QwtPlot how to save/restore zoom settings

[d_stranz]

Store the x and y extents in member variables of whatever widget holds your plot, and use QSettings as a way to store them persistently on disk. Override the widget's showEvent() and closeEvent() methods. In showEvent(), read the settings in and set the zoom extents. In closeEvent(), save the settings.

If the current zoom extents are accessible from QwtPlot, then you may not need the member variables. Just read or write them directly from the plot on load and save.

[Darent]

Thanks for the response.
I looked through all relevant classes APIs starting with QwtPlot, I just can't find the API to get/set zoom extents.. (starting point/ending value for each x/y axis or equivalent data)

[Darent]

A solution that worked for me was saving "zoomRect" and then restoring using "setZoomRect"

QRectF zoomRect()
{
    const QwtScaleDiv &xs = this->axisScaleDiv( QwtPlot::xBottom);
    const QwtScaleDiv &ys = this->axisScaleDiv( QwtPlot::yLeft );
    QRectF rect = QRectF( xs.lowerBound(), ys.lowerBound(), xs.range(), ys.range() );
    return rect;
}
 
void setZoomRect(const QRectF& r)
{
    d->zoomer->zoom(r);
}

QRectF zoomRect()
{
    const QwtScaleDiv &xs = this->axisScaleDiv( QwtPlot::xBottom);
    const QwtScaleDiv &ys = this->axisScaleDiv( QwtPlot::yLeft );
    QRectF rect = QRectF( xs.lowerBound(), ys.lowerBound(), xs.range(), ys.range() );
    return rect;
}

void setZoomRect(const QRectF& r)
{
    d->zoomer->zoom(r);
}

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[Uwe]

You don't need a zoomer to set the scale intervals - simply use setAxisScale or setAxisScaleDiv.

Uwe

[Darent]

Thanks Uwe.
now using:

QRectF CGraph::zoomRect()
{
    const QwtScaleDiv &xs = this->axisScaleDiv( QwtPlot::xBottom);
    const QwtScaleDiv &ys = this->axisScaleDiv( QwtPlot::yLeft );
    return QRectF( xs.lowerBound(), ys.lowerBound(), xs.range(), ys.range() );
}
 
void CGraph::setZoomRect(const QRectF& r)
{
    this->setAxisScale(QwtPlot::xBottom, r.left(), r.right());
    this->setAxisScale(QwtPlot::yLeft, r.top(), r.bottom());
}

QRectF CGraph::zoomRect()
{
    const QwtScaleDiv &xs = this->axisScaleDiv( QwtPlot::xBottom);
    const QwtScaleDiv &ys = this->axisScaleDiv( QwtPlot::yLeft );
    return QRectF( xs.lowerBound(), ys.lowerBound(), xs.range(), ys.range() );
}

void CGraph::setZoomRect(const QRectF& r)
{
    this->setAxisScale(QwtPlot::xBottom, r.left(), r.right());
    this->setAxisScale(QwtPlot::yLeft, r.top(), r.bottom());
}

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