TCutG

Class Description

                                                                      
 TCutG                                                                
                                                                      
  A Graphical cut.                                                    
  A TCutG object defines a closed polygon in a x,y plot.              
  It can be created via the graphics editor option "CutG"             
  or directly by invoking its constructor.                            
  To create a TCutG via the graphics editor, use the left button      
  to select the points building the contour of the cut. Click on      
  the right button to close the TCutG.                                
  When it is created via the graphics editor, the TCutG object        
  is named "CUTG". It is recommended to immediatly change the name    
  by using the context menu item "SetName".                           //                                                                      
   When the graphics editor is used, the names of the variables X,Y   
   are automatically taken from the current pad title.                
  Example:                                                            
  Assume a TTree object T and:                                        
     Root > T.Draw("abs(fMomemtum)%fEtot")                            
  the TCutG members fVarX, fVary will be set to:                      
     fVarx = fEtot                                                    
     fVary = abs(fMomemtum)                                           
                                                                      
  A graphical cut can be used in a TTree selection expression:        
    Root > T.Draw("fEtot","cutg1")                                    
    where "cutg1" is the name of an existing graphical cut.           
                                                                      
  Note that, as shown in the example above, a graphical cut may be    
  used in a selection expression when drawing TTrees expressions      
  of 1-d, 2-d or 3-dimensions.                                        
  The expressions used in TTree::Draw can reference the variables     
  in the fVarX, fVarY of the graphical cut plus other variables.      
                                                                      
  When the TCutG object is created, it is added to the list of special
  objects in the main TROOT object pointed by gROOT. To retrieve a    
  pointer to this object from the code or command line, do:           
      TCutG *mycutg;                                                  
      mycutg = (TCutG*)gROOT->GetListOfSpecials()->FindObject("CUTG") 
      mycutg->SetName("mycutg");                                      
                                                                      
  Example of use of a TCutG in TTree::Draw:                           
       tree.Draw("x:y","mycutg && z>0 %% sqrt(x)>1")                  
                                                                      
  A Graphical cut may be drawn via TGraph::Draw.                      
  It can be edited like a normal TGraph.                              
                                                                      
  A Graphical cut may be saved to a file via TCutG::Write.            //