xcb: Fix artifacts on the tray background with lock screens

With the current method of painting the tray icon with 24 bpp
visuals we grab the window's background once on the first show
and then use it in all paint operations. This leads to a wrong
background if an application shows the system tray icon when
the lock screen is active.

We can avoid this by painting with XRender when it's available.

This change introduces QXcbSystemTrayBackingStore and moves the
selection of a suitable painting method from QSystemTrayIconSys
into it. In addition the visual for the window is selected
according to the system tray specification and the platform window
for the tray icon is created without needless OpenGL and Vulkan
support.

Task-number: QTBUG-55540
Change-Id: Ib3ca42bc02dcbdd4ccfe5d6e23f870ef22f0d25a
Reviewed-by: Gatis Paeglis <gatis.paeglis@qt.io>

1 files changed, 21 insertions, 8 deletions

diff --git a/src/plugins/platforms/xcb/qxcbsystemtraytracker.cpp b/src/plugins/platforms/xcb/qxcbsystemtraytracker.cpp
index c98879c7df..8b9c67e98a 100644
--- a/src/plugins/platforms/xcb/qxcbsystemtraytracker.cpp
+++ b/src/plugins/platforms/xcb/qxcbsystemtraytracker.cpp
@@ -162,10 +162,28 @@ void QXcbSystemTrayTracker::handleDestroyNotifyEvent(const xcb_destroy_notify_ev
     }
 }
 
+xcb_visualid_t QXcbSystemTrayTracker::visualId()
+{
+    xcb_visualid_t visual = netSystemTrayVisual();
+    if (visual == XCB_NONE)
+        visual = m_connection->primaryScreen()->screen()->root_visual;
+    return visual;
+}
+
 bool QXcbSystemTrayTracker::visualHasAlphaChannel()
 {
+    const xcb_visualid_t systrayVisualId = netSystemTrayVisual();
+    if (systrayVisualId != XCB_NONE) {
+        quint8 depth = m_connection->primaryScreen()->depthOfVisual(systrayVisualId);
+        return depth == 32;
+    }
+    return false;
+}
+
+xcb_visualid_t QXcbSystemTrayTracker::netSystemTrayVisual()
+{
     if (m_trayWindow == XCB_WINDOW_NONE)
-        return false;
+        return XCB_NONE;
 
     xcb_atom_t tray_atom = m_connection->atom(QXcbAtom::_NET_SYSTEM_TRAY_VISUAL);
 
@@ -174,7 +192,7 @@ bool QXcbSystemTrayTracker::visualHasAlphaChannel()
                                                     false, m_trayWindow,
                                                     tray_atom, XCB_ATOM_VISUALID, 0, 1);
     if (!systray_atom_reply)
-        return false;
+        return XCB_NONE;
 
     xcb_visualid_t systrayVisualId = XCB_NONE;
     if (systray_atom_reply->value_len > 0 && xcb_get_property_value_length(systray_atom_reply.get()) > 0) {
@@ -182,12 +200,7 @@ bool QXcbSystemTrayTracker::visualHasAlphaChannel()
         systrayVisualId = vids[0];
     }
 
-    if (systrayVisualId != XCB_NONE) {
-        quint8 depth = m_connection->primaryScreen()->depthOfVisual(systrayVisualId);
-        return depth == 32;
-    }
-
-    return false;
+    return systrayVisualId;
 }
 
 QT_END_NAMESPACE