Speed Problem with Qchart and Drawing BarChart in Qt5.7

[hadi_m]

Hello to All
I have serious problem with drawing Chart in Qt, I created the following simple project base on Qt Bar chart Sample project, My chart changes over time dynamically. My problem with it is, when I increase the number of bars the program is too slow and it takes a long time to drawing chart. I use a thread but it does not matter at all. So how can I increase the speed of drawing chart?

#define BinNumber 100
#define BinLenght   0.002
unsigned long hist[BinNumber];
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
        QMainWindow window;
        window.show();
        QList<QBarSet*> Bins;
        QBarSeries *series;
        QChart *chart;
        QChartView *chartView;
        float deltaV = BinLenght / float(BinNumber);
        series = new QBarSeries();
        chart = new QChart();
        chart->setVisible(false);
        clock_t chartStart = clock();
        for (int i = 0; i < BinNumber; i++) {
            hist[i] = (int)qrand() % 1000;
            QBarSet * bar = new QBarSet(QString::number((i + 1)*deltaV));
            *bar << hist[i];
            Bins.append(bar);

            series->append(bar);
        }
        while (false)
        {
            int i = 0;
            hist[i] = 0;
            QBarSet * bar = new QBarSet(QString::number((i + 1)*deltaV));
            *bar << 0;
            Bins.append(bar);

            series->append(bar);
        }
        QValueAxis *axisX = new QValueAxis;
        axisX->setRange(0, 5);
        QValueAxis *axisY = new QValueAxis;
        axisY->setRange(0, 1000);
        chart->addSeries(series);
        chart->setTitle("Histogram Of Input Signal");
        chart->createDefaultAxes();
        chart->setAxisY(axisY, series);
        chartView = new QChartView(chart);
        chartView->setRenderHint(QPainter::Antialiasing);
        window.setCentralWidget(chartView);
        window.resize(420, 300);
        chart->setVisible(true);
        clock_t chartend = clock();
        qDebug()<< "Execution time is :" << (float(chartend - chartStart) /CLOCKS_PER_SEC);
    return a.exec();
}

I should mention that I measure my code with some powerful profiler and the command “chart->addSeries(series);” take 510 millisecond to execute my forloop take 3039 ms for 100 BinNumber. QChart does any method for fast drawing? How can I edit this code for increasing drawing speed?

[Flotisable]

@hadi_m
I think maybe the new statement in the for loop dominate the speed.

you have already knows how many bars you need, why not use a QList or QVector to allocate the memory first, and then go though it and set the proper information to the elements?

[hadi_m]

Thanks for your replying
I tested with local QBarSet Qlist instead of dynamically created it but it doesn’t matter on speed.
I should mention I test my program by some powerful performance validator tools and I notice the line “chart->addSeries(series);” take too long time and of course my forloop take time when BarNumber Increases to 1000.

[wanghl]

@hadi_m bar set is slow。unfortunately，no way resolve it

[Venkatesh V]

@hadi_m
Try by taking different thread for those two loops and addSeries can do it in main thread only.

[jsulm]

@Venkatesh-V If chart->addSeries(series); is the problem, then I don't think using multi threading will give any advantage (instead it will complicate stuff).