xcb: Use a placeholder QScreen when there are no outputs connected

If no screens are available, windows could disappear, could stop rendering
graphics, or the application could crash.  This is a real use case in several
scenarios: with x11vnc, when all monitors are physically disconnected from a
desktop machine, or in some cases even when the monitor sleeps.  Now when the
last screen is disconnected, it is transformed into a fake screen.  When a
physical screen appears, the fake QScreen is transformed into a representation
of the physical screen.  Every virtual desktop has its own fake screen, and
primary screens must belong to the primary virtual desktop. It fixes updating
screen geometry on temporarily disabled screens in the middle of the mode
switch.

Expected results: Windows don't disappear, the application doesn't
crash, and QMenu is displayed on the appropriate screen.

This reverts patch 51ada7734ad780178ecced11e0dff454dfc2e5f2

Change-Id: I6e8eb682b0c8425d08ffdaecbd4c6c7700c914b4
Task-number: QTBUG-42985
Reviewed-by: Shawn Rutledge <shawn.rutledge@theqtcompany.com>

1 files changed, 8 insertions, 30 deletions

diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index 6add0a6333..bdbb9e9fe0 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -622,14 +622,6 @@ void QXcbWindow::destroy()
         m_pendingSyncRequest->invalidate();
 }
 
-void QXcbWindow::maybeSetScreen(QXcbScreen *screen)
-{
-    if (!window()->screen() && screen->geometry().contains(geometry().topLeft())) {
-        QWindowSystemInterface::handleWindowScreenChanged(window(), static_cast<QPlatformScreen *>(screen)->screen());
-        QWindowSystemInterface::handleExposeEvent(window(), QRegion(QRect(QPoint(0, 0), window()->size())));
-    }
-}
-
 void QXcbWindow::setGeometry(const QRect &rect)
 {
     QPlatformWindow::setGeometry(rect);
@@ -845,15 +837,13 @@ void QXcbWindow::hide()
     Q_XCB_CALL(xcb_unmap_window(xcb_connection(), m_window));
 
     // send synthetic UnmapNotify event according to icccm 4.1.4
-    if (xcbScreen()) {
-        xcb_unmap_notify_event_t event;
-        event.response_type = XCB_UNMAP_NOTIFY;
-        event.event = xcbScreen()->root();
-        event.window = m_window;
-        event.from_configure = false;
-        Q_XCB_CALL(xcb_send_event(xcb_connection(), false, xcbScreen()->root(),
-                                  XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY | XCB_EVENT_MASK_SUBSTRUCTURE_REDIRECT, (const char *)&event));
-    }
+    xcb_unmap_notify_event_t event;
+    event.response_type = XCB_UNMAP_NOTIFY;
+    event.event = xcbScreen()->root();
+    event.window = m_window;
+    event.from_configure = false;
+    Q_XCB_CALL(xcb_send_event(xcb_connection(), false, xcbScreen()->root(),
+                              XCB_EVENT_MASK_SUBSTRUCTURE_NOTIFY | XCB_EVENT_MASK_SUBSTRUCTURE_REDIRECT, (const char *)&event));
 
     xcb_flush(xcb_connection());
 
@@ -1181,8 +1171,6 @@ void QXcbWindow::changeNetWmState(bool set, xcb_atom_t one, xcb_atom_t two)
     event.data.data32[3] = 0;
     event.data.data32[4] = 0;
 
-    if (!xcbScreen())
-        return;
     Q_XCB_CALL(xcb_send_event(xcb_connection(), 0, xcbScreen()->root(), XCB_EVENT_MASK_STRUCTURE_NOTIFY | XCB_EVENT_MASK_SUBSTRUCTURE_REDIRECT, (const char *)&event));
 }
 
@@ -1435,8 +1423,6 @@ void QXcbWindow::setParent(const QPlatformWindow *parent)
         xcb_parent_id = qXcbParent->xcb_window();
         m_embedded = qXcbParent->window()->type() == Qt::ForeignWindow;
     } else {
-        if (!xcbScreen())
-            return;
         xcb_parent_id = xcbScreen()->root();
         m_embedded = false;
     }
@@ -1992,7 +1978,7 @@ void QXcbWindow::handleConfigureNotifyEvent(const xcb_configure_notify_event_t *
 {
     bool fromSendEvent = (event->response_type & 0x80);
     QPoint pos(event->x, event->y);
-    if (!parent() && !fromSendEvent && xcbScreen()) {
+    if (!parent() && !fromSendEvent) {
         // Do not trust the position, query it instead.
         xcb_translate_coordinates_cookie_t cookie = xcb_translate_coordinates(xcb_connection(), xcb_window(),
                                                                               xcbScreen()->root(), 0, 0);
@@ -2305,8 +2291,6 @@ void QXcbWindow::handleEnterNotifyEvent(const xcb_enter_notify_event_t *event)
         return;
 
     const QPoint local(event->event_x, event->event_y);
-    if (!xcbScreen())
-        return;
     QPoint global = QPoint(event->root_x, event->root_y);
     QWindowSystemInterface::handleEnterEvent(window(), local, global);
 }
@@ -2324,8 +2308,6 @@ void QXcbWindow::handleLeaveNotifyEvent(const xcb_leave_notify_event_t *event)
 
     if (enterWindow) {
         QPoint local(enter->event_x, enter->event_y);
-        if (!xcbScreen())
-            return;
         QPoint global = QPoint(event->root_x, event->root_y);
 
         QWindowSystemInterface::handleEnterLeaveEvent(enterWindow->window(), window(), local, global);
@@ -2341,8 +2323,6 @@ void QXcbWindow::handlePropertyNotifyEvent(const xcb_property_notify_event_t *ev
     connection()->setTime(event->time);
 
     const bool propertyDeleted = event->state == XCB_PROPERTY_DELETE;
-    if (!xcbScreen())
-        return;
 
     if (event->atom == atom(QXcbAtom::_NET_WM_STATE) || event->atom == atom(QXcbAtom::WM_STATE)) {
         if (propertyDeleted)
@@ -2662,8 +2642,6 @@ bool QXcbWindow::needsSync() const
 
 void QXcbWindow::postSyncWindowRequest()
 {
-    if (!xcbScreen())
-        return;
     if (!m_pendingSyncRequest) {
         QXcbSyncWindowRequest *e = new QXcbSyncWindowRequest(this);
         m_pendingSyncRequest = e;