disabled QwtPlotPanner is not immediately functional after being enabled

Hello,

I disable QwtPlotPanner when I'm dealing with QGestureEvents in my MouseZoomer class (a QwtPlotMagnifier) because the panner is executing in priority (I can't pinch) and I enable the panner when the gesture is finished (Qt::GestureFinished).

The panner is executing, IIRC, because Qt is generating mouse move events when pinching...

My probelm is that after finishing the pinching gesture, the panner is not immediately functional : only, the mouse cursor is moving when I'm moving my finger over the canvas !

I have to press elsewhere a second time to make the panner functionnal again !

Is there something else I can do to make the panner functionnal again after finishing the pinch gesture ?

I've already read the QwtPanner code and I didn't find what can be done to fix this issue. Should I manually post a mouse event after re-enabling the panner (and what kind of event) ? is it interesting to also grab gesture events in the panner and make this last do nothing between a pinch gesture ?

Thank you for any tip !

This is my MouseZoomer class (it zooms around mouse pointer and not the center of the canvas unlike the base class - and it handles both mouse wheel and pinch gestures) :

Code:

class MouseZoomer : public QwtPlotMagnifier
{
    typedef QwtPlotMagnifier Superclass;
public:
    explicit MouseZoomer(QWidget* parent = nullptr);
 
    void setPanner(QwtPlotPanner* const panner);
 
protected:
    bool eventFilter( QObject *, QEvent * ) override;
    void rescale(double factor) override;
    void widgetWheelEvent(QWheelEvent* evt) override;
 
protected:
    /* zoom around this position (mouse or pinch gesture)
     * (translated into an axis value of course) */
    QPointF m_mouseOrPinchPos;
 
    // panner need to be disabled while using the pinch gesture
    QPointer<QwtPlotPanner> m_panner;
 
    //double m_wheelSteps;
private:
    bool gestureEvent(QGestureEvent* event);
 
};

Code:

MouseZoomer::MouseZoomer(QWidget* parent /*= nullptr*/) :
    QwtPlotMagnifier(parent)
{
    // parent must be the QwtPlot's canvas widget
    parent->grabGesture(Qt::PinchGesture);
}
 
void MouseZoomer::setPanner(QwtPlotPanner* const panner)
{
    m_panner = panner;
}
 
// overriden to handle pinch gesture on G1C devices
bool MouseZoomer::eventFilter(QObject* obj, QEvent* event)
{
    if (event->type() == QEvent::Gesture)
    {
        return gestureEvent(static_cast<QGestureEvent*>(event));
    }
 
    // Make sure the rest of events are handled
    return Superclass::eventFilter(obj, event);
}
 
bool MouseZoomer::gestureEvent(QGestureEvent* event)
{
    if (QGesture* pinch = event->gesture(Qt::PinchGesture))
    {
        QPinchGesture* pinchGesture = static_cast<QPinchGesture*>(pinch);
 
        if (m_panner && pinchGesture->state() == Qt::GestureStarted)
        {
            // panner need to be disabled when pinching starts
            m_panner->setEnabled(false);
        }
 
        if (/*pinchGesture->state() == Qt::GestureUpdated &&*/
                 pinchGesture->changeFlags() & QPinchGesture::ScaleFactorChanged)
        {
            // gesture positions are defined in screen coordinate and not in widget one (unlike mouse positions)
            const QPoint pos(pinchGesture->centerPoint().x(), pinchGesture->centerPoint().y());
            m_mouseOrPinchPos = canvas()->mapFromGlobal(pos);
 
            rescale(pinchGesture->scaleFactor());
        }
 
        // panner can be re-enabled after finishing the pinch gesture
        if (m_panner && pinchGesture->state() == Qt::GestureFinished)
        {
            m_panner->setEnabled(true);
        }
    }
 
    return true;
}