TCanvas *c1 = NULL;
const UInt_t kNPMT = 5;
void example(Bool_t draw_text=kTRUE)
{
  Double_t **pos = new Double_t*[kNPMT];
  for( UInt_t i = 0; i < kNPMT; i++ )
    pos[i] = new Double_t[3];

  delete c1;
  c1 = new TCanvas( "c1", "PMT layout", 10, 10, 700, 700 );
  Double_t rmax = 1;
  TH1F *frame = gPad->DrawFrame( -rmax, -rmax, rmax, rmax );

  TText *txt;
  if( draw_text )
    txt = new TText( 0, 0, "" );
  for( UInt_t i = 0; i < kNPMT; i++ )
    {
      if( draw_text )
        {
          TString s( "" );
          s += i;
          txt->DrawText( pos[i][0], pos[i][1], s );
        }
    }
  c1->Modified();
  c1->Update();

  for( UInt_t i = 0; i < kNPMT; i++ )
    delete [] pos[i];
  delete [] pos;
}