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  1. Qt
  2. QTBUG-97454

Touchscreen press(down) events appear with a delay



    • Platform/s:


      Dear Qt team,
      I discovered a touch input problem with QtQuick (qml) in Qt 5 and Qt 6 on Ubuntu. Press(down) events appear with a delay of ~170ms in Qt. The weird thing is, that release(up) and click events are working as expected. Only press(down) has this delay. To exclude a system/hardware problem I checked the logs from xinput, press events have no delay there.
      The problem appears in PySide2, PySide6 and qmlscene (Qt 5 and Qt 6). I did not check older versions.
      I used different types of Iiyama touch screens (e.g. IIYAMA PROLITE TF2415MC-B2).
      How to reproduce the problem:

      • Connect a touchscreen to your Ubuntu system (20.04.3 LTS)
      • Download the online installer for Ubuntu and install Qt 6.2.0
      • Install moreutils to add time stamps to xinput outputs:
        sudo apt install moreutils
      • Create a qml file with (main.qml):
        import QtQuick 2.2
        import QtQuick.Window 2.2
        Window {
            title: "test"
            width: 800
            height: 600
            visible: true
            Rectangle {
                anchors.fill: parent
                color: "blue"
      • Start the Qt application with qmlscene: QT_LOGGING_RULES="qt.quick.touch=true" QT_MESSAGE_PATTERN="%{time hh:mm:ss.zzzzzz}: %{message}" qmlscene main.qml
      • Start xinput logging to proof the delay (check xinput list to get the ID of your touch device):
        xinput test 10 | ts '%H:%M:%.S'
      • Press the blue Qt window
      • Output qmlscene:
      15:45:01.999999: QQuickDeliveryAgent(root=QQuickRootItem) QTouchEvent(TouchBegin device: "eGalax Inc. eGalaxTouch EXC3188-4623-" states: Pressed, 1 points: QList(QEventPoint(id=133 ts=93229220 pos=461.982,384.642 scn=461.982,384.642 gbl=1169.98,658.642 Pressed vel=0,0 press=461.982,384.642 last=461.982,384.642 \u0394 0,0)))
      15:45:04.004004: QQuickDeliveryAgent(root=QQuickRootItem) QTouchEvent(TouchEnd device: "eGalax Inc. eGalaxTouch EXC3188-4623-" states: Released, 1 points: QList(QEventPoint(id=133 ts=93231399 pos=461.982,384.642 scn=461.982,384.642 gbl=1169.98,658.642 Released vel=0,0 press=461.982,384.642 last=461.982,384.642 \u0394 0,0)))
      • Output xinput:
      15:45:01.825381 motion a[0]=39935 a[1]=39967 
      15:45:01.825792 button press   1 a[0]=39935 a[1]=39967
      15:45:04.004288 motion a[0]=39935 a[1]=39967 
      15:45:04.004419 button release 1 a[0]=39935 a[1]=39967 

      You will see the delay of press events the terminal outputs
      Please let me know if this problem could be solved.
      Thank you.


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            qt.team.quick.subscriptions Qt Quick and Widgets Team
            neelz Nils Gründl
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