How to print coordinates of fingers in Qt6 for QOpenGLWindow?

[8Observer8]

Hello,

I tried to accept touch events in Qt6 like this, in main.cpp:

QApplication::setAttribute(Qt::ApplicationAttribute::WA_AcceptTouchEvents);

error: no member named 'WA_AcceptTouchEvents' in 'Qt::ApplicationAttribute'

and like this:

QApplication::setAttribute(Qt::WA_AcceptTouchEvents);

error: cannot initialize a parameter of type 'Qt::ApplicationAttribute' with an rvalue of type 'Qt::WidgetAttribute'

I tried to accept it in the window constructor but QOpenGLWindow doesn't have the setAttribute method:

error: use of undeclared identifier 'setAttribute'; did you mean 'QInputMethodEvent::Attribute'?

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(350, 350);
    setAttribute(Qt::WA_AcceptTouchEvents);
}

My pro-file:

QT += core gui opengl widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# disables all the APIs deprecated before Qt 6.0.0
# DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000

SOURCES += \
    main.cpp \
    opengl_window.cpp

HEADERS += \
    opengl_window.h

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

Cross-ref: https://stackoverflow.com/questions/78087509/how-to-accept-touch-events-in-qt6

[8Observer8]

Solution:

opengl_window.h

#ifndef OPENGL_WINDOW_H
#define OPENGL_WINDOW_H

#include <QtGui/QTouchEvent>
#include <QtOpenGL/QOpenGLWindow>

class OpenGLWindow : public QOpenGLWindow
{
    Q_OBJECT

public:
    OpenGLWindow();

private:
    void touchEvent(QTouchEvent *event) override;
    int m_counter = 0;
};

#endif // OPENGL_WINDOW_H

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(350, 350);
}

void OpenGLWindow::touchEvent(QTouchEvent *event)
{
    switch (event->type())
    {
        case QEvent::TouchBegin:
            qDebug() << "touch begin";
            event->accept();
            break;
        case QEvent::TouchEnd:
            qDebug() << "touch end";
            break;
        case QEvent::TouchUpdate:
            qDebug() << "counter = " << m_counter;
            m_counter++;
            for (int i = 0; i < event->points().length(); i++) {
                int x = event->points()[i].position().x();
                int y = event->points()[i].position().y();
                qDebug() << x << " " << y;
            }
            break;
    }
}

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication a(argc, argv);
    OpenGLWindow w;
    w.show();
    return a.exec();
}

pro:

QT       += core gui opengl widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# disables all the APIs deprecated before Qt 6.0.0
DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000

SOURCES += \
    main.cpp \
    opengl_window.cpp

HEADERS += \
    opengl_window.h

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

[SGaist]

Hi,

WA is for Widget Attribute, QOpenGLWindow is QWindow.

You need to change to QOpenGLWidget.

[8Observer8]

@SGaist said in How to accept touch events in Qt6?:

You need to change to QOpenGLWidget.

No, I don't need because:

Unlike widgets, QWindows receive touch events always, there is no need to opt in. When working directly with a QWindow, it is enough to reimplement QWindow::touchEvent().

https://doc.qt.io/qt-6/qtouchevent.html#event-handling

It was answer from musicamante: https://stackoverflow.com/questions/78087509/how-to-accept-touch-events-in-qt6?noredirect=1#comment137666237_78087509

I don't like QOpenGLWidget because it cannot make a smooth animation with QTimer. QOpenGLWindow has the frameSwapped signal:

    QSurfaceFormat surfaceFormat;
    surfaceFormat.setSwapInterval(1);
    connect(this, SIGNAL(frameSwapped()), this, SLOT(update()));
    setFormat(surfaceFormat);

But the Qt Creator's autocompletion systems shows that Qt::ApplicationAttribute has WA_AcceptTouchEvents. I think it is a bug of Qt Creator:

I created the topic: Qt Creator assumes that WA_AcceptTouchEvents is in the Qt::ApplicationAttribute

[8Observer8]

But when I run the next code on the real device, touch a screen (it prints counter = 0), holding a finger on the screen, try to touch with another finger and doesn't print the next line like counter = 1. It seams like multi touch is disabled.

void OpenGLWindow::touchEvent(QTouchEvent *event)
{
    switch (event->type())
    {
        case QEvent::TouchBegin:
            qDebug() << "counter = " << m_counter;
            m_counter++;
            break;
    }
}

[8Observer8]

Solution:

opengl_window.h

#ifndef OPENGL_WINDOW_H
#define OPENGL_WINDOW_H

#include <QtGui/QTouchEvent>
#include <QtOpenGL/QOpenGLWindow>

class OpenGLWindow : public QOpenGLWindow
{
    Q_OBJECT

public:
    OpenGLWindow();

private:
    void touchEvent(QTouchEvent *event) override;
    int m_counter = 0;
};

#endif // OPENGL_WINDOW_H

opengl_window.cpp

#include "opengl_window.h"

OpenGLWindow::OpenGLWindow()
{
    setTitle("OpenGL ES 2.0, Qt6, C++");
    resize(350, 350);
}

void OpenGLWindow::touchEvent(QTouchEvent *event)
{
    switch (event->type())
    {
        case QEvent::TouchBegin:
            qDebug() << "touch begin";
            event->accept();
            break;
        case QEvent::TouchEnd:
            qDebug() << "touch end";
            break;
        case QEvent::TouchUpdate:
            qDebug() << "counter = " << m_counter;
            m_counter++;
            for (int i = 0; i < event->points().length(); i++) {
                int x = event->points()[i].position().x();
                int y = event->points()[i].position().y();
                qDebug() << x << " " << y;
            }
            break;
    }
}

main.cpp

#include <QtWidgets/QApplication>
#include "opengl_window.h"

int main(int argc, char *argv[])
{
    QApplication::setAttribute(Qt::ApplicationAttribute::AA_UseDesktopOpenGL);
    QApplication a(argc, argv);
    OpenGLWindow w;
    w.show();
    return a.exec();
}

pro:

QT       += core gui opengl widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
# disables all the APIs deprecated before Qt 6.0.0
DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000

SOURCES += \
    main.cpp \
    opengl_window.cpp

HEADERS += \
    opengl_window.h

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

[SGaist]

@8Observer8 said in How to print coordinates of fingers in Qt6 for QOpenGLWindow?:

@SGaist said in How to accept touch events in Qt6?:

You need to change to QOpenGLWidget.

No, I don't need because:

Unlike widgets, QWindows receive touch events always, there is no need to opt in. When working directly with a QWindow, it is enough to reimplement QWindow::touchEvent().

https://doc.qt.io/qt-6/qtouchevent.html#event-handling

That's correct, I just wanted to give the correct class in the context of WA_AcceptTouchEvents.