hist028_THStack_multicolor.C

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/// \file
/// \ingroup tutorial_hist
/// \notebook
/// \preview Use a THStack to show a 2-D hist with cells with different colors.
/// ~~~{.cpp}
///  root > .x multicolor.C
///  root > .x multicolor.C(1)
/// ~~~
/// \macro_image
/// \macro_code
///
/// \date August 2016
/// \author Rene Brun
 
#include "TCanvas.h"
#include "TH2.h"
#include "THStack.h"
#include "TRandom.h"
 
void hist028_THStack_multicolor(Int_t isStack = 0)
{
   TCanvas *c1 = new TCanvas;
   Int_t nbins = 20;
   TH2F *h1 = new TH2F("h1", "h1", nbins, -4, 4, nbins, -4, 4);
   h1->SetFillColor(kBlue);
   TH2F *h2 = new TH2F("h2", "h2", nbins, -4, 4, nbins, -4, 4);
   h2->SetFillColor(kRed);
   TH2F *h3 = new TH2F("h3", "h3", nbins, -4, 4, nbins, -4, 4);
   h3->SetFillColor(kYellow);
   THStack *hs = new THStack("hs", "three plots");
   hs->Add(h1);
   hs->Add(h2);
   hs->Add(h3);
   TRandom r;
   Int_t i;
   for (i = 0; i < 20000; i++)
      h1->Fill(r.Gaus(), r.Gaus());
   for (i = 0; i < 200; i++) {
      Int_t ix = (Int_t)r.Uniform(0, nbins);
      Int_t iy = (Int_t)r.Uniform(0, nbins);
      Int_t bin = h1->GetBin(ix, iy);
      Double_t val = h1->GetBinContent(bin);
      if (val <= 0)
         continue;
      if (!isStack)
         h1->SetBinContent(bin, 0);
      if (r.Rndm() > 0.5) {
         if (!isStack)
            h2->SetBinContent(bin, 0);
         h3->SetBinContent(bin, val);
      } else {
         if (!isStack)
            h3->SetBinContent(bin, 0);
         h2->SetBinContent(bin, val);
      }
   }
   hs->Draw("lego1");
}