xcb: fix cursorTheme update issue

Clear the cache when cursor theme changed.

Idealy we should subscribe root window's RESOURCE_MANAGER property
to update cursor theme via Xcursor. KDE already has a daemon
KDE GTK Configurator to sync KDE settings to GTK. Then we can
register the fallback there both for KDE and GTK changes. See also
https://invent.kde.org/plasma/kde-gtk-config

Fixes: QTBUG-94538
Change-Id: Ia4de30930a0dc1dc306c61e1553970c3dab67bd6
Reviewed-by: Liang Qi <liang.qi@qt.io>
(cherry picked from commit 7311cdc0d2c10d47511e5b4850e3b348ea10e0d8)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/plugins/platforms/xcb/qxcbcursor.cpp b/src/plugins/platforms/xcb/qxcbcursor.cpp
index 42c7a52bd4..e58e181e49 100644
--- a/src/plugins/platforms/xcb/qxcbcursor.cpp
+++ b/src/plugins/platforms/xcb/qxcbcursor.cpp
@@ -534,6 +534,8 @@ bool updateCursorTheme(void *dpy, const QByteArray &theme) {
     Q_UNUSED(screen);
     Q_UNUSED(name);
     QXcbCursor *self = static_cast<QXcbCursor *>(handle);
+    self->m_cursorHash.clear();
+
     updateCursorTheme(self->connection()->xlib_display(),property.toByteArray());
 }
 
@@ -559,14 +561,16 @@ xcb_cursor_t QXcbCursor::createFontCursor(int cshape)
     int cursorId = cursorIdForShape(cshape);
     xcb_cursor_t cursor = XCB_NONE;
 
-    // Try Xcursor first
 #if QT_CONFIG(xcb_xlib) && QT_CONFIG(library)
+    if (m_screen->xSettings()->initialized())
+        m_screen->xSettings()->registerCallbackForProperty("Gtk/CursorThemeName",cursorThemePropertyChanged,this);
+
+    // Try Xcursor first
     if (cshape >= 0 && cshape <= Qt::LastCursor) {
         void *dpy = connection()->xlib_display();
         cursor = loadCursor(dpy, cshape);
         if (!cursor && !m_gtkCursorThemeInitialized && m_screen->xSettings()->initialized()) {
             QByteArray gtkCursorTheme = m_screen->xSettings()->setting("Gtk/CursorThemeName").toByteArray();
-            m_screen->xSettings()->registerCallbackForProperty("Gtk/CursorThemeName",cursorThemePropertyChanged,this);
             if (updateCursorTheme(dpy,gtkCursorTheme)) {
                 cursor = loadCursor(dpy, cshape);
             }