Implement XEmbed protocol

Add a static QWindow::fromWinId(WId id) constructor which can be used to
create a QWindow object representing windows created by other processes.
Then, QWindow::setParent() can be used to embed a window into a foreign
window socket and QWindow::setTransientParent() to stick the current
window on top of a foreign window.

The changes in the QtWidgets module ensure that the focus chain (TAB
navigation) correctly works when a QtWidgets-based window is embedded
into another application.

As far as the platform implementation is concerned, this commit only
implements the embedding functionality in the XCB plugin. So, this is
roughly equivalent to the Qt4 QX11EmbedWidget functionality.

Change-Id: Iff8f7b9ee974d33fb30f36056f7838b433a413c7
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>

src/corelib/global/qnamespace.h

@@ -284,6 +284,7 @@ public:
         SplashScreen = ToolTip | Dialog,
         Desktop = 0x00000010 | Window,
         SubWindow = 0x00000012,
+        ForeignWindow = 0x00000020 | Window,
 
         WindowType_Mask = 0x000000ff,
         MSWindowsFixedSizeDialogHint = 0x00000100,

src/corelib/global/qnamespace.qdoc

@@ -1966,6 +1966,10 @@
     \value SubWindow  Indicates that this widget is a sub-window, such
                       as a QMdiSubWindow widget.
 
+    \value ForeignWindow Indicates that this window object is a handle
+                         representing a native platform window created by
+                         another process or by manually using native code.
+
     There are also a number of flags which you can use to customize
     the appearance of top-level windows. These have no effect on other
     windows:

src/gui/kernel/qguiapplication.cpp

@@ -1605,7 +1605,7 @@ void QGuiApplicationPrivate::processActivatedEvent(QWindowSystemInterfacePrivate
     }
 
     if (QGuiApplicationPrivate::focus_window) {
-        QFocusEvent focusIn(QEvent::FocusIn);
+        QFocusEvent focusIn(QEvent::FocusIn, e->reason);
         QCoreApplication::sendSpontaneousEvent(QGuiApplicationPrivate::focus_window, &focusIn);
         QObject::connect(QGuiApplicationPrivate::focus_window, SIGNAL(focusObjectChanged(QObject*)),
                          qApp, SLOT(_q_updateFocusObject(QObject*)));

src/gui/kernel/qplatformintegration.cpp

@@ -206,6 +206,10 @@ QPlatformServices *QPlatformIntegration::services() const
     state explicitly by using QWindowSystemInterface::handleApplicationStateChanged().
     If not set, application state will follow window activation, which is the normal
     behavior for desktop platforms.
+
+    \value ForeignWindows The platform allows creating QWindows which represent
+    native windows created by other processes or anyway created by using native
+    libraries.
  */
 
 

src/gui/kernel/qplatformintegration.h

@@ -89,7 +89,8 @@ public:
         BufferQueueingOpenGL,
         WindowMasks,
         MultipleWindows,
-        ApplicationState
+        ApplicationState,
+        ForeignWindows
     };
 
     virtual ~QPlatformIntegration() { }

src/gui/kernel/qwindow.cpp

@@ -474,6 +474,10 @@ void QWindow::create()
 WId QWindow::winId() const
 {
     Q_D(const QWindow);
+
+    if (type() == Qt::ForeignWindow)
+        return WId(property("_q_foreignWinId").value<WId>());
+
     if(!d->platformWindow)
         const_cast<QWindow *>(this)->create();
 
@@ -499,8 +503,11 @@ QWindow *QWindow::parent() const
     the clip of the window, so it will be clipped to the \a parent window.
 
     Setting \a parent to be 0 will make the window become a top level window.
-*/
 
+    If \a parent is a window created by fromWinId(), then the current window
+    will be embedded inside \a parent, if the platform supports it. Window
+    embedding is currently supported only by the X11 platform plugin.
+*/
 void QWindow::setParent(QWindow *parent)
 {
     Q_D(QWindow);
@@ -2104,6 +2111,34 @@ void QWindowPrivate::maybeQuitOnLastWindowClosed()
 
 }
 
+/*!
+    Creates a local representation of a window created by another process or by
+    using native libraries below Qt.
+
+    Given the handle \a id to a native window, this method creates a QWindow
+    object which can be used to represent the window when invoking methods like
+    setParent() and setTransientParent().
+    This can be used, on platforms which support it, to embed a window inside a
+    container or to make a window stick on top of a window created by another
+    process.
+
+    \sa setParent()
+    \sa setTransientParent()
+*/
+QWindow *QWindow::fromWinId(WId id)
+{
+    if (!QGuiApplicationPrivate::platformIntegration()->hasCapability(QPlatformIntegration::ForeignWindows)) {
+        qWarning() << "QWindow::fromWinId(): platform plugin does not support foreign windows.";
+        return 0;
+    }
+
+    QWindow *window = new QWindow;
+    window->setFlags(Qt::ForeignWindow);
+    window->setProperty("_q_foreignWinId", QVariant::fromValue(id));
+    window->create();
+    return window;
+}
+
 #ifndef QT_NO_CURSOR
 /*!
     \brief set the cursor shape for this window

src/gui/kernel/qwindow.h

@@ -257,6 +257,8 @@ public:
     void unsetCursor();
 #endif
 
+    static QWindow *fromWinId(WId id);
+
 public Q_SLOTS:
     void setVisible(bool visible);
 

src/gui/kernel/qwindowsysteminterface.cpp

@@ -112,9 +112,10 @@ void QWindowSystemInterface::handleEnterLeaveEvent(QWindow *enter, QWindow *leav
     }
 }
 
-void QWindowSystemInterface::handleWindowActivated(QWindow *tlw)
+void QWindowSystemInterface::handleWindowActivated(QWindow *tlw, Qt::FocusReason r)
 {
-    QWindowSystemInterfacePrivate::ActivatedWindowEvent *e = new QWindowSystemInterfacePrivate::ActivatedWindowEvent(tlw);
+    QWindowSystemInterfacePrivate::ActivatedWindowEvent *e =
+        new QWindowSystemInterfacePrivate::ActivatedWindowEvent(tlw, r);
     QWindowSystemInterfacePrivate::handleWindowSystemEvent(e);
 }
 

src/gui/kernel/qwindowsysteminterface.h

@@ -135,7 +135,8 @@ public:
     static void handleEnterEvent(QWindow *w, const QPointF &local = QPointF(), const QPointF& global = QPointF());
     static void handleLeaveEvent(QWindow *w);
     static void handleEnterLeaveEvent(QWindow *enter, QWindow *leave, const QPointF &local = QPointF(), const QPointF& global = QPointF());
-    static void handleWindowActivated(QWindow *w);
+    static void handleWindowActivated(QWindow *w, Qt::FocusReason r = Qt::OtherFocusReason);
+
     static void handleWindowStateChanged(QWindow *w, Qt::WindowState newState);
 
     static void handleApplicationStateChanged(Qt::ApplicationState newState);

src/gui/kernel/qwindowsysteminterface_p.h

@@ -139,10 +139,11 @@ public:
 
     class ActivatedWindowEvent : public WindowSystemEvent {
     public:
-        explicit ActivatedWindowEvent(QWindow *activatedWindow)
+        explicit ActivatedWindowEvent(QWindow *activatedWindow, Qt::FocusReason r)
-            : WindowSystemEvent(ActivatedWindow), activated(activatedWindow)
+            : WindowSystemEvent(ActivatedWindow), activated(activatedWindow), reason(r)
         { }
         QPointer<QWindow> activated;
+        Qt::FocusReason reason;
     };
 
     class WindowStateChangedEvent : public WindowSystemEvent {

src/plugins/platforms/xcb/qxcbconnection.cpp

@@ -1066,7 +1066,7 @@ void QXcbConnection::processXcbEvents()
             while (it != m_peekFuncs.end()) {
                 // These callbacks return true if the event is what they were
                 // waiting for, remove them from the list in that case.
-                if ((*it)(event))
+                if ((*it)(this, event))
                     it = m_peekFuncs.erase(it);
                 else
                     ++it;
@@ -1086,7 +1086,7 @@ void QXcbConnection::processXcbEvents()
     // Indicate with a null event that the event the callbacks are waiting for
     // is not in the queue currently.
     Q_FOREACH (PeekFunc f, m_peekFuncs)
-        f(0);
+        f(this, 0);
     m_peekFuncs.clear();
 
     xcb_flush(xcb_connection());

src/plugins/platforms/xcb/qxcbconnection.h

@@ -364,7 +364,7 @@ public:
     template<typename T>
     inline xcb_generic_event_t *checkEvent(T &checker);
 
-    typedef bool (*PeekFunc)(xcb_generic_event_t *);
+    typedef bool (*PeekFunc)(QXcbConnection *, xcb_generic_event_t *);
     void addPeekFunc(PeekFunc f);
 
     inline xcb_timestamp_t time() const { return m_time; }

src/plugins/platforms/xcb/qxcbintegration.cpp

@@ -228,6 +228,7 @@ bool QXcbIntegration::hasCapability(QPlatformIntegration::Capability cap) const
     case ThreadedOpenGL: return m_connections.at(0)->supportsThreadedRendering();
     case WindowMasks: return true;
     case MultipleWindows: return true;
+    case ForeignWindows: return true;
     default: return QPlatformIntegration::hasCapability(cap);
     }
 }

src/plugins/platforms/xcb/qxcbwindow.cpp

@@ -122,6 +122,36 @@ enum {
 
 QT_BEGIN_NAMESPACE
 
+#undef FocusIn
+
+enum QX11EmbedFocusInDetail {
+    XEMBED_FOCUS_CURRENT = 0,
+    XEMBED_FOCUS_FIRST = 1,
+    XEMBED_FOCUS_LAST = 2
+};
+
+enum QX11EmbedInfoFlags {
+    XEMBED_MAPPED = (1 << 0),
+};
+
+enum QX11EmbedMessageType {
+    XEMBED_EMBEDDED_NOTIFY = 0,
+    XEMBED_WINDOW_ACTIVATE = 1,
+    XEMBED_WINDOW_DEACTIVATE = 2,
+    XEMBED_REQUEST_FOCUS = 3,
+    XEMBED_FOCUS_IN = 4,
+    XEMBED_FOCUS_OUT = 5,
+    XEMBED_FOCUS_NEXT = 6,
+    XEMBED_FOCUS_PREV = 7,
+    XEMBED_MODALITY_ON = 10,
+    XEMBED_MODALITY_OFF = 11,
+    XEMBED_REGISTER_ACCELERATOR = 12,
+    XEMBED_UNREGISTER_ACCELERATOR = 13,
+    XEMBED_ACTIVATE_ACCELERATOR = 14
+};
+
+static unsigned int XEMBED_VERSION = 0;
+
 // Returns true if we should set WM_TRANSIENT_FOR on \a w
 static inline bool isTransient(const QWindow *w)
 {
@@ -157,6 +187,7 @@ QXcbWindow::QXcbWindow(QWindow *window)
     , m_mapped(false)
     , m_transparent(false)
     , m_deferredActivation(false)
+    , m_embedded(false)
     , m_netWmUserTimeWindow(XCB_NONE)
     , m_dirtyFrameMargins(false)
 #if defined(XCB_USE_EGL)
@@ -168,7 +199,10 @@ QXcbWindow::QXcbWindow(QWindow *window)
 
     setConnection(m_screen->connection());
 
+    if (window->type() != Qt::ForeignWindow)
         create();
+    else
+        m_window = window->winId();
 }
 
 void QXcbWindow::create()
@@ -235,8 +269,10 @@ void QXcbWindow::create()
     }
 
     xcb_window_t xcb_parent_id = m_screen->root();
-    if (parent())
+    if (parent()) {
         xcb_parent_id = static_cast<QXcbWindow *>(parent())->xcb_window();
+        m_embedded = parent()->window()->type() == Qt::ForeignWindow;
+    }
 
     m_format = window()->requestedFormat();
 
@@ -368,6 +404,14 @@ void QXcbWindow::create()
                                    atom(QXcbAtom::WM_CLIENT_LEADER), XCB_ATOM_WINDOW, 32,
                                    1, &leader));
 
+    /* Add XEMBED info; this operation doesn't initiate the embedding. */
+    long data[] = { XEMBED_VERSION, XEMBED_MAPPED };
+    Q_XCB_CALL(xcb_change_property(xcb_connection(), XCB_PROP_MODE_REPLACE, m_window,
+                                   atom(QXcbAtom::_XEMBED_INFO),
+                                   atom(QXcbAtom::_XEMBED_INFO),
+                                   32, 2, (void *)data));
+
+
 #ifdef XCB_USE_XINPUT2_MAEMO
     if (connection()->isUsingXInput2Maemo()) {
         XIEventMask xieventmask;
@@ -410,6 +454,7 @@ void QXcbWindow::create()
 
 QXcbWindow::~QXcbWindow()
 {
+    if (window()->type() != Qt::ForeignWindow)
         destroy();
 }
 
@@ -574,9 +619,10 @@ void QXcbWindow::show()
         propagateSizeHints();
 
         // update WM_TRANSIENT_FOR
-        if (isTransient(window())) {
+        const QWindow *tp = window()->transientParent();
+        if (isTransient(window()) || tp != 0) {
             xcb_window_t transientXcbParent = 0;
-            if (const QWindow *tp = window()->transientParent())
+            if (tp)
                 transientXcbParent = static_cast<const QXcbWindow *>(tp->handle())->winId();
             // Default to client leader if there is no transient parent, else modal dialogs can
             // be hidden by their parents.
@@ -1140,7 +1186,15 @@ void QXcbWindow::setParent(const QPlatformWindow *parent)
 {
     QPoint topLeft = geometry().topLeft();
 
-    xcb_window_t xcb_parent_id = parent ? static_cast<const QXcbWindow *>(parent)->xcb_window() : m_screen->root();
+    xcb_window_t xcb_parent_id;
+    if (parent) {
+        const QXcbWindow *qXcbParent = static_cast<const QXcbWindow *>(parent);
+        xcb_parent_id = qXcbParent->xcb_window();
+        m_embedded = qXcbParent->window()->type() == Qt::ForeignWindow;
+    } else {
+        xcb_parent_id = m_screen->root();
+        m_embedded = false;
+    }
     Q_XCB_CALL(xcb_reparent_window(xcb_connection(), xcb_window(), xcb_parent_id, topLeft.x(), topLeft.y()));
 }
 
@@ -1271,6 +1325,13 @@ void QXcbWindow::propagateSizeHints()
 
 void QXcbWindow::requestActivateWindow()
 {
+    /* Never activate embedded windows; doing that would prevent the container
+     * to re-gain the keyboard focus later. */
+    if (m_embedded) {
+        QPlatformWindow::requestActivateWindow();
+        return;
+    }
+
     if (!m_mapped) {
         m_deferredActivation = true;
         return;
@@ -1434,7 +1495,8 @@ void QXcbWindow::handleClientMessageEvent(const xcb_client_message_event_t *even
     } else if (event->type == atom(QXcbAtom::XdndDrop)) {
         connection()->drag()->handleDrop(window(), event);
 #endif
-    } else if (event->type == atom(QXcbAtom::_XEMBED)) { // QSystemTrayIcon
+    } else if (event->type == atom(QXcbAtom::_XEMBED)) {
+        handleXEmbedMessage(event);
     } else {
         qWarning() << "QXcbWindow: Unhandled client message:" << connection()->atomName(event->type);
     }
@@ -1476,6 +1538,53 @@ bool QXcbWindow::isExposed() const
     return m_mapped;
 }
 
+bool QXcbWindow::isEmbedded(const QPlatformWindow *parentWindow) const
+{
+    if (!m_embedded)
+        return false;
+
+    return parentWindow ? (parentWindow == parent()) : true;
+}
+
+QPoint QXcbWindow::mapToGlobal(const QPoint &pos) const
+{
+    if (!m_embedded)
+        return pos;
+
+    QPoint ret;
+    xcb_translate_coordinates_cookie_t cookie =
+        xcb_translate_coordinates(xcb_connection(), xcb_window(), m_screen->root(),
+                                  pos.x(), pos.y());
+    xcb_translate_coordinates_reply_t *reply =
+        xcb_translate_coordinates_reply(xcb_connection(), cookie, NULL);
+    if (reply) {
+        ret.setX(reply->dst_x);
+        ret.setY(reply->dst_y);
+        free(reply);
+    }
+
+    return ret;
+}
+
+QPoint QXcbWindow::mapFromGlobal(const QPoint &pos) const
+{
+    if (!m_embedded)
+        return pos;
+    QPoint ret;
+    xcb_translate_coordinates_cookie_t cookie =
+        xcb_translate_coordinates(xcb_connection(), m_screen->root(), xcb_window(),
+                                  pos.x(), pos.y());
+    xcb_translate_coordinates_reply_t *reply =
+        xcb_translate_coordinates_reply(xcb_connection(), cookie, NULL);
+    if (reply) {
+        ret.setX(reply->dst_x);
+        ret.setY(reply->dst_y);
+        free(reply);
+    }
+
+    return ret;
+}
+
 void QXcbWindow::handleMapNotifyEvent(const xcb_map_notify_event_t *event)
 {
     if (event->window == m_window) {
@@ -1506,6 +1615,15 @@ void QXcbWindow::handleButtonPressEvent(const xcb_button_press_event_t *event)
 
     updateNetWmUserTime(event->time);
 
+    if (m_embedded) {
+        if (window() != QGuiApplication::focusWindow()) {
+            const QXcbWindow *container = static_cast<const QXcbWindow *>(parent());
+            Q_ASSERT(container != 0);
+
+            sendXEmbedMessage(container->xcb_window(), XEMBED_REQUEST_FOCUS);
+        }
+    }
+
     QPoint local(event->event_x, event->event_y);
     QPoint global(event->root_x, event->root_y);
 
@@ -1661,6 +1779,25 @@ void QXcbWindow::handlePropertyNotifyEvent(const xcb_property_notify_event_t *ev
             QWindowSystemInterface::handleWindowStateChanged(window(), newState);
             m_lastWindowStateEvent = newState;
         }
+        return;
+    }
+
+    const xcb_atom_t xEmbedInfoAtom = atom(QXcbAtom::_XEMBED_INFO);
+    if (event->atom == xEmbedInfoAtom) {
+        const xcb_get_property_cookie_t get_cookie =
+            xcb_get_property(xcb_connection(), 0, m_window, xEmbedInfoAtom,
+                             XCB_ATOM_ANY, 0, 3);
+
+        xcb_get_property_reply_t *reply =
+            xcb_get_property_reply(xcb_connection(), get_cookie, NULL);
+        if (reply && reply->length >= 2) {
+            const long *data = (const long *)xcb_get_property_value(reply);
+            if (data[1] & XEMBED_MAPPED)
+                Q_XCB_CALL(xcb_map_window(xcb_connection(), m_window));
+            else
+                Q_XCB_CALL(xcb_unmap_window(xcb_connection(), m_window));
+        }
+        free(reply);
     }
 }
 
@@ -1672,7 +1809,7 @@ void QXcbWindow::handleFocusInEvent(const xcb_focus_in_event_t *)
     QWindowSystemInterface::handleWindowActivated(w);
 }
 
-static bool focusInPeeker(xcb_generic_event_t *event)
+static bool focusInPeeker(QXcbConnection *connection, xcb_generic_event_t *event)
 {
     if (!event) {
         // FocusIn event is not in the queue, proceed with FocusOut normally.
@@ -1680,7 +1817,18 @@ static bool focusInPeeker(xcb_generic_event_t *event)
         return true;
     }
     uint response_type = event->response_type & ~0x80;
-    return response_type == XCB_FOCUS_IN;
+    if (response_type == XCB_FOCUS_IN)
+        return true;
+
+    /* We are also interested in XEMBED_FOCUS_IN events */
+    if (response_type == XCB_CLIENT_MESSAGE) {
+        xcb_client_message_event_t *cme = (xcb_client_message_event_t *)event;
+        if (cme->type == connection->atom(QXcbAtom::_XEMBED)
+            && cme->data.data32[1] == XEMBED_FOCUS_IN)
+            return true;
+    }
+
+    return false;
 }
 
 void QXcbWindow::handleFocusOutEvent(const xcb_focus_out_event_t *)
@@ -1744,6 +1892,35 @@ void QXcbWindow::setCursor(xcb_cursor_t cursor)
     xcb_flush(xcb_connection());
 }
 
+void QXcbWindow::windowEvent(QEvent *event)
+{
+    switch (event->type()) {
+    case QEvent::FocusIn:
+        if (m_embedded && !event->spontaneous()) {
+            QFocusEvent *focusEvent = static_cast<QFocusEvent *>(event);
+            switch (focusEvent->reason()) {
+            case Qt::TabFocusReason:
+            case Qt::BacktabFocusReason:
+                {
+                const QXcbWindow *container =
+                    static_cast<const QXcbWindow *>(parent());
+                sendXEmbedMessage(container->xcb_window(),
+                                  focusEvent->reason() == Qt::TabFocusReason ?
+                                  XEMBED_FOCUS_NEXT : XEMBED_FOCUS_PREV);
+                event->accept();
+                }
+                break;
+            default:
+                break;
+            }
+        }
+        break;
+    default:
+        break;
+    }
+    QPlatformWindow::windowEvent(event);
+}
+
 bool QXcbWindow::startSystemResize(const QPoint &pos, Qt::Corner corner)
 {
     const xcb_atom_t moveResize = connection()->atom(QXcbAtom::_NET_WM_MOVERESIZE);
@@ -1772,6 +1949,71 @@ bool QXcbWindow::startSystemResize(const QPoint &pos, Qt::Corner corner)
     return true;
 }
 
+// Sends an XEmbed message.
+void QXcbWindow::sendXEmbedMessage(xcb_window_t window, long message,
+                                   long detail, long data1, long data2)
+{
+    xcb_client_message_event_t event;
+
+    event.response_type = XCB_CLIENT_MESSAGE;
+    event.format = 32;
+    event.window = window;
+    event.type = atom(QXcbAtom::_XEMBED);
+    event.data.data32[0] = connection()->time();
+    event.data.data32[1] = message;
+    event.data.data32[2] = detail;
+    event.data.data32[3] = data1;
+    event.data.data32[4] = data2;
+    Q_XCB_CALL(xcb_send_event(xcb_connection(), false, window,
+                              XCB_EVENT_MASK_NO_EVENT, (const char *)&event));
+}
+
+static bool activeWindowChangeQueued(const QWindow *window)
+{
+    /* Check from window system event queue if the next queued activation
+     * targets a window other than @window.
+     */
+    QWindowSystemInterfacePrivate::ActivatedWindowEvent *systemEvent =
+        static_cast<QWindowSystemInterfacePrivate::ActivatedWindowEvent *>
+        (QWindowSystemInterfacePrivate::peekWindowSystemEvent(QWindowSystemInterfacePrivate::ActivatedWindow));
+    return systemEvent && systemEvent->activated != window;
+}
+
+void QXcbWindow::handleXEmbedMessage(const xcb_client_message_event_t *event)
+{
+    connection()->setTime(event->data.data32[0]);
+    switch (event->data.data32[1]) {
+    case XEMBED_WINDOW_ACTIVATE:
+    case XEMBED_WINDOW_DEACTIVATE:
+    case XEMBED_EMBEDDED_NOTIFY:
+        break;
+    case XEMBED_FOCUS_IN:
+        Qt::FocusReason reason;
+        switch (event->data.data32[2]) {
+        case XEMBED_FOCUS_FIRST:
+            reason = Qt::TabFocusReason;
+            break;
+        case XEMBED_FOCUS_LAST:
+            reason = Qt::BacktabFocusReason;
+            break;
+        case XEMBED_FOCUS_CURRENT:
+        default:
+            reason = Qt::OtherFocusReason;
+            break;
+        }
+        connection()->setFocusWindow(static_cast<QXcbWindow*>(window()->handle()));
+        QWindowSystemInterface::handleWindowActivated(window(), reason);
+        break;
+    case XEMBED_FOCUS_OUT:
+        if (window() == QGuiApplication::focusWindow()
+            && !activeWindowChangeQueued(window())) {
+            connection()->setFocusWindow(0);
+            QWindowSystemInterface::handleWindowActivated(0);
+        }
+        break;
+    }
+}
+
 #if !defined(QT_NO_SHAPE)
 
 static inline xcb_rectangle_t qRectToXCBRectangle(const QRect &r)

src/plugins/platforms/xcb/qxcbwindow.h

@@ -87,6 +87,9 @@ public:
     void setParent(const QPlatformWindow *window);
 
     bool isExposed() const;
+    bool isEmbedded(const QPlatformWindow *parentWindow) const;
+    QPoint mapToGlobal(const QPoint &pos) const;
+    QPoint mapFromGlobal(const QPoint &pos) const;
 
     void setWindowTitle(const QString &title);
     void setWindowIcon(const QIcon &icon);
@@ -107,6 +110,8 @@ public:
 
     QSurfaceFormat format() const;
 
+    void windowEvent(QEvent *event);
+
     bool startSystemResize(const QPoint &pos, Qt::Corner corner);
 
     void setOpacity(qreal level);
@@ -158,6 +163,9 @@ private:
     void updateDoesNotAcceptFocus(bool doesNotAcceptFocus);
 
     QRect windowToWmGeometry(QRect r) const;
+    void sendXEmbedMessage(xcb_window_t window, long message,
+                           long detail = 0, long data1 = 0, long data2 = 0);
+    void handleXEmbedMessage(const xcb_client_message_event_t *event);
 
     void create();
     void destroy();
@@ -184,6 +192,7 @@ private:
     bool m_deferredActivation;
     bool m_deferredExpose;
     bool m_configureNotifyPending;
+    bool m_embedded;
     xcb_window_t m_netWmUserTimeWindow;
 
     QSurfaceFormat m_format;

src/widgets/kernel/qapplication.cpp

@@ -2010,7 +2010,8 @@ void QApplication::setActiveWindow(QWidget* act)
  * Returns 0 if a new focus widget could not be found.
  * Shared with QGraphicsProxyWidgetPrivate::findFocusChild()
 */
-QWidget *QApplicationPrivate::focusNextPrevChild_helper(QWidget *toplevel, bool next)
+QWidget *QApplicationPrivate::focusNextPrevChild_helper(QWidget *toplevel, bool next,
+                                                        bool *wrappingOccurred)
 {
     uint focus_flag = qt_tab_all_widgets() ? Qt::TabFocus : Qt::StrongFocus;
 
@@ -2020,18 +2021,29 @@ QWidget *QApplicationPrivate::focusNextPrevChild_helper(QWidget *toplevel, bool
 
     QWidget *w = f;
     QWidget *test = f->d_func()->focus_next;
+    bool seenWindow = false;
+    bool focusWidgetAfterWindow = false;
     while (test && test != f) {
+        if (test->isWindow())
+            seenWindow = true;
+
         if ((test->focusPolicy() & focus_flag) == focus_flag
             && !(test->d_func()->extra && test->d_func()->extra->focus_proxy)
             && test->isVisibleTo(toplevel) && test->isEnabled()
             && !(w->windowType() == Qt::SubWindow && !w->isAncestorOf(test))
             && (toplevel->windowType() != Qt::SubWindow || toplevel->isAncestorOf(test))) {
             w = test;
+            if (seenWindow)
+                focusWidgetAfterWindow = true;
             if (next)
                 break;
         }
         test = test->d_func()->focus_next;
     }
+
+    if (wrappingOccurred != 0)
+        *wrappingOccurred = next ? focusWidgetAfterWindow : !focusWidgetAfterWindow;
+
     if (w == f) {
         if (qt_in_tab_key_event) {
             w->window()->setAttribute(Qt::WA_KeyboardFocusChange);

src/widgets/kernel/qapplication_p.h

@@ -165,7 +165,8 @@ public:
     void closePopup(QWidget *popup);
     void openPopup(QWidget *popup);
     static void setFocusWidget(QWidget *focus, Qt::FocusReason reason);
-    static QWidget *focusNextPrevChild_helper(QWidget *toplevel, bool next);
+    static QWidget *focusNextPrevChild_helper(QWidget *toplevel, bool next,
+                                              bool *wrappingOccurred = 0);
 
 #ifndef QT_NO_GRAPHICSVIEW
     // Maintain a list of all scenes to ensure font and palette propagation to

src/widgets/kernel/qwidget.cpp

@@ -6138,10 +6138,34 @@ bool QWidget::focusNextPrevChild(bool next)
     if (d->extra && d->extra->proxyWidget)
         return d->extra->proxyWidget->focusNextPrevChild(next);
 #endif
-    QWidget *w = QApplicationPrivate::focusNextPrevChild_helper(this, next);
+
+    bool wrappingOccurred = false;
+    QWidget *w = QApplicationPrivate::focusNextPrevChild_helper(this, next,
+                                                                &wrappingOccurred);
     if (!w) return false;
 
-    w->setFocus(next ? Qt::TabFocusReason : Qt::BacktabFocusReason);
+    Qt::FocusReason reason = next ? Qt::TabFocusReason : Qt::BacktabFocusReason;
+
+    /* If we are about to wrap the focus chain, give the platform
+     * implementation a chance to alter the wrapping behavior.  This is
+     * especially needed when the window is embedded in a window created by
+     * another process.
+     */
+    if (wrappingOccurred) {
+        QWindow *window = windowHandle();
+        if (window != 0) {
+            QWindowPrivate *winp = qt_window_private(window);
+
+            if (winp->platformWindow != 0) {
+                QFocusEvent event(QEvent::FocusIn, reason);
+                event.ignore();
+                winp->platformWindow->windowEvent(&event);
+                if (event.isAccepted()) return true;
+            }
+        }
+    }
+
+    w->setFocus(reason);
     return true;
 }
 

src/widgets/kernel/qwidgetwindow.cpp

@@ -52,6 +52,8 @@
 
 QT_BEGIN_NAMESPACE
 
+Q_WIDGETS_EXPORT extern bool qt_tab_all_widgets();
+
 QWidget *qt_button_down = 0; // widget got last button-down
 static QWidget *qt_tablet_target = 0;
 
@@ -123,6 +125,8 @@ bool QWidgetWindow::event(QEvent *event)
     // these should not be sent to QWidget, the corresponding events
     // are sent by QApplicationPrivate::notifyActiveWindowChange()
     case QEvent::FocusIn:
+        handleFocusInEvent(static_cast<QFocusEvent *>(event));
+        // Fallthrough
     case QEvent::FocusOut: {
 #ifndef QT_NO_ACCESSIBILITY
         QAccessible::State state;
@@ -284,6 +288,42 @@ void QWidgetWindow::handleEnterLeaveEvent(QEvent *event)
     }
 }
 
+QWidget *QWidgetWindow::getFocusWidget(FocusWidgets fw)
+{
+    QWidget *tlw = m_widget;
+    QWidget *w = tlw->nextInFocusChain();
+
+    QWidget *last = tlw;
+
+    uint focus_flag = qt_tab_all_widgets() ? Qt::TabFocus : Qt::StrongFocus;
+
+    while (w != tlw)
+    {
+        if (((w->focusPolicy() & focus_flag) == focus_flag)
+            && w->isVisibleTo(m_widget) && w->isEnabled())
+        {
+            last = w;
+            if (fw == FirstFocusWidget)
+                break;
+        }
+        w = w->nextInFocusChain();
+    }
+
+    return last;
+}
+
+void QWidgetWindow::handleFocusInEvent(QFocusEvent *e)
+{
+    QWidget *focusWidget = 0;
+    if (e->reason() == Qt::BacktabFocusReason)
+        focusWidget = getFocusWidget(LastFocusWidget);
+    else if (e->reason() == Qt::TabFocusReason)
+        focusWidget = getFocusWidget(FirstFocusWidget);
+
+    if (focusWidget != 0)
+        focusWidget->setFocus();
+}
+
 void QWidgetWindow::handleNonClientAreaMouseEvent(QMouseEvent *e)
 {
     QApplication::sendSpontaneousEvent(m_widget, e);

src/widgets/kernel/qwidgetwindow_qpa_p.h

@@ -70,6 +70,7 @@ protected:
 
     void handleCloseEvent(QCloseEvent *);
     void handleEnterLeaveEvent(QEvent *);
+    void handleFocusInEvent(QFocusEvent *);
     void handleKeyEvent(QKeyEvent *);
     void handleMouseEvent(QMouseEvent *);
     void handleNonClientAreaMouseEvent(QMouseEvent *);
@@ -100,6 +101,12 @@ private slots:
 private:
     void updateGeometry();
 
+    enum FocusWidgets {
+        FirstFocusWidget,
+        LastFocusWidget
+    };
+    QWidget *getFocusWidget(FocusWidgets fw);
+
     QWidget *m_widget;
     QPointer<QWidget> m_implicit_mouse_grabber;
 #ifndef QT_NO_DRAGANDDROP