FirstContour.C
void FirstContour()
{
//this macro generates a color contour plot by selecting entries
//from an ntuple file.
//The TGraph object corresponding to the first contour line is
//accessed and displayed into a separate canvas.
//Author: Rene Brun
TString dir = gSystem->UnixPathName(TCint::GetCurrentMacroName());
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");
TList *lcontour1 = (TList*)contours->At(0);
TGraph *gc1 = (TGraph*)lcontour1->First();
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();
}
//--------------end of script contours.C