How to implement Panning/Zooming in QGraphicsScene with two finger gestures on laptop trackpad (win/mac)?

stefanwoe

I have a Qt 6.2 Application (Windows/Mac) using QGraphicsScene and want to use 2 fingers on the touch pad of my laptop for panning - as many other applications do.

Zooming in/out works fine, but using 2 fingers for panning always results in zoom out.

I found a number of questions and some fragmentary samples. But no half way complete example:

https://stackoverflow.com/questions/8089838/finger-scrolling-in-qgraphicsview-in-qt
https://forum.qt.io/topic/119221/how-to-listen-to-qtouchevent-originating-from-a-precision-touch-pad
https://doc.qt.io/qt-5/gestures-overview.html]([link url](link url))

What is the right way to do this?

What i tried so far (on Windows):

MyGraphicsView::MyGraphicsView(...) : QGraphicsView()
{
    viewport()->setAttribute(Qt::WA_AcceptTouchEvents);

...
bool MyGraphicsView::viewportEvent ( QEvent * event )
{
     switch (event->type())
    {
    case QEvent::TouchBegin:
    case QEvent::TouchUpdate:
    case QEvent::TouchEnd:
        {
        // never called
        }

MyDocWin::MyDocWin(...) : CMDIAppDocWin(),
{
    setAttribute(Qt::WA_AcceptTouchEvents);
...
bool MyDocWin::event(QEvent *event)
{
    switch (event->type())
    {
    case QEvent::TouchBegin:
    case QEvent::TouchUpdate:
    case QEvent::TouchEnd:
        {
            // never called
        }
...

std::vector<Qt::GestureType> sgGestureTypes = {Qt::TapGesture, Qt::TapAndHoldGesture,Qt::PanGesture       ,Qt::PinchGesture     ,Qt::SwipeGesture         };
    
    
    MyGraphicsView::MyGraphicsView(...) : QGraphicsView()
    {
       for(Qt::GestureType gesture : sgGestureTypes)
            grabGesture(gesture);
    ...
    bool MyGraphicsView::event(QEvent *event)
    {
      switch (event->type())
        {
        case QEvent::Gesture:
        case QEvent::NativeGesture:
                    // never called

4)
  
[MyDocWin::MyDocWin(...) : CMDIAppDocWin(),
    {
    for (Qt::GestureType gesture : sgGestureTypes)
        grabGesture(gesture);
...
    bool MyDocWin::event(QEvent *event)
    {
        switch (event->type())
        {
        case QEvent::Gesture:
        case QEvent::NativeGesture:
                // never called]([link url](link url))

I already posted this on SO: https://stackoverflow.com/questions/70037430/how-to-pan-in-qgraphicsscene-with-two-fingers-on-laptop-trackpad

stefanwoe

I finaly found out how to handle this. See the SO post at https://stackoverflow.com/questions/70037430/qt-how-to-implement-panning-in-qgraphicsscene-with-two-fingers-on-laptop-trackp/70263559#70263559

JoeCFD

Touchpad gesture support for Wayland has landed in the Qt framework. This will be released as Qt 6.2.
Touchpad gesture support for X server on Qt framework has been submitted for review.
if you use 6.2 on Wayland, your code may work.
https://bill.harding.blog/2021/06/06/linux-touchpad-like-macbook-update-touchpad-gestures-land-to-qt-gimp-and-x-server/

stefanwoe

I finaly found out how to handle this. See the SO post at https://stackoverflow.com/questions/70037430/qt-how-to-implement-panning-in-qgraphicsscene-with-two-fingers-on-laptop-trackp/70263559#70263559