plotmatrix canvas size after rescale

Hi all.

I'm playing with Qwt and having some trouble with the plotmatrix example. In the example, I added a line in the MainWindow constructor after the calls to setAxisScale, as follows:

Code:

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setAxisScale(QwtPlot::yLeft, 2, -2, 2);

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which calls setScaleAxis on the leftmost plot in the bottom row with limits -2 and 2. When I run the program, the scale comes out right, but the bottom row of plots is taller than the other rows. A screenshot is attached. What I want is for all the plots in the matrix to have the same size. How can I acheive that?

Thanks.

The size hints of a plot widget depend on its tick labels - guess this is the reason, why the grid layout acts this way. Try to change the size policies of the plot, if this doesn't work you have to derive from QwtPlot and overload minimumSizeHint()/sizeHint().

See QWidget::setSizePolicy(), QWidget::sizeHint(), QWidget::minimumSizeHint().

Uwe

Thanks for the input. I fiddled with the size policies on the plots, but I wasn't able to get anywhere with that. I also derived from QwtPlot and overrode the size hints. That seemed promising, but it was still doing unexpected things. In the end I decided to just lay out the plots by hand in my application. The tricky part was figuring out how much space would be taken up by the axes. In the end I settled on

Code:

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void PlotStack::resizeEvent(QResizeEvent* ev)
{
    int w = width();
    int h = height();
 
    QList<QwtPlot*> plots = findChildren<QwtPlot*>();
    int n = plots.size();
 
    QwtPlot* last = plots.at(n-1);
 
    // Figure out how much space is used by the axis
    QwtScaleWidget* scaleWidget = last->axisWidget(QwtPlot::xBottom);
    QwtScaleDraw* sd = scaleWidget->scaleDraw();
    sd->setMinimumExtent(0);
    int extent = sd->extent(scaleWidget->font());
    extent += scaleWidget->spacing();
    h -= extent;
 
    // Resize all plots except the bottom
    for (int i = 0; i < n-1; ++i) {
        QwtPlot* plot = plots.at(i);
        plot->setGeometry(0, h / n * i, w, h / n);
        plot->replot();
    }
 
    // Resize the bottom plot
    last->setGeometry(0, h / n * (n-1), w, h / n + extent);
    last->replot();
 
    alignLeftAxes();
}

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I'm not sure this is quite right, but the plots look good.

Thanks again.