TFitSeries issues with TUserDefinedChartSource
lazarus / 55-TAChart

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wp · 2012-08-05 21:49

While preparing a new tutorial I came across a situation that a
TFitSeries getting its data from a UserDefinedChartSource tries to
redraw before the fit is performed. As a consequence, the
DrawFuncHelper crashes becauses of the NaNs produced along the way.

A workaround would be to exit the Draw method if the fit had not yet
beein performed or was not successful.

The new TFitSeries.Draw method, therefore, should be like this:
Code: [Select]procedure TFitSeries.Draw(ADrawer: IChartDrawer);
var
  de : TIntervalList;
begin
  if IsEmpty or (not FValidFitParams) then exit;  // wp: added
FValidFitParams

  ADrawer.Pen := Pen;
  de := PrepareIntervals;
  try
    with TDrawFuncHelper.Create(Self, de, @Calculate, Step) do
      try
        DrawFunction(ADrawer);
      finally
        Free;
      end;
  finally
    de.Free;
  end;
end;

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Ask · 2012-08-06 13:02

Applied in r38179.
A couple of notes:
NaNs should not crash drawing of function series, I already know of
the problem, but did not fix it yet -- this will be rather complex.
Anyway, even without crash, this change would be an optimization, so
it is good.I suspect that you forgot to call Reset to notify the chart
about changes in the source. I have added a note about it to the
documentation.

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wp · 2012-08-06 21:13

Thank you.

QuoteNaNs should not crash drawing of function series
The fit series had crashed in TDrawFuncHelper.CalcAt after FCalc(AXa)
(calling TFitFunction.Calculate) returned a NaN because the fit had
not yet been done.

QuoteI suspect that you forgot to call Reset
Good guess, yes I did not call Reset. After calling Reset, the project
runs fine, even without yesterday's patch.