Macro working in root 5 does not work in root 6

ROOT
2

Try:

void show_quad(const char *filename0,
               const char *filename1,
               const char *filename2,
               const char *filename3)
{
  gROOT->cd();
  delete gROOT->FindObject("hs"); // prevent "memory leak"
  TH2F *hs = new TH2F("hs", ";X;Y", 512, -0.5, 511.5, 512, -0.5, 511.5);
  hs->SetStats(kFALSE);
  hs->Print();
  
  TFile *f;
  TTree *t;
  
  f = TFile::Open(filename0);
  f->GetObject("rawtree", t);
  gROOT->cd();
  t->Draw("511-Row:255-Col>>hs", "", "goff");
  delete f;
  hs->Print();
  
  f = TFile::Open(filename1);
  f->GetObject("rawtree", t);
  gROOT->cd();
  t->Draw("Row:Col>>+hs", "", "goff");
  delete f;
  hs->Print();
  
  f = TFile::Open(filename2);
  f->GetObject("rawtree", t);
  gROOT->cd();
  t->Draw("Row:Col+256>>+hs", "", "goff");
  delete f;
  hs->Print();
  
  f = TFile::Open(filename3);
  f->GetObject("rawtree", t);
  gROOT->cd();
  t->Draw("511-Row:511-Col>>+hs", "", "goff");
  delete f;
  hs->Print();
  
  TCanvas *c1 = ((TCanvas *)(gROOT->GetListOfCanvases()->FindObject("c1")));
  if (!c1) c1 = new TCanvas("c1", "c1", 800, 800);
  else c1->Clear();
  
  // gStyle->SetOptStat("");
  hs->Draw("colz");
}