Details
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Bug
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Resolution: Fixed
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P1: Critical
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None
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5.15.1, 6.2.0, 6.3.0
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None
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Linux/Wayland
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2419064c3532e2efd3bcf2f23c9c690b0a0fdd00(qt/qtwayland/dev) 7ce31f7f65f8d79c1f8763eb75b3ea238b727654(qt/tqtc-qtwayland/lts-5.15) 54d886d420bc0bc0a5d1c8fa28336665d8c77812(qt/qtwayland/6.3) 612a45059eae4cb7b30b70228f2debaf11f4e4cb(qt/qtwayland/6.2)
Description
Touch event may be ignored when main GUI thread is slow.
*. Current implementation
1. qwaylandintegration.cpp
Wayland event dispatch is done in the main GUI thread.
void QWaylandIntegration::initialize()
{
QAbstractEventDispatcher *dispatcher = QGuiApplicationPrivate::eventDispatcher;
QObject::connect(dispatcher, SIGNAL(aboutToBlock()), mDisplay.data(), SLOT(flushRequests()));
QObject::connect(dispatcher, SIGNAL(awake()), mDisplay.data(), SLOT(flushRequests()));
int fd = wl_display_get_fd(mDisplay->wl_display());
QSocketNotifier *sn = new QSocketNotifier(fd, QSocketNotifier::Read, mDisplay.data());
QObject::connect(sn, SIGNAL(activated(QSocketDescriptor)), mDisplay.data(), SLOT(flushRequests()));
// Qt does not support running with no screens
mDisplay->ensureScreen();
}
2. Currently, the time stamp is set when event dispatch occurs in the main GUI thread, not when touch.frame occurs from wayland compositor.
qwaylandinputdevice.cpp
void QWaylandInputDevice::Touch::touch_frame()
{
...
QWindowSystemInterface::handleTouchEvent(window, mParent->mTouchDevice, mPendingTouchPoints);
...
}
qwindowsysteminterface.cpp: timestamp will be set here using QWindowSystemInterfacePrivate::eventTime.elapsed() which is millisecond unit.
So, several touch events are likely to be ignored when the main thread is slow.
QT_DEFINE_QPA_EVENT_HANDLER(bool, handleTouchEvent, QWindow *window, QTouchDevice *device,
const QList<TouchPoint> &points, Qt::KeyboardModifiers mods)
{
unsigned long time = QWindowSystemInterfacePrivate::eventTime.elapsed();
return handleTouchEvent<Delivery>(window, time, device, points, mods);
}
QT_DEFINE_QPA_EVENT_HANDLER(bool, handleTouchEvent, QWindow *window, ulong timestamp, QTouchDevice *device,
const QList<TouchPoint> &points, Qt::KeyboardModifiers mods)
{
if (!points.size()) // Touch events must have at least one point
return false; if (!QTouchDevicePrivate::isRegistered(device)) // Disallow passing bogus, non-registered devices.
return false; QEvent::Type type;
QList<QTouchEvent::TouchPoint> touchPoints =
QWindowSystemInterfacePrivate::fromNativeTouchPoints(points, window, QTouchDevicePrivate::get(device)->id, &type); QWindowSystemInterfacePrivate::TouchEvent *e =
new QWindowSystemInterfacePrivate::TouchEvent(window, timestamp, type, device, touchPoints, mods);
return QWindowSystemInterfacePrivate::handleWindowSystemEvent<Delivery>(e);
}
For example, touch event could be ignored at this point.
void QQuickFlickablePrivate::handleMouseMoveEvent(QMouseEvent *event)
{
...
if (currentTimestamp == lastTimestamp) {
return; // events are too close together: velocity would be infinite
}
...
}