:00:00 2001
From: Axel Spoerl <axel.spoerl@qt.io>
Date: Fri, 28 Feb 2025 09:08:37 +0100
Subject: [PATCH] Re-implement QPlatformTheme::requestColorScheme() in
 QGtk3Theme

QGtk3Theme remained unresponsive to programmatic color scheme changes,
after QPlatformTheme::requestColorScheme() had been introduced.

Add functionality to QGtk3Theme.
Fall back to qt_fusion_palette, when the requested color scheme isn't
supported by the current GTK3 theme (e.g. Adwaita-dark doesn't support
light mode).

Functionality has to be manually tested with the widget gallery
example.

Fixes: QTBUG-134022
Task-number: QTBUG-132929
Pick-to: 6.9 6.8
Change-Id: I1160c7afc1f1fcb6ec93d65ef54cb45a65a63863
Reviewed-by: Santhosh Kumar <santhosh.kumar.selvaraj@qt.io>
---
 .../platformthemes/gtk3/qgtk3theme.cpp        | 33 +++++++++++++++++--
 src/plugins/platformthemes/gtk3/qgtk3theme.h  |  2 ++
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/src/plugins/platformthemes/gtk3/qgtk3theme.cpp b/src/plugins/platformthemes/gtk3/qgtk3theme.cpp
index b21c45da7a0..ec54872347e 100644
--- a/src/plugins/platformthemes/gtk3/qgtk3theme.cpp
+++ b/src/plugins/platformthemes/gtk3/qgtk3theme.cpp
@@ -159,10 +159,28 @@ QString QGtk3Theme::gtkFontName() const
     return QGnomeTheme::gtkFontName();
 }
 
+void QGtk3Theme::requestColorScheme(Qt::ColorScheme scheme)
+{
+    if (m_requestedColorScheme == scheme)
+        return;
+    qCDebug(lcQGtk3Interface) << scheme << "has been requested. Theme supports color scheme:"
+                              << m_storage->colorScheme();
+    m_requestedColorScheme = scheme;
+    m_storage->handleThemeChange();
+}
+
 Qt::ColorScheme QGtk3Theme::colorScheme() const
 {
     Q_ASSERT(m_storage);
-    return m_storage->colorScheme();
+#ifdef QT_DEBUG
+    if (m_requestedColorScheme != Qt::ColorScheme::Unknown
+        && m_requestedColorScheme != m_storage->colorScheme()) {
+        qCDebug(lcQGtk3Interface) << "Requested color scheme" << m_requestedColorScheme
+                                  << "differs from theme color scheme" << m_storage->colorScheme();
+    }
+#endif
+    return m_requestedColorScheme == Qt::ColorScheme::Unknown ? m_storage->colorScheme()
+                                                              : m_requestedColorScheme;
 }
 
 bool QGtk3Theme::usePlatformNativeDialog(DialogType type) const
@@ -211,7 +229,18 @@ bool QGtk3Theme::useNativeFileDialog()
 const QPalette *QGtk3Theme::palette(Palette type) const
 {
     Q_ASSERT(m_storage);
-    return m_storage->palette(type);
+#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"
+                                  << m_requestedColorScheme << "Falling back to fusion palette.";
+        return QPlatformTheme::palette(type);
+    }
+#endif
+
+    return (m_requestedColorScheme != Qt::ColorScheme::Unknown
+            && m_requestedColorScheme != m_storage->colorScheme())
+               ? QPlatformTheme::palette(type) : m_storage->palette(type);
 }
 
 QPixmap QGtk3Theme::standardPixmap(StandardPixmap sp, const QSizeF &size) const
diff --git a/src/plugins/platformthemes/gtk3/qgtk3theme.h b/src/plugins/platformthemes/gtk3/qgtk3theme.h
index 5b67ca07658..7eb62bf4c84 100644
--- a/src/plugins/platformthemes/gtk3/qgtk3theme.h
+++ b/src/plugins/platformthemes/gtk3/qgtk3theme.h
@@ -19,6 +19,7 @@ public:
     virtual QString gtkFontName() const override;
 
     Qt::ColorScheme colorScheme() const override;
+    void requestColorScheme(Qt::ColorScheme scheme) override;
 
     bool usePlatformNativeDialog(DialogType type) const override;
     QPlatformDialogHelper *createPlatformDialogHelper(DialogType type) const override;
@@ -31,6 +32,7 @@ public:
 
     static const char *name;
 private:
+    Qt::ColorScheme m_requestedColorScheme = Qt::ColorScheme::Unknown;
     static bool useNativeFileDialog();
     std::unique_ptr<QGtk3Storage> m_storage;
 };