Multiple real time plots/charts

framet

@VRonin I'm currently not in the office so I cannot check to be 100% but i think i just added the to the respective QLineSeries.

framet

@VRonin said in Multiple real time plots/charts:

Nope. actually it QAbstractTableModel is perfect for when you have more than 1 chart.

hey @VRonin im currently working on a test with QAbstractTableModel.
I have a model with 100 rows and 4 columns. If new values would overflow the memory a just start at row zero again.
The problem what I have and I can't find any solution for it is that when I update a specific row and emit dataChanged(topLeft,bottomRight) with the updated values QChart updates/repaints the hole model which leads to flickering when you go above 10 HZ.

Is there a way to reimplement this QChart behavior or is there a flag to set?

Cheers
framet

Edit: here is an example with 2 HZ https://imgur.com/a/DYR7L

Edit 2: just found out with linesSeries.setUseOpenGL() decreases the flickering

VRonin

Wow, it's unbelievably slow... I'll prepare a minimal example and see if I get the same

framet

Below are two tests with TableModel (100,4)

Both tests run with 20 HZ
With OpenGL on LineSeries enabled

Test 1) Single chart https://imgur.com/a/Sfe20
Test 2) 6 charts http://imgur.com/a/Fpicu

With OpenGL on LineSeries disabled
Test 3) 6 charts http://imgur.com/a/mnFag

As you can see the problem of QT getting slower with more charts relaying on the same Model still exists.

Edit: just to clarify YES the test before was with 2 HZ and those tests here are with 20 HZ :)

VRonin

Tryed:

#include <QWidget>
#include <QTimer>
#include <QStandardItemModel>
#include <QtCharts/QChart>
#include <QtCharts/QChartView>
#include <QGridLayout>
#include <QtCharts/QVXYModelMapper>
#include <QtCharts/QLineSeries>
#include <cmath>

QT_CHARTS_USE_NAMESPACE

class TestChart : public QWidget
{
    Q_OBJECT
        Q_DISABLE_COPY(TestChart)
public:
    explicit TestChart(QWidget *parent = Q_NULLPTR)
        :QWidget(parent)
        , maixLength(360)
        , frequency(20.0)
        , shift(0.0)
        , currentCounter(0.0)
        , pi(std::acos(-1))
    {
        m_model = new QStandardItemModel(this);
        m_model->insertColumns(0, 3);
        //m_model->insertRows(0, maixLength);

        m_updateTimer = new QTimer(this);
        m_updateTimer->setInterval(1000.0 / frequency);
        connect(m_updateTimer, &QTimer::timeout, this, &TestChart::addSeriesData);

        QGridLayout* mainLay = new QGridLayout(this);

        

        for (int i = 0; i < 15; ++i) {
            QLineSeries *sineSeries = new QLineSeries;
            sineSeries->setName("Sine Wave");
            QVXYModelMapper *mapper = new QVXYModelMapper(this);
            mapper->setXColumn(0);
            mapper->setYColumn(1);
            mapper->setSeries(sineSeries);
            mapper->setModel(m_model);
            sineSeries->setColor(Qt::red);

            QLineSeries *cosineSeries = new QLineSeries;
            cosineSeries->setName("Cosine Wave");
            mapper = new QVXYModelMapper(this);
            mapper->setXColumn(0);
            mapper->setYColumn(2);
            mapper->setSeries(cosineSeries);
            mapper->setModel(m_model);
            cosineSeries->setColor(Qt::blue);

            QChart *chart = new QChart();
            chart->legend()->hide();
            chart->addSeries(sineSeries);
            chart->addSeries(cosineSeries);
            chart->createDefaultAxes();
            chart->axisX(sineSeries)->setMin(0);
            chart->axisX(sineSeries)->setMax(maixLength);
            chart->axisX(cosineSeries)->setMin(0);
            chart->axisX(cosineSeries)->setMax(maixLength);
            chart->axisY(sineSeries)->setMin(-1);
            chart->axisY(sineSeries)->setMax(1);
            chart->axisY(cosineSeries)->setMin(-1);
            chart->axisY(cosineSeries)->setMax(1);

            chart->setTitle("Simple line chart example");
            QChartView *chartView = new QChartView(chart);
            chartView->setRenderHint(QPainter::Antialiasing);
            mainLay->addWidget(chartView,i/5,i%5 );
        }

        m_updateTimer->start();
    }
private slots:
    void addSeriesData()
    {
        if (m_model->rowCount() <= currentCounter)
            m_model->insertRows(m_model->rowCount(), currentCounter - m_model->rowCount() + 1);
        m_model->setData(m_model->index(currentCounter, 0), currentCounter);
        m_model->setData(m_model->index(currentCounter, 1), std::sin((shift+currentCounter)*pi / 180.0));
        m_model->setData(m_model->index(currentCounter, 2), std::cos((shift + currentCounter)*pi / 180.0));
        currentCounter += 1.0;
        if (currentCounter >= maixLength) {
            currentCounter = 0.0;
            shift += 90;
        }
    }

private:
    const double pi;
    double shift;
    double currentCounter;
    double frequency;
    QTimer* m_updateTimer;
    QAbstractItemModel* m_model;
    const int maixLength;
};

15 charts, you are right, 20Hz it's not great even if in release mode is better.

framet

Do you have any idea how to get 15 charts without severe performance issues?
Except outsourcing single Charts to seperate Qt-Applications and send data over ipc or something in this direction.

VRonin

I think yo have to decouple the data arrival frequency to the frequency you send the data to the chart.

In the QAbstractTableModel instead of emitting dataChanged() directly, every time a new datapoint arrives (re)start a signle shot timer that emits the signal. I'll try implementing it and update this post

EDIT:

My method increased but not to an acceptable level. I have to give up

framet

@VRonin thank you for your time and effort!!!

I still have some ideas left. Will post it here when one gives an acceptable result.

cheers!

MaxBec

@framet Hey framet. Did you find a solution?

LeandroTeixeira

I am working with a application that has 12 curves and I am have the same problem, if I increase the number of curves, the performance decrease. I use qcustomplot. I need to plot 300pixels/second. Does anyone have some ideas?