C++ code not receiving QQuickItem::wheelEvent()

Tom asso

I’ve subclassed QQuickFrameBufferObject to QVtkItem and overridden wheelEvent() (originally defined in the QQuickItem base class):

class QVtkItem : public QQuickFramebufferObject {
 
protected:
 
   /// Handle mouse wheel event
   virtual void wheelEvent(QWheelEvent *event) override;

When I instantiate a QVtkItem in QML, the item is visible but QVtkItem::wheelEvent() is never called when I put the mouse over the item and spin the wheel. I tried defining a MouseArea as a child, but QVtkItem::wheelEvent() is still not called. The QML looks like:

QVtkItem {
     id: qVtkItem
     objectName: "qVtkItem"
     anchors.fill: parent
        width: 1000
        height: 1000
 
     MouseArea {
        acceptedButtons: Qt.LeftButton
        anchors.fill: parent
     }
}

What am I missing? QQuickItem documentation says this about wheelEvent(): “The event is accepted by default, so it is not necessary to explicitly accept the event if you reimplement this function."
Thanks!

fcarney

MouseArea will block events of the QtkItem. I just did a mock of this and the c++ event works.

Tom asso

This post is deleted!

Tom asso

@fcarney - I did 'make clean' and 'make' and now QVtkItem::wheelEvent() is called - with or without the MouseArea. Thanks for your help!

fcarney

I am doing onWheel event.
main.qml:

import QtQuick 2.15
import QtQuick.Controls 2.12
import QtQuick.Window 2.15
import FBOs 1.0

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Mouse Testing")

    FBO {
        anchors.fill: parent
    }

    MouseArea {
        id: mousearea

        enabled: false // set to true and it blocks events from FBO

        anchors.fill: parent

        acceptedButtons: Qt.LeftButton

        onWheel: {
            console.log(wheel.x, wheel.y, wheel.angleDelta, wheel.pixelDelta)
        }
    }

    Button {
        text: "toggle mousearea: %1".arg(mousearea.enabled)
        onClicked: {
            mousearea.enabled = !mousearea.enabled
        }
    }
}

main.cpp:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickItem>
#include <QQuickFramebufferObject>
#include <QOpenGLFramebufferObjectFormat>

class FBORenderer : public QQuickFramebufferObject::Renderer
{
    QOpenGLFramebufferObject *createFramebufferObject(const QSize &size)
    {
        QOpenGLFramebufferObjectFormat format;
        format.setAttachment(QOpenGLFramebufferObject::CombinedDepthStencil);
        // optionally enable multisampling by doing format.setSamples(4);
        return new QOpenGLFramebufferObject(size, format);
    }

    void render()
    {
        // Called with the FBO bound and the viewport set.
        // Issue OpenGL commands.
    }
};

class FBO : public QQuickFramebufferObject
{
    Q_OBJECT
public:
    FBO(){};

protected:
    virtual void wheelEvent(QWheelEvent *event) override {
        qInfo() << "c++:" << event->pos() << event->angleDelta();
    }

    QQuickFramebufferObject::Renderer *createRenderer() const
    {
        return new FBORenderer;
    }
};

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;

    qmlRegisterType<FBO>("FBOs",1,0,"FBO");

    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

#include "main.moc"

Does that make any difference?

fcarney

If I do this:

        onWheel: {
            console.log(wheel.x, wheel.y, wheel.angleDelta, wheel.pixelDelta)
            wheel.accepted = false
        }

Then I get both sets of printouts. So yeah, it ignores wheel in mousearea if you don't have onWheel callback defined. If I don't accept then it trigger wheel events on FBO object.