Any tricks to increase QtChart responsiveness?

[CJha]

Hi! I need to make a line plot of a large amount of data in a short period of time. The goal is to have 100,000 data points plotted in a line series in less than 50 milliseconds. I am able to do this through QPainterPath by painting on a QWidget, but I would like to give QtChart another shot because the QXYSeries class involves some basic interactions that I am unable to implement otherwise through QPainterPath. To check the responsiveness of the QtChart I made a small test application, here is the entire code for that:

mainWindow.h

#include <QtWidgets/QMainWindow>
#include <QtCharts/qchartview.h>
#include <QtCharts/qlineseries.h>
#include <QtMath>
#include <QElapsedTimer>
#include <QDebug>
#include "ui_mainWindow.h"

using namespace QtCharts;

class mainWindow : public QMainWindow
{
    Q_OBJECT

public:
    mainWindow(QWidget *parent = Q_NULLPTR);

private:
    Ui::mainWindowClass ui;

    QLineSeries *series;
    QChartView *view;
    QChart *chart;

    double data;

protected:
    virtual void resizeEvent(QResizeEvent *event) override;
};

mainWindow.cpp

#include "mainWindow.h"

mainWindow::mainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);

    /* Creating Line Series */
    series = new QLineSeries();
    for(int ii = 0; ii < 100000; ++ii)
    {
        data = 2 * sin(2 * M_PI * 3 * ii / 100000);
        *series << QPointF(ii, data);
    }

    /* Creating Chart */
    chart = new QChart();
    chart->addSeries(series);
    chart->createDefaultAxes();
    chart->setAnimationOptions(QChart::NoAnimation);

    /* Creating Chart View */
    view = new QChartView(chart);
    view->setChart(chart);
    view->setRenderHint(QPainter::Antialiasing);
    view->setParent(ui.horizontalFrame);
}

void mainWindow::resizeEvent(QResizeEvent *event)
{
    QElapsedTimer timer;
    timer.start();

    chart->resize(width(), height());

    qDebug() << timer.elapsed() << "milliseconds";
}

I am getting a response time of more than 500 milliseconds. I have already disabled all animations. Is there any way I can improve this response time significantly?

For reference, I am using Qt 5.15.0 with Visual Studio Community 2019.

[SGaist]

Hi,

Likely not the answer you are looking for but you might want to check the Qwt project. It may have better performance for that kind of cases.

[CJha]

@SGaist Thanks! I have considered Qwt Project, however, it doesn't have proper documentation to tell me if it has the interactions that I need. On top of that, I am quite sure plotting the same amount of data on Qwt will take upwards of 100 milliseconds which is still beyond the limits of my requirements.

[Pl45m4]

@CJha

Nobody can look at 100.000 data points.
Use downsampling to reduce the amount of points shown at a time. While zooming in or so, you can increase that amount again until you show that area with all the data.

[CJha]

@Pl45m4 I know, I have developed my own method of downsampling for a line plot, so that peaks and overall data values are preserved. I can use it with QWidget and draw there much faster (15 - 20 ms). However, even if I use the raw method of plotting all the data points in QWidget it takes slightly more than 100 milliseconds, the same raw method in QChart takes between 500 - 600 milliseconds.

[J.Hilk]

@CJha Charts is far from optimized, especially the QWidget version, have you tried a QQuickWidget/View and the QML Chart view?

usually results in better overall performance

[CJha]

@J-Hilk Thanks for the suggestion.
I haven't tried it, I am working with C++ only. As far as I understand for Qt Quick I will have to use QML which I haven't learned yet (I started with C++ a few a month back). Hopefully, the Qt 6 release in December this year will bring huge improvements to Qt Charts.

[A.A.SEZEN]

@CJha We agree when it's a little late. I tried without changing your code. Output was 52 milliseconds. Maybe not a contribution, but the difference is not 1/10. QChart seems to do what you want.
Windows 10 x64, Qt 6.1, MinGW 64 and AMD Ryzen 7 PRO 4750U 8Gb RAM.

[samon_sg]

@CJha try to useOpenGL for series, for qml i use series.useOpenGL = true