How to pick line of QwtPlotMarker using QwtPlotPicker without affecting zooming

[npatil15]

I have added event filter which identify the wheel up/down and based on that I have manage to increase the 5 using setting variable m_pickPoint in the event and it work for normal condition.

if (sqrt( pow( (m_mark->xValue() - pos.x()), 2 )) <= m_pickPoint || sqrt( pow( (m_mark->yValue() - pos.y()), 2 )) <=m_pickPoint )

if (sqrt( pow( (m_mark->xValue() - pos.x()), 2 )) <= m_pickPoint || sqrt( pow( (m_mark->yValue() - pos.y()), 2 )) <=m_pickPoint )

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So here I'm unable to understand at what factor I should increase or decrease the value m_pickPoint, so that the above logic work properly and pick the exact line.

case QEvent::Wheel:
            QWheelEvent* we = static_cast<QWheelEvent*>(e);
            if(we->angleDelta().y()>0)
            {
                m_pickPoint = m_pickPoint + m_pickPoint*0.05;
                qDebug()<<"Position"<<m_pickPoint;
            }
            else
            {
                m_pickPoint = m_pickPoint - m_pickPoint*0.05;
                qDebug()<<"Negative"<<m_pickPoint;
            }

case QEvent::Wheel:
            QWheelEvent* we = static_cast<QWheelEvent*>(e);
            if(we->angleDelta().y()>0)
            {
                m_pickPoint = m_pickPoint + m_pickPoint*0.05;
                qDebug()<<"Position"<<m_pickPoint;
            }
            else
            {
                m_pickPoint = m_pickPoint - m_pickPoint*0.05;
                qDebug()<<"Negative"<<m_pickPoint;
            }

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Please provide your solution, where as this above solution looks kind of dirty, so if their is some elegant solution then please suggest.