QwtRescaler issue

[mqt]

Hi,
I posted this question as a replay to an old post. But there was no response. So posting new thread.
I have inherited a class from QWTPlot and inside that I am calling

QwtPlotRescaler rescaler(canvas());
rescaler.setReferenceAxis(QwtPlot::xBottom);
rescaler.setAspectRatio(QwtPlot::yLeft, 1.0);

QwtPlotRescaler rescaler(canvas());
rescaler.setReferenceAxis(QwtPlot::xBottom);
rescaler.setAspectRatio(QwtPlot::yLeft, 1.0);

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My requirement is
Initially my plot's X Y axes have same range, 0 to 1. But My data changes such that y axis range is -1 to 1 (this is only an example. The range change dynamically to -0.5 to 1.0, -0.2 to 1.5 etc ) keeping x axis range 0 to 1 and now my aspect ratio is changed which I don't want. I expected that the rescaler will make the plot rectangle of height=2*width to maintain aspect ratio. But it remains as a square and Y axis got shrunk. I need to dynamically change the Y axis range and need to maintain aspect ratio. What I need to do? I also need to maintain aspect ratio when user shrinks the parent window.

[Uwe]

The rescaler automatically adjusts the scales to resize events of the canvas. When changing the scale range of the reference axis you have to call QwtPlotRescaler::rescale() manually.

Plot::Plot()
{
    m_rescaler = new QwtPlotRescaler( canvas(), QwtPlot::xBottom, QwtPlotRescaler::Fixed );
    m_rescaler->setAspectRatio( QwtPlot::yLeft, 1.0 );
}

Plot::Plot()
{
    m_rescaler = new QwtPlotRescaler( canvas(), QwtPlot::xBottom, QwtPlotRescaler::Fixed );
    m_rescaler->setAspectRatio( QwtPlot::yLeft, 1.0 );
}

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and something like this:

void Plot::expandReferenceAxis()
{
    const QwtInterval interval = axisInterval( m_rescaler->referenceAxis() );
    plot->setAxisScale( m_rescaler->referenceAxis(), interval.minValue(), interval.minValue() + interval.width() + 1000 );
    plot->updateAxes(); // no relot to avoid flickering
 
    m_rescaler->rescale(); // now sync the y axis + replot
}

void Plot::expandReferenceAxis()
{
    const QwtInterval interval = axisInterval( m_rescaler->referenceAxis() );
    plot->setAxisScale( m_rescaler->referenceAxis(), interval.minValue(), interval.minValue() + interval.width() + 1000 );
    plot->updateAxes(); // no relot to avoid flickering

    m_rescaler->rescale(); // now sync the y axis + replot
}

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It might be possible to connect QwtPlotRescaler::rescale() to QwtScaleWidget::scaleDivChanged() signal of the reference axis - but I have not tried it.

Uwe

[mqt]

Thanks Uwe,
I will try this. One question: what is 1000 hard coded in expandReferenceAxis ?
What I am trying is to achieve is a circle looks like a circle. I would like this happen even when user zoom with zoomer.

I have one more requirement which I am not able to figure out
When I change my data I don't want to change my current zoom reached by zoomer and/or magnifier. But I want to reset zoomer, so that I can Fit the view to new data (when a button clicked) with zoomer::zoom(0) call. How to achieve this?

[Uwe]

One question: what is 1000 hard coded in expandReferenceAxis ?

Just an example that modifies the scale somehow.

What I am trying is to achieve is a circle looks like a circle. I would like this happen even when user zoom with zoomer.

Then you should overload QwtPlotZoomer::rescale() ( have a look at the implementation ). Set the x axis like in the default implementation, but the y axis like in my code snippet above.

When I change my data I don't want to change my current zoom reached by zoomer and/or magnifier. But I want to reset zoomer, so that I can Fit the view to new data (when a button clicked) with zoomer::zoom(0) call.

Sounds like you want to modify the first entry of the zoom stack. See QwtPlotZoomer::setZoomStack() + QwtPlotZoomer::zoomStack().

Uwe