Getting a `No alignment specified !` when setting alignment Qt::AlignCenter when adding axis using addAxis()

Stavros Vaionitis · 11 Aug 2022, 08:28

Hi there,

I have the following snippet of code which initializes 2 QCharts

void InitializeCharts()
    {
        // pan
        panPositionChart = new QChart();
        panPositionChart->setTitle("Pan Position");

        QValueAxis *panAxisX = new QValueAxis();
        panAxisX->setTickCount(5);
        panPositionChart->addAxis(panAxisX, Qt::AlignCenter);

        QValueAxis *panAxisY = new QValueAxis();
        panAxisY->setTickCount(5);
        panPositionChart->addAxis(panAxisY, Qt::AlignCenter);

        ui->gimbalPositionPanChartview->setChart(panPositionChart);
        ui->gimbalPositionPanChartview->setRenderHint(QPainter::Antialiasing);

        // tilt
        tiltPositionChart = new QChart();
        tiltPositionChart->setTitle("Tilt Position");

        QValueAxis *tiltAxisX = new QValueAxis();
        tiltAxisX->setTickCount(5);
        tiltPositionChart->addAxis(tiltAxisX, Qt::AlignCenter);

        QValueAxis *tiltAxisY = new QValueAxis();
        tiltAxisY->setTickCount(5);
        tiltPositionChart->addAxis(tiltAxisY, Qt::AlignLeft);

        ui->gimbalPositionTiltChartview->setChart(tiltPositionChart);
        ui->gimbalPositionTiltChartview->setRenderHint(QPainter::Antialiasing);
    }

For both of the QChart I want the X axis to be centered aligned. I want the Y axis to be center aligned for one of the charts and left aligned for the other. The above code is based on the QtCharts multiaxis example https://doc.qt.io/qt-6.2/qtcharts-multiaxis-example.html. When I run the above code, I get the following error

No alignment specified !
Segmentation fault (core dumped)

If I use the Qt::AlignBottom as it is in the example, I get no error.
If I use the Qt::AlignHCenter or Qt::AlignVCenter, I get the No alignment specified ! error.

What am I doing wrong? Do I need to add something else?

FYI I use the Qt 6.2.3 and for the ChartView I have compiled the designer plugin from the git repo https://code.qt.io/cgit/qt/qtcharts.git/tree/?h=6.2.3 and add it in the designers plugin directory.

Next following how I want the chart's axis to be like and possibly there is another way to achieve this

Pan chart

Tilt chart

Let me know if you need any more information

Kind regards,

Stavros

Stavros Vaionitis · replied to J.Hilk on 12 Aug 2022, 07:36

Hi @J-Hilk,

thanks for your reply and your suggestions. I was looking the Qwt myself yesterday and I used it, as you suggested, to create the charts as I wanted. Next following the function InitializeCharts() at my first comment but with the Qwt module/library now

#include <QwtPlot>
#include <QwtPlotScaleItem>

void InitializeCharts()
{
	// pan
	ui->gimbalPositionPanQwtPlot->setTitle("Pan Position");
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionPanQwtPlot->setAxisScale(QwtAxis::YLeft, -90.0, 90.0);
	ui->gimbalPositionPanQwtPlot->setAxisScale(QwtAxis::XBottom, -90.0, 90.0);

	QwtPlotScaleItem *panVerticalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::RightScale, 0.0);
	panVerticalAxisScale->attach(ui->gimbalPositionPanQwtPlot);
	QwtPlotScaleItem *panHorizontalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::BottomScale, 0.0);
	panHorizontalAxisScale->attach(ui->gimbalPositionPanQwtPlot);

	// tilt
	ui->gimbalPositionTiltQwtPlot->setTitle("Tilt Position");
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionTiltQwtPlot->setAxisScale(QwtAxis::YLeft, -90.0, 90.0);
	ui->gimbalPositionTiltQwtPlot->setAxisScale(QwtAxis::XBottom, 0.0, 90.0);

	QwtPlotScaleItem *tiltVerticalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::RightScale, 0.0);
	tiltVerticalAxisScale->attach(ui->gimbalPositionTiltQwtPlot);
	QwtPlotScaleItem *tiltHorizontalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::BottomScale, 0.0);
	tiltHorizontalAxisScale->attach(ui->gimbalPositionTiltQwtPlot);
}

The output would look like the following

which is close enough for me of what I wanted to achieve.

Thanks again @J-Hilk for your time replying to my issue.

Kind regards,

Stavros

J.Hilk · 11 Aug 2022, 08:55

@Stavros-Vaionitis

thats because QCharts only accepts a limited amount of alignments:

void QAbstractAxisPrivate::setAlignment(Qt::Alignment alignment)
{
    switch (alignment) {
    case Qt::AlignTop:
    case Qt::AlignBottom:
        m_orientation = Qt::Horizontal;
        break;
    case Qt::AlignLeft:
    case Qt::AlignRight:
        m_orientation = Qt::Vertical;
        break;
    default:
        qWarning("No alignment specified !");
        break;
    }
    m_alignment = alignment;
}

https://github.com/qt/qtcharts/blob/dev/src/charts/axis/qabstractaxis.cpp

Stavros Vaionitis · 8 Nov 2022, 09:43

@J-Hilk

Great thanks for your prompt reply and this info. So it seems that the alignment in the chart axis is actually orientation.

So I suppose there is no way to move the axis as I want using the QtCharts, is this correct?

J.Hilk · 8 Dec 2022, 05:56

@Stavros-Vaionitis said in Getting a `No alignment specified !` when setting alignment Qt::AlignCenter when adding axis using addAxis():

So I suppose there is no way to move the axis as I want using the QtCharts, is this correct?

not that I know of, but I'm by no means an expert in QtCharts 😅

going by this SO thread, Qwt seems to have this feature

Personally I wouldn't use QCharts for anything half way complex/custom. It is nice and easy when you want a graph for some data you have. But it's far from perfekt, and to my knowledge hasn't been actively worked on in years.

Stavros Vaionitis · replied to J.Hilk on 12 Aug 2022, 07:36

Hi @J-Hilk,

thanks for your reply and your suggestions. I was looking the Qwt myself yesterday and I used it, as you suggested, to create the charts as I wanted. Next following the function InitializeCharts() at my first comment but with the Qwt module/library now

#include <QwtPlot>
#include <QwtPlotScaleItem>

void InitializeCharts()
{
	// pan
	ui->gimbalPositionPanQwtPlot->setTitle("Pan Position");
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionPanQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionPanQwtPlot->setAxisScale(QwtAxis::YLeft, -90.0, 90.0);
	ui->gimbalPositionPanQwtPlot->setAxisScale(QwtAxis::XBottom, -90.0, 90.0);

	QwtPlotScaleItem *panVerticalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::RightScale, 0.0);
	panVerticalAxisScale->attach(ui->gimbalPositionPanQwtPlot);
	QwtPlotScaleItem *panHorizontalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::BottomScale, 0.0);
	panHorizontalAxisScale->attach(ui->gimbalPositionPanQwtPlot);

	// tilt
	ui->gimbalPositionTiltQwtPlot->setTitle("Tilt Position");
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::YLeft, false);
	ui->gimbalPositionTiltQwtPlot->enableAxis(QwtAxis::XBottom, false);
	ui->gimbalPositionTiltQwtPlot->setAxisScale(QwtAxis::YLeft, -90.0, 90.0);
	ui->gimbalPositionTiltQwtPlot->setAxisScale(QwtAxis::XBottom, 0.0, 90.0);

	QwtPlotScaleItem *tiltVerticalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::RightScale, 0.0);
	tiltVerticalAxisScale->attach(ui->gimbalPositionTiltQwtPlot);
	QwtPlotScaleItem *tiltHorizontalAxisScale = new QwtPlotScaleItem(QwtScaleDraw::BottomScale, 0.0);
	tiltHorizontalAxisScale->attach(ui->gimbalPositionTiltQwtPlot);
}

The output would look like the following

which is close enough for me of what I wanted to achieve.

Thanks again @J-Hilk for your time replying to my issue.

Kind regards,

Stavros