why extra lines appear here by QCharts

[mr.five]

hello,i have used the QChats to draw one line,but when i finish,there are some extra line appeared,could you tell me why these lines here ,thank you so much

void createCharts()
{
    QChart *fenshiChart = new QChart();
    fenshiChart->setBackgroundBrush(QBrush(Qt::black));
    fenshiChart->legend()->setVisible(false);
    fenshiChart->setMargins(QMargins(0,0,0,0));
    fenshiChart->layout()->setContentsMargins(0,0,0,0);
    fenshiChart->setBackgroundRoundness(0);

    ui->fenshiLineChart->setChart(fenshiChart);
    ui->fenshiLineChart->setRenderHint(QPainter::Antialiasing);
    ui->fenshiLineChart->setContentsMargins(QMargins(0,0,0,0));

    QLineSeries *series0 = new QLineSeries();

    QPen pen;
    pen.setStyle(Qt::SolidLine);
    pen.setWidth(1);
    pen.setColor(Qt::white);
    series0->setPen(pen);
    fenshiChart->addSeries(series0);

    pen.setWidth(1);
    pen.setColor(QColor(176,0,0));
    QValueAxis *axisX = new QValueAxis;
    axisX->setLabelsVisible(false);
    axisX->setRange(1,240);
    axisX->setTickCount(5);
    axisX->setLinePen(pen);
    axisX->setGridLinePen(pen);
    axisX->setMinorTickCount(1);
    axisX->setShadesVisible(false);
    QValueAxis *axisY = new QValueAxis;
    axisY->setTickCount(27);
    axisY->setLinePen(pen);
    axisY->setGridLinePen(pen);
    axisY->setLabelsColor(Qt::white);
    axisY->setLabelFormat("%.2f");
    pen.setStyle(Qt::DotLine);
    axisX->setMinorGridLinePen(pen);

    fenshiChart->addAxis(axisX,Qt::AlignBottom);
    fenshiChart->addAxis(axisY,Qt::AlignLeft);
    series0->attachAxis(axisX);
    series0->attachAxis(axisY);
}

void addData()
{
    //data
    int itemNumInt = itemNum;
    QLineSeries *series0 = (QLineSeries *)ui->fenshiLineChart->chart()->series().at(0);
    series0->clear();
    qreal index = 0;
    for (int i=0;i<itemNumInt;i++)
    {
        if((time[i]>=93000 && time[i]<113000) || (time[i]>130000 && time[i]<=150000))
        {
            index += 1;
            points.append(QPointF(index,QString::asprintf("%.2f",hstTodayClose[index-1]/100.00).toDouble()));
        }
    }
    series0->append(points);
}

[JoeCFD]

there could be junk data in the input. Add them one after another and you may be able to find out which ones are junk.

[mr.five]

@JoeCFD thank you ,i have checked ,all points data are normal ,there is no junk

[mchinand]

What if you exclude the number->QString formatting->number step when you are appending your points. Do you still get these artifacts?

[mr.five]

@mchinand thank you ,i know that is not a good method to do so , but i need the required precision ,so have any other better method to take place? in the other hand, i have exclude that ,but there is still have the extra line on the graph , alas~~~

[mchinand]

I think the preferred way to do that formatting (format to two decimal places) is:

QString::number(hstTodayClose[index-1]/100.00, 'f', 2).toDouble();

There's nothing weird with your indexing of time[] with i and hstTodayClose[] with index? This depends on how those arrays are populated, so could be correct.

[mchinand]

Also, where is points defined and initialized? Perhaps try clearing that at the start of addData()

[mr.five]

@mchinand ```
QString::number(hstTodayClose[index-1]/100.00, 'f', 2).toDouble();

this method i have used, but  it  loss precision when i debug out the number.    the points was initialized like this:```
QList<QPointF> points={};

and i tried to add points.clear() ,but it seems like have no help on the grap ,the extra lines are still there.

[JonB]

@mr-five

• Check @mchinand's comment: if points is not empty (left over from before?) you would "jump back" to x == 0, could make it look screwy.
• Verify how it looks using just all points as QPointF(index, index) instead. Should be diagonal line. Any artefacts?
• Verify the length of hstTodayClose, is [index-1] always within bounds?
• Binary chop the number of points you plot, do the artefacts still appear? Keep chopping in half.
• To pass a floating point number of 2 decimal places you shouldn't need to convert to a string and then back to a number. Something like int(num * 100 + 0.5) / 100.0 should work.

[mr.five]

@JonB thank you.

1. the points is empty when i used points.clear() before add data, but it is not works
   2.it is not diagonal line, like this ,and i do not know why?
   
   

[JonB]

@mr-five
Looks like two separate diagonal lines. Does your x value change from positive to negative?? What is the range of your index variable? Make it int index instead of qreal, any difference? Only print the first 50% of all the points, do you then get just the left-hand line?

[mr.five]

@JonB

i found one probable cause is that i forgot to initialize the range of the Y axis, and after i do so:

ui->fenshiLineChart->chart()->axes(Qt::Vertical).at(0)->setRange(todayLow[itemNum-1],todayHigh[itemNum-1]);

the graph only leave one extra line like this,and i do not know the reason again,thank you

[JonB]

@mr-five
It looks like that would be produced if you somehow have an extra (0, 0) at the end of the series?

[mr.five]

@JonB @JoeCFD @mchinand thank you all! i have found the reason,the axis count not suit my series count,if some missed ,there will have extra lines