doc/v606/FirstContour_8C.html

void FirstContour()

{

   TString dir = gSystem->UnixPathName(__FILE__);

   dir.ReplaceAll("FirstContour.C","../hsimple.C");

   dir.ReplaceAll("/./","/");

   if (!gInterpreter->IsLoaded(dir.Data())) gInterpreter->LoadMacro(dir.Data());

   TFile *file = (TFile*)gROOT->ProcessLineFast("hsimple(1)");

   if (!file) return;

   TTree *ntuple = (TTree*)file->Get("ntuple");


   TCanvas *c1 = new TCanvas("c1","Contours",10,10,800,600);

   gStyle->SetPalette(1);

   ntuple->Draw("py:px","px*px+py*py < 20", "contz,list");


   //we must call Update to force the canvas to be painted.  When

   //painting the contour plot, the list of contours is generated

   //and a reference to it added to the Root list of special objects

   c1->Update();


   TCanvas *c2 = new TCanvas("c2","First contour",100,100,800,600);


   TObjArray *contours =

      (TObjArray*)gROOT->GetListOfSpecials()->FindObject("contours");

   if (!contours) return;

   TList *lcontour1 = (TList*)contours->At(0);

   if (!lcontour1) return;

   TGraph *gc1 = (TGraph*)lcontour1->First();

   if (!gc1) return;

   if (gc1->GetN() < 10) return;

   gc1->SetMarkerStyle(21);

   gc1->Draw("alp");


   //We make a TCutG object with the array obtained from this graph

   TCutG *cutg = new TCutG("cutg",gc1->GetN(),gc1->GetX(),gc1->GetY());


   //We create a polymarker object with npmax points.

   const Int_t npmax = 50000;

   TPolyMarker *pm = new TPolyMarker(npmax);

   Int_t np = 0;

   while(1) {

      Double_t x = -4 +8*gRandom->Rndm();

      Double_t y = -4 +8*gRandom->Rndm();

      if (cutg->IsInside(x,y)) {

         pm->SetPoint(np,x,y);

         np++;

         if (np == npmax) break;

      }

   }

   pm->Draw();

}