How to plot a simple function with QDateTime X axis and int/double Y axis?

[falconium]

OK, I have managed to fill the gaps in the chart by using Floating attribute:

QwtLinearScaleEngine *scaleEngineX = new QwtLinearScaleEngine;
    scaleEngineX->setAttribute(QwtScaleEngine::Floating, true);
    setAxisScaleEngine(QwtPlot::xBottom, scaleEngineX);

QwtLinearScaleEngine *scaleEngineX = new QwtLinearScaleEngine;
    scaleEngineX->setAttribute(QwtScaleEngine::Floating, true);
    setAxisScaleEngine(QwtPlot::xBottom, scaleEngineX);

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Now, the question is still, how to set major ticks to exact values of the original, source data, not some intermediate, calculated ones. (And of course, if there are too many discrete values on axis, to show only part of them based on an algorithm.)

I have tried to play around with:

setAxisMaxMinor(QwtPlot::xBottom, <some value>);
setAxisMaxMajor(QwtPlot::xBottom, <model->rowCount() or other values>);

No success. They always put ticks to wrong positions.
Thank you for the help in advance! This would be the only critical thing to me.

[falconium]

Now I know i would have had to use QwtScaleDiv class for this purpose:

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];
 
    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];
 
    foreach (double val, xData)
        majorTicks += val;
 
    QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
    for (int i = 0; i < xData.count() - 1; ++i)
        mediumTicks += QDateTime::fromTime_t(xData[i]).addSecs(900).toTime_t();
 
    QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
    for (int i = 0; i < xData.count() - 1; ++i)
            minorTicks += QDateTime::fromTime_t(xData[i]).addSecs(300).toTime_t();
 
    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];

    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];

    foreach (double val, xData)
        majorTicks += val;

    QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
    for (int i = 0; i < xData.count() - 1; ++i)
        mediumTicks += QDateTime::fromTime_t(xData[i]).addSecs(900).toTime_t();

    QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
    for (int i = 0; i < xData.count() - 1; ++i)
            minorTicks += QDateTime::fromTime_t(xData[i]).addSecs(300).toTime_t();

    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

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Simply call this function to set axis scale divisions in your QwtPlot instance as following:

setAxisScaleDiv(QwtPlot::xBottom, scaleDiv());

setAxisScaleDiv(QwtPlot::xBottom, scaleDiv());

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The only problem now I have is to set one minor tick to 1/10 of major tick and one medium tick to 1/5 of major tick. Thanks for suggestions in advance!

[falconium]

I solved it, please, find it here for future reference:

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];
 
    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];
 
    foreach (double val, xData)
        majorTicks += val;
 
    if (xData.count()>1)
    {
        QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
        for (int i = 0; i < xData.count() - 1; i++)
            for (int j = 1; j < 6; j++)
                mediumTicks += xData[i] + j * (xData[i+1] - xData[i]) / 5;
 
        QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
        for (int i = 0; i < xData.count()*10 - 1; i++)
            for (int j = 1; j < 11; j++)
                minorTicks += xData[i] + j * (xData[i+1] - xData[i]) / 10;
    }
 
    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

QwtScaleDiv ChartPlot::scaleDiv()
{
    QList<double> ticks[QwtScaleDiv::NTickTypes];

    QList<double> &majorTicks = ticks[QwtScaleDiv::MajorTick];

    foreach (double val, xData)
        majorTicks += val;

    if (xData.count()>1)
    {
        QList<double> &mediumTicks = ticks[QwtScaleDiv::MediumTick];
        for (int i = 0; i < xData.count() - 1; i++)
            for (int j = 1; j < 6; j++)
                mediumTicks += xData[i] + j * (xData[i+1] - xData[i]) / 5;

        QList<double> &minorTicks = ticks[QwtScaleDiv::MinorTick];
        for (int i = 0; i < xData.count()*10 - 1; i++)
            for (int j = 1; j < 11; j++)
                minorTicks += xData[i] + j * (xData[i+1] - xData[i]) / 10;
    }

    return QwtScaleDiv(xData.first(), xData.last(), ticks);
}

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