Need Help to Improve QML QChartView and CPP Interaction

Sandip Rakhasiya

Hello,

I am developing a Qt QML application for Embedded devices. And wants some guide to smooth Qt Charts interaction.

Below is my code description.
I have created ChartView in plotPage.ui.qml and also added Axis in ChartView as follows.

    ChartView {
        id: chartView
        visible: true
        anchors.left: parent.left
        anchors.right: parent.right
        anchors.top: dividerBar.bottom
        anchors.bottom: imageShiftRight.top
        anchors.rightMargin: -20
        anchors.leftMargin: -20
        anchors.bottomMargin: -20
        anchors.topMargin: -20
        backgroundColor: "transparent"
        plotAreaColor: whiteColor
        antialiasing: true
        legend.visible: false

        ValueAxis {
            id: xAxis
            labelsFont.pointSize: fontSizeSmall
            titleText: "Freq"
            labelsColor: "white"
            min: 0
            max: 500
            tickCount: 8
        }

        ValueAxis {
            id: yAxis
            labelsFont.pointSize: fontSizeSmall
            titleText: "Magnitudes"
            labelsColor: "white"
            min: 0
            max: 50
            tickCount: 8
        }
    }

I have created spline series for ChartView dynamically with the below code.

onCurve: {
            var series = chartView.createSeries(ChartView.SeriesTypeSpline, title, xAxis, yAxis)
            interface.plotUpdate(series) //interface is CPP file instance and plotUpdate is CPP function.
}

I have collecting data in CPP and creating points with QPointF.
Note: In one chart there are 1000+ points and I will need to update 8 or 24 charts in one instance.
So, I am updating with the below function.

void Interface::plotUpdate(QAbstractSeries *series)
{
    if (series) {
        QSplineSeries *splineseries = static_cast<QSplineSeries *>(series);
        QVector<QPointF> points = m_data;
        splineseries->replace(points);
    }
}

void Interface::createPlotData(int converted[], float data[], int start_idx, int totalPoints, bool inverted)
{
    m_data.clear();
    int counter = 0;

    for(counter = 0; counter < totalPoints; counter++) {
        m_data.append(QPointF(((double)converted[counter] * 0.001), (inverted ? (double)data[counter + start_idx] * -1.0 : (double)data[counter + start_idx])));
    }
}

Calling in other functions.

        createPlotData(Freq, data[0], 0, points);
        emit curve(tr("Main"), true);

emit curve goes to QML and In QML -> onCurve {} updating data from CPP.

All things are working fine but For one graph, it is taking too much time.
I need to reduce time to update the plot each time. I have use linuxfb as a QT Platform to render UI.

GrecKo

Take a look at VXYModelMapper . It lets you create series from a QAbstractTableModel with not all the glue code you did here.