Xcb: fix crash on screen power save

Handle various cases where we have null QScreen or QPlatformScreen
pointers. With this change, I can run Qt Creator for several days.
Before, it would crash multiple times per day with a two-monitor
setup.

Change-Id: I0923d886ae2a4199ac37edd711ddd4f6f99df93d
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>

3 files changed, 14 insertions, 4 deletions

diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.cpp b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
index 25f1ea5236..1825a463d0 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.cpp
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.cpp
@@ -311,9 +311,12 @@ QPaintDevice *QXcbBackingStore::paintDevice()
 
 void QXcbBackingStore::beginPaint(const QRegion &region)
 {
+    if (!m_image && !m_size.isEmpty())
+        resize(m_size, QRegion());
+
     if (!m_image)
         return;
-
+    m_size = QSize();
     m_paintRegion = region;
     m_image->preparePaint(m_paintRegion);
 
@@ -420,7 +423,8 @@ void QXcbBackingStore::resize(const QSize &size, const QRegion &)
         return;
     Q_XCB_NOOP(connection());
 
-    QXcbScreen *screen = static_cast<QXcbScreen *>(window()->screen()->handle());
+
+    QXcbScreen *screen = window()->screen() ? static_cast<QXcbScreen *>(window()->screen()->handle()) : 0;
     QPlatformWindow *pw = window()->handle();
     if (!pw) {
         window()->create();
@@ -429,6 +433,11 @@ void QXcbBackingStore::resize(const QSize &size, const QRegion &)
     QXcbWindow* win = static_cast<QXcbWindow *>(pw);
 
     delete m_image;
+    if (!screen) {
+        m_image = 0;
+        m_size = size;
+        return;
+    }
     m_image = new QXcbShmImage(screen, size, win->depth(), win->imageFormat());
     // Slow path for bgr888 VNC: Create an additional image, paint into that and
     // swap R and B while copying to m_image after each paint.
diff --git a/src/plugins/platforms/xcb/qxcbbackingstore.h b/src/plugins/platforms/xcb/qxcbbackingstore.h
index b58a32d313..1bea36d423 100644
--- a/src/plugins/platforms/xcb/qxcbbackingstore.h
+++ b/src/plugins/platforms/xcb/qxcbbackingstore.h
@@ -71,6 +71,7 @@ private:
     QXcbShmImage *m_image;
     QRegion m_paintRegion;
     QImage m_rgbImage;
+    QSize m_size;
 };
 
 QT_END_NAMESPACE
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index bde8826792..b691c7550f 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -652,7 +652,7 @@ void QXcbWindow::setGeometry(const QRect &rect)
     m_xcbScreen = newScreen;
     const QRect wmGeometry = windowToWmGeometry(rect);
 
-    if (newScreen != currentScreen)
+    if (newScreen && newScreen != currentScreen)
         QWindowSystemInterface::handleWindowScreenChanged(window(), newScreen->QPlatformScreen::screen());
 
     if (qt_window_private(window())->positionAutomatic) {
@@ -1606,7 +1606,7 @@ void QXcbWindow::requestActivateWindow()
         return;
     }
 
-    if (!m_mapped) {
+    if (!m_mapped || !xcbScreen()) {
         m_deferredActivation = true;
         return;
     }