QwtPlotPicker problem with QTimer

[phenoboy]

I have created my own curvetracker. My intention is to execute trackerTextF virtual function but it would be processed within time limits. So if user moves more tracer is updated max 10times/second. So timer interval is 100ms.

For some reason i'm getting slot error:

Object::connect: No such slot QwtPlotPicker::tracked() in \src\curvetracker.cpp:27

I can't see any problem in my code


CurveTracker.h

class QwtPlotCurve;
 
class CurveTracker: public QwtPlotPicker
{
public:
    CurveTracker( QWidget * );
 
protected:
    virtual QwtText trackerTextF( const QPointF & ) const;
    virtual QRect trackerRect( const QFont & ) const;
 
public slots:
    void tracked();
 
 
protected:
    QTimer* timer;
 
private:
    QString curveInfoAt( const CustomQwtCurve *, const QPointF & ) const;
    QLineF curveLineAt( const CustomQwtCurve *, double x ) const;
};

class QwtPlotCurve;

class CurveTracker: public QwtPlotPicker
{
public:
    CurveTracker( QWidget * );

protected:
    virtual QwtText trackerTextF( const QPointF & ) const;
    virtual QRect trackerRect( const QFont & ) const;

public slots:
    void tracked();


protected:
    QTimer* timer;

private:
    QString curveInfoAt( const CustomQwtCurve *, const QPointF & ) const;
    QLineF curveLineAt( const CustomQwtCurve *, double x ) const;
};

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CurveTracker.cpp

CurveTracker::CurveTracker( QWidget *canvas ):
    QwtPlotPicker( canvas )
{
    setTrackerMode( QwtPlotPicker::ActiveOnly );
    setRubberBand( CrossRubberBand);
    setStateMachine( new QwtPickerDragPointMachine() );
 
    timer=new QTimer(this);
    connect(timer,SIGNAL(timeout()), this, SLOT(tracked()));
    timer->start(100);
 
}

CurveTracker::CurveTracker( QWidget *canvas ):
    QwtPlotPicker( canvas )
{
    setTrackerMode( QwtPlotPicker::ActiveOnly );
    setRubberBand( CrossRubberBand);
    setStateMachine( new QwtPickerDragPointMachine() );

    timer=new QTimer(this);
    connect(timer,SIGNAL(timeout()), this, SLOT(tracked()));
    timer->start(100);

}

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[Uwe]

Y ou have to add the QOBJECT macro and run moc.

Uwe

[phenoboy]

Thanks! It works..

but I can't resolve my problem.. I don't know how to use timer properly here. Can you help ? I want to update trackerText maximum of 10 times per second. I have so many polygons it takes too much CPU when user drags mouse over them. Since I have to return QwtText in trackerTextF it becomes a problem to use timer. Or I don't know how to do it..Thanks.

[Uwe]

I have so many polygons it takes too much CPU when user drags mouse over them.

For drawing the tracker text the number of polygons doesn't matter, so I assume the time gets lost when trying to find the information you want to display.
Second guess: you are iterating over all points to find some information.

Before trying to continue with your timer approach I would have a look if you can't improve the performance of finding the info. F.e. are your points ordered in x or y direction ?

Uwe

[phenoboy]

Hello Uwe. Thanks for reply.

I'm using code from playground\curvetracker basically which is basically unmodified. So I guess I need to look at function 'QwtText trackerTextF(const QPointF& pos) ' since it is iterating over points. Any ideas how to make it faster? Points are ordered in x direction.

[Uwe]

This code iterates over all curves, but finds the points using qwtUpperSampleIndex, what is a binary search algo ( should be no performance issue: O(log n) ) using the sorted order of the points. So beside you have trillions of curves there should be no performance problem with this code. As the tracker text itself is painted as widget overlay on top of the plot ( without having to replot, as long as you didn't disable the canvas cache ) this won't also be a perfrormance issue.

• How is the performance when you simply return QwtPlotPicker::trackerTextF() ?
• Do you do any other updates of your user interface according to the mouse movements ?
• Also check if you run into replots by accident, when moving the mouse.

Uwe

[phenoboy]

This code iterates over all curves, but finds the points using qwtUpperSampleIndex, what is a binary search algo ( should be no performance issue: O(log n) ) using the sorted order of the points. So beside you have trillions of curves there should be no performance problem with this code. As the tracker text itself is painted as widget overlay on top of the plot ( without having to replot, as long as you didn't disable the canvas cache ) this won't also be a perfrormance issue.

• How is the performance when you simply return QwtPlotPicker::trackerTextF() ?
• Do you do any other updates of your user interface according to the mouse movements ?
• Also check if you run into replots by accident, when moving the mouse.

Uwe

Thanks for help. Actually I found out that my plot is drawing and adding items to curve at about 1000items (values) / second. That is the reason to slow down. I have now separated adding items (can be of rate 1000 items/sec or even higher ) and redrawing. Redrawing happens now at 50 fps and now there is no performance issues at all. tracerTextF function is very fast.

what do you suggest is the best way to replot whot plot after dragging mouse and when tracerTextF() is called ?

[Uwe]

what do you suggest is the best way to replot whot plot after dragging mouse and when tracerTextF() is called ?

The picker draws the text to a widget overlay, not to the plot canvas, so there is no replot on mouse movements. When you didn't disable the canvas baclking store the area below the previous text rect will be restored from it.
So there is no best way as nothing is going on, that is of relevance in terms of being performance critical.

Uwe