Drawing Histograms in Canvas

From: Anton Fokin (kosu_fokin@garbo.lucas.lu.se)
Date: Mon Mar 29 1999 - 23:15:40 MEST 

Hi rooters,

Having in mind that one should not call Draw() in a loop; for an object in
a canvas (because TPad adds poiter to an object every time one calls
Draw()), I find this example a little bit strange (taken from Consumer
example) :

   Int_t oldentries = 0;
   while (1) {
      hpx    = (TH1F *) mfile->Get("hpx", hpx);
      hpxpy  = (TH2F *) mfile->Get("hpxpy", hpxpy);
      hprof  = (TProfile *) mfile->Get("hprof", hprof);
      if (hpx->GetEntries() == oldentries) break;
      oldentries = hpx->GetEntries();
      if (!gROOT->IsBatch()) {
         pad1->cd();
         hpx->Draw();
         pad2->cd();
         hprof->Draw();
         pad3->cd();
         hpxpy->Draw("cont");
         c1->Modified();
         c1->Update();
      } else {
         printf("Entries, hpx=%d, Mean=%g,
RMS=%g\n",hpx->GetEntries(),hpx->GetMean(),hpx->GetRMS());
      }
      gSystem->Sleep(100);   // sleep for 0.1 seconds
   }


Of course every time we call TMapFile.Get(); we get a new object, but then
what about multiple Draw(); calls for the same TPad(); ? Is it ok, or can
we avoid it somehow?

Best regards,

Dr. Anton Fokin

Division of Cosmic and Subatomic Physics
Lund University
Sweden

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