QT QML realtime chart

vicky_mac

Hi this my code which is working file. It takes data from C++ "valfromCpluplus" and plot on the chart.

My concern is whether this approach is fine or not. Because my application may be running for days and increment of "yval" and "scrolleft()" is bothering me.

Because after sometime yval and scrolleft will reach their max limit and then there may be unknown situations in the application.

I want to maintain the history of around 200 updates on chart and new entry will remove the oldest and the hart will be kept on scrolling with new values.

import QtQuick 2.0
import QtCharts 2.0

Item {
    anchors.fill: parent

    property int valfromCplusplus: 0
    propery LineSeries series: NULL 
    property int yval:0
   Text{
       id:txt
      text: valfromCplusplus

     onTextChanged{
                    yval++;
                    chart.series(0).append(valfromCplusplus,yval);
                   if(yval >200)
                    {
                      chart.series(0).remove();
                      chart.scrolleft(1);
                    }
           }
}


    ChartView {
        title: chart
        anchors.fill: parent
        legend.visible: false
        antialiasing: true

        ValueAxis {
            id: axisX

        }

        ValueAxis {
            id: axisY

        }

component.onComplete{
series = chart.createSeries(ChartView.SeriesLineSeries, "Line", axisX, axisY);
}
 }

Please ignore if there is any mistake in the code because i have running code similar to this. Please consider it as a pseudo code(algo) and suggest some suitable solution how i can achieve the intended goal without uncertainties.

@SGaist @jsulm

Bob64

I think this looks OK in principle. I have a dynamically updating chart in my application and I update the x-axis range rather than using scroll left. I don't know is better or worse for any reason.

vicky_mac

@Bob64 I am worried about yval and scrolleft() values.If i keep it on for days , yval will teacher to max value of int and may rollover similar with scrolleft . Will that not be a problem?

J.Hilk

@vicky_mac the highest number int can become in qml is 2^31 - 1 aka 2147483647, if you increment your int every second, you will have an integer overflow after roughly 68 years.

so I think you will be fine.

vicky_mac

@J-Hilk
Ok that's enough I think.

One more question what will happen to scrolleft().

If I keep on incrementing these, will there be any increase in runtime memory or processor load?