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Details

Type: Bug
Resolution: Done
Priority: P1: Critical
Fix Version/s: 6.4.0 RC1, 6.5.0 Beta1
Affects Version/s: 6.3.1
Component/s: GUI: Wacom Tablet Input, QPA: X11/XCB
Labels:
None

Commits:
8824a4e19c (qt/qtbase/dev) 8824a4e19c (qt/tqtc-qtbase/dev) 90070aaef3 (qt/qtbase/6.3) 90070aaef3 (qt/tqtc-qtbase/6.3) 58df309425 (qt/qtbase/6.4) 58df309425 (qt/tqtc-qtbase/6.4)

Description

Can be demonstrated with qtbase/tests/manual/qtabletevent/device_information , or with any application if you have enabled the qt.qpa.input.events logging category. Then when you bring a stylus near the top surface of the tablet (but not necessarily touching) you should get log output like this:

[     2.531 D] qt.qpa.input.devices QXcbConnection::xi2HandleTabletEvent - XI2 proximity change on tablet 23 Wacom Intuos3 6x8 Pen stylus (USB b1): last tool: 12c00001 id 885 current tool: 12c00001 id 885 Stylus

When the bug is fixed, the stack should look like this:

1  QXcbConnection::xi2HandleTabletEvent   qxcbconnection_xi2.cpp    1524 0x7ffff21d1a92 
2  QXcbConnection::xi2HandleEvent         qxcbconnection_xi2.cpp    728  0x7ffff21cc8b1 
3  QXcbConnection::handleXcbEvent         qxcbconnection.cpp        699  0x7ffff21af580 
4  QXcbConnection::processXcbEvents       qxcbconnection.cpp        1061 0x7ffff21b08d4 
5  xcbSourceDispatch                      qxcbeventdispatcher.cpp   55   0x7ffff21ec8a6 
6  g_main_context_dispatch                                               0x7ffff5592c6b 
7  ??                                                                    0x7ffff55e9001 
8  g_main_context_iteration                                              0x7ffff5590392 
9  QEventDispatcherGlib::processEvents    qeventdispatcher_glib.cpp 393  0x7ffff63c5c90 
10 QXcbGlibEventDispatcher::processEvents qxcbeventdispatcher.cpp   96   0x7ffff21ecafa 
11 QEventLoop::processEvents              qeventloop.cpp            100  0x7ffff5fdc293 
12 QEventLoop::exec                       qeventloop.cpp            182  0x7ffff5fdc5fe 
13 QCoreApplication::exec                 qcoreapplication.cpp      1347 0x7ffff5fc9497 
14 QGuiApplication::exec                  qguiapplication.cpp       1860 0x7ffff69278d6 
15 QApplication::exec                     qapplication.cpp          2586 0x7ffff75eef33 
16 main                                   main.cpp                  21   0x55555555892c

It got broken in https://codereview.qt-project.org/c/qt/qtbase/+/343520, so it can be fixed by avoiding the early returns in xi2HandleEvent() when event_type == XCB_INPUT_PROPERTY:

void QXcbConnection::xi2HandleEvent(xcb_ge_event_t *event)
{
    auto *xiEvent = reinterpret_cast<qt_xcb_input_device_event_t *>(event);
    setTime(xiEvent->time);
    if (m_xiSlavePointerIds.contains(xiEvent->deviceid) && xiEvent->event_type != XCB_INPUT_PROPERTY) {
        if (!m_duringSystemMoveResize)
            return;
        if (xiEvent->event == XCB_NONE)
            return;

        if (xiEvent->event_type == XCB_INPUT_BUTTON_RELEASE
            && xiEvent->detail == XCB_BUTTON_INDEX_1 ) {
            abortSystemMoveResize(xiEvent->event);
        } else if (xiEvent->event_type == XCB_INPUT_TOUCH_END) {
            abortSystemMoveResize(xiEvent->event);
            return;
        } else {
            return;
        }
    }
...