xcb: Don't assume creating a window will result in ConfigureNotify event

We assumed that creating a window would always result in a configure
notify event, so we delayed sending the initial expose event until
receiving the configure notify.

That strategy fails in cases where the window does not need a reconfigure
after being created, such as when not running a window manager, or when
creating child windows. In those cases the window is just mapped, and
we ended up never sending an expose event.

The problem was masked by sometimes receiving an explicit expose event
from X, just after the mapped notification, which we then sent without
waiting for configure. Unfortunately we can't rely on this behavior
and need to remove the deferred expose event logic, so that we always
ensure that at least one expose event is sent to Qt.

Change-Id: I702be7f24de2a1e89c085fb6bd95bb8ff7792a27
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Reviewed-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@theqtcompany.com>

2 files changed, 3 insertions, 13 deletions

diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index d76f1245e8..6023ee6b29 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -314,8 +314,6 @@ void QXcbWindow::create()
 
     destroy();
 
-    m_deferredExpose = false;
-    m_configureNotifyPending = true;
     m_windowState = Qt::WindowNoState;
 
     Qt::WindowType type = window()->type();
@@ -2022,12 +2020,8 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
     if (newScreen != currentScreen)
         QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->screen());
 
-    m_configureNotifyPending = false;
-
-    if (m_deferredExpose) {
-        m_deferredExpose = false;
+    if (m_mapped)
         QWindowSystemInterface::handleExposeEvent(window(), QRect(QPoint(), geometry().size()));
-    }
 
     if (m_usingSyncProtocol && m_syncState == SyncReceived)
         m_syncState = SyncAndConfigureReceived;
@@ -2094,10 +2088,8 @@ void QXcbWindow::handleMapNotifyEvent(const xcb_map_notify_event_t *event)
         m_mapped = true;
         if (m_deferredActivation)
             requestActivateWindow();
-        if (m_configureNotifyPending)
-            m_deferredExpose = true;
-        else
-            QWindowSystemInterface::handleExposeEvent(window(), QRect(QPoint(), geometry().size()));
+
+        QWindowSystemInterface::handleExposeEvent(window(), QRect(QPoint(), geometry().size()));
     }
 }
 
diff --git a/src/plugins/platforms/xcb/qxcbwindow.h b/src/plugins/platforms/xcb/qxcbwindow.h
index 41c4b4443d..43e66a774d 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.h
+++ b/src/plugins/platforms/xcb/qxcbwindow.h
@@ -231,8 +231,6 @@ protected:
     bool m_transparent;
     bool m_usingSyncProtocol;
     bool m_deferredActivation;
-    bool m_deferredExpose;
-    bool m_configureNotifyPending;
     bool m_embedded;
     bool m_alertState;
     xcb_window_t m_netWmUserTimeWindow;