auto c1 = new TCanvas("c1","The HSUM example",200,10,600,400);
c1->SetGrid();

gBenchmark->Start("hsum");

auto total  = new TH1F("total","This is the total distribution",100,-4,4);
auto main   = new TH1F("main","Main contributor",100,-4,4);
auto s1     = new TH1F("s1","This is the first signal",100,-4,4);
auto s2     = new TH1F("s2","This is the second signal",100,-4,4);
total->Sumw2();   // this makes sure that the sum of squares of weights will be stored
total->SetMarkerStyle(21);
total->SetMarkerSize(0.7);
main->SetFillColor(16);
s1->SetFillColor(42);
s2->SetFillColor(46);
TSlider *slider = 0;
gSystem->Unlink("hsumanim.gif"); // delete old file

gRandom->SetSeed();
const Int_t kUPDATE = 500;
Float_t xs1, xs2, xmain;
Int_t gifcnt = 0;
for ( Int_t i=0; i<10000; i++) {
   xmain = gRandom->Gaus(-1,1.5);
   xs1   = gRandom->Gaus(-0.5,0.5);
   xs2   = gRandom->Landau(1,0.15);
   main->Fill(xmain);
   s1->Fill(xs1,0.3);
   s2->Fill(xs2,0.2);
   total->Fill(xmain);
   total->Fill(xs1,0.3);
   total->Fill(xs2,0.2);
   if (i && (i%kUPDATE) == 0) {
      if (i == kUPDATE) {
         total->Draw("e1p");
         main->Draw("same");
         s1->Draw("same");
         s2->Draw("same");
         c1->Update();
         slider = new TSlider("slider","test",4.2,0,4.6,total->GetMaximum(),38);
         slider->SetFillColor(46);
      }
      if (slider) slider->SetRange(0,Float_t(i)/10000.);
      c1->Modified();
      c1->Update();
      if (gROOT->IsBatch()) {
         // c1->Print("hsumanim.gif+");
         printf("i = %d\n", i);
      } else {
         if (gSystem->ProcessEvents())
            break;
      }
   }
}
slider->SetRange(0,1);
total->Draw("sameaxis"); // to redraw axis hidden by the fill area
c1->Modified();

gBenchmark->Show("hsum");

gROOT->GetListOfCanvases()->Draw()