geomTest(){
  gSystem->Load("libGeom");

  TGeoManager *mgr = new TGeoManager("test","test");

  TGeoVolume *top=mgr->MakeBox("World",0,100.,100.,100.);
  mgr->SetTopVolume(top);

  TGeoVolume *tube1=mgr->MakeTube("Tube1",0,10.,20.,20.);
  tube1->SetLineColor(kBlue);

  TGeoVolume *tube2=mgr->MakeTube("Tube2",0,30.,40.,40.);
  tube2->SetLineColor(kRed);

  top->AddNode(tube1,1);
  top->AddNode(tube2,2);


  mgr->CloseGeometry();


  top->Draw("ogl");

  TGLViewer * v = (TGLViewer *)gPad->GetViewer3D();
  v->GetClipSet()->SetClipType(1);
  v->RefreshPadEditor(v);
  Double_t clipdata[4]={-1.,0.,0.,-.1};
  v->GetClipSet()->SetClipState(1, clipdata);

}