QCustomPlot - Plots in various tabs

Question

I am currently receiving information via serial communication, see below for example of data coming in:

"A Ch1:45.23 Ch2:23.58 Ch3:12.45 Ch4:1.56"
"B Ch1:12.63 Ch2:15.45 Ch3:6.23 Ch4:45.32"
"C Ch1:22.20 Ch2:3.85 Ch3:2.45 Ch4:51.58"
"D Ch1:21.25 Ch2:2.58 Ch3:12.13 Ch4:61.52"
"A Ch1:4.27 Ch2:25.52 Ch3:22.15 Ch4:31.56" etc.

Now what I am trying to do is take all the incoming data and plot it. So to do this I have created a Qt application with multiple tabs.

Tab 1 - All Sections
Tab 2 - Section A
Tab 3 - Section B
Tab 4 - Section C
Tab 5 - Section D

I added a widget to each tab and promoted it to a QCustomPlot.

I setup each QCustomPlot as follows:

// Would be nice to improve this
setupGraph(ui->sectionA);   // Setup Section A QCustomPlot
setupGraph(ui->sectionB);   // Setup Section B QCustomPlot
setupGraph(ui->sectionC);   // Setup Section C QCustomPlot
setupGraph(ui->sectionD);   // Setup Section D QCustomPlot

void MainWindow::setupGraph(QCustomPlot *graphPlot)
{
    QStringList legend;

    legend << "Load Cell 1" << "Load Cell 2" << "Load Cell 3" << "Load Cell 4" << "Total Weight";

    graphPlot->legend->setVisible(true);
    graphPlot->legend->setFont(QFont("Helvetica",9));

    for (int i = 0; i < legend.size(); i++)
    {
        graphPlot->addGraph();
        graphPlot->graph(i)->setName(legend[i]);
        graphPlot->graph(i)->setLineStyle(QCPGraph::lsLine);
    }

    graphPlot->graph(0)->setPen(QPen(Qt::blue));
    graphPlot->graph(1)->setPen(QPen(Qt::red));
    graphPlot->graph(2)->setPen(QPen(Qt::green));
    graphPlot->graph(3)->setPen(QPen(Qt::darkCyan));
    graphPlot->axisRect()->setupFullAxesBox();
    graphPlot->xAxis->setRange(-10,0);
    graphPlot->yAxis->setRange(0,5);
    connect(graphPlot->xAxis, SIGNAL(rangeChanged(QCPRange)), graphPlot->xAxis2, SLOT(setRange(QCPRange)));
    connect(graphPlot->yAxis, SIGNAL(rangeChanged(QCPRange)), graphPlot->yAxis2, SLOT(setRange(QCPRange)));
}

Once this is done, I open the serial port and connect to the ReadyRead signal. Every time new data is available, I check where the new data is coming from and I want to plot it.

void MainWindow::readData()
{
    QByteArray serialData;

    if (serial->canReadLine())
        serialData = serial->readLine();

    if (serialData.startsWith('A'))
        realtimePlot(ui->sectionA) // Plot the data for Section A
    if (serialData.startsWith('B'))
        realtimePlot(ui->sectionB) // Plot the data for Section B
    if (serialData.startsWith('C'))
        realtimePlot(ui->sectionC) // Plot the data for Section C
    if (serialData.startsWith('D'))
        realtimePlot(ui->sectionD) // Plot the data for Section D
}

I have omitted the code that extracts the actual values from the incoming data.

void MainWindow::realtimePlot(QCustomPlot *graphPlot)
{
    range_y_min = 0;
    range_y_max = 100;
    // Add data to the lines
    graphPlot->graph(0)->addData(key_x, ch1);
    graphPlot->graph(1)->addData(key_x, ch2);
    graphPlot->graph(2)->addData(key_x, ch3);
    graphPlot->graph(3)->addData(key_x, ch4);
    // Remove data outside the visible range
    graphPlot->graph(0)->removeDataBefore(key_x-10);
    graphPlot->graph(1)->removeDataBefore(key_x-10);
    graphPlot->graph(2)->removeDataBefore(key_x-10);
    graphPlot->graph(3)->removeDataBefore(key_x-10);
    // Make the x-axis range scroll with the data (at a constant range size of 10):
    graphPlot->xAxis->setRange(key_x+1/frequency,10,Qt::AlignRight);
    // Set the range of the y-axis
    graphPlot->yAxis->setRange(range_y_min,range_y_max+5);
    // Replot the graph
    graphPlot->replot();
    key_x += 1/frequency; // defines horizontal gap between two data points on graph
}

Now I am hoping that removeDataBefore(key_x-10) removes all the data before that point, because I find my memory fill up quite quickly. key_x and frequency is defined somewhere else.

The code I currently have (similar to that above) does work, but after a while everything starts slowing down and everything is delayed. So I am not quite sure what is wrong or causing this to happen. I would also like to know how to use the plots for Section A, Section B, Section C and Section D on Tab 1, as I don't want to create another 4 widgets on the 1st tab to plot the data.

I hope I have given you enough background information.

Thank you for your help in advance.

Answer 1

With regard to your second question, its easy. Simply add the graphs to one widget ( and maybe change the color etc )

Just call addGraph() to one graph object.

This may also increase your speed as you won't be calling replot() for each graph object.