Qt Touch Event Handling Issue: Positional Offset and Poor Finger Response on Resistive Screen

Ramanujum

Hello Qt Community,

I am currently working on an embedded project using the Allwinner A133 processor with the following configuration:

Operating System: Ubuntu 18.04
Kernel: Linux 4.9
Qt Version: Qt 5.12.12 (Qt Widgets)
Touch Type: Resistive touchscreen

For touch detection, I am using the following implementation:
void MainWindow::enableTouchOnAllWidgets(QWidget *widget)
{
if (!widget) return;
widget->setAttribute(Qt::WA_AcceptTouchEvents);
foreach (QWidget child, widget->findChildren<QWidget>()) {
child->setAttribute(Qt::WA_AcceptTouchEvents);
}
}

bool MainWindow::event(QEvent *event)
{
if (event->type() == QEvent::TouchBegin ||
event->type() == QEvent::TouchUpdate ||
event->type() == QEvent::TouchEnd)
{
QTouchEvent touchEvent = static_cast<QTouchEvent>(event);
if (touchEvent->touchPoints().isEmpty()) {
event->accept();
return true;
}

    if (event->type() == QEvent::TouchBegin)
    {
        touchProcessing = false;
    }

    if (event->type() == QEvent::TouchEnd)
    {
        if (touchProcessing)
        {
            event->accept();
            return true;
        }

        QPoint globalPos = touchEvent->touchPoints().first().screenPos().toPoint();

        QWidget *widget = QApplication::widgetAt(globalPos);

        if (widget)
        {
            QWidget *current = widget;
            while (current)
            {
                QPushButton *button = qobject_cast<QPushButton*>(current);
                if (button && button->isEnabled() && button->isVisible())
                {
                    touchProcessing = true;
                    emit button->clicked();
                    event->accept();
                    return true;
                }
                current = current->parentWidget();
            }

            QPoint targetPos = widget->mapFromGlobal(globalPos);

            QMouseEvent press(QEvent::MouseButtonPress,
                targetPos,
                Qt::LeftButton,
                Qt::LeftButton,
                Qt::NoModifier);
            QApplication::sendEvent(widget, &press);

            QMouseEvent release(QEvent::MouseButtonRelease,
                targetPos,
                Qt::LeftButton,
                Qt::LeftButton,
                Qt::NoModifier);
            QApplication::sendEvent(widget, &release);

            touchProcessing = true;
        }
    }

    event->accept();
    return true;
}

return QWidget::event(event);

}
However, I am experiencing a positional offset issue with the touch input. For buttons located at the bottom of the display, the touch response is shifted approximately 1 cm downward—meaning the button only responds when I touch about 1 cm below its actual position. Similarly, for buttons on the right side, the touch response is shifted approximately 1 cm to the right. The same behavior is observed for other directions as well.

Additionally, I am facing another issue with the resistive touchscreen: touch input using a fingernail is detected accurately, but touch input using a finger is inconsistent or unreliable.

Could you please help me understand the possible causes of these issues and suggest solutions to resolve them?

Thank you.

jsulm

@Ramanujum Why are you doing all this? QPushButton already supports touch events.

Ramanujum

In my case it is not working after this only my qt ui is reacting for touch event and added #include<QTouchEvent>

jsulm

@Ramanujum Not sure I understand. You get touch events in your Qt app, right?

Ramanujum

Yes i got but not perfectly i got , i am getting my buttons in offset places

sbela

You have to calibrate the screen?! I think.

Ramanujum

I did ts_calibrate many times and in ts_test also working only