TAChart Plot while execution not terminated
lazarus / 55-TAChart

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Jones · 2022-03-30 08:22

Hi,
I have a TAChart that displays the evolution in time of the pressure
of different gas filled tanks that are filled or emptied.
The calculation can take up to 5 minutes, so instead of only showing
the graph at the end of the execution of the program, I want to plot
'live'. Basically, I want to plot every point in time, at the moment
it is calculated. In this way, the graph is being plotted gradually
along the X-axis. Is this possible with TAChart and how should I do
this?
Thanks!

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wp · 2022-03-30 09:50

Simply AddXY the new data point to the series when it is available,
and the chart will grow automatically.

Here is a simple example requiring a chart, a lineseries and a button
(and add a boolean variable FRunning to the form):
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
TForm1.Button1Click(Sender: TObject);const  SECONDS_PER_DAY = 24 * 60
* 60;var  t, t0, p: Double;begin  if FRunning then begin    FRunning
:= false;    Button1.Caption := 'Start';  end else  begin   
Button1.Caption := 'Stop';    FRunning := true;   
Chart1LineSeries1.Clear;    t0 := Now;    while FRunning do begin    
t := (Now - t0) * SECONDS_PER_DAY;  // Elapsed time in seconds     
Sleep(2000);                        // Simulates a lengthy
calculation      p := 1000 * exp(-t/60);     
Chart1LineSeries1.AddXY(t, p);      Application.ProcessMessages;   
end;  end;end;

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Jones · 2022-03-31 15:52

Thanks!
it was actually just Application.ProcessMessages; that was missing.
Do you think this will increase execution time?

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wp · 2022-03-31 16:10

It depends on how often you call it and how long each loop cycle
takes. In my sample code, which simulated some lengthy calculation of
2 seconds by a Sleep command you certainly will not notice any delay.
But when each calculation takes only a fraction of a millisecond you
will notice it severely. The delay will not be due to the
Application.processmessages itself, but due to repainting of the chart
with every cycle.

But I should tell you also that if you have a long calculation time
per cycle you generally have a very poor usability of your application
which mostly is not responsive. Rather than calling
Application.ProcessMessages, it would be much better to put the
calculation into a separate thread (look for TThread).