Install Event Filter instead of PlotPanner

[missoni]

Hey!
I had been trying to modify QwtPlotPanner to repaint plot canvas during panning, until I read that this is impossible and I should install an event filter instead, which would catch mouse clicks and repaint the plot using setAxisScale(). I did this, but I the event filter is not called. My code is like the following:

Plot::Plot(QWidget *parent):
    QwtPlot(parent)
{
        ...
        createAxes();
        createLegend();
	installEventFilter(m_eventFilter);
        ...
        installPlotZoomer();
        installPlotPicker();
}

Plot::Plot(QWidget *parent):
    QwtPlot(parent)
{
        ...
        createAxes();
        createLegend();
	installEventFilter(m_eventFilter);
        ...
        installPlotZoomer();
        installPlotPicker();
}

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where event filter is the following short calss:

class MyEventFilter : public QObject
{
protected:
	bool eventFilter(QObject *, QEvent *) {
	        std::cout << "MyEventFilter::eventFilter()" << std::endl;
	        return true;
        }
};

class MyEventFilter : public QObject
{
protected:
	bool eventFilter(QObject *, QEvent *) {
	        std::cout << "MyEventFilter::eventFilter()" << std::endl;
	        return true;
        }
};

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MyEventFilter is not called. Any ideas why not?

Thank you in advance!

[d_stranz]

I think you probably need to install the event filter on the canvas, not the plot.

I think that in general, event filters are not stand-alone QObject classes, but are implemented as part of another class, in your case the Plot class. Try making your eventFilter() method a member of Plot. (Note that I am not sure of this, but if you look at the example under QObject::eventFilter(), that's how it is done there).

Besides, how do you know that your event filter isn't being called? Because you don't see anything on std::cout? Because of the potential for buffering and flushing in use of cout, I don't think that is very reliable. Either set a breakpoint inside you event filter and see what happens in the debugger, or use qDebug() instead of std::cout.

[Uwe]

I had been trying to modify QwtPlotPanner to repaint plot canvas during panning, ...

There are reasons why it is not implemented this way and as long as you don't have a plot where all scales are hidden you are wasting your time.

Uwe