qt chart move view with pressed middle mouse button

Question

I'm currently working with Qts Chart plotting tool. I have now a plot where I can zoom in and out by using the chartview class provieded by this example (with small adjustments). I would like to see the ability to not only zoom, but also move my view a pressed middle mouse button (which is used a lot in other applications and therefore is very intuitive).

How can I do this in Qt? How can I check if a middle mouse button is pressed and released and change my view at the plot if the mouse moves during a pressed middle mouse button...

I'm sure someone has coded this before and would really appreciate a small example/help.

Possible duplicate of: https://stackoverflow.com/questions/18551466/qt-proper-method-to-implement-panningdrag/ — Jeremy Friesner, Oct 20 '17 at 02:00
Possible duplicate of [Qt: Proper Method to Implement Panning(Drag)](https://stackoverflow.com/questions/18551466/qt-proper-method-to-implement-panningdrag) — eyllanesc, May 23 '18 at 18:54

Nicolas Holthaus · Accepted Answer · 2017-10-31T14:50:54.540

you need to derive a class from QChartView and overload the mouse events:

class ChartView: public QChartView
{
    Q_OBJECT

public:
    ChartView(Chart* chart, QWidget *parent = 0);

protected:

    virtual void mousePressEvent(QMouseEvent *event) override;
    virtual void mouseMoveEvent(QMouseEvent *event) override;

private:

    QPointF m_lastMousePos;
};

ChartView::ChartView(Chart* chart, QWidget *parent)
    : QChartView(chart, parent)
{
    setDragMode(QGraphicsView::NoDrag);
    this->setMouseTracking(true);
}

void ChartView::mousePressEvent(QMouseEvent *event)
{
    if (event->button() == Qt::MiddleButton)
    {
        QApplication::setOverrideCursor(QCursor(Qt::SizeAllCursor));
        m_lastMousePos = event->pos();
        event->accept();
    }

    QChartView::mousePressEvent(event);
}

void ChartView::mouseMoveEvent(QMouseEvent *event)
{
    // pan the chart with a middle mouse drag
    if (event->buttons() & Qt::MiddleButton)
    {
        QRectF bounds = QRectF(0,0,0,0);
        for(auto series : this->chart()->series())
            bounds.united(series->bounds())

        auto dPos = this->chart()->mapToValue(event->pos()) - this->chart()->mapToValue(m_lastMousePos);

        if (this->rubberBand() == QChartView::RectangleRubberBand)
            this->chart()->zoom(bounds.translated(-dPos.x(), -dPos.y()));
        else if (this->rubberBand() == QChartView::HorizontalRubberBand)
            this->chart()->zoom(bounds.translated(-dPos.x(), 0));
        else if (this->rubberBand() == QChartView::VerticalRubberBand)
            this->chart()->zoom(bounds.translated(0, -dPos.y()));

        m_lastMousePos = event->pos();
        event->accept();
    }

    QChartView::mouseMoveEvent(event);
}

this was part of a larger project (https://github.com/nholthaus/chart) which also extended chart and handled zooming. I've edited the answer, but `m_zoomRect` in this case is the union of all the charts series boundaries. — Nicolas Holthaus, Oct 31 '17 at 14:52

score 2 · Answer 2 · answered May 23 '18 at 18:48

I'd like to offer a simpler version of Nicolas's mouseMoveEvent():

    void ChartView::mouseMoveEvent(QMouseEvent *event)
    {
        // pan the chart with a middle mouse drag
        if (event->buttons() & Qt::MiddleButton)
        {
            auto dPos = event->pos() - lastMousePos_;
            chart()->scroll(-dPos.x(), dPos.y());

            lastMousePos_ = event->pos();
            event->accept();

            QApplication::restoreOverrideCursor();
        }

        QChartView::mouseMoveEvent(event);
    }

Also, be sure to include QApplication::restoreOverrideCursor() so the cursor returns to usual after the move is done.

You will need to initialize `lastMousePos_` first. – Adrian W May 23 '18 at 20:08 — Adrian W, May 23 '18 at 20:08

qt chart move view with pressed middle mouse button

2 Answers2