How to draw a cruve with increasing data?

[anson97209]

Hi everyone. I have a problem of how to draw a cruve with growing data. In my application, i need to draw a curve which data is collected from AD channel. I found the "realtime_plot" example, it used the draw(from,to) method. So i use this code for reference. But in my code, it doesn't work. My code like this:
d_data->append(x, y, size);
d_curve->setRawData(d_data->x(), d_data->y(), d_data->count());
canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
d_curve->draw(d_curve->dataSize() - size, d_curve->dataSize() - 1);

used above code, the cruve desn't show, but used replot() method, the curve can display:
d_data->append(x, y, size);
d_curve->setRawData(d_data->x(), d_data->y(), d_data->count());
canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
replot();

so i want to ask , how to used draw(from,to) method? And i want to draw a curve as quickly as it can. QPaintEngine::PaintOutsidePaintEvent feathure is needed, but it is not supported by qt4, and how i can realize?

[Uwe]

1) Which platform are you on ?
2) Does the realtime example work ?

Uwe

[anson97209]

1) Which platform are you on ?
2) Does the realtime example work ?

Uwe

I use linux-2.6.13 kernel on arm9 board. Qt version is qt-core-4.3.2, and qwt is 5.20
the realtime example can work, it can show a series points, but i want to display a curve not just points, so i edit this code and and debug it, the original code is
if ( d_curve == NULL )
{
d_curve = new QwtPlotCurve("Test Curve");
d_curve->setStyle(QwtPlotCurve::NoCurve);
d_curve->setPaintAttribute(QwtPlotCurve::PaintFiltered);

const QColor &c = Qt::white;
d_curve->setSymbol(QwtSymbol(QwtSymbol::XCross,
QBrush(c), QPen(c), QSize(5, 5)) );

d_curve->attach(this);
}

and i delete "d_curve->setStyle(QwtPlotCurve::NoCurve)" and "d_curve->setSymbol(QwtSymbol(QwtSymbol::XCross, QBrush(c), QPen(c), QSize(5, 5)) )";
it can't show any points, but when i left-click the mouse in the screen , it can show the curve. other more, when i just delete "d_curve->setStyle(QwtPlotCurve::NoCurve)" sentence, it can show points but no curve and when i left-click the mouse in the screen , the cruve is also showed.
But in my code, no matter what i do , it can not show anything.

[Uwe]

I use linux-2.6.13 kernel on arm9 board. Qt version is qt-core-4.3.2, and qwt is 5.20

Qt has been renamed so often - I can't remember if qt-core was Qt Embedded or Qt X11. This is important as on X11 you can paint outside of paint events - while on Qt embedded ( and all platforms with the raster paint engine like Windows ) QwtPlotCurve::draw is implemented using internal dummy paint events.

Also Qt 4.3 is pretty old - better upgrade if possible.

the realtime example can work,...

Then check all the flags that are temporarily enabled in IncrementalPlot::appendData.

You could also have a look at the new spectrogram example in Qwt SVN trunk. Maybe this is closer to your use case ( but I'm not sure if it works with Qt 4.3 ).

Uwe

[anson97209]

Qt has been renamed so often - I can't remember if qt-core was Qt Embedded or Qt X11. This is important as on X11 you can paint outside of paint events - while on Qt embedded ( and all platforms with the raster paint engine like Windows ) QwtPlotCurve::draw is implemented using internal dummy paint events.

Also Qt 4.3 is pretty old - better upgrade if possible.

Then check all the flags that are temporarily enabled in IncrementalPlot::appendData.

You could also have a look at the new spectrogram example in Qwt SVN trunk. Maybe this is closer to your use case ( but I'm not sure if it works with Qt 4.3 ).

Uwe

Thank you for your answer, and i find something has change of the realtime plot example of the latest version of qwt. Maybe I should try to debug again to find a suitable way to solve the problem.

[anson97209]

In the Incrememtalplot.cpp , the orginal code is this:
void IncrementalPlot::appendData(double *x, double *y, int size)
{
if ( d_data == NULL )
d_data = new CurveData;

if ( d_curve == NULL )
{
d_curve = new QwtPlotCurve("Test Curve");
d_curve->setStyle(QwtPlotCurve::NoCurve);
d_curve->setPaintAttribute(QwtPlotCurve::PaintFiltered);

const QColor &c = Qt::white;
d_curve->setSymbol(QwtSymbol(QwtSymbol::XCross,
QBrush(c), QPen(c), QSize(5, 5)) );

d_curve->attach(this);
}

d_data->append(x, y, size);
d_curve->setRawData(d_data->x(), d_data->y(), d_data->count());
#ifdef __GNUC__
#endif

const bool cacheMode =
canvas()->testPaintAttribute(QwtPlotCanvas::PaintCached);

#if QT_VERSION >= 0x040000 && defined(Q_WS_X11)
// Even if not recommended by TrollTech, Qt::WA_PaintOutsidePaintEvent
// works on X11. This has an tremendous effect on the performance..

canvas()->setAttribute(Qt::WA_PaintOutsidePaintEvent, true);
#endif

canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
d_curve->draw(d_curve->dataSize() - size, d_curve->dataSize() - 1);
canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, cacheMode);

#if QT_VERSION >= 0x040000 && defined(Q_WS_X11)
canvas()->setAttribute(Qt::WA_PaintOutsidePaintEvent, false);
#endif
}

and I delete all the flag, and the code like this:

void IncrementalPlot::appendData(double *x, double *y, int size)
{
if ( d_data == NULL )
d_data = new CurveData;

if ( d_curve == NULL )
{
d_curve = new QwtPlotCurve("Test Curve");
d_curve->setStyle(QwtPlotCurve::NoCurve);
d_curve->setPaintAttribute(QwtPlotCurve::PaintFiltered);

const QColor &c = Qt::white;
d_curve->setSymbol(QwtSymbol(QwtSymbol::XCross,
QBrush(c), QPen(c), QSize(5, 5)) );

d_curve->attach(this);
}

d_data->append(x, y, size);
d_curve->setRawData(d_data->x(), d_data->y(), d_data->count());

canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, false);
d_curve->draw(d_curve->dataSize() - size, d_curve->dataSize() - 1);
canvas()->setPaintAttribute(QwtPlotCanvas::PaintCached, cacheMode);

}
the example also can work. But in my own code , it cannot show anything except using the replot() method. I guess other files (such as Randomplot.cpp) impacted the plot?

[anson97209]

I have find the problem. when I add zoomer class in my code, use draw() method can work. But I have another two problems:
1 the points can display in the realtime, but the curve can not display unless I left-clicked the mouse in the canvas.
2 when I enble the Qt::WA_PaintOutsidePaintEvent and disable QwtPlotCanvas::PaintCached, it can plot very fast, but it will print the debug information
"QWidget:aintEngine:should no nolonger be called"
"QPainter:begin:Paint device returned engine == 0, type:1"
"QPainter::setClipping:Painter not active, state will be reset by begin"
"QPainter::save:Painter not active"
"QPainter::store:Unbalanced save/restore"

[Uwe]

Qwt 5.2.0 doesn't call any QWidget::paintEngine() anymore. If you are really using it try to find out, where QWidget::paintEngine() is called ( f.e setting a breakpoint in qWarning() ).

Uwe

[anson97209]

Thank you!
I want to ask the frist question, why the points can display in the realtime, but the curve can't.

[Uwe]

If you want to see connecting lines between the points you need to pass the start and endpoint for these lines - not only a single point. So if you want to paint point by point you always have to add the previous point to QwtPlotCurve::draw().

Uwe

[anson97209]

Uwe, Thank you very much, you really help me a lot!
Follow you tips, I just changed the code like that
d_curve->draw(d_curve->dataSize() - 2, d_curve->dataSize() - 1);
and the curve can display in the realtime.
But it must disable Qt::WA_PaintOutsidePaintEvent. As a result, it plot very slowly, Can i have a method to let it plot faster ?