# illustrates how to make an animated gif file and view it

    {
    //
    // This script is a slightly modified version of hsum.C
    // It produces an animated gif file. See comments below

      gROOT->Reset();

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

      gBenchmark->Start("hsum");

    // Create some histograms.
      total  = new TH1F("total","This is the total distribution",100,-4,4);
      main   = new TH1F("main","Main contributor",100,-4,4);
      s1     = new TH1F("s1","This is the first signal",100,-4,4);
      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;

    // Fill histograms randomly
      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();
            char gif[24];
            sprintf(gif, "hsumanim_%.3d.gif", gifcnt++);
            c1->SaveAs(gif);
         }
      }
      slider->SetRange(0,1);
      total->Draw("sameaxis"); // to redraw axis hidden by the fill area
      c1->Modified();
      c1->SaveAs("hsumanim_019.gif");

      //make an animated gif file using gifsicle.
      //for information about gifsicle, see http://www.lcdf.org/~eddietwo/gifsicle/
      gSystem->Exec("gifsicle --delay=10 --loop=5 hsum*.gif > anim.gif");
      gSystem->Exec("rm -f hsum*.gif");

      //You can view the animated file anim.gif with Netscape/IE
      //or with gifview as shown below (finish by typing "q" in the window)
      //for more info about gifsicle, gifview, see above url or do
      // gifsicle --help     gifview --help
      gSystem->Exec("gifview -a anim.gif");

      gBenchmark->Show("hsum");
    }