TH1::Draw() fill patterns when histo has negative entries

ROOT
1

I have histograms that have positive and negative entries. If I supply a fill color and use TH1::Draw() - I get the top plot below. If I use TH1::Draw(“lf2”), I get the bottom plot. Is there a way to get a smooth outline (bottom plot) AND fill between zero and histogram contents (top plot)? Thanks…
Ed Oltman

fill.gif734×601 7.42 KB

2

Have you an example showing your problem ? here is one I derived from hsimple.C, and it does what you want.

{
// Create a new canvas.
  c1 = new TCanvas("c1","Dynamic Filling Example",200,10,700,500);
  c1->SetFillColor(42);
  c1->GetFrame()->SetFillColor(21);
  c1->GetFrame()->SetBorderSize(6);
  c1->GetFrame()->SetBorderMode(-1);

  hpx    = new TH1F("hpx","This is the px distribution",100,-4,4);
  hpx->SetFillColor(48);

// Fill histograms randomly
  gRandom->SetSeed();
  Float_t px, py, pz;
  const Int_t kUPDATE = 1000;
  for (Int_t i = 0; i < 25000; i++) {
     gRandom->Rannor(px,py);
     pz = px*px + py*py;
     Float_t random = gRandom->Rndm(1);
     if(px<0){
        hpx->Fill(px,-1);
     } else {
        hpx->Fill(px);
     }
     if (i && (i%kUPDATE) == 0) {
        if (i == kUPDATE) hpx->Draw("C");  
        c1->Modified();
        c1->Update();
        if (gSystem->ProcessEvents())
           break;
     }
  }
}
3

Yes, the Draw(“C”) does what I want - thanks!

Note: there is a slight bug - if you zoom to a region where the histogram value<0 (e.g. x<0 in your example), the fill extends above the frame limits.

Ed

PS - you asked if I had an example - can’t you see the attached .gif I included?

4

I will check the slight bug you mentionned.

Yes, I saw you plot but I was interrested in the macro which produced it. I could not make an example reproducing what you show on that plot.

5

Hi Ed,

[quote]
Note: there is a slight bug - if you zoom to a region where the histogram value<0 (e.g. x<0 in your example), the fill extends above the frame limits. [/quote]

This problem is now fixed.

Olivier