Check perfomance of QwtPlotCurve with setPaintAttribute for displaying large data

[Vasya]

Uwe,

I'm trying to explore QwtPlotOpenGLCanvas. I successfully built QWT 6.3.0 from SVN trunk.
I found your discussion about perfomance and OpenGL issues: https://www.qtcentre.org/threads/666...ming-is-*SLOW*
Now I can run your code from there. But when I change canvas to QwtPlotOpenGLCanvas *canvas = new QwtPlotOpenGLCanvas(); my launched application looks like green window (black or yellow on the picture) without curves. And there is a warning:
DXGI WARNING: IDXGIFactory::CreateSwapChain: Blt-model swap effects (DXGI_SWAP_EFFECT_DISCARD and DXGI_SWAP_EFFECT_SEQUENTIAL) are legacy swap effects that are predominantly superceded by their flip-model counterparts (DXGI_SWAP_EFFECT_FLIP_SEQUENTIAL and DXGI_SWAP_EFFECT_FLIP_DISCARD). Please consider updating your application to leverage flip-model swap effects to benefit from modern presentation enhancements. More information is available at http://aka.ms/dxgiflipmodel. [ MISCELLANEOUS WARNING #294: ]
QSize(600, 400) 0
Since I'm not quite familiar with graphics and OpenGL it is difficult to understand what is blamed for this app behaviour.
If you know something that possibly could help with that please give me a hint.

I'm on Windows 10 x64, DirectX 12, Qt 5.14.1, compilator MSVC 2017 x64.

Here is the code that I use:

#include <QApplication>
#include <QElapsedTimer>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_canvas.h>
#include <qwt_plot_opengl_canvas.h>
#include <QtMath>
#include <QDebug>
#include <QtOpenGL>
 
class MyPlot: public QwtPlot
{
public:
    MyPlot()
    {
        const int numPoints = 10;
 
        //QwtPlotCanvas* canvas = new QwtPlotCanvas();
        QwtPlotOpenGLCanvas *canvas = new QwtPlotOpenGLCanvas(); // NEW OpenGL Canvas
#if 0
        canvas->setPaintAttribute( QwtPlotCanvas::OpenGLBuffer, true );
#endif
        setCanvas( canvas );
        setCanvasBackground( Qt::white );
        setAxisScale( QwtPlot::yLeft, -1.5, 1.5 );
        setAxisScale( QwtPlot::xBottom, 0.0, numPoints );
 
        QwtPlotCurve *curve = new QwtPlotCurve();
        curve->setTitle( "Some Points" );
        curve->setPaintAttribute(QwtPlotCurve::FilterPointsAggressive, true);
 
        QPolygonF points;
        for ( int i = 0; i < numPoints; i++ )
            points += QPointF( i, qSin( i ) );
 
        curve->setSamples( points );
        curve->attach( this );
    }
 
    virtual void drawCanvas( QPainter *painter )
    {
        QElapsedTimer timer;
        timer.start();
 
        QwtPlot::drawCanvas( painter );
 
        qDebug() << size() << timer.elapsed();
    }
};
 
int main( int argc, char **argv )
{
    QApplication a( argc, argv );
 
    MyPlot plot;
 
    plot.resize( 600, 400 );
    plot.show();
 
    return a.exec();
}

#include <QApplication>
#include <QElapsedTimer>
#include <qwt_plot.h>
#include <qwt_plot_curve.h>
#include <qwt_plot_canvas.h>
#include <qwt_plot_opengl_canvas.h>
#include <QtMath>
#include <QDebug>
#include <QtOpenGL>

class MyPlot: public QwtPlot
{
public:
    MyPlot()
    {
        const int numPoints = 10;

        //QwtPlotCanvas* canvas = new QwtPlotCanvas();
        QwtPlotOpenGLCanvas *canvas = new QwtPlotOpenGLCanvas(); // NEW OpenGL Canvas
#if 0
        canvas->setPaintAttribute( QwtPlotCanvas::OpenGLBuffer, true );
#endif
        setCanvas( canvas );
        setCanvasBackground( Qt::white );
        setAxisScale( QwtPlot::yLeft, -1.5, 1.5 );
        setAxisScale( QwtPlot::xBottom, 0.0, numPoints );

        QwtPlotCurve *curve = new QwtPlotCurve();
        curve->setTitle( "Some Points" );
        curve->setPaintAttribute(QwtPlotCurve::FilterPointsAggressive, true);

        QPolygonF points;
        for ( int i = 0; i < numPoints; i++ )
            points += QPointF( i, qSin( i ) );

        curve->setSamples( points );
        curve->attach( this );
    }

    virtual void drawCanvas( QPainter *painter )
    {
        QElapsedTimer timer;
        timer.start();

        QwtPlot::drawCanvas( painter );

        qDebug() << size() << timer.elapsed();
    }
};

int main( int argc, char **argv )
{
    QApplication a( argc, argv );

    MyPlot plot;

    plot.resize( 600, 400 );
    plot.show();

    return a.exec();
}

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