xcb: remove QT_XCB_NO_XI2_MOUSE code path

This code path was deprecated in 5.12 and scheduled for
removal in Qt 6. See 9184384bc9d9d71a146fff535021357258a0295e.

According to the source comments from f48170b479df359f47af12b03a501d9d0c386e66,
apperantly XInput2 had some issues when running on Xinerama screens
and therefore there was a check for it in xi2MouseEventsDisabled().
We plan to remove Xinerama support, therefore Xinerama handling in
xi2MouseEventsDisabled() is irrelevant.

Task-number: QTBUG-69412
Change-Id: I384d7c46337358caecccf644acc8ffbd381dc69d
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

4 files changed, 13 insertions, 134 deletions

diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp
index a703a46cf8..7435e124dc 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection.cpp
@@ -597,12 +597,16 @@ void QXcbConnection::handleXcbEvent(xcb_generic_event_t *event)
         HANDLE_PLATFORM_WINDOW_EVENT(xcb_client_message_event_t, window, handleClientMessageEvent);
     }
     case XCB_ENTER_NOTIFY:
-        if (hasXInput2() && !xi2MouseEventsDisabled())
+        if (hasXInput2()) {
+            // Prefer XI2 enter (XCB_INPUT_ENTER) events over core events.
             break;
+        }
         HANDLE_PLATFORM_WINDOW_EVENT(xcb_enter_notify_event_t, event, handleEnterNotifyEvent);
     case XCB_LEAVE_NOTIFY:
-        if (hasXInput2() && !xi2MouseEventsDisabled())
+        if (hasXInput2()) {
+            // Prefer XI2 leave (XCB_INPUT_LEAVE) events over core events.
             break;
+        }
         m_keyboard->updateXKBStateFromCore(reinterpret_cast<xcb_leave_notify_event_t *>(event)->state);
         HANDLE_PLATFORM_WINDOW_EVENT(xcb_leave_notify_event_t, event, handleLeaveNotifyEvent);
     case XCB_FOCUS_IN:
diff --git a/src/plugins/platforms/xcb/qxcbconnection.h b/src/plugins/platforms/xcb/qxcbconnection.h
index a097604643..77a9c9d934 100644
--- a/src/plugins/platforms/xcb/qxcbconnection.h
+++ b/src/plugins/platforms/xcb/qxcbconnection.h
@@ -225,9 +225,8 @@ public:
 
     void xi2SelectStateEvents();
     void xi2SelectDeviceEvents(xcb_window_t window);
-    void xi2SelectDeviceEventsCompatibility(xcb_window_t window);
     bool xi2SetMouseGrabEnabled(xcb_window_t w, bool grab);
-    bool xi2MouseEventsDisabled() const;
+
     Qt::MouseButton xiToQtMouseButton(uint32_t b);
     void xi2UpdateScrollingDevices();
     bool startSystemMoveResizeForTouch(xcb_window_t window, int edges);
diff --git a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
index dc8a533388..b754476d61 100644
--- a/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
+++ b/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
@@ -500,108 +500,6 @@ void QXcbConnection::xi2SetupDevices()
         qCDebug(lcQpaXInputDevices) << "multi-pointer X detected";
 }
 
-/*! \internal
-
-    Notes on QT_XCB_NO_XI2_MOUSE Handling:
-
-    Here we don't select pointer button press/release and motion events on master devices, instead
-    we select these events directly on slave devices. This means that a master device will fallback
-    to sending core events for every XI_* event that is sent directly by a slave device. For more
-    details see "Event processing for attached slave devices" in XInput2 specification. To prevent
-    handling of the same event twice, we have checks for xi2MouseEventsDisabled() in XI2 event
-    handlers (but this is somewhat inconsistent in some situations). If the purpose for
-    QT_XCB_NO_XI2_MOUSE was so that an application using QAbstractNativeEventFilter would see core
-    mouse events before they are handled by Qt then QT_XCB_NO_XI2_MOUSE won't always work as
-    expected (e.g. we handle scroll event directly from a slave device event, before an application
-    has seen the fallback core event from a master device).
-
-    The commit introducing QT_XCB_NO_XI2_MOUSE also states that setting this envvar "restores the
-    old behavior with broken grabbing". It did not elaborate why grabbing was not fixed for this
-    code path. The issue that this envvar tries to solve seem to be less important than broken
-    grabbing (broken apparently only for touch events). Thus, if you really want core mouse events
-    in your application and do not care about broken touch, then use QT_XCB_NO_XI2 (more on this
-    below) to disable the extension all together. The reason why grabbing might have not been fixed
-    is that calling XIGrabDevice with this code path for some reason always returns AlreadyGrabbed
-    (by debugging X server's code it appears that when we call XIGrabDevice, an X server first grabs
-    pointer via core pointer and then fails to do XI2 grab with AlreadyGrabbed; disclaimer - I did
-    not debug this in great detail). When we try supporting odd setups like QT_XCB_NO_XI2_MOUSE, we
-    are asking for trouble anyways.
-
-    In conclusion, introduction of QT_XCB_NO_XI2_MOUSE causes more issues than solves - the above
-    mentioned inconsistencies, maintenance of this code path and that QT_XCB_NO_XI2_MOUSE replaces
-    less important issue with somewhat more important issue. It also makes us to use less optimal
-    code paths in certain situations (see xi2HandleHierarchyEvent). Using of QT_XCB_NO_XI2 has its
-    drawbacks too - no tablet and touch events. So the only real fix in this case is at an
-    application side (teach the application about xcb_ge_event_t events). Based on this,
-    QT_XCB_NO_XI2_MOUSE will be removed in ### Qt 6. It should not have existed in the first place,
-    native events seen by QAbstractNativeEventFilter is not really a public API, applications should
-    expect changes at this level and do ifdefs if something changes between Qt version.
-*/
-void QXcbConnection::xi2SelectDeviceEventsCompatibility(xcb_window_t window)
-{
-    if (window == rootWindow())
-        return;
-
-    uint32_t mask = 0;
-
-    if (isAtLeastXI22()) {
-        mask |= XCB_INPUT_XI_EVENT_MASK_TOUCH_BEGIN;
-        mask |= XCB_INPUT_XI_EVENT_MASK_TOUCH_UPDATE;
-        mask |= XCB_INPUT_XI_EVENT_MASK_TOUCH_END;
-
-        qt_xcb_input_event_mask_t xiMask;
-        xiMask.header.deviceid = XCB_INPUT_DEVICE_ALL_MASTER;
-        xiMask.header.mask_len = 1;
-        xiMask.mask = mask;
-
-        xcb_void_cookie_t cookie =
-                xcb_input_xi_select_events_checked(xcb_connection(), window, 1, &xiMask.header);
-        xcb_generic_error_t *error = xcb_request_check(xcb_connection(), cookie);
-        if (error) {
-            qCDebug(lcQpaXInput, "failed to select events, window %x, error code %d", window, error->error_code);
-            free(error);
-        } else {
-            QWindowSystemInterfacePrivate::TabletEvent::setPlatformSynthesizesMouse(false);
-        }
-    }
-
-    mask = XCB_INPUT_XI_EVENT_MASK_BUTTON_PRESS;
-    mask |= XCB_INPUT_XI_EVENT_MASK_BUTTON_RELEASE;
-    mask |= XCB_INPUT_XI_EVENT_MASK_MOTION;
-
-#if QT_CONFIG(tabletevent)
-    QSet<int> tabletDevices;
-    if (!m_tabletData.isEmpty()) {
-        const int nrTablets = m_tabletData.count();
-        QList<qt_xcb_input_event_mask_t> xiEventMask(nrTablets);
-        for (int i = 0; i < nrTablets; ++i) {
-            int deviceId = m_tabletData.at(i).deviceId;
-            tabletDevices.insert(deviceId);
-            xiEventMask[i].header.deviceid = deviceId;
-            xiEventMask[i].header.mask_len = 1;
-            xiEventMask[i].mask = mask;
-        }
-        xcb_input_xi_select_events(xcb_connection(), window, nrTablets, &(xiEventMask.data()->header));
-    }
-#endif
-
-    if (!m_scrollingDevices.isEmpty()) {
-        QList<qt_xcb_input_event_mask_t> xiEventMask(m_scrollingDevices.size());
-        int i = 0;
-        for (const ScrollingDevice& scrollingDevice : qAsConst(m_scrollingDevices)) {
-#if QT_CONFIG(tabletevent)
-            if (tabletDevices.contains(scrollingDevice.deviceId))
-                continue; // All necessary events are already captured.
-#endif
-            xiEventMask[i].header.deviceid = scrollingDevice.deviceId;
-            xiEventMask[i].header.mask_len = 1;
-            xiEventMask[i].mask = mask;
-            i++;
-        }
-        xcb_input_xi_select_events(xcb_connection(), window, i, &(xiEventMask.data()->header));
-    }
-}
-
 QXcbConnection::TouchDeviceData *QXcbConnection::touchDeviceForId(int id)
 {
     TouchDeviceData *dev = nullptr;
@@ -769,8 +667,7 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
         case XCB_INPUT_BUTTON_PRESS:
         case XCB_INPUT_BUTTON_RELEASE:
         case XCB_INPUT_MOTION:
-            if (!xi2MouseEventsDisabled() && eventListener &&
-                    !(xiDeviceEvent->flags & XCB_INPUT_POINTER_EVENT_FLAGS_POINTER_EMULATED))
+            if (eventListener && !(xiDeviceEvent->flags & XCB_INPUT_POINTER_EVENT_FLAGS_POINTER_EMULATED))
                 eventListener->handleXIMouseEvent(event);
             break;
 
@@ -786,7 +683,7 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
                 xi2ProcessTouch(xiDeviceEvent, platformWindow);
             break;
         }
-    } else if (xiEnterEvent && !xi2MouseEventsDisabled() && eventListener) {
+    } else if (xiEnterEvent && eventListener) {
         switch (xiEnterEvent->event_type) {
         case XCB_INPUT_ENTER:
         case XCB_INPUT_LEAVE:
@@ -796,14 +693,6 @@ void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
     }
 }
 
-bool QXcbConnection::xi2MouseEventsDisabled() const
-{
-    static bool xi2MouseDisabled = qEnvironmentVariableIsSet("QT_XCB_NO_XI2_MOUSE");
-    // FIXME: Don't use XInput2 mouse events when Xinerama extension
-    // is enabled, because it causes problems with multi-monitor setup.
-    return xi2MouseDisabled || hasXinerama();
-}
-
 bool QXcbConnection::isTouchScreen(int id)
 {
     auto device = touchDeviceForId(id);
@@ -1064,15 +953,6 @@ void QXcbConnection::xi2HandleHierarchyEvent(void *event)
         return;
 
     xi2SetupDevices();
-
-    if (xi2MouseEventsDisabled()) {
-        // In compatibility mode (a.k.a xi2MouseEventsDisabled() mode) we select events for
-        // each device separately. When a new device appears, we have to select events from
-        // this device on all event-listening windows. This is not needed when events are
-        // selected via XIAllDevices/XIAllMasterDevices (as in xi2SelectDeviceEvents()).
-        for (auto it = m_mapper.cbegin(), end = m_mapper.cend(); it != end; ++it)
-            xi2SelectDeviceEventsCompatibility(it.key());
-    }
 }
 
 void QXcbConnection::xi2HandleDeviceChangedEvent(void *event)
diff --git a/src/plugins/platforms/xcb/qxcbwindow.cpp b/src/plugins/platforms/xcb/qxcbwindow.cpp
index eba6cc0712..0dba120e30 100644
--- a/src/plugins/platforms/xcb/qxcbwindow.cpp
+++ b/src/plugins/platforms/xcb/qxcbwindow.cpp
@@ -480,12 +480,8 @@ void QXcbWindow::create()
                         atom(QXcbAtom::_XEMBED_INFO),
                         32, 2, (void *)data);
 
-    if (connection()->hasXInput2()) {
-        if (connection()->xi2MouseEventsDisabled())
-            connection()->xi2SelectDeviceEventsCompatibility(m_window);
-        else
-            connection()->xi2SelectDeviceEvents(m_window);
-    }
+    if (connection()->hasXInput2())
+        connection()->xi2SelectDeviceEvents(m_window);
 
     setWindowState(window()->windowStates());
     setWindowFlags(window()->flags());
@@ -1915,7 +1911,7 @@ static inline bool doCheckUnGrabAncestor(QXcbConnection *conn)
     */
     if (conn) {
         const bool mouseButtonsPressed = (conn->buttonState() != Qt::NoButton);
-        return mouseButtonsPressed || (conn->hasXInput2() && !conn->xi2MouseEventsDisabled());
+        return mouseButtonsPressed || conn->hasXInput2();
     }
     return true;
 }
@@ -2266,7 +2262,7 @@ bool QXcbWindow::setMouseGrabEnabled(bool grab)
     if (grab && !connection()->canGrab())
         return false;
 
-    if (connection()->hasXInput2() && !connection()->xi2MouseEventsDisabled()) {
+    if (connection()->hasXInput2()) {
         bool result = connection()->xi2SetMouseGrabEnabled(m_window, grab);
         if (grab && result)
             connection()->setMouseGrabber(this);