xcb: qxcbconnection_screens

Moved all screen handling method implementations into
qxcbconnection_screens, the same way we are doing with
xinput2 code in qxcbconnection_xi.cpp.  The goal was to
reduce the size of qxcbconnection.h/cpp.

Change-Id: I9bad55ca4b0874171b7313d923b13c66034c3b3e
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

4 files changed, 426 insertions, 382 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index 10d07c37bb..9e857ea2ff 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -38,12 +38,10 @@
 ****************************************************************************/
 
 #include <QtGui/private/qguiapplication_p.h>
-#include <QtGui/private/qhighdpiscaling_p.h>
 #include <QtCore/QDebug>
 
 #include "qxcbconnection.h"
 #include "qxcbkeyboard.h"
-#include "qxcbscreen.h"
 #include "qxcbwindow.h"
 #include "qxcbclipboard.h"
 #if QT_CONFIG(draganddrop)
@@ -67,7 +65,6 @@
 #include <errno.h>
 
 #include <xcb/xfixes.h>
-#include <xcb/xinerama.h>
 #if QT_CONFIG(xkb)
 #define explicit dont_use_cxx_explicit
 #include <xcb/xkb.h>
@@ -95,373 +92,6 @@ Q_LOGGING_CATEGORY(lcQpaXDnd, "qt.qpa.xdnd")
 #define XCB_GE_GENERIC 35
 #endif
 
-void QXcbConnection::selectXRandrEvents()
-{
-    xcb_screen_iterator_t rootIter = xcb_setup_roots_iterator(setup());
-    for (; rootIter.rem; xcb_screen_next(&rootIter)) {
-        xcb_randr_select_input(xcb_connection(),
-            rootIter.data->root,
-            XCB_RANDR_NOTIFY_MASK_SCREEN_CHANGE |
-            XCB_RANDR_NOTIFY_MASK_OUTPUT_CHANGE |
-            XCB_RANDR_NOTIFY_MASK_CRTC_CHANGE |
-            XCB_RANDR_NOTIFY_MASK_OUTPUT_PROPERTY
-        );
-    }
-}
-
-QXcbScreen* QXcbConnection::findScreenForCrtc(xcb_window_t rootWindow, xcb_randr_crtc_t crtc) const
-{
-    for (QXcbScreen *screen : m_screens) {
-        if (screen->root() == rootWindow && screen->crtc() == crtc)
-            return screen;
-    }
-
-    return 0;
-}
-
-QXcbScreen* QXcbConnection::findScreenForOutput(xcb_window_t rootWindow, xcb_randr_output_t output) const
-{
-    for (QXcbScreen *screen : m_screens) {
-        if (screen->root() == rootWindow && screen->output() == output)
-            return screen;
-    }
-
-    return 0;
-}
-
-QXcbVirtualDesktop* QXcbConnection::virtualDesktopForRootWindow(xcb_window_t rootWindow) const
-{
-    for (QXcbVirtualDesktop *virtualDesktop : m_virtualDesktops) {
-        if (virtualDesktop->screen()->root == rootWindow)
-            return virtualDesktop;
-    }
-
-    return 0;
-}
-
-/*!
-    \brief Synchronizes the screen list, adds new screens, removes deleted ones
-*/
-void QXcbConnection::updateScreens(const xcb_randr_notify_event_t *event)
-{
-    if (event->subCode == XCB_RANDR_NOTIFY_CRTC_CHANGE) {
-        xcb_randr_crtc_change_t crtc = event->u.cc;
-        QXcbVirtualDesktop *virtualDesktop = virtualDesktopForRootWindow(crtc.window);
-        if (!virtualDesktop)
-            // Not for us
-            return;
-
-        QXcbScreen *screen = findScreenForCrtc(crtc.window, crtc.crtc);
-        qCDebug(lcQpaScreen) << "QXcbConnection: XCB_RANDR_NOTIFY_CRTC_CHANGE:" << crtc.crtc
-                             << "mode" << crtc.mode << "relevant screen" << screen;
-        // Only update geometry when there's a valid mode on the CRTC
-        // CRTC with node mode could mean that output has been disabled, and we'll
-        // get RRNotifyOutputChange notification for that.
-        if (screen && crtc.mode) {
-            if (crtc.rotation == XCB_RANDR_ROTATION_ROTATE_90 ||
-                crtc.rotation == XCB_RANDR_ROTATION_ROTATE_270)
-                std::swap(crtc.width, crtc.height);
-            screen->updateGeometry(QRect(crtc.x, crtc.y, crtc.width, crtc.height), crtc.rotation);
-            if (screen->mode() != crtc.mode)
-                screen->updateRefreshRate(crtc.mode);
-        }
-
-    } else if (event->subCode == XCB_RANDR_NOTIFY_OUTPUT_CHANGE) {
-        xcb_randr_output_change_t output = event->u.oc;
-        QXcbVirtualDesktop *virtualDesktop = virtualDesktopForRootWindow(output.window);
-        if (!virtualDesktop)
-            // Not for us
-            return;
-
-        QXcbScreen *screen = findScreenForOutput(output.window, output.output);
-        qCDebug(lcQpaScreen) << "QXcbConnection: XCB_RANDR_NOTIFY_OUTPUT_CHANGE:" << output.output;
-
-        if (screen && output.connection == XCB_RANDR_CONNECTION_DISCONNECTED) {
-            qCDebug(lcQpaScreen) << "screen" << screen->name() << "has been disconnected";
-            destroyScreen(screen);
-        } else if (!screen && output.connection == XCB_RANDR_CONNECTION_CONNECTED) {
-            // New XRandR output is available and it's enabled
-            if (output.crtc != XCB_NONE && output.mode != XCB_NONE) {
-                auto outputInfo = Q_XCB_REPLY(xcb_randr_get_output_info, xcb_connection(),
-                                              output.output, output.config_timestamp);
-                // Find a fake screen
-                const auto scrs = virtualDesktop->screens();
-                for (QPlatformScreen *scr : scrs) {
-                    QXcbScreen *xcbScreen = static_cast<QXcbScreen *>(scr);
-                    if (xcbScreen->output() == XCB_NONE) {
-                        screen = xcbScreen;
-                        break;
-                    }
-                }
-
-                if (screen) {
-                    QString nameWas = screen->name();
-                    // Transform the fake screen into a physical screen
-                    screen->setOutput(output.output, outputInfo.get());
-                    updateScreen(screen, output);
-                    qCDebug(lcQpaScreen) << "output" << screen->name()
-                                         << "is connected and enabled; was fake:" << nameWas;
-                } else {
-                    screen = createScreen(virtualDesktop, output, outputInfo.get());
-                    qCDebug(lcQpaScreen) << "output" << screen->name() << "is connected and enabled";
-                }
-                QHighDpiScaling::updateHighDpiScaling();
-            }
-        } else if (screen) {
-            if (output.crtc == XCB_NONE && output.mode == XCB_NONE) {
-                // Screen has been disabled
-                auto outputInfo = Q_XCB_REPLY(xcb_randr_get_output_info, xcb_connection(),
-                                              output.output, output.config_timestamp);
-                if (outputInfo->crtc == XCB_NONE) {
-                    qCDebug(lcQpaScreen) << "output" << screen->name() << "has been disabled";
-                    destroyScreen(screen);
-                } else {
-                    qCDebug(lcQpaScreen) << "output" << screen->name() << "has been temporarily disabled for the mode switch";
-                    // Reset crtc to skip RRCrtcChangeNotify events,
-                    // because they may be invalid in the middle of the mode switch
-                    screen->setCrtc(XCB_NONE);
-                }
-            } else {
-                updateScreen(screen, output);
-                qCDebug(lcQpaScreen) << "output has changed" << screen;
-            }
-        }
-
-        qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
-    }
-}
-
-bool QXcbConnection::checkOutputIsPrimary(xcb_window_t rootWindow, xcb_randr_output_t output)
-{
-    auto primary = Q_XCB_REPLY(xcb_randr_get_output_primary, xcb_connection(), rootWindow);
-    if (!primary)
-        qWarning("failed to get the primary output of the screen");
-
-    const bool isPrimary = primary ? (primary->output == output) : false;
-
-    return isPrimary;
-}
-
-void QXcbConnection::updateScreen(QXcbScreen *screen, const xcb_randr_output_change_t &outputChange)
-{
-    screen->setCrtc(outputChange.crtc); // Set the new crtc, because it can be invalid
-    screen->updateGeometry(outputChange.config_timestamp);
-    if (screen->mode() != outputChange.mode)
-        screen->updateRefreshRate(outputChange.mode);
-    // Only screen which belongs to the primary virtual desktop can be a primary screen
-    if (screen->screenNumber() == primaryScreenNumber()) {
-        if (!screen->isPrimary() && checkOutputIsPrimary(outputChange.window, outputChange.output)) {
-            screen->setPrimary(true);
-
-            // If the screen became primary, reshuffle the order in QGuiApplicationPrivate
-            const int idx = m_screens.indexOf(screen);
-            if (idx > 0) {
-                qAsConst(m_screens).first()->setPrimary(false);
-                m_screens.swap(0, idx);
-            }
-            screen->virtualDesktop()->setPrimaryScreen(screen);
-            QXcbIntegration::instance()->setPrimaryScreen(screen);
-        }
-    }
-}
-
-QXcbScreen *QXcbConnection::createScreen(QXcbVirtualDesktop *virtualDesktop,
-                                         const xcb_randr_output_change_t &outputChange,
-                                         xcb_randr_get_output_info_reply_t *outputInfo)
-{
-    QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, outputChange.output, outputInfo);
-    // Only screen which belongs to the primary virtual desktop can be a primary screen
-    if (screen->screenNumber() == primaryScreenNumber())
-        screen->setPrimary(checkOutputIsPrimary(outputChange.window, outputChange.output));
-
-    if (screen->isPrimary()) {
-        if (!m_screens.isEmpty())
-            qAsConst(m_screens).first()->setPrimary(false);
-
-        m_screens.prepend(screen);
-    } else {
-        m_screens.append(screen);
-    }
-    virtualDesktop->addScreen(screen);
-    QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
-
-    return screen;
-}
-
-void QXcbConnection::destroyScreen(QXcbScreen *screen)
-{
-    QXcbVirtualDesktop *virtualDesktop = screen->virtualDesktop();
-    if (virtualDesktop->screens().count() == 1) {
-        // If there are no other screens on the same virtual desktop,
-        // then transform the physical screen into a fake screen.
-        const QString nameWas = screen->name();
-        screen->setOutput(XCB_NONE, nullptr);
-        qCDebug(lcQpaScreen) << "transformed" << nameWas << "to fake" << screen;
-    } else {
-        // There is more than one screen on the same virtual desktop, remove the screen
-        m_screens.removeOne(screen);
-        virtualDesktop->removeScreen(screen);
-
-        // When primary screen is removed, set the new primary screen
-        // which belongs to the primary virtual desktop.
-        if (screen->isPrimary()) {
-            QXcbScreen *newPrimary = static_cast<QXcbScreen *>(virtualDesktop->screens().at(0));
-            newPrimary->setPrimary(true);
-            const int idx = m_screens.indexOf(newPrimary);
-            if (idx > 0)
-                m_screens.swap(0, idx);
-            QXcbIntegration::instance()->setPrimaryScreen(newPrimary);
-        }
-
-        QXcbIntegration::instance()->destroyScreen(screen);
-    }
-}
-
-void QXcbConnection::initializeScreens()
-{
-    xcb_screen_iterator_t it = xcb_setup_roots_iterator(setup());
-    int xcbScreenNumber = 0;    // screen number in the xcb sense
-    QXcbScreen *primaryScreen = nullptr;
-    while (it.rem) {
-        // Each "screen" in xcb terminology is a virtual desktop,
-        // potentially a collection of separate juxtaposed monitors.
-        // But we want a separate QScreen for each output (e.g. DVI-I-1, VGA-1, etc.)
-        // which will become virtual siblings.
-        xcb_screen_t *xcbScreen = it.data;
-        QXcbVirtualDesktop *virtualDesktop = new QXcbVirtualDesktop(this, xcbScreen, xcbScreenNumber);
-        m_virtualDesktops.append(virtualDesktop);
-        QList<QPlatformScreen *> siblings;
-        if (hasXRender()) {
-            // RRGetScreenResourcesCurrent is fast but it may return nothing if the
-            // configuration is not initialized wrt to the hardware. We should call
-            // RRGetScreenResources in this case.
-            auto resources_current = Q_XCB_REPLY(xcb_randr_get_screen_resources_current,
-                                                 xcb_connection(), xcbScreen->root);
-            if (!resources_current) {
-                qWarning("failed to get the current screen resources");
-            } else {
-                xcb_timestamp_t timestamp = 0;
-                xcb_randr_output_t *outputs = nullptr;
-                int outputCount = xcb_randr_get_screen_resources_current_outputs_length(resources_current.get());
-                if (outputCount) {
-                    timestamp = resources_current->config_timestamp;
-                    outputs = xcb_randr_get_screen_resources_current_outputs(resources_current.get());
-                } else {
-                    auto resources = Q_XCB_REPLY(xcb_randr_get_screen_resources,
-                                                 xcb_connection(), xcbScreen->root);
-                    if (!resources) {
-                        qWarning("failed to get the screen resources");
-                    } else {
-                        timestamp = resources->config_timestamp;
-                        outputCount = xcb_randr_get_screen_resources_outputs_length(resources.get());
-                        outputs = xcb_randr_get_screen_resources_outputs(resources.get());
-                    }
-                }
-
-                if (outputCount) {
-                    auto primary = Q_XCB_REPLY(xcb_randr_get_output_primary, xcb_connection(), xcbScreen->root);
-                    if (!primary) {
-                        qWarning("failed to get the primary output of the screen");
-                    } else {
-                        for (int i = 0; i < outputCount; i++) {
-                            auto output = Q_XCB_REPLY_UNCHECKED(xcb_randr_get_output_info,
-                                                                xcb_connection(), outputs[i], timestamp);
-                            // Invalid, disconnected or disabled output
-                            if (!output)
-                                continue;
-
-                            if (output->connection != XCB_RANDR_CONNECTION_CONNECTED) {
-                                qCDebug(lcQpaScreen, "Output %s is not connected", qPrintable(
-                                            QString::fromUtf8((const char*)xcb_randr_get_output_info_name(output.get()),
-                                                              xcb_randr_get_output_info_name_length(output.get()))));
-                                continue;
-                            }
-
-                            if (output->crtc == XCB_NONE) {
-                                qCDebug(lcQpaScreen, "Output %s is not enabled", qPrintable(
-                                            QString::fromUtf8((const char*)xcb_randr_get_output_info_name(output.get()),
-                                                              xcb_randr_get_output_info_name_length(output.get()))));
-                                continue;
-                            }
-
-                            QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, outputs[i], output.get());
-                            siblings << screen;
-                            m_screens << screen;
-
-                            // There can be multiple outputs per screen, use either
-                            // the first or an exact match.  An exact match isn't
-                            // always available if primary->output is XCB_NONE
-                            // or currently disconnected output.
-                            if (primaryScreenNumber() == xcbScreenNumber) {
-                                if (!primaryScreen || (primary && outputs[i] == primary->output)) {
-                                    if (primaryScreen)
-                                        primaryScreen->setPrimary(false);
-                                    primaryScreen = screen;
-                                    primaryScreen->setPrimary(true);
-                                    siblings.prepend(siblings.takeLast());
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-        } else if (hasXinerama()) {
-            // Xinerama is available
-            auto screens = Q_XCB_REPLY(xcb_xinerama_query_screens, xcb_connection());
-            if (screens) {
-                xcb_xinerama_screen_info_iterator_t it = xcb_xinerama_query_screens_screen_info_iterator(screens.get());
-                while (it.rem) {
-                    xcb_xinerama_screen_info_t *screen_info = it.data;
-                    QXcbScreen *screen = new QXcbScreen(this, virtualDesktop,
-                                                        XCB_NONE, nullptr,
-                                                        screen_info, it.index);
-                    siblings << screen;
-                    m_screens << screen;
-                    xcb_xinerama_screen_info_next(&it);
-                }
-            }
-        }
-        if (siblings.isEmpty()) {
-            // If there are no XRandR outputs or XRandR extension is missing,
-            // then create a fake/legacy screen.
-            QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, XCB_NONE, nullptr);
-            qCDebug(lcQpaScreen) << "created fake screen" << screen;
-            m_screens << screen;
-            if (primaryScreenNumber() == xcbScreenNumber) {
-                primaryScreen = screen;
-                primaryScreen->setPrimary(true);
-            }
-            siblings << screen;
-        }
-        virtualDesktop->setScreens(siblings);
-        xcb_screen_next(&it);
-        ++xcbScreenNumber;
-    } // for each xcb screen
-
-    for (QXcbVirtualDesktop *virtualDesktop : qAsConst(m_virtualDesktops))
-        virtualDesktop->subscribeToXFixesSelectionNotify();
-
-    if (m_virtualDesktops.isEmpty()) {
-        qFatal("QXcbConnection: no screens available");
-    } else {
-        // Ensure the primary screen is first on the list
-        if (primaryScreen) {
-            if (qAsConst(m_screens).first() != primaryScreen) {
-                m_screens.removeOne(primaryScreen);
-                m_screens.prepend(primaryScreen);
-            }
-        }
-
-        // Push the screens to QGuiApplication
-        for (QXcbScreen *screen : qAsConst(m_screens)) {
-            qCDebug(lcQpaScreen) << "adding" << screen << "(Primary:" << screen->isPrimary() << ")";
-            QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
-        }
-
-        qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
-    }
-}
-
 QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGrabServer, xcb_visualid_t defaultVisualId, const char *displayName)
     : QXcbBasicConnection(displayName)
     , m_canGrabServer(canGrabServer)
@@ -475,8 +105,6 @@ QXcbConnection::QXcbConnection(QXcbNativeInterface *nativeInterface, bool canGra
 
     m_xdgCurrentDesktop = qgetenv("XDG_CURRENT_DESKTOP").toLower();
 
-    selectXRandrEvents();
-
     initializeScreens();
 
 #if QT_CONFIG(xcb_xinput)
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index fcc1309afe..49e79ec3fd 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -330,7 +330,15 @@ private:
     ScrollingDevice *scrollingDeviceForId(int id);
 
     static bool xi2GetValuatorValueIfSet(const void *event, int valuatorNum, double *value);
-#endif
+
+    QHash<int, TouchDeviceData> m_touchDevices;
+    struct StartSystemMoveResizeInfo {
+        xcb_window_t window = XCB_NONE;
+        uint16_t deviceid;
+        uint32_t pointid;
+        int corner;
+    } m_startSystemMoveResizeInfo;
+#endif // QT_CONFIG(xcb_xinput)
 
     const bool m_canGrabServer;
     const xcb_visualid_t m_defaultVisualId;
@@ -353,15 +361,6 @@ private:
 
     QXcbEventQueue *m_eventQueue = nullptr;
 
-#if QT_CONFIG(xcb_xinput)
-    QHash<int, TouchDeviceData> m_touchDevices;
-    struct StartSystemMoveResizeInfo {
-        xcb_window_t window = XCB_NONE;
-        uint16_t deviceid;
-        uint32_t pointid;
-        int corner;
-    } m_startSystemMoveResizeInfo;
-#endif
     WindowMapper m_mapper;
 
     QVector<PeekFunc> m_peekFuncs;
diff --git a/src/plugins/platforms/xcb/qxcbconnection_screens.cpp b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
new file mode 100644
index 0000000000..4c380bf39f
--- /dev/null
+++ b/src/plugins/platforms/xcb/qxcbconnection_screens.cpp
@@ -0,0 +1,416 @@
+/****************************************************************************
+**
+** Copyright (C) 2018 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#include "qxcbconnection.h"
+#include "qxcbscreen.h"
+#include "qxcbintegration.h"
+
+#include <QtGui/private/qhighdpiscaling_p.h>
+#include <QtCore/QString>
+#include <QtCore/QList>
+
+#include <xcb/xinerama.h>
+
+void QXcbConnection::selectXRandrEvents()
+{
+    xcb_screen_iterator_t rootIter = xcb_setup_roots_iterator(setup());
+    for (; rootIter.rem; xcb_screen_next(&rootIter)) {
+        xcb_randr_select_input(xcb_connection(),
+            rootIter.data->root,
+            XCB_RANDR_NOTIFY_MASK_SCREEN_CHANGE |
+            XCB_RANDR_NOTIFY_MASK_OUTPUT_CHANGE |
+            XCB_RANDR_NOTIFY_MASK_CRTC_CHANGE |
+            XCB_RANDR_NOTIFY_MASK_OUTPUT_PROPERTY
+        );
+    }
+}
+
+QXcbScreen* QXcbConnection::findScreenForCrtc(xcb_window_t rootWindow, xcb_randr_crtc_t crtc) const
+{
+    for (QXcbScreen *screen : m_screens) {
+        if (screen->root() == rootWindow && screen->crtc() == crtc)
+            return screen;
+    }
+
+    return nullptr;
+}
+
+QXcbScreen* QXcbConnection::findScreenForOutput(xcb_window_t rootWindow, xcb_randr_output_t output) const
+{
+    for (QXcbScreen *screen : m_screens) {
+        if (screen->root() == rootWindow && screen->output() == output)
+            return screen;
+    }
+
+    return nullptr;
+}
+
+QXcbVirtualDesktop* QXcbConnection::virtualDesktopForRootWindow(xcb_window_t rootWindow) const
+{
+    for (QXcbVirtualDesktop *virtualDesktop : m_virtualDesktops) {
+        if (virtualDesktop->screen()->root == rootWindow)
+            return virtualDesktop;
+    }
+
+    return nullptr;
+}
+
+/*!
+    \brief Synchronizes the screen list, adds new screens, removes deleted ones
+*/
+void QXcbConnection::updateScreens(const xcb_randr_notify_event_t *event)
+{
+    if (event->subCode == XCB_RANDR_NOTIFY_CRTC_CHANGE) {
+        xcb_randr_crtc_change_t crtc = event->u.cc;
+        QXcbVirtualDesktop *virtualDesktop = virtualDesktopForRootWindow(crtc.window);
+        if (!virtualDesktop)
+            // Not for us
+            return;
+
+        QXcbScreen *screen = findScreenForCrtc(crtc.window, crtc.crtc);
+        qCDebug(lcQpaScreen) << "QXcbConnection: XCB_RANDR_NOTIFY_CRTC_CHANGE:" << crtc.crtc
+                             << "mode" << crtc.mode << "relevant screen" << screen;
+        // Only update geometry when there's a valid mode on the CRTC
+        // CRTC with node mode could mean that output has been disabled, and we'll
+        // get RRNotifyOutputChange notification for that.
+        if (screen && crtc.mode) {
+            if (crtc.rotation == XCB_RANDR_ROTATION_ROTATE_90 ||
+                crtc.rotation == XCB_RANDR_ROTATION_ROTATE_270)
+                std::swap(crtc.width, crtc.height);
+            screen->updateGeometry(QRect(crtc.x, crtc.y, crtc.width, crtc.height), crtc.rotation);
+            if (screen->mode() != crtc.mode)
+                screen->updateRefreshRate(crtc.mode);
+        }
+
+    } else if (event->subCode == XCB_RANDR_NOTIFY_OUTPUT_CHANGE) {
+        xcb_randr_output_change_t output = event->u.oc;
+        QXcbVirtualDesktop *virtualDesktop = virtualDesktopForRootWindow(output.window);
+        if (!virtualDesktop)
+            // Not for us
+            return;
+
+        QXcbScreen *screen = findScreenForOutput(output.window, output.output);
+        qCDebug(lcQpaScreen) << "QXcbConnection: XCB_RANDR_NOTIFY_OUTPUT_CHANGE:" << output.output;
+
+        if (screen && output.connection == XCB_RANDR_CONNECTION_DISCONNECTED) {
+            qCDebug(lcQpaScreen) << "screen" << screen->name() << "has been disconnected";
+            destroyScreen(screen);
+        } else if (!screen && output.connection == XCB_RANDR_CONNECTION_CONNECTED) {
+            // New XRandR output is available and it's enabled
+            if (output.crtc != XCB_NONE && output.mode != XCB_NONE) {
+                auto outputInfo = Q_XCB_REPLY(xcb_randr_get_output_info, xcb_connection(),
+                                              output.output, output.config_timestamp);
+                // Find a fake screen
+                const auto scrs = virtualDesktop->screens();
+                for (QPlatformScreen *scr : scrs) {
+                    QXcbScreen *xcbScreen = static_cast<QXcbScreen *>(scr);
+                    if (xcbScreen->output() == XCB_NONE) {
+                        screen = xcbScreen;
+                        break;
+                    }
+                }
+
+                if (screen) {
+                    QString nameWas = screen->name();
+                    // Transform the fake screen into a physical screen
+                    screen->setOutput(output.output, outputInfo.get());
+                    updateScreen(screen, output);
+                    qCDebug(lcQpaScreen) << "output" << screen->name()
+                                         << "is connected and enabled; was fake:" << nameWas;
+                } else {
+                    screen = createScreen(virtualDesktop, output, outputInfo.get());
+                    qCDebug(lcQpaScreen) << "output" << screen->name() << "is connected and enabled";
+                }
+                QHighDpiScaling::updateHighDpiScaling();
+            }
+        } else if (screen) {
+            if (output.crtc == XCB_NONE && output.mode == XCB_NONE) {
+                // Screen has been disabled
+                auto outputInfo = Q_XCB_REPLY(xcb_randr_get_output_info, xcb_connection(),
+                                              output.output, output.config_timestamp);
+                if (outputInfo->crtc == XCB_NONE) {
+                    qCDebug(lcQpaScreen) << "output" << screen->name() << "has been disabled";
+                    destroyScreen(screen);
+                } else {
+                    qCDebug(lcQpaScreen) << "output" << screen->name() << "has been temporarily disabled for the mode switch";
+                    // Reset crtc to skip RRCrtcChangeNotify events,
+                    // because they may be invalid in the middle of the mode switch
+                    screen->setCrtc(XCB_NONE);
+                }
+            } else {
+                updateScreen(screen, output);
+                qCDebug(lcQpaScreen) << "output has changed" << screen;
+            }
+        }
+
+        qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
+    }
+}
+
+bool QXcbConnection::checkOutputIsPrimary(xcb_window_t rootWindow, xcb_randr_output_t output)
+{
+    auto primary = Q_XCB_REPLY(xcb_randr_get_output_primary, xcb_connection(), rootWindow);
+    if (!primary)
+        qWarning("failed to get the primary output of the screen");
+
+    const bool isPrimary = primary ? (primary->output == output) : false;
+
+    return isPrimary;
+}
+
+void QXcbConnection::updateScreen(QXcbScreen *screen, const xcb_randr_output_change_t &outputChange)
+{
+    screen->setCrtc(outputChange.crtc); // Set the new crtc, because it can be invalid
+    screen->updateGeometry(outputChange.config_timestamp);
+    if (screen->mode() != outputChange.mode)
+        screen->updateRefreshRate(outputChange.mode);
+    // Only screen which belongs to the primary virtual desktop can be a primary screen
+    if (screen->screenNumber() == primaryScreenNumber()) {
+        if (!screen->isPrimary() && checkOutputIsPrimary(outputChange.window, outputChange.output)) {
+            screen->setPrimary(true);
+
+            // If the screen became primary, reshuffle the order in QGuiApplicationPrivate
+            const int idx = m_screens.indexOf(screen);
+            if (idx > 0) {
+                qAsConst(m_screens).first()->setPrimary(false);
+                m_screens.swap(0, idx);
+            }
+            screen->virtualDesktop()->setPrimaryScreen(screen);
+            QXcbIntegration::instance()->setPrimaryScreen(screen);
+        }
+    }
+}
+
+QXcbScreen *QXcbConnection::createScreen(QXcbVirtualDesktop *virtualDesktop,
+                                         const xcb_randr_output_change_t &outputChange,
+                                         xcb_randr_get_output_info_reply_t *outputInfo)
+{
+    QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, outputChange.output, outputInfo);
+    // Only screen which belongs to the primary virtual desktop can be a primary screen
+    if (screen->screenNumber() == primaryScreenNumber())
+        screen->setPrimary(checkOutputIsPrimary(outputChange.window, outputChange.output));
+
+    if (screen->isPrimary()) {
+        if (!m_screens.isEmpty())
+            qAsConst(m_screens).first()->setPrimary(false);
+
+        m_screens.prepend(screen);
+    } else {
+        m_screens.append(screen);
+    }
+    virtualDesktop->addScreen(screen);
+    QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
+
+    return screen;
+}
+
+void QXcbConnection::destroyScreen(QXcbScreen *screen)
+{
+    QXcbVirtualDesktop *virtualDesktop = screen->virtualDesktop();
+    if (virtualDesktop->screens().count() == 1) {
+        // If there are no other screens on the same virtual desktop,
+        // then transform the physical screen into a fake screen.
+        const QString nameWas = screen->name();
+        screen->setOutput(XCB_NONE, nullptr);
+        qCDebug(lcQpaScreen) << "transformed" << nameWas << "to fake" << screen;
+    } else {
+        // There is more than one screen on the same virtual desktop, remove the screen
+        m_screens.removeOne(screen);
+        virtualDesktop->removeScreen(screen);
+
+        // When primary screen is removed, set the new primary screen
+        // which belongs to the primary virtual desktop.
+        if (screen->isPrimary()) {
+            QXcbScreen *newPrimary = static_cast<QXcbScreen *>(virtualDesktop->screens().at(0));
+            newPrimary->setPrimary(true);
+            const int idx = m_screens.indexOf(newPrimary);
+            if (idx > 0)
+                m_screens.swap(0, idx);
+            QXcbIntegration::instance()->setPrimaryScreen(newPrimary);
+        }
+
+        QXcbIntegration::instance()->destroyScreen(screen);
+    }
+}
+
+void QXcbConnection::initializeScreens()
+{
+    selectXRandrEvents();
+
+    xcb_screen_iterator_t it = xcb_setup_roots_iterator(setup());
+    int xcbScreenNumber = 0;    // screen number in the xcb sense
+    QXcbScreen *primaryScreen = nullptr;
+    while (it.rem) {
+        // Each "screen" in xcb terminology is a virtual desktop,
+        // potentially a collection of separate juxtaposed monitors.
+        // But we want a separate QScreen for each output (e.g. DVI-I-1, VGA-1, etc.)
+        // which will become virtual siblings.
+        xcb_screen_t *xcbScreen = it.data;
+        QXcbVirtualDesktop *virtualDesktop = new QXcbVirtualDesktop(this, xcbScreen, xcbScreenNumber);
+        m_virtualDesktops.append(virtualDesktop);
+        QList<QPlatformScreen *> siblings;
+        if (hasXRender()) {
+            // RRGetScreenResourcesCurrent is fast but it may return nothing if the
+            // configuration is not initialized wrt to the hardware. We should call
+            // RRGetScreenResources in this case.
+            auto resources_current = Q_XCB_REPLY(xcb_randr_get_screen_resources_current,
+                                                 xcb_connection(), xcbScreen->root);
+            if (!resources_current) {
+                qWarning("failed to get the current screen resources");
+            } else {
+                xcb_timestamp_t timestamp = 0;
+                xcb_randr_output_t *outputs = nullptr;
+                int outputCount = xcb_randr_get_screen_resources_current_outputs_length(resources_current.get());
+                if (outputCount) {
+                    timestamp = resources_current->config_timestamp;
+                    outputs = xcb_randr_get_screen_resources_current_outputs(resources_current.get());
+                } else {
+                    auto resources = Q_XCB_REPLY(xcb_randr_get_screen_resources,
+                                                 xcb_connection(), xcbScreen->root);
+                    if (!resources) {
+                        qWarning("failed to get the screen resources");
+                    } else {
+                        timestamp = resources->config_timestamp;
+                        outputCount = xcb_randr_get_screen_resources_outputs_length(resources.get());
+                        outputs = xcb_randr_get_screen_resources_outputs(resources.get());
+                    }
+                }
+
+                if (outputCount) {
+                    auto primary = Q_XCB_REPLY(xcb_randr_get_output_primary, xcb_connection(), xcbScreen->root);
+                    if (!primary) {
+                        qWarning("failed to get the primary output of the screen");
+                    } else {
+                        for (int i = 0; i < outputCount; i++) {
+                            auto output = Q_XCB_REPLY_UNCHECKED(xcb_randr_get_output_info,
+                                                                xcb_connection(), outputs[i], timestamp);
+                            // Invalid, disconnected or disabled output
+                            if (!output)
+                                continue;
+
+                            if (output->connection != XCB_RANDR_CONNECTION_CONNECTED) {
+                                qCDebug(lcQpaScreen, "Output %s is not connected", qPrintable(
+                                            QString::fromUtf8((const char*)xcb_randr_get_output_info_name(output.get()),
+                                                              xcb_randr_get_output_info_name_length(output.get()))));
+                                continue;
+                            }
+
+                            if (output->crtc == XCB_NONE) {
+                                qCDebug(lcQpaScreen, "Output %s is not enabled", qPrintable(
+                                            QString::fromUtf8((const char*)xcb_randr_get_output_info_name(output.get()),
+                                                              xcb_randr_get_output_info_name_length(output.get()))));
+                                continue;
+                            }
+
+                            QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, outputs[i], output.get());
+                            siblings << screen;
+                            m_screens << screen;
+
+                            // There can be multiple outputs per screen, use either
+                            // the first or an exact match.  An exact match isn't
+                            // always available if primary->output is XCB_NONE
+                            // or currently disconnected output.
+                            if (primaryScreenNumber() == xcbScreenNumber) {
+                                if (!primaryScreen || (primary && outputs[i] == primary->output)) {
+                                    if (primaryScreen)
+                                        primaryScreen->setPrimary(false);
+                                    primaryScreen = screen;
+                                    primaryScreen->setPrimary(true);
+                                    siblings.prepend(siblings.takeLast());
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+        } else if (hasXinerama()) {
+            // Xinerama is available
+            auto screens = Q_XCB_REPLY(xcb_xinerama_query_screens, xcb_connection());
+            if (screens) {
+                xcb_xinerama_screen_info_iterator_t it = xcb_xinerama_query_screens_screen_info_iterator(screens.get());
+                while (it.rem) {
+                    xcb_xinerama_screen_info_t *screen_info = it.data;
+                    QXcbScreen *screen = new QXcbScreen(this, virtualDesktop,
+                                                        XCB_NONE, nullptr,
+                                                        screen_info, it.index);
+                    siblings << screen;
+                    m_screens << screen;
+                    xcb_xinerama_screen_info_next(&it);
+                }
+            }
+        }
+        if (siblings.isEmpty()) {
+            // If there are no XRandR outputs or XRandR extension is missing,
+            // then create a fake/legacy screen.
+            QXcbScreen *screen = new QXcbScreen(this, virtualDesktop, XCB_NONE, nullptr);
+            qCDebug(lcQpaScreen) << "created fake screen" << screen;
+            m_screens << screen;
+            if (primaryScreenNumber() == xcbScreenNumber) {
+                primaryScreen = screen;
+                primaryScreen->setPrimary(true);
+            }
+            siblings << screen;
+        }
+        virtualDesktop->setScreens(siblings);
+        xcb_screen_next(&it);
+        ++xcbScreenNumber;
+    } // for each xcb screen
+
+    for (QXcbVirtualDesktop *virtualDesktop : qAsConst(m_virtualDesktops))
+        virtualDesktop->subscribeToXFixesSelectionNotify();
+
+    if (m_virtualDesktops.isEmpty()) {
+        qFatal("QXcbConnection: no screens available");
+    } else {
+        // Ensure the primary screen is first on the list
+        if (primaryScreen) {
+            if (qAsConst(m_screens).first() != primaryScreen) {
+                m_screens.removeOne(primaryScreen);
+                m_screens.prepend(primaryScreen);
+            }
+        }
+
+        // Push the screens to QGuiApplication
+        for (QXcbScreen *screen : qAsConst(m_screens)) {
+            qCDebug(lcQpaScreen) << "adding" << screen << "(Primary:" << screen->isPrimary() << ")";
+            QXcbIntegration::instance()->screenAdded(screen, screen->isPrimary());
+        }
+
+        qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
+    }
+}
diff --git a/src/plugins/platforms/xcb/xcb_qpa_lib.pro b/src/plugins/platforms/xcb/xcb_qpa_lib.pro
index c0704e4c18..c65b145fb6 100644
--- a/src/plugins/platforms/xcb/xcb_qpa_lib.pro
+++ b/src/plugins/platforms/xcb/xcb_qpa_lib.pro
@@ -33,6 +33,7 @@ SOURCES = \
         qxcbeventqueue.cpp \
         qxcbeventdispatcher.cpp \
         qxcbconnection_basic.cpp \
+        qxcbconnection_screens.cpp \
         qxcbatom.cpp
 
 HEADERS = \