x11: Drop support for multi-head

The main reason to drop multi-head support is that it has been simply
unmaintained for many many years. When implementing a feature, we don't
even bother checking if multi-head is broken, KCMs don't handle
multihead, window management features are written for Xinerama. KWin
is optimized for Xinerama-like operation mode in general, which is
provided out of the box.

If you use multihead for esoteric gpu stuff, consider using kwin_wayland!

src/backends/x11/standalone/x11_platform.cpp

@@ -207,16 +207,14 @@ bool X11StandalonePlatform::requiresCompositing() const
 
 bool X11StandalonePlatform::openGLCompositingIsBroken() const
 {
-    const QString unsafeKey(QLatin1String("OpenGLIsUnsafe") + (kwinApp()->isX11MultiHead() ? QString::number(kwinApp()->x11ScreenNumber()) : QString()));
+    return KConfigGroup(kwinApp()->config(), "Compositing").readEntry(QLatin1String("OpenGLIsUnsafe"), false);
-    return KConfigGroup(kwinApp()->config(), "Compositing").readEntry(unsafeKey, false);
 }
 
 QString X11StandalonePlatform::compositingNotPossibleReason() const
 {
     // first off, check whether we figured that we'll crash on detection because of a buggy driver
     KConfigGroup gl_workaround_group(kwinApp()->config(), "Compositing");
-    const QString unsafeKey(QLatin1String("OpenGLIsUnsafe") + (kwinApp()->isX11MultiHead() ? QString::number(kwinApp()->x11ScreenNumber()) : QString()));
+    if (gl_workaround_group.readEntry("Backend", "OpenGL") == QLatin1String("OpenGL") && gl_workaround_group.readEntry(QLatin1String("OpenGLIsUnsafe"), false)) {
-    if (gl_workaround_group.readEntry("Backend", "OpenGL") == QLatin1String("OpenGL") && gl_workaround_group.readEntry(unsafeKey, false)) {
         return i18n("<b>OpenGL compositing (the default) has crashed KWin in the past.</b><br>"
                     "This was most likely due to a driver bug."
                     "<p>If you think that you have meanwhile upgraded to a stable driver,<br>"
@@ -236,10 +234,9 @@ bool X11StandalonePlatform::compositingPossible() const
 {
     // first off, check whether we figured that we'll crash on detection because of a buggy driver
     KConfigGroup gl_workaround_group(kwinApp()->config(), "Compositing");
-    const QString unsafeKey(QLatin1String("OpenGLIsUnsafe") + (kwinApp()->isX11MultiHead() ? QString::number(kwinApp()->x11ScreenNumber()) : QString()));
+    if (gl_workaround_group.readEntry("Backend", "OpenGL") == QLatin1String("OpenGL") && gl_workaround_group.readEntry(QLatin1String("OpenGLIsUnsafe"), false)) {
-    if (gl_workaround_group.readEntry("Backend", "OpenGL") == QLatin1String("OpenGL") && gl_workaround_group.readEntry(unsafeKey, false)) {
         qCWarning(KWIN_X11STANDALONE) << "Compositing disabled: video driver seems unstable. If you think it's a false positive, please remove "
-                                      << unsafeKey << " from [Compositing] in kwinrc and restart kwin.";
+                                      << "OpenGLIsUnsafe from [Compositing] in kwinrc and restart kwin.";
         return false;
     }
 
@@ -270,11 +267,10 @@ bool X11StandalonePlatform::hasGlx()
 
 void X11StandalonePlatform::createOpenGLSafePoint(OpenGLSafePoint safePoint)
 {
-    const QString unsafeKey(QLatin1String("OpenGLIsUnsafe") + (kwinApp()->isX11MultiHead() ? QString::number(kwinApp()->x11ScreenNumber()) : QString()));
     auto group = KConfigGroup(kwinApp()->config(), "Compositing");
     switch (safePoint) {
     case OpenGLSafePoint::PreInit:
-        group.writeEntry(unsafeKey, true);
+        group.writeEntry(QLatin1String("OpenGLIsUnsafe"), true);
         group.sync();
         // Deliberately continue with PreFrame
         Q_FALLTHROUGH();
@@ -293,9 +289,8 @@ void X11StandalonePlatform::createOpenGLSafePoint(OpenGLSafePoint safePoint)
             connect(
                 m_openGLFreezeProtection, &QTimer::timeout, m_openGLFreezeProtection,
                 [configName] {
-                    const QString unsafeKey(QLatin1String("OpenGLIsUnsafe") + (kwinApp()->isX11MultiHead() ? QString::number(kwinApp()->x11ScreenNumber()) : QString()));
                     auto group = KConfigGroup(KSharedConfig::openConfig(configName), "Compositing");
-                    group.writeEntry(unsafeKey, true);
+                    group.writeEntry(QLatin1String("OpenGLIsUnsafe"), true);
                     group.sync();
                     KCrash::setDrKonqiEnabled(false);
                     qFatal("Freeze in OpenGL initialization detected");
@@ -307,7 +302,7 @@ void X11StandalonePlatform::createOpenGLSafePoint(OpenGLSafePoint safePoint)
         }
         break;
     case OpenGLSafePoint::PostInit:
-        group.writeEntry(unsafeKey, false);
+        group.writeEntry(QLatin1String("OpenGLIsUnsafe"), false);
         group.sync();
         // Deliberately continue with PostFrame
         Q_FALLTHROUGH();

src/composite.cpp

@@ -70,11 +70,6 @@ Q_DECLARE_METATYPE(KWin::X11Compositor::SuspendReason)
 namespace KWin
 {
 
-// See main.cpp:
-extern int screen_number;
-
-extern bool is_multihead;
-
 Compositor *Compositor::s_compositor = nullptr;
 Compositor *Compositor::self()
 {

src/dbusinterface.cpp

@@ -46,10 +46,6 @@ DBusInterface::DBusInterface(QObject *parent)
 
     QDBusConnection dbus = QDBusConnection::sessionBus();
     dbus.registerObject(QStringLiteral("/KWin"), this);
-    const QByteArray dBusSuffix = qgetenv("KWIN_DBUS_SERVICE_SUFFIX");
-    if (!dBusSuffix.isNull()) {
-        m_serviceName = m_serviceName + QLatin1Char('.') + dBusSuffix;
-    }
     dbus.registerService(m_serviceName);
     dbus.connect(QString(), QStringLiteral("/KWin"), QStringLiteral("org.kde.KWin"), QStringLiteral("reloadConfig"),
                  Workspace::self(), SLOT(slotReloadConfig()));

src/main.cpp

@@ -64,20 +64,9 @@ Options *options;
 Atoms *atoms;
 
 int screen_number = -1;
-bool is_multihead = false;
 
 int Application::crashes = 0;
 
-bool Application::isX11MultiHead()
-{
-    return is_multihead;
-}
-
-void Application::setX11MultiHead(bool multiHead)
-{
-    is_multihead = multiHead;
-}
-
 void Application::setX11ScreenNumber(int screenNumber)
 {
     screen_number = screenNumber;

src/main.h

@@ -157,14 +157,6 @@ public:
      * Sets the X11 screen number of this KWin instance to @p screenNumber.
      */
     static void setX11ScreenNumber(int screenNumber);
-    /**
-     * @returns whether this is a multi head setup on X11.
-     */
-    static bool isX11MultiHead();
-    /**
-     * Sets whether this is a multi head setup on X11.
-     */
-    static void setX11MultiHead(bool multiHead);
 
     /**
      * @returns the X11 root window.

src/main_x11.cpp

@@ -355,64 +355,6 @@ int main(int argc, char *argv[])
     KWin::Application::setupMalloc();
     KWin::Application::setupLocalizedString();
 
-    int primaryScreen = 0;
-    xcb_connection_t *c = xcb_connect(nullptr, &primaryScreen);
-    if (!c || xcb_connection_has_error(c)) {
-        fprintf(stderr, "%s: FATAL ERROR while trying to open display %s\n",
-                argv[0], qgetenv("DISPLAY").constData());
-        exit(1);
-    }
-
-    const int number_of_screens = xcb_setup_roots_length(xcb_get_setup(c));
-    xcb_disconnect(c);
-    c = nullptr;
-
-    // multi head
-    auto isMultiHead = []() -> bool {
-        QByteArray multiHead = qgetenv("KDE_MULTIHEAD");
-        if (!multiHead.isEmpty()) {
-            return (multiHead.toLower() == "true");
-        }
-        return true;
-    };
-    if (number_of_screens != 1 && isMultiHead()) {
-        KWin::Application::setX11MultiHead(true);
-        KWin::Application::setX11ScreenNumber(primaryScreen);
-        int pos; // Temporarily needed to reconstruct DISPLAY var if multi-head
-        QByteArray display_name = qgetenv("DISPLAY");
-
-        if ((pos = display_name.lastIndexOf('.')) != -1) {
-            display_name.remove(pos, 10); // 10 is enough to be sure we removed ".s"
-        }
-
-        for (int i = 0; i < number_of_screens; i++) {
-            // If execution doesn't pass by here, then kwin
-            // acts exactly as previously
-            if (i != KWin::Application::x11ScreenNumber() && fork() == 0) {
-                KWin::Application::setX11ScreenNumber(i);
-                QByteArray dBusSuffix = qgetenv("KWIN_DBUS_SERVICE_SUFFIX");
-                if (!dBusSuffix.isNull()) {
-                    dBusSuffix.append(".");
-                }
-                dBusSuffix.append(QByteArrayLiteral("head-")).append(QByteArray::number(i));
-                qputenv("KWIN_DBUS_SERVICE_SUFFIX", dBusSuffix);
-                // Break here because we are the child process, we don't
-                // want to fork() anymore
-                break;
-            }
-        }
-        // In the next statement, display_name shouldn't contain a screen
-        // number. If it had it, it was removed at the "pos" check
-        const QString envir = QStringLiteral("DISPLAY=%1.%2")
-                                  .arg(display_name.data())
-                                  .arg(KWin::Application::x11ScreenNumber());
-
-        if (putenv(strdup(envir.toLatin1().constData()))) {
-            fprintf(stderr, "%s: WARNING: unable to set DISPLAY environment variable\n", argv[0]);
-            perror("putenv()");
-        }
-    }
-
     if (signal(SIGTERM, KWin::sighandler) == SIG_IGN) {
         signal(SIGTERM, SIG_IGN);
     }

src/tabbox/tabbox.cpp

@@ -1036,7 +1036,7 @@ static bool areModKeysDepressed(const QKeySequence &seq)
 
 void TabBox::navigatingThroughWindows(bool forward, const QKeySequence &shortcut, TabBoxMode mode)
 {
-    if (!m_ready || isGrabbed() || !Workspace::self()->isOnCurrentHead()) {
+    if (!m_ready || isGrabbed()) {
         return;
     }
     if (!options->focusPolicyIsReasonable()) {
@@ -1098,7 +1098,7 @@ void TabBox::slotWalkBackThroughCurrentAppWindowsAlternative()
 
 void TabBox::slotWalkThroughDesktops()
 {
-    if (!m_ready || isGrabbed() || !Workspace::self()->isOnCurrentHead()) {
+    if (!m_ready || isGrabbed()) {
         return;
     }
     if (areModKeysDepressed(m_cutWalkThroughDesktops)) {
@@ -1112,7 +1112,7 @@ void TabBox::slotWalkThroughDesktops()
 
 void TabBox::slotWalkBackThroughDesktops()
 {
-    if (!m_ready || isGrabbed() || !Workspace::self()->isOnCurrentHead()) {
+    if (!m_ready || isGrabbed()) {
         return;
     }
     if (areModKeysDepressed(m_cutWalkThroughDesktopsReverse)) {
@@ -1126,7 +1126,7 @@ void TabBox::slotWalkBackThroughDesktops()
 
 void TabBox::slotWalkThroughDesktopList()
 {
-    if (!m_ready || isGrabbed() || !Workspace::self()->isOnCurrentHead()) {
+    if (!m_ready || isGrabbed()) {
         return;
     }
     if (areModKeysDepressed(m_cutWalkThroughDesktopList)) {
@@ -1140,7 +1140,7 @@ void TabBox::slotWalkThroughDesktopList()
 
 void TabBox::slotWalkBackThroughDesktopList()
 {
-    if (!m_ready || isGrabbed() || !Workspace::self()->isOnCurrentHead()) {
+    if (!m_ready || isGrabbed()) {
         return;
     }
     if (areModKeysDepressed(m_cutWalkThroughDesktopListReverse)) {

src/workspace.cpp

@@ -66,9 +66,6 @@
 namespace KWin
 {
 
-extern int screen_number;
-extern bool is_multihead;
-
 X11EventFilterContainer::X11EventFilterContainer(X11EventFilter *filter)
     : m_filter(filter)
 {
@@ -1295,34 +1292,6 @@ void Workspace::sendWindowToDesktop(Window *window, int desk, bool dont_activate
     updateClientArea();
 }
 
-/**
- * checks whether the X Window with the input focus is on our X11 screen
- * if the window cannot be determined or inspected, resturn depends on whether there's actually
- * more than one screen
- *
- * this is NOT in any way related to XRandR multiscreen
- *
- */
-extern bool is_multihead; // main.cpp
-bool Workspace::isOnCurrentHead()
-{
-    if (!is_multihead) {
-        return true;
-    }
-
-    Xcb::CurrentInput currentInput;
-    if (currentInput.window() == XCB_WINDOW_NONE) {
-        return !is_multihead;
-    }
-
-    Xcb::WindowGeometry geometry(currentInput.window());
-    if (geometry.isNull()) { // should not happen
-        return !is_multihead;
-    }
-
-    return kwinApp()->x11RootWindow() == geometry->root;
-}
-
 void Workspace::sendWindowToOutput(Window *window, Output *output)
 {
     window->sendToOutput(output);
@@ -1560,13 +1529,6 @@ QString Workspace::supportInformation() const
     }
     support.append(QStringLiteral("\nScreens\n"));
     support.append(QStringLiteral("=======\n"));
-    support.append(QStringLiteral("Multi-Head: "));
-    if (is_multihead) {
-        support.append(QStringLiteral("yes\n"));
-        support.append(QStringLiteral("Head: %1\n").arg(screen_number));
-    } else {
-        support.append(QStringLiteral("no\n"));
-    }
     support.append(QStringLiteral("Active screen follows mouse: "));
     if (options->activeMouseScreen()) {
         support.append(QStringLiteral(" yes\n"));
@@ -2238,11 +2200,6 @@ QRectF Workspace::clientArea(clientAreaOption opt, const Output *output, const V
     QRectF workArea;
     QRectF screenArea;
 
-    const Output *effectiveOutput = output;
-    if (is_multihead) {
-        effectiveOutput = xineramaIndexToOutput(screen_number);
-    }
-
     if (auto desktopIt = m_screenAreas.constFind(desktop); desktopIt != m_screenAreas.constEnd()) {
         if (auto outputIt = desktopIt->constFind(output); outputIt != desktopIt->constEnd()) {
             screenArea = *outputIt;
@@ -2250,12 +2207,12 @@ QRectF Workspace::clientArea(clientAreaOption opt, const Output *output, const V
     }
 
     if (screenArea.isNull()) { // screens may be missing during KWin initialization or screen config changes
-        screenArea = effectiveOutput->geometry();
+        screenArea = output->geometry();
     }
 
     workArea = m_workAreas.value(desktop);
     if (workArea.isNull()) {
-        workArea = is_multihead ? effectiveOutput->geometry() : m_geometry;
+        workArea = m_geometry;
     }
 
     switch (opt) {
@@ -2266,9 +2223,9 @@ QRectF Workspace::clientArea(clientAreaOption opt, const Output *output, const V
     case FullScreenArea:
     case MovementArea:
     case ScreenArea:
-        return effectiveOutput->geometry();
+        return output->geometry();
     case WorkArea:
-        return is_multihead ? screenArea : workArea;
+        return workArea;
     case FullArea:
         return m_geometry;
     default:

src/workspace.h

@@ -268,7 +268,6 @@ private:
     // Unsorted
 
 public:
-    bool isOnCurrentHead();
     // True when performing Workspace::updateClientArea().
     // The calls below are valid only in that case.
     bool inUpdateClientArea() const;