Flickering with QChartView display

[rahult]

I am running a code on group of images and i have a function "updateGraph" used to plot a line graph to observe the number of cars encountered. I am calling this function for every image to update the graph, but i observe the flickering when graph is updated. I feel it is because i am creating a new widget every time i update the graph. Is there any way update the graph is same widget.?

void MainWindow::updateGraph()
{
    QChart *chart = new QChart();
    chart->legend()->hide();
    chart->addSeries(series);
    chart->createDefaultAxes();
    chart->setTitle("Counts");

    QChartView *chartview = new QChartView(chart);
    chartview->setRenderHint(QPainter::Antialiasing);
    gridLayout->addWidget(chartview,0,0);
}

[Christian Ehrlicher]

@rahult said in Flickering with QChartView display:

feel it is because i am creating a new widget every time i update the graph.

Correct, and even more - you forgot to delete the old ones and create a big memory leak.

You only have to update your series container, the rest is done automatically.

[rahult]

@Christian-Ehrlicher Thank you

How to delete the old ones.
Just by updating the series how can i update my graph. Where to call my updateGraph().

[Christian Ehrlicher]

@rahult said in Flickering with QChartView display:

How to delete the old ones.

You mean old points? See e.g. https://doc.qt.io/qt-5/qxyseries.html#removePoints

[rahult]

@Christian-Ehrlicher Thank you..
As you said

You only have to update your series container, the rest is done automatically.

i have declared the following in my mainwindow constructor

    QChart *chart = new QChart();
    chart->legend()->hide();
    chart->addSeries(series);
    chart->createDefaultAxes();
    chart->setTitle("Counts");

    QChartView *chartview = new QChartView(chart);
    chartview->setRenderHint(QPainter::Antialiasing);
    gridLayout->addWidget(chartview,0,0);

But when i am trying to access to chart from my other function it is not in scope. Did i get it correctly can you tell me whats going wrong.

[Christian Ehrlicher]

Looks like basic c++ stuff is missing here...
You can for example make the chart or seriesa member variable.

[rahult]

@Christian-Ehrlicher thank you.. solved the above issue declaring in constructor.

Series is getting updated but the chart is not getting updated.

[rahult]

@Christian-Ehrlicher I can able to solve the issue by adding chart->removeSeries(series); before updating the series. It works now.

But when i update the axes with chart->createDefaultAxes(); after chart->removeSeries(series); i see a blury chart likethis..

is there any other way to update the axes with updating the series.

[Christian Ehrlicher]

There is no need to reset the series afaics. QChart::update() should suffice. If not please provide a testcase.