QwtPlotMagnifier not working with push buttons

[Momergil]

Hello Uwe and others,

I wanted to implement a Qwt graph aplication with zooming capabilities, and I know that QwtPlotMagnifier is the right guy to do such a job. The problem is that the user won't have a mouse and neither a keyboard to do the scrolling/zooming effects, having only a touchscreen with a "+" and a "-" pushbuttons.

Looking at the Qwt assistant files, I noticed that there was no "zoom in" and "zoom out" slots to which I could connect the clicked() signal from my two pushbuttons (using Qwt 6.0.2). Any reasons why? Wouldn't it be a good idea to have them?

But anyway, I later thought that I should implement the setZoomInKey and setZoomOutKey methods with some given key and then configure my pushbuttons with that same key using the QAbstractButton::setShortcut method. Later I noticed that wouldn't work, but before noticing this I tested the system and I figured out not only that the graph didn't react with the pressing of the buttons (expected), but also that when using the keyboard the magnifier wouldn't work as well.

I managed to make my zooming work by creating a zoomIn() slot on the graph and calling setAxysScale(QwtPlot::xBottom,0,value() +- 50) and it's working fine, but I'm still curious why the QwtPlotManager implementation didn't work when the keyboard was used, as well as if there is another way to use QwtPlotManager instead of calling setAxisScale to do this in the mentioned situation.


Thanks,


Momergil

[Uwe]

QwtPlotMagnifier is about connecting key and mouse events to rescale operations. In your case only the rescale operation is left, what is only some code around setAxisScale:

void rescale( QwtPlot* plot, double factor )
{
    factor = qAbs( factor );
    if ( factor == 1.0 || factor == 0.0 )
        return;
 
    bool doReplot = false;
 
    const bool autoReplot = plot->autoReplot();
    plot->setAutoReplot( false );
 
    for ( int axisId = 0; axisId < QwtPlot::axisCnt; axisId++ )
    {
        const QwtScaleDiv &scaleDiv = plot->axisScaleDiv( axisId );
 
        const double center = scaleDiv.lowerBound() + scaleDiv.range() / 2;
        const double width_2 = scaleDiv.range() / 2 * factor;
 
        plot->setAxisScale( axisId, center - width_2, center + width_2 );
        doReplot = true;
    }
 
    plot->setAutoReplot( autoReplot );
 
    if ( doReplot )
        plot->replot();
}

void rescale( QwtPlot* plot, double factor )
{
    factor = qAbs( factor );
    if ( factor == 1.0 || factor == 0.0 )
        return;

    bool doReplot = false;

    const bool autoReplot = plot->autoReplot();
    plot->setAutoReplot( false );

    for ( int axisId = 0; axisId < QwtPlot::axisCnt; axisId++ )
    {
        const QwtScaleDiv &scaleDiv = plot->axisScaleDiv( axisId );

        const double center = scaleDiv.lowerBound() + scaleDiv.range() / 2;
        const double width_2 = scaleDiv.range() / 2 * factor;

        plot->setAxisScale( axisId, center - width_2, center + width_2 );
        doReplot = true;
    }

    plot->setAutoReplot( autoReplot );

    if ( doReplot )
        plot->replot();
}

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