qwtplot and mouse tracking

[fearu]

I have an application with a qwtplot, grid and qwtcurve or histogram_item.h (I think this is irrelevant). I want to show the user the axis values in the plot that correspond to where the cursor is. So I did it like this:

First I declare an eventfilter from qwtplot to a class that I have, and I activate mousetracking:

m_plot->setMouseTracking(true);
m_plot->canvas()->setMouseTracking(true);
m_plot->installEventFilter(this);

in the eventFilter I do this (of course after detecting mouse move event):

statusbar->showMessage( QString("X: ") +
QString::number((int) (0.5 + m_plot->invTransform(QwtPlot::xBottom, mouseEvent->pos().x()))) +
QString(" Y: ") +
QString::number((int) (0.5 + m_plot->invTransform(QwtPlot::yLeft, mouseEvent->pos().y()))));

so basically, I receive mouse position, and I use invTransform method to convert it from pixel position to the values in the plot.

The axis are defined like this:

m_plot->setAxisScale(QwtPlot::yLeft, 0.0, max);
m_plot->setAxisScale(QwtPlot::xBottom, 0.0, numValues);

And now my problem. I have many plots (histograms, curves, etc.) and in all of them, I have an error of measure in the X value, this error depends on the position inside the parent (widget or frame) and/or size of the qwtplot. I don't know if the error is already in the pixels or if it is after invTransform. I can correct the difference if I don't allow to resize the plot, but I want to know where this error comes from.

If you need more code or information, please ask for it, and thanks for your help.

[Uwe]

You need to filter the mouse events from the plot canvas not from the plot widget itsself.
Nevertheless have a look at QwtPlotPicker before you continue.

Uwe

[fearu]

Thanks for your answer. I've been busy lately so I haven't tried it. I'll post here if it worked when I have time to work on it.

[fearu]

It worked filtering from canvas(). I won't use qwtplotpicker as the current code works, but I will use it the next time. Thanks again.

[FelixB]

Is it possible to use a QwtPlotPicker to show something in the statusbar? I have a Spectrogram and want to show the z-value to the current coordinates (and other things, but that is not so important at the moment). I tried to use "moved"-signal, but that works only if the mouse is clicked (as in "bode"-example).

How can I change that?

[FelixB]

got it I had to write my own subclass of QwtPlotPicker and overriding the "trackerText" method:

class MyPicker : public QwtPlotPicker
    {
        Q_OBJECT
 
    public:
        MyPicker(int xAxis, int yAxis, int selectionFlags, RubberBand rubberBand, DisplayMode trackerMode, QwtPlotCanvas* canvas);
 
    signals:
        void mouseMoved(const QPoint& pos) const;    
 
    protected:
            virtual QwtText trackerText (const QwtDoublePoint & pos) const;
 
    };

class MyPicker : public QwtPlotPicker
    {
        Q_OBJECT

    public:
        MyPicker(int xAxis, int yAxis, int selectionFlags, RubberBand rubberBand, DisplayMode trackerMode, QwtPlotCanvas* canvas);

    signals:
        void mouseMoved(const QPoint& pos) const;    

    protected:
            virtual QwtText trackerText (const QwtDoublePoint & pos) const;
                
    };

To copy to clipboard, switch view to plain text mode 

MyPicker::MyPicker(int xAxis, int yAxis, int selectionFlags, RubberBand rubberBand, DisplayMode trackerMode, QwtPlotCanvas* canvas)
            : QwtPlotPicker(xAxis, yAxis, selectionFlags, rubberBand, trackerMode, canvas)
        {}
 
QwtText MyPicker::trackerText (const QwtDoublePoint & pos) const
    {
        const QPoint point = pos.toPoint();
        emit mouseMoved(point);
        return QwtText(QString::number(point.x()) + ", " + QString::number(point.y()));
    }

MyPicker::MyPicker(int xAxis, int yAxis, int selectionFlags, RubberBand rubberBand, DisplayMode trackerMode, QwtPlotCanvas* canvas)
            : QwtPlotPicker(xAxis, yAxis, selectionFlags, rubberBand, trackerMode, canvas)
        {}

QwtText MyPicker::trackerText (const QwtDoublePoint & pos) const
    {
        const QPoint point = pos.toPoint();
        emit mouseMoved(point);
        return QwtText(QString::number(point.x()) + ", " + QString::number(point.y()));
    }

To copy to clipboard, switch view to plain text mode 

now I can react to the "mouseMoved"-signal

[FelixB]

I'm not sure if this is related to QwtPlotPicker or general to Qt...

as written above, I want to react to the mouseMoved-signal. Currently, I write text into the statusBar. But I want to do this only as long as the mouse is on my plot. When the user moves the mouse outside the canvas, I don't want to do anything. Is there a possibility to check if the cursor is on the canvas? Or the get a signal when the cursor has left the canvas?