void test() {

  TH1F * hALL = new TH1F("hALL","hALL",100,-3,3);
  //TFile f("test.root","READ") ;
  hALL->FillRandom("gaus",1000);
  TCanvas * c1 = new TCanvas("c1");
  hALL->Draw();
  c1->Update();
  c1->AddExec("test","exectest()");
  
}

void exectest(){
  
  int event = gPad->GetEvent();
  float iix = gPad->GetEventX();
  float iiy = gPad->GetEventY();
  float roix = gPad->AbsPixeltoX(iix);
  float roiy = gPad->AbsPixeltoY(iiy);
    
  if (event == 1){ //button down
    
    TMarker *m = new TMarker(roix, roiy, 800) ;
    m->SetMarkerStyle(3);
    m->SetMarkerColor(2);
    
    m->Draw("SAME");
    
  
  }
  
}