There is a bug in Qt in which multiple touch screens causes Qt to be in an inconsistent state. More about the issue here.
As a short-term patch, I'd to use event filters (which Qt provides for xcb events) to prevent multiple devices from being processed by Qt at a time.
The steps would be as followed.
- A sequence of events for input is beginning (mouse button down, touch press, etc).
- Block all other events for devices that don't belong to the current device being used.
- When the sequence of events is completed, Resume events for all devices, starting back at step 1.
Effectively, I want to gate the events, so that only one device can be used at a time. I'm hoping this get's around Qt's bug.
First, I am trying to just filter events for a hard-coded device to see if this even gets around Qt's bug, but it doesn't.
class DuplicateHardwareEventFilter : public QAbstractNativeEventFilter
{
public:
DuplicateHardwareEventFilter() {}
bool nativeEventFilter(const QByteArray &eventType, void *message, long *) override
{
if (eventType == "xcb_generic_event_t") {
xcb_generic_event_t* ev = static_cast<xcb_generic_event_t *>(message);
uint responseType = ev->response_type & ~0x80;
if(responseType == XCB_GE_GENERIC) {
xcb_ge_event_t* gev = reinterpret_cast<xcb_ge_event_t*>(ev);
// assume input event
xcb_input_button_press_event_t* xiEvent = reinterpret_cast<xcb_input_button_press_event_t*>(ev);
if(xiEvent->event_type == XCB_INPUT_DEVICE_CHANGED) {
auto inputChangedEvent = reinterpret_cast<xcb_input_device_changed_event_t *>(gev);
if(inputChangedEvent->sourceid == 11) {
return true;
}
qDebug("xcb device changed: %d source: %d", xiEvent->deviceid, inputChangedEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_MOTION) {
auto inputMotionEvent = reinterpret_cast<xcb_input_motion_event_t*>(gev);
if(inputMotionEvent->sourceid == 11) {
return true;
}
qDebug("xcb motion: %d source: %d", inputMotionEvent->deviceid, inputMotionEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_ENTER) {
auto inputEnterEvent = reinterpret_cast<xcb_input_enter_event_t*>(gev);
if(inputEnterEvent->sourceid == 11) {
return true;
}
qDebug("xcb enter: %d source: %d", inputEnterEvent->deviceid, inputEnterEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_LEAVE) {
auto inputLeaveEvent = reinterpret_cast<xcb_input_leave_event_t*>(gev);
qDebug("xcb leave: %d source: %d", inputLeaveEvent->deviceid, inputLeaveEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_BUTTON_PRESS) {
auto buttonPressEvent = reinterpret_cast<xcb_input_button_press_event_t*>(gev);
qDebug("xcb buttonPress: %d source: %d", buttonPressEvent->deviceid, buttonPressEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_BUTTON_RELEASE) {
auto buttonReleaseEvent = reinterpret_cast<xcb_input_button_release_event_t*>(gev);
qDebug("xcb buttonRelease: %d source: %d", buttonReleaseEvent->deviceid, buttonReleaseEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_TOUCH_BEGIN) {
auto touchBeginEvent = reinterpret_cast<xcb_input_touch_begin_event_t*>(gev);
if(touchBeginEvent->sourceid == 11) {
return true;
}
qDebug("xcb touchBegin: %d source: %d", touchBeginEvent->deviceid, touchBeginEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_TOUCH_UPDATE) {
auto touchUpdateEvent = reinterpret_cast<xcb_input_touch_update_event_t*>(gev);
if(touchUpdateEvent->sourceid == 11) {
return true;
}
qDebug("xcb touchUpdate: %d source: %d", touchUpdateEvent->deviceid, touchUpdateEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_TOUCH_END) {
auto touchEndEvent = reinterpret_cast<xcb_input_touch_end_event_t*>(gev);
if(touchEndEvent->sourceid == 11) {
return true;
}
qDebug("touchEnd: %d source: %d", touchEndEvent->deviceid, touchEndEvent->sourceid);
return false;
}
if(xiEvent->event_type == XCB_INPUT_PROPERTY) {
auto propertyEvent = reinterpret_cast<xcb_input_property_event_t*>(gev);
qDebug("property: %d", propertyEvent->deviceid);
return false;
}
return false;
}
}
return false;
}
};
Qt still get's into it's quirky state.
How do I block a device completely, with filtering of the events of xcb_wait_for_event?
