diff --git a/autotests/integration/shell_client_test.cpp b/autotests/integration/shell_client_test.cpp
index b95916807..edfefc272 100644
--- a/autotests/integration/shell_client_test.cpp
+++ b/autotests/integration/shell_client_test.cpp
@@ -1,692 +1,713 @@
 /********************************************************************
 KWin - the KDE window manager
 This file is part of the KDE project.
 
 Copyright (C) 2016 Martin Gräßlin <mgraesslin@kde.org>
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
 (at your option) any later version.
 
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "kwin_wayland_test.h"
 #include "cursor.h"
 #include "effects.h"
 #include "platform.h"
 #include "shell_client.h"
 #include "screens.h"
 #include "wayland_server.h"
 #include "workspace.h"
 
 #include <KWayland/Client/connection_thread.h>
 #include <KWayland/Client/compositor.h>
 #include <KWayland/Client/shell.h>
 #include <KWayland/Client/server_decoration.h>
 #include <KWayland/Client/surface.h>
 #include <KWayland/Client/xdgshell.h>
 
 #include <KWayland/Server/clientconnection.h>
 #include <KWayland/Server/display.h>
 #include <KWayland/Server/shell_interface.h>
 
 // system
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <unistd.h>
 
 using namespace KWin;
 using namespace KWayland::Client;
 
 static const QString s_socketName = QStringLiteral("wayland_test_kwin_shell_client-0");
 
 class TestShellClient : public QObject
 {
     Q_OBJECT
 private Q_SLOTS:
     void initTestCase();
     void init();
     void cleanup();
 
     void testMapUnmapMap_data();
     void testMapUnmapMap();
     void testDesktopPresenceChanged();
     void testTransientPositionAfterRemap();
     void testMinimizeActiveWindow_data();
     void testMinimizeActiveWindow();
     void testFullscreen_data();
     void testFullscreen();
     void testMaximizedToFullscreen_data();
     void testMaximizedToFullscreen();
     void testWindowOpensLargerThanScreen_data();
     void testWindowOpensLargerThanScreen();
     void testHidden_data();
     void testHidden();
     void testDesktopFileName();
     void testCaptionSimplified();
     void testKillWindow_data();
     void testKillWindow();
+    void testX11WindowId_data();
+    void testX11WindowId();
 };
 
 void TestShellClient::initTestCase()
 {
     qRegisterMetaType<KWin::ShellClient*>();
     qRegisterMetaType<KWin::AbstractClient*>();
     QSignalSpy workspaceCreatedSpy(kwinApp(), &Application::workspaceCreated);
     QVERIFY(workspaceCreatedSpy.isValid());
     kwinApp()->platform()->setInitialWindowSize(QSize(1280, 1024));
     QMetaObject::invokeMethod(kwinApp()->platform(), "setOutputCount", Qt::DirectConnection, Q_ARG(int, 2));
     QVERIFY(waylandServer()->init(s_socketName.toLocal8Bit()));
 
     kwinApp()->start();
     QVERIFY(workspaceCreatedSpy.wait());
     QCOMPARE(screens()->count(), 2);
     QCOMPARE(screens()->geometry(0), QRect(0, 0, 1280, 1024));
     QCOMPARE(screens()->geometry(1), QRect(1280, 0, 1280, 1024));
     waylandServer()->initWorkspace();
 }
 
 void TestShellClient::init()
 {
     QVERIFY(Test::setupWaylandConnection(Test::AdditionalWaylandInterface::Decoration));
 
     screens()->setCurrent(0);
     KWin::Cursor::setPos(QPoint(1280, 512));
 }
 
 void TestShellClient::cleanup()
 {
     Test::destroyWaylandConnection();
 }
 
 void TestShellClient::testMapUnmapMap_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
 }
 
 void TestShellClient::testMapUnmapMap()
 {
     // this test verifies that mapping a previously mapped window works correctly
     QSignalSpy clientAddedSpy(waylandServer(), &WaylandServer::shellClientAdded);
     QVERIFY(clientAddedSpy.isValid());
     QSignalSpy effectsWindowShownSpy(effects, &EffectsHandler::windowShown);
     QVERIFY(effectsWindowShownSpy.isValid());
     QSignalSpy effectsWindowHiddenSpy(effects, &EffectsHandler::windowHidden);
     QVERIFY(effectsWindowHiddenSpy.isValid());
 
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
 
     // now let's render
     Test::render(surface.data(), QSize(100, 50), Qt::blue);
 
     QVERIFY(clientAddedSpy.isEmpty());
     QVERIFY(clientAddedSpy.wait());
     auto client = clientAddedSpy.first().first().value<ShellClient*>();
     QVERIFY(client);
     QVERIFY(client->isShown(true));
     QCOMPARE(client->isHiddenInternal(), false);
     QCOMPARE(client->readyForPainting(), true);
     QCOMPARE(client->depth(), 32);
     QVERIFY(client->hasAlpha());
     QCOMPARE(workspace()->activeClient(), client);
     QVERIFY(effectsWindowShownSpy.isEmpty());
     QVERIFY(client->isMaximizable());
     QVERIFY(client->isMovable());
     QVERIFY(client->isMovableAcrossScreens());
     QVERIFY(client->isResizable());
     QVERIFY(client->property("maximizable").toBool());
     QVERIFY(client->property("moveable").toBool());
     QVERIFY(client->property("moveableAcrossScreens").toBool());
     QVERIFY(client->property("resizeable").toBool());
 
     // now unmap
     QSignalSpy hiddenSpy(client, &ShellClient::windowHidden);
     QVERIFY(hiddenSpy.isValid());
     QSignalSpy windowClosedSpy(client, &ShellClient::windowClosed);
     QVERIFY(windowClosedSpy.isValid());
     surface->attachBuffer(Buffer::Ptr());
     surface->commit(Surface::CommitFlag::None);
     QVERIFY(hiddenSpy.wait());
     QCOMPARE(client->readyForPainting(), true);
     QCOMPARE(client->isHiddenInternal(), true);
     QVERIFY(windowClosedSpy.isEmpty());
     QVERIFY(!workspace()->activeClient());
     QCOMPARE(effectsWindowHiddenSpy.count(), 1);
     QCOMPARE(effectsWindowHiddenSpy.first().first().value<EffectWindow*>(), client->effectWindow());
 
     QSignalSpy windowShownSpy(client, &ShellClient::windowShown);
     QVERIFY(windowShownSpy.isValid());
     Test::render(surface.data(), QSize(100, 50), Qt::blue, QImage::Format_RGB32);
     QCOMPARE(clientAddedSpy.count(), 1);
     QVERIFY(windowShownSpy.wait());
     QCOMPARE(windowShownSpy.count(), 1);
     QCOMPARE(clientAddedSpy.count(), 1);
     QCOMPARE(client->readyForPainting(), true);
     QCOMPARE(client->isHiddenInternal(), false);
     QCOMPARE(client->depth(), 24);
     QVERIFY(!client->hasAlpha());
     QCOMPARE(workspace()->activeClient(), client);
     QCOMPARE(effectsWindowShownSpy.count(), 1);
     QCOMPARE(effectsWindowShownSpy.first().first().value<EffectWindow*>(), client->effectWindow());
 
     // let's unmap again
     surface->attachBuffer(Buffer::Ptr());
     surface->commit(Surface::CommitFlag::None);
     QVERIFY(hiddenSpy.wait());
     QCOMPARE(hiddenSpy.count(), 2);
     QCOMPARE(client->readyForPainting(), true);
     QCOMPARE(client->isHiddenInternal(), true);
     QVERIFY(windowClosedSpy.isEmpty());
     QCOMPARE(effectsWindowHiddenSpy.count(), 2);
     QCOMPARE(effectsWindowHiddenSpy.last().first().value<EffectWindow*>(), client->effectWindow());
 
     shellSurface.reset();
     surface.reset();
     QVERIFY(windowClosedSpy.wait());
     QCOMPARE(windowClosedSpy.count(), 1);
     QCOMPARE(effectsWindowHiddenSpy.count(), 2);
 }
 
 void TestShellClient::testDesktopPresenceChanged()
 {
     // this test verifies that the desktop presence changed signals are properly emitted
     QScopedPointer<Surface> surface(Test::createSurface());
     QScopedPointer<ShellSurface> shellSurface(Test::createShellSurface(surface.data()));
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QCOMPARE(c->desktop(), 1);
     effects->setNumberOfDesktops(4);
     QSignalSpy desktopPresenceChangedClientSpy(c, &ShellClient::desktopPresenceChanged);
     QVERIFY(desktopPresenceChangedClientSpy.isValid());
     QSignalSpy desktopPresenceChangedWorkspaceSpy(workspace(), &Workspace::desktopPresenceChanged);
     QVERIFY(desktopPresenceChangedWorkspaceSpy.isValid());
     QSignalSpy desktopPresenceChangedEffectsSpy(effects, &EffectsHandler::desktopPresenceChanged);
     QVERIFY(desktopPresenceChangedEffectsSpy.isValid());
 
     // let's change the desktop
     workspace()->sendClientToDesktop(c, 2, false);
     QCOMPARE(c->desktop(), 2);
     QCOMPARE(desktopPresenceChangedClientSpy.count(), 1);
     QCOMPARE(desktopPresenceChangedWorkspaceSpy.count(), 1);
     QCOMPARE(desktopPresenceChangedEffectsSpy.count(), 1);
 
     // verify the arguments
     QCOMPARE(desktopPresenceChangedClientSpy.first().at(0).value<AbstractClient*>(), c);
     QCOMPARE(desktopPresenceChangedClientSpy.first().at(1).toInt(), 1);
     QCOMPARE(desktopPresenceChangedWorkspaceSpy.first().at(0).value<AbstractClient*>(), c);
     QCOMPARE(desktopPresenceChangedWorkspaceSpy.first().at(1).toInt(), 1);
     QCOMPARE(desktopPresenceChangedEffectsSpy.first().at(0).value<EffectWindow*>(), c->effectWindow());
     QCOMPARE(desktopPresenceChangedEffectsSpy.first().at(1).toInt(), 1);
     QCOMPARE(desktopPresenceChangedEffectsSpy.first().at(2).toInt(), 2);
 }
 
 void TestShellClient::testTransientPositionAfterRemap()
 {
     // this test simulates the situation that a transient window gets reused and the parent window
     // moved between the two usages
     QScopedPointer<Surface> surface(Test::createSurface());
     QScopedPointer<ShellSurface> shellSurface(Test::createShellSurface(surface.data()));
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
 
     // create the Transient window
     QScopedPointer<Surface> transientSurface(Test::createSurface());
     QScopedPointer<ShellSurface> transientShellSurface(Test::createShellSurface(transientSurface.data()));
     transientShellSurface->setTransient(surface.data(), QPoint(5, 10));
     auto transient = Test::renderAndWaitForShown(transientSurface.data(), QSize(50, 40), Qt::blue);
     QVERIFY(transient);
     QCOMPARE(transient->geometry(), QRect(c->geometry().topLeft() + QPoint(5, 10), QSize(50, 40)));
 
     // unmap the transient
     QSignalSpy windowHiddenSpy(transient, &ShellClient::windowHidden);
     QVERIFY(windowHiddenSpy.isValid());
     transientSurface->attachBuffer(Buffer::Ptr());
     transientSurface->commit(Surface::CommitFlag::None);
     QVERIFY(windowHiddenSpy.wait());
 
     // now move the parent surface
     c->setGeometry(c->geometry().translated(5, 10));
 
     // now map the transient again
     QSignalSpy windowShownSpy(transient, &ShellClient::windowShown);
     QVERIFY(windowShownSpy.isValid());
     Test::render(transientSurface.data(), QSize(50, 40), Qt::blue);
     QVERIFY(windowShownSpy.wait());
     QCOMPARE(transient->geometry(), QRect(c->geometry().topLeft() + QPoint(5, 10), QSize(50, 40)));
 }
 
 void TestShellClient::testMinimizeActiveWindow_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
 }
 
 void TestShellClient::testMinimizeActiveWindow()
 {
     // this test verifies that when minimizing the active window it gets deactivated
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->isActive());
     QCOMPARE(workspace()->activeClient(), c);
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
     QVERIFY(c->isShown(true));
 
     workspace()->slotWindowMinimize();
     QVERIFY(!c->isShown(true));
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
     QVERIFY(!c->isActive());
     QVERIFY(!workspace()->activeClient());
     QVERIFY(c->isMinimized());
 
     // unminimize again
     c->unminimize();
     QVERIFY(!c->isMinimized());
     QVERIFY(c->isActive());
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
     QVERIFY(c->isShown(true));
     QCOMPARE(workspace()->activeClient(), c);
 }
 
 void TestShellClient::testFullscreen_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
     QTest::addColumn<ServerSideDecoration::Mode>("decoMode");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell << ServerSideDecoration::Mode::Client;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5 << ServerSideDecoration::Mode::Client;
 
     QTest::newRow("wlShell - deco") << Test::ShellSurfaceType::WlShell << ServerSideDecoration::Mode::Server;
     QTest::newRow("xdgShellV5 - deco") << Test::ShellSurfaceType::XdgShellV5 << ServerSideDecoration::Mode::Server;
 }
 
 void TestShellClient::testFullscreen()
 {
     // this test verifies that a window can be properly fullscreened
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
 
     // create deco
     QScopedPointer<ServerSideDecoration> deco(Test::waylandServerSideDecoration()->create(surface.data()));
     QSignalSpy decoSpy(deco.data(), &ServerSideDecoration::modeChanged);
     QVERIFY(decoSpy.isValid());
     QVERIFY(decoSpy.wait());
     QFETCH(ServerSideDecoration::Mode, decoMode);
     deco->requestMode(decoMode);
     QVERIFY(decoSpy.wait());
     QCOMPARE(deco->mode(), decoMode);
 
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->isActive());
     QCOMPARE(c->layer(), NormalLayer);
     QVERIFY(!c->isFullScreen());
     QCOMPARE(c->clientSize(), QSize(100, 50));
     QCOMPARE(c->isDecorated(), decoMode == ServerSideDecoration::Mode::Server);
     QCOMPARE(c->sizeForClientSize(c->clientSize()), c->geometry().size());
     QSignalSpy fullscreenChangedSpy(c, &ShellClient::fullScreenChanged);
     QVERIFY(fullscreenChangedSpy.isValid());
     QSignalSpy geometryChangedSpy(c, &ShellClient::geometryChanged);
     QVERIFY(geometryChangedSpy.isValid());
     QSignalSpy sizeChangeRequestedSpy(shellSurface.data(), SIGNAL(sizeChanged(QSize)));
     QVERIFY(sizeChangeRequestedSpy.isValid());
 
     // fullscreen the window
     switch (type) {
     case Test::ShellSurfaceType::WlShell:
         qobject_cast<ShellSurface*>(shellSurface.data())->setFullscreen();
         break;
     case Test::ShellSurfaceType::XdgShellV5:
         qobject_cast<XdgShellSurface*>(shellSurface.data())->setFullscreen(true);
         break;
     default:
         Q_UNREACHABLE();
         break;
     }
     QVERIFY(fullscreenChangedSpy.wait());
     QVERIFY(sizeChangeRequestedSpy.wait());
     QCOMPARE(sizeChangeRequestedSpy.count(), 1);
     QCOMPARE(sizeChangeRequestedSpy.first().first().toSize(), QSize(screens()->size(0)));
     // TODO: should switch to fullscreen once it's updated
     QVERIFY(c->isFullScreen());
     QCOMPARE(c->clientSize(), QSize(100, 50));
     QVERIFY(geometryChangedSpy.isEmpty());
 
     // render at the new size
     Test::render(surface.data(), sizeChangeRequestedSpy.first().first().toSize(), Qt::red);
     QVERIFY(geometryChangedSpy.wait());
     QCOMPARE(geometryChangedSpy.count(), 1);
     QVERIFY(c->isFullScreen());
     QVERIFY(!c->isDecorated());
     QCOMPARE(c->geometry(), QRect(QPoint(0, 0), sizeChangeRequestedSpy.first().first().toSize()));
     QCOMPARE(c->layer(), ActiveLayer);
 
     // swap back to normal
     switch (type) {
     case Test::ShellSurfaceType::WlShell:
         qobject_cast<ShellSurface*>(shellSurface.data())->setToplevel();
         break;
     case Test::ShellSurfaceType::XdgShellV5:
         qobject_cast<XdgShellSurface*>(shellSurface.data())->setFullscreen(false);
         break;
     default:
         Q_UNREACHABLE();
         break;
     }
     QVERIFY(fullscreenChangedSpy.wait());
     QVERIFY(sizeChangeRequestedSpy.wait());
     QCOMPARE(sizeChangeRequestedSpy.count(), 2);
     QCOMPARE(sizeChangeRequestedSpy.last().first().toSize(), QSize(100, 50));
     // TODO: should switch to fullscreen once it's updated
     QVERIFY(!c->isFullScreen());
     QCOMPARE(c->layer(), NormalLayer);
     QCOMPARE(c->isDecorated(), decoMode == ServerSideDecoration::Mode::Server);
 }
 
 
 void TestShellClient::testMaximizedToFullscreen_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
     QTest::addColumn<ServerSideDecoration::Mode>("decoMode");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell << ServerSideDecoration::Mode::Client;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5 << ServerSideDecoration::Mode::Client;
 
     QTest::newRow("wlShell - deco") << Test::ShellSurfaceType::WlShell << ServerSideDecoration::Mode::Server;
     QTest::newRow("xdgShellV5 - deco") << Test::ShellSurfaceType::XdgShellV5 << ServerSideDecoration::Mode::Server;
 }
 
 void TestShellClient::testMaximizedToFullscreen()
 {
     // this test verifies that a window can be properly fullscreened after maximizing
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
 
     // create deco
     QScopedPointer<ServerSideDecoration> deco(Test::waylandServerSideDecoration()->create(surface.data()));
     QSignalSpy decoSpy(deco.data(), &ServerSideDecoration::modeChanged);
     QVERIFY(decoSpy.isValid());
     QVERIFY(decoSpy.wait());
     QFETCH(ServerSideDecoration::Mode, decoMode);
     deco->requestMode(decoMode);
     QVERIFY(decoSpy.wait());
     QCOMPARE(deco->mode(), decoMode);
 
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->isActive());
     QVERIFY(!c->isFullScreen());
     QCOMPARE(c->clientSize(), QSize(100, 50));
     QCOMPARE(c->isDecorated(), decoMode == ServerSideDecoration::Mode::Server);
     QSignalSpy fullscreenChangedSpy(c, &ShellClient::fullScreenChanged);
     QVERIFY(fullscreenChangedSpy.isValid());
     QSignalSpy geometryChangedSpy(c, &ShellClient::geometryChanged);
     QVERIFY(geometryChangedSpy.isValid());
     QSignalSpy sizeChangeRequestedSpy(shellSurface.data(), SIGNAL(sizeChanged(QSize)));
     QVERIFY(sizeChangeRequestedSpy.isValid());
 
     // change to maximize
     switch (type) {
     case Test::ShellSurfaceType::WlShell:
         qobject_cast<ShellSurface*>(shellSurface.data())->setMaximized();
         break;
     case Test::ShellSurfaceType::XdgShellV5:
         qobject_cast<XdgShellSurface*>(shellSurface.data())->setMaximized(true);
         break;
     default:
         Q_UNREACHABLE();
         break;
     }
     QVERIFY(sizeChangeRequestedSpy.wait());
     QCOMPARE(sizeChangeRequestedSpy.count(), 1);
     QCOMPARE(c->maximizeMode(), MaximizeFull);
     QCOMPARE(geometryChangedSpy.isEmpty(), false);
     geometryChangedSpy.clear();
 
     // fullscreen the window
     switch (type) {
     case Test::ShellSurfaceType::WlShell:
         qobject_cast<ShellSurface*>(shellSurface.data())->setFullscreen();
         break;
     case Test::ShellSurfaceType::XdgShellV5:
         qobject_cast<XdgShellSurface*>(shellSurface.data())->setFullscreen(true);
         break;
     default:
         Q_UNREACHABLE();
         break;
     }
     QVERIFY(fullscreenChangedSpy.wait());
     if (decoMode == ServerSideDecoration::Mode::Server) {
         QVERIFY(sizeChangeRequestedSpy.wait());
         QCOMPARE(sizeChangeRequestedSpy.count(), 2);
     }
     QCOMPARE(sizeChangeRequestedSpy.last().first().toSize(), QSize(screens()->size(0)));
     // TODO: should switch to fullscreen once it's updated
     QVERIFY(c->isFullScreen());
     QCOMPARE(c->clientSize(), QSize(100, 50));
     QVERIFY(geometryChangedSpy.isEmpty());
 
     // render at the new size
     Test::render(surface.data(), sizeChangeRequestedSpy.last().first().toSize(), Qt::red);
     QVERIFY(geometryChangedSpy.wait());
     QCOMPARE(geometryChangedSpy.count(), 1);
     QVERIFY(c->isFullScreen());
     QVERIFY(!c->isDecorated());
     QCOMPARE(c->geometry(), QRect(QPoint(0, 0), sizeChangeRequestedSpy.last().first().toSize()));
     sizeChangeRequestedSpy.clear();
 
     // swap back to normal
     switch (type) {
     case Test::ShellSurfaceType::WlShell:
         qobject_cast<ShellSurface*>(shellSurface.data())->setToplevel();
         break;
     case Test::ShellSurfaceType::XdgShellV5:
         qobject_cast<XdgShellSurface*>(shellSurface.data())->setFullscreen(false);
         break;
     default:
         Q_UNREACHABLE();
         break;
     }
     QVERIFY(fullscreenChangedSpy.wait());
     QVERIFY(sizeChangeRequestedSpy.wait());
     QCOMPARE(sizeChangeRequestedSpy.count(), 1);
     QEXPECT_FAIL("wlShell - deco", "With decoration incorrect geometry requested", Continue);
     QEXPECT_FAIL("xdgShellV5 - deco", "With decoration incorrect geometry requested", Continue);
     QCOMPARE(sizeChangeRequestedSpy.last().first().toSize(), QSize(100, 50));
     // TODO: should switch to fullscreen once it's updated
     QVERIFY(!c->isFullScreen());
     QCOMPARE(c->isDecorated(), decoMode == ServerSideDecoration::Mode::Server);
 }
 
 void TestShellClient::testWindowOpensLargerThanScreen_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
 }
 
 void TestShellClient::testWindowOpensLargerThanScreen()
 {
     // this test creates a window which is as large as the screen, but is decorated
     // the window should get resized to fit into the screen, BUG: 366632
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
     QSignalSpy sizeChangeRequestedSpy(shellSurface.data(), SIGNAL(sizeChanged(QSize)));
     QVERIFY(sizeChangeRequestedSpy.isValid());
 
     // create deco
     QScopedPointer<ServerSideDecoration> deco(Test::waylandServerSideDecoration()->create(surface.data()));
     QSignalSpy decoSpy(deco.data(), &ServerSideDecoration::modeChanged);
     QVERIFY(decoSpy.isValid());
     QVERIFY(decoSpy.wait());
     deco->requestMode(ServerSideDecoration::Mode::Server);
     QVERIFY(decoSpy.wait());
     QCOMPARE(deco->mode(), ServerSideDecoration::Mode::Server);
 
     auto c = Test::renderAndWaitForShown(surface.data(), screens()->size(0), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->isActive());
     QCOMPARE(c->clientSize(), screens()->size(0));
     QVERIFY(c->isDecorated());
     QEXPECT_FAIL("", "BUG 366632", Continue);
     QVERIFY(sizeChangeRequestedSpy.wait());
 }
 
 void TestShellClient::testHidden_data()
 {
     QTest::addColumn<Test::ShellSurfaceType>("type");
 
     QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
     QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
 }
 
 void TestShellClient::testHidden()
 {
     // this test verifies that when hiding window it doesn't get shown
     QScopedPointer<Surface> surface(Test::createSurface());
     QFETCH(Test::ShellSurfaceType, type);
     QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->isActive());
     QCOMPARE(workspace()->activeClient(), c);
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
     QVERIFY(c->isShown(true));
 
     c->hideClient(true);
     QVERIFY(!c->isShown(true));
     QVERIFY(!c->isActive());
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
 
     // unhide again
     c->hideClient(false);
     QVERIFY(c->isShown(true));
     QVERIFY(c->wantsInput());
     QVERIFY(c->wantsTabFocus());
 
     //QCOMPARE(workspace()->activeClient(), c);
 }
 
 void TestShellClient::testDesktopFileName()
 {
     QIcon::setThemeName(QStringLiteral("breeze"));
     // this test verifies that desktop file name is passed correctly to the window
     QScopedPointer<Surface> surface(Test::createSurface());
     // only xdg-shell as ShellSurface misses the setter
     QScopedPointer<XdgShellSurface> shellSurface(qobject_cast<XdgShellSurface*>(Test::createShellSurface(Test::ShellSurfaceType::XdgShellV5, surface.data())));
     shellSurface->setAppId(QByteArrayLiteral("org.kde.foo"));
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QCOMPARE(c->desktopFileName(), QByteArrayLiteral("org.kde.foo"));
     // the desktop file does not exist, so icon should be generic Wayland
     QCOMPARE(c->icon().name(), QStringLiteral("wayland"));
 
     QSignalSpy desktopFileNameChangedSpy(c, &AbstractClient::desktopFileNameChanged);
     QVERIFY(desktopFileNameChangedSpy.isValid());
     QSignalSpy iconChangedSpy(c, &ShellClient::iconChanged);
     QVERIFY(iconChangedSpy.isValid());
     shellSurface->setAppId(QByteArrayLiteral("org.kde.bar"));
     QVERIFY(desktopFileNameChangedSpy.wait());
     QCOMPARE(c->desktopFileName(), QByteArrayLiteral("org.kde.bar"));
     // icon should still be wayland
     QCOMPARE(c->icon().name(), QStringLiteral("wayland"));
     QVERIFY(iconChangedSpy.isEmpty());
 
     const QString dfPath = QFINDTESTDATA("data/example.desktop");
     shellSurface->setAppId(dfPath.toUtf8());
     QVERIFY(desktopFileNameChangedSpy.wait());
     QCOMPARE(iconChangedSpy.count(), 1);
     QCOMPARE(QString::fromUtf8(c->desktopFileName()), dfPath);
     QCOMPARE(c->icon().name(), QStringLiteral("kwin"));
 }
 
 void TestShellClient::testCaptionSimplified()
 {
     // this test verifies that caption is properly trimmed
     // see BUG 323798 comment #12
     QScopedPointer<Surface> surface(Test::createSurface());
     // only done for xdg-shell as ShellSurface misses the setter
     QScopedPointer<XdgShellSurface> shellSurface(qobject_cast<XdgShellSurface*>(Test::createShellSurface(Test::ShellSurfaceType::XdgShellV5, surface.data())));
     const QString origTitle = QString::fromUtf8(QByteArrayLiteral("Was tun, wenn Schüler Autismus haben?\342\200\250\342\200\250\342\200\250 – Marlies Hübner - Mozilla Firefox"));
     shellSurface->setTitle(origTitle);
     auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(c);
     QVERIFY(c->caption() != origTitle);
     QCOMPARE(c->caption(), origTitle.simplified());
 }
 
 void TestShellClient::testKillWindow_data()
 {
     QTest::addColumn<bool>("socketMode");
 
     QTest::newRow("display") << false;
     QTest::newRow("socket") << true;
 }
 
 void TestShellClient::testKillWindow()
 {
     // this test verifies that killWindow properly terminates a process
     // for this an external binary is launched
     const QString kill = QFINDTESTDATA(QStringLiteral("helper/kill"));
     QVERIFY(!kill.isEmpty());
     QSignalSpy shellClientAddedSpy(waylandServer(), &WaylandServer::shellClientAdded);
     QVERIFY(shellClientAddedSpy.isValid());
 
     QScopedPointer<QProcess> process(new QProcess);
     QProcessEnvironment env = QProcessEnvironment::systemEnvironment();
     QFETCH(bool, socketMode);
     if (socketMode) {
         int sx[2];
         QVERIFY(socketpair(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0, sx) >= 0);
         waylandServer()->display()->createClient(sx[0]);
         int socket = dup(sx[1]);
         QVERIFY(socket != -1);
         env.insert(QStringLiteral("WAYLAND_SOCKET"), QByteArray::number(socket));
         env.remove("WAYLAND_DISPLAY");
     } else {
         env.insert("WAYLAND_DISPLAY", s_socketName);
     }
     process->setProcessEnvironment(env);
     process->setProcessChannelMode(QProcess::ForwardedChannels);
     process->setProgram(kill);
     process->start();
     QVERIFY(process->waitForStarted());
 
     AbstractClient *killClient = nullptr;
     QVERIFY(shellClientAddedSpy.wait());
     killClient = shellClientAddedSpy.first().first().value<AbstractClient*>();
     QVERIFY(killClient);
     QSignalSpy finishedSpy(process.data(), static_cast<void(QProcess::*)(int,QProcess::ExitStatus)>(&QProcess::finished));
     QVERIFY(finishedSpy.isValid());
     killClient->killWindow();
     QVERIFY(finishedSpy.wait());
     QVERIFY(!finishedSpy.isEmpty());
 }
 
+void TestShellClient::testX11WindowId_data()
+{
+    QTest::addColumn<Test::ShellSurfaceType>("type");
+
+    QTest::newRow("wlShell") << Test::ShellSurfaceType::WlShell;
+    QTest::newRow("xdgShellV5") << Test::ShellSurfaceType::XdgShellV5;
+}
+
+void TestShellClient::testX11WindowId()
+{
+    QScopedPointer<Surface> surface(Test::createSurface());
+    QFETCH(Test::ShellSurfaceType, type);
+    QScopedPointer<QObject> shellSurface(Test::createShellSurface(type, surface.data()));
+    auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
+    QVERIFY(c);
+    QVERIFY(c->windowId() != 0);
+    QCOMPARE(c->window(), 0u);
+}
+
 WAYLANDTEST_MAIN(TestShellClient)
 #include "shell_client_test.moc"
diff --git a/autotests/integration/x11_client_test.cpp b/autotests/integration/x11_client_test.cpp
index 490a76430..50013f76f 100644
--- a/autotests/integration/x11_client_test.cpp
+++ b/autotests/integration/x11_client_test.cpp
@@ -1,320 +1,380 @@
 /********************************************************************
 KWin - the KDE window manager
 This file is part of the KDE project.
 
 Copyright (C) 2016 Martin Gräßlin <mgraesslin@kde.org>
 
 This program is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or
 (at your option) any later version.
 
 This program is distributed in the hope that it will be useful,
 but WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 GNU General Public License for more details.
 
 You should have received a copy of the GNU General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *********************************************************************/
 #include "kwin_wayland_test.h"
 #include "composite.h"
 #include "effects.h"
 #include "effectloader.h"
 #include "cursor.h"
 #include "platform.h"
 #include "scene_qpainter.h"
 #include "screens.h"
 #include "shell_client.h"
 #include "wayland_server.h"
 #include "workspace.h"
 
 #include <KWayland/Client/surface.h>
 #include <KWayland/Client/shell.h>
 
 #include <netwm.h>
 #include <xcb/xcb_icccm.h>
 
 using namespace KWin;
 using namespace KWayland::Client;
 static const QString s_socketName = QStringLiteral("wayland_test_x11_client-0");
 
 class X11ClientTest : public QObject
 {
 Q_OBJECT
 private Q_SLOTS:
     void initTestCase();
     void init();
     void cleanup();
 
     void testCaptionSimplified();
     void testFullscreenLayerWithActiveWaylandWindow();
     void testFocusInWithWaylandLastActiveWindow();
+    void testX11WindowId();
 };
 
 void X11ClientTest::initTestCase()
 {
     qRegisterMetaType<KWin::ShellClient*>();
     qRegisterMetaType<KWin::AbstractClient*>();
     QSignalSpy workspaceCreatedSpy(kwinApp(), &Application::workspaceCreated);
     QVERIFY(workspaceCreatedSpy.isValid());
     kwinApp()->platform()->setInitialWindowSize(QSize(1280, 1024));
     QVERIFY(waylandServer()->init(s_socketName.toLocal8Bit()));
     kwinApp()->setConfig(KSharedConfig::openConfig(QString(), KConfig::SimpleConfig));
 
     kwinApp()->start();
     QVERIFY(workspaceCreatedSpy.wait());
     QVERIFY(KWin::Compositor::self());
     waylandServer()->initWorkspace();
 }
 
 void X11ClientTest::init()
 {
     QVERIFY(Test::setupWaylandConnection());
 }
 
 void X11ClientTest::cleanup()
 {
     Test::destroyWaylandConnection();
 }
 
 struct XcbConnectionDeleter
 {
     static inline void cleanup(xcb_connection_t *pointer)
     {
         xcb_disconnect(pointer);
     }
 };
 
 
 void X11ClientTest::testCaptionSimplified()
 {
     // this test verifies that caption is properly trimmed
     // see BUG 323798 comment #12
     QSignalSpy windowAddedSpy(effects, &EffectsHandler::windowAdded);
     QVERIFY(windowAddedSpy.isValid());
 
     // create an xcb window
     QScopedPointer<xcb_connection_t, XcbConnectionDeleter> c(xcb_connect(nullptr, nullptr));
     QVERIFY(!xcb_connection_has_error(c.data()));
     const QRect windowGeometry(0, 0, 100, 200);
     xcb_window_t w = xcb_generate_id(c.data());
     xcb_create_window(c.data(), XCB_COPY_FROM_PARENT, w, rootWindow(),
                       windowGeometry.x(),
                       windowGeometry.y(),
                       windowGeometry.width(),
                       windowGeometry.height(),
                       0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, 0, nullptr);
     xcb_size_hints_t hints;
     memset(&hints, 0, sizeof(hints));
     xcb_icccm_size_hints_set_position(&hints, 1, windowGeometry.x(), windowGeometry.y());
     xcb_icccm_size_hints_set_size(&hints, 1, windowGeometry.width(), windowGeometry.height());
     xcb_icccm_set_wm_normal_hints(c.data(), w, &hints);
     NETWinInfo winInfo(c.data(), w, rootWindow(), NET::Properties(), NET::Properties2());
     const QByteArray origTitle = QByteArrayLiteral("Was tun, wenn Schüler Autismus haben?\342\200\250\342\200\250\342\200\250 – Marlies Hübner - Mozilla Firefox");
     winInfo.setName(origTitle.constData());
     xcb_map_window(c.data(), w);
     xcb_flush(c.data());
 
     // we should get a client for it
     QSignalSpy windowCreatedSpy(workspace(), &Workspace::clientAdded);
     QVERIFY(windowCreatedSpy.isValid());
     QVERIFY(windowCreatedSpy.wait());
     Client *client = windowCreatedSpy.first().first().value<Client*>();
     QVERIFY(client);
     QCOMPARE(client->window(), w);
     QVERIFY(client->caption() != QString::fromUtf8(origTitle));
     QCOMPARE(client->caption(), QString::fromUtf8(origTitle).simplified());
 
     // and destroy the window again
     xcb_unmap_window(c.data(), w);
     xcb_flush(c.data());
 
     QSignalSpy windowClosedSpy(client, &Client::windowClosed);
     QVERIFY(windowClosedSpy.isValid());
     QVERIFY(windowClosedSpy.wait());
     xcb_destroy_window(c.data(), w);
     c.reset();
 }
 
 void X11ClientTest::testFullscreenLayerWithActiveWaylandWindow()
 {
     // this test verifies that an X11 fullscreen window does not stay in the active layer
     // when a Wayland window is active, see BUG: 375759
     QCOMPARE(screens()->count(), 1);
 
     // first create an X11 window
     QScopedPointer<xcb_connection_t, XcbConnectionDeleter> c(xcb_connect(nullptr, nullptr));
     QVERIFY(!xcb_connection_has_error(c.data()));
     const QRect windowGeometry(0, 0, 100, 200);
     xcb_window_t w = xcb_generate_id(c.data());
     xcb_create_window(c.data(), XCB_COPY_FROM_PARENT, w, rootWindow(),
                       windowGeometry.x(),
                       windowGeometry.y(),
                       windowGeometry.width(),
                       windowGeometry.height(),
                       0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, 0, nullptr);
     xcb_size_hints_t hints;
     memset(&hints, 0, sizeof(hints));
     xcb_icccm_size_hints_set_position(&hints, 1, windowGeometry.x(), windowGeometry.y());
     xcb_icccm_size_hints_set_size(&hints, 1, windowGeometry.width(), windowGeometry.height());
     xcb_icccm_set_wm_normal_hints(c.data(), w, &hints);
     xcb_map_window(c.data(), w);
     xcb_flush(c.data());
 
     // we should get a client for it
     QSignalSpy windowCreatedSpy(workspace(), &Workspace::clientAdded);
     QVERIFY(windowCreatedSpy.isValid());
     QVERIFY(windowCreatedSpy.wait());
     Client *client = windowCreatedSpy.first().first().value<Client*>();
     QVERIFY(client);
     QCOMPARE(client->window(), w);
     QVERIFY(!client->isFullScreen());
     QVERIFY(client->isActive());
     QCOMPARE(client->layer(), NormalLayer);
 
     workspace()->slotWindowFullScreen();
     QVERIFY(client->isFullScreen());
     QCOMPARE(client->layer(), ActiveLayer);
     QCOMPARE(workspace()->stackingOrder().last(), client);
 
     // now let's open a Wayland window
     QScopedPointer<Surface> surface(Test::createSurface());
     QScopedPointer<ShellSurface> shellSurface(Test::createShellSurface(surface.data()));
     auto waylandClient = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(waylandClient);
     QVERIFY(waylandClient->isActive());
     QCOMPARE(waylandClient->layer(), NormalLayer);
     QCOMPARE(workspace()->stackingOrder().last(), waylandClient);
     QCOMPARE(workspace()->xStackingOrder().last(), waylandClient);
     QCOMPARE(client->layer(), NormalLayer);
 
     // now activate fullscreen again
     workspace()->activateClient(client);
     QTRY_VERIFY(client->isActive());
     QCOMPARE(client->layer(), ActiveLayer);
     QCOMPARE(workspace()->stackingOrder().last(), client);
     QCOMPARE(workspace()->xStackingOrder().last(), client);
 
     // activate wayland window again
     workspace()->activateClient(waylandClient);
     QTRY_VERIFY(waylandClient->isActive());
     QCOMPARE(workspace()->stackingOrder().last(), waylandClient);
     QCOMPARE(workspace()->xStackingOrder().last(), waylandClient);
 
     // back to x window
     workspace()->activateClient(client);
     QTRY_VERIFY(client->isActive());
     // remove fullscreen
     QVERIFY(client->isFullScreen());
     workspace()->slotWindowFullScreen();
     QVERIFY(!client->isFullScreen());
     // and fullscreen again
     workspace()->slotWindowFullScreen();
     QVERIFY(client->isFullScreen());
     QCOMPARE(workspace()->stackingOrder().last(), client);
     QCOMPARE(workspace()->xStackingOrder().last(), client);
 
     // activate wayland window again
     workspace()->activateClient(waylandClient);
     QTRY_VERIFY(waylandClient->isActive());
     QCOMPARE(workspace()->stackingOrder().last(), waylandClient);
     QCOMPARE(workspace()->xStackingOrder().last(), waylandClient);
 
     // back to X11 window
     workspace()->activateClient(client);
     QTRY_VERIFY(client->isActive());
     // remove fullscreen
     QVERIFY(client->isFullScreen());
     workspace()->slotWindowFullScreen();
     QVERIFY(!client->isFullScreen());
     // and fullscreen through X API
     NETWinInfo info(c.data(), w, kwinApp()->x11RootWindow(), NET::Properties(), NET::Properties2());
     info.setState(NET::FullScreen, NET::FullScreen);
     NETRootInfo rootInfo(c.data(), NET::Properties());
     rootInfo.setActiveWindow(w, NET::FromApplication, XCB_CURRENT_TIME, XCB_WINDOW_NONE);
     xcb_flush(c.data());
     QTRY_VERIFY(client->isFullScreen());
     QCOMPARE(workspace()->stackingOrder().last(), client);
     QCOMPARE(workspace()->xStackingOrder().last(), client);
 
     // activate wayland window again
     workspace()->activateClient(waylandClient);
     QTRY_VERIFY(waylandClient->isActive());
     QCOMPARE(workspace()->stackingOrder().last(), waylandClient);
     QCOMPARE(workspace()->xStackingOrder().last(), waylandClient);
     QCOMPARE(client->layer(), NormalLayer);
 
     // close the window
     shellSurface.reset();
     surface.reset();
     QVERIFY(Test::waitForWindowDestroyed(waylandClient));
     QTRY_VERIFY(client->isActive());
     QCOMPARE(client->layer(), ActiveLayer);
 
     // and destroy the window again
     xcb_unmap_window(c.data(), w);
     xcb_flush(c.data());
 }
 
 void X11ClientTest::testFocusInWithWaylandLastActiveWindow()
 {
     // this test verifies that Workspace::allowClientActivation does not crash if last client was a Wayland client
 
     // create an X11 window
     QScopedPointer<xcb_connection_t, XcbConnectionDeleter> c(xcb_connect(nullptr, nullptr));
     QVERIFY(!xcb_connection_has_error(c.data()));
     const QRect windowGeometry(0, 0, 100, 200);
     xcb_window_t w = xcb_generate_id(c.data());
     xcb_create_window(c.data(), XCB_COPY_FROM_PARENT, w, rootWindow(),
                       windowGeometry.x(),
                       windowGeometry.y(),
                       windowGeometry.width(),
                       windowGeometry.height(),
                       0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, 0, nullptr);
     xcb_size_hints_t hints;
     memset(&hints, 0, sizeof(hints));
     xcb_icccm_size_hints_set_position(&hints, 1, windowGeometry.x(), windowGeometry.y());
     xcb_icccm_size_hints_set_size(&hints, 1, windowGeometry.width(), windowGeometry.height());
     xcb_icccm_set_wm_normal_hints(c.data(), w, &hints);
     xcb_map_window(c.data(), w);
     xcb_flush(c.data());
 
     // we should get a client for it
     QSignalSpy windowCreatedSpy(workspace(), &Workspace::clientAdded);
     QVERIFY(windowCreatedSpy.isValid());
     QVERIFY(windowCreatedSpy.wait());
     Client *client = windowCreatedSpy.first().first().value<Client*>();
     QVERIFY(client);
     QCOMPARE(client->window(), w);
     QVERIFY(client->isActive());
 
     // create Wayland window
     QScopedPointer<Surface> surface(Test::createSurface());
     QScopedPointer<ShellSurface> shellSurface(Test::createShellSurface(surface.data()));
     auto waylandClient = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
     QVERIFY(waylandClient);
     QVERIFY(waylandClient->isActive());
     // activate no window
     workspace()->setActiveClient(nullptr);
     QVERIFY(!waylandClient->isActive());
     QVERIFY(!workspace()->activeClient());
     // and close Wayland window again
     shellSurface.reset();
     surface.reset();
     QVERIFY(Test::waitForWindowDestroyed(waylandClient));
 
     // and try to activate the x11 client through X11 api
     const auto cookie = xcb_set_input_focus_checked(c.data(), XCB_INPUT_FOCUS_NONE, w, XCB_CURRENT_TIME);
     auto error = xcb_request_check(c.data(), cookie);
     QVERIFY(!error);
     // this accesses last_active_client on trying to activate
     QTRY_VERIFY(client->isActive());
 
     // and destroy the window again
     xcb_unmap_window(c.data(), w);
     xcb_flush(c.data());
 }
 
+void X11ClientTest::testX11WindowId()
+{
+    // create an X11 window
+    QScopedPointer<xcb_connection_t, XcbConnectionDeleter> c(xcb_connect(nullptr, nullptr));
+    QVERIFY(!xcb_connection_has_error(c.data()));
+    const QRect windowGeometry(0, 0, 100, 200);
+    xcb_window_t w = xcb_generate_id(c.data());
+    xcb_create_window(c.data(), XCB_COPY_FROM_PARENT, w, rootWindow(),
+                      windowGeometry.x(),
+                      windowGeometry.y(),
+                      windowGeometry.width(),
+                      windowGeometry.height(),
+                      0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, 0, nullptr);
+    xcb_size_hints_t hints;
+    memset(&hints, 0, sizeof(hints));
+    xcb_icccm_size_hints_set_position(&hints, 1, windowGeometry.x(), windowGeometry.y());
+    xcb_icccm_size_hints_set_size(&hints, 1, windowGeometry.width(), windowGeometry.height());
+    xcb_icccm_set_wm_normal_hints(c.data(), w, &hints);
+    xcb_map_window(c.data(), w);
+    xcb_flush(c.data());
+
+    // we should get a client for it
+    QSignalSpy windowCreatedSpy(workspace(), &Workspace::clientAdded);
+    QVERIFY(windowCreatedSpy.isValid());
+    QVERIFY(windowCreatedSpy.wait());
+    Client *client = windowCreatedSpy.first().first().value<Client*>();
+    QVERIFY(client);
+    QCOMPARE(client->windowId(), w);
+    QVERIFY(client->isActive());
+    QCOMPARE(client->window(), w);
+
+    NETRootInfo rootInfo(c.data(), NET::WMAllProperties);
+    QCOMPARE(rootInfo.activeWindow(), client->window());
+
+    // activate a wayland window
+    QScopedPointer<Surface> surface(Test::createSurface());
+    QScopedPointer<ShellSurface> shellSurface(Test::createShellSurface(surface.data()));
+    auto waylandClient = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
+    QVERIFY(waylandClient);
+    QVERIFY(waylandClient->isActive());
+    xcb_flush(kwinApp()->x11Connection());
+
+    NETRootInfo rootInfo2(c.data(), NET::WMAllProperties);
+    QCOMPARE(rootInfo2.activeWindow(), 0u);
+
+    // back to X11 client
+    shellSurface.reset();
+    surface.reset();
+    QVERIFY(Test::waitForWindowDestroyed(waylandClient));
+
+    QTRY_VERIFY(client->isActive());
+    NETRootInfo rootInfo3(c.data(), NET::WMAllProperties);
+    QCOMPARE(rootInfo3.activeWindow(), client->window());
+
+    // and destroy the window again
+    xcb_unmap_window(c.data(), w);
+    xcb_flush(c.data());
+}
+
 WAYLANDTEST_MAIN(X11ClientTest)
 #include "x11_client_test.moc"