Legend: fit curve entry and transparency

[arilo]

Dear all,
This is a legend question.

Q1: how to make the legend fill opaque, in a way the plot details (e.g., lines) on which it sits are not visible. I tried different colors, including white, but the legend fill is always transparent.

Q2: how to add a legend entry for the fit curve/line that is returned by FitFunction.cpp in the pseudo code below.

Main.cpp

   TH1* h1 = new TH1I("h1", "histo", 100, 0.0, 5.0);
   double xmin = 0.1;
   double xmax= 4.5;
   h1->Draw();
   PolFit(h1, polinom, xmin, xmax);
   TLegend *legend = new TLegend(0.1, 0.7, 0.5, 0.9);
   legend->SetFillColor(0);
   legend->AddEntry("h1", "hist", "l");
  // ideal: legend->AddEntry("fitted h1", "fit", "l")
   legend->Draw();
   

FunctionFit.cpp

double polinom(double *x, double *par) {
      return par[0] + par[1]*x[0] + par[2]*x[0]*x[0];
   }

  double PolFit(TH1* hist, double x_low, double x_up){
   TF1 *fitFunction = new TF1("fitFunction", polinom, x_low, x_up, 3);
   hist->Fit("fitFunction");
}

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[Wile_E_Coyote]

A1: The legend should be “opaque” by default, i.e. unless you make it “hollow”, e.g. using somewhere something like “SetFillStyle(0)”.

A2: legend->AddEntry("fitFunction", "fitted h1", "l");

BTW. Before you try to “Fit” your histogram, you should set some “reasonable” initial values for all parameters of your function.

[arilo]

Thanks so much @Wile_E_Coyote.

For A1: I couldn’t find -explicitly- anything that SetFillStyle(0). Is there a way I can set the background to opaque?

[Wile_E_Coyote]

It’s not about the “background”, it’s about the “legend”.

Make sure that the “legend” is drawn as the last one, i.e. that you do not have any histo->Draw("same") later.

[arilo]

Thank you very much! Drawing the legend last worked.