fix: Multi-screen launcher display anomaly

log: When retrieving wallpaper, the function GetCurrentWorkspaceBackgroundForMonitor was called using only the main screen or an incorrect screen name instead of the screen where the launcher currently resides. If this fails to return a valid result, the wallpaper won't update. Consequently, the appearance service consistently returns the main screen's wallpaper.

pms: bug-343521

Author: JWWTSL

src/ddeintegration/appearance.cpp

@@ -65,20 +65,32 @@ void Appearance::updateCurrentWallpaperBlurhash()
         return;
     }
 
-    // Use the current screen where the launcher is displayed
-    // Priority: 1. LauncherController.currentScreen, 2. Dock position, 3. Cursor position, 4. Primary screen
-    QString screenName = LauncherController::instance().currentScreen();
-    if (screenName.isEmpty()) {
-        // Try to get screen from dock position (launcher opens on the same screen as dock)
-        QRect dockGeometry = DesktopIntegration::instance().dockGeometry();
-        if (dockGeometry.isValid() && dockGeometry.x() >= 0) {
-            QPoint dockCenter = dockGeometry.center();
-            QScreen *screenAtDock = qApp->screenAt(dockCenter);
-            if (screenAtDock) {
-                screenName = screenAtDock->name();
-            }
+    // TODO: LauncherController.currentScreen is sometimes empty when read here (QML sets it from dock later),
+    // so we fallback to dock geometry / cursor / primary. In practice we always hit dockGeometry; currentScreen
+    // and dock are the same logical source. Could simplify to use only dock geometry first if desired.
+    auto screenByName = [](const QString &name) -> QScreen * {
+        if (name.isEmpty())
+            return nullptr;
+        for (QScreen *s : qApp->screens()) {
+            if (s && s->name() == name)
+                return s;
         }
+        return nullptr;
+    };
+    QString requestedScreenName = LauncherController::instance().currentScreen();
+    QScreen *targetScreen = screenByName(requestedScreenName);
+    if (!targetScreen) {
+        QRect dockGeometry = DesktopIntegration::instance().dockGeometry();
+        if (dockGeometry.isValid() && dockGeometry.width() > 0 && dockGeometry.height() > 0)
+            targetScreen = qApp->screenAt(dockGeometry.center());
     }
+    if (!targetScreen)
+        targetScreen = qApp->screenAt(QCursor::pos());
+    if (!targetScreen)
+        targetScreen = QGuiApplication::primaryScreen();
+    QString screenName = targetScreen ? targetScreen->name() : QString();
+    if (screenName.isEmpty() || !m_dbusAppearanceIface->isValid())
+        return;
     qCDebug(logDdeIntegration) << "Getting wallpaper for screen:" << screenName;
     QDBusPendingReply<QString> async = m_dbusAppearanceIface->GetCurrentWorkspaceBackgroundForMonitor(screenName);
     QDBusPendingCallWatcher *watcher = new QDBusPendingCallWatcher(async, this);