Re: (2) painting an object derived from TH1

From: Rene Brun (Rene.Brun@cern.ch)
Date: Thu Oct 21 1999 - 23:33:24 MEST


Hi Victor,
You do not need to reimplement a complete painter.
Simply derive your painter from the existing painter
and redefine only one or a few functions.
In a separate mail from Fons (that did not reach roottalk), he says:
>  we clearly did not describe clearly enough how to derive from 
 > TVirtualHistPainter or from THistPainter and how to make your new
> painter the default painter.
 > 
 > Assume you want to modify the existing default THistPainter:
 > 
 > - class TMyHistPainter : public THistPainter { ... };
 >   override only the few paint methods you want to change
 > 
 > - compile into a shared lib libMyHistPainter.so
 > 
 > - in rootlogon.C add the following:
 > 
> >   // make sure the base class is loaded
> >   gROOT->LoadClass("THistPainter","HistPainter");
> >   gROOT->LoadClass("TMyHistPainter", MyHistPainter");
> >   TVirtualHistPainter::SetPainter("TMyHistPainter");
> > 
> > - from now on all histograms will be painted using the new
TMyHistPainter.
> > 

Rene Brun


On Thu, 21 Oct 1999, Victor Perevoztchikov wrote:

> Hi Rene,
> 
> > Once this is called (once per job), TH1::Paint will automatically
> > invoke your painter.
> 
> no, it is good only if user does not want standard Painter at all.
> But usually standard painter is good enough, but for very special
> histograms, user wants provide modified painter do NOT AFFECTING all others histograms.
> For this case method SetPainter() is very usefull and safe.
> And it is very easy to implement, just 3 lines of code and no more discussion
> 
> Victor
> 
> 
> Rene Brun wrote:
> > 
> > Hi Victor, Damir,
> > There is no need for TH1::SetPainter
> > You can directly use the static function
> >   TVirtualHistPainter::SetPainter(const char* myPainterClassname)
> > Once this is called (once per job), TH1::Paint will automatically
> > invoke your painter.
> > Note that each histogram has its own painter instance in such a way
> > that the system can work in a multithreaded environment.
> > 
> > Rene Brun
> > 
> > On Thu, 21 Oct 1999, Victor Perevoztchikov wrote:
> > 
> > >   Hi Damir,
> > > in new TH1 class no method SetPainter(TVirtualHistPainter *userPainter);
> > > If Rene & Fons will add it, then you can create your painter
> > > object derived from TVirtualHistPainter and set it to histogram.
> > >
> > > As a temporary solution you can use the following "barbaric" function
> > > to add your method to histogram. When rene will add SetPainter to TH1
> > > then you can remove it.
> > >
> > > void SetPainter(TH1 *h,TVirtualHistPainter *p)
> > > {
> > >   TVirtualHistPainter **s =   (TVirtualHistPainter **)((int*)h+117);
> > >   p->SetHistogram(h);
> > >   *s = p;
> > > }
> > >
> > > Victor
> > >
> > > "Valeri Fine (Faine)" wrote:
> > > >
> > > > ----- Original Message -----
> > > > From: Valeri Fine (Faine) <fine@bnl.gov>
> > > > To: Damir Buskulic <buskulic@lapp.in2p3.fr>; ROOT mailing list <roottalk@hpsalo.cern.ch>
> > > > Subject: Re: painting an object derived from TH1
> > > >
> > > > ----- Original Message -----
> > > > From: Damir Buskulic <buskulic@lapp.in2p3.fr>
> > > > To: ROOT mailing list <roottalk@hpsalo.cern.ch>
> > > > Subject: painting an object derived from TH1
> > > >
> > > > > Hi,
> > > > >
> > > > > with the new library scheme of ROOT, the Painter and Hist are separated.
> > > > > I have a class that derives from TH1F, but I would like to paint some
> > > > > parts differently, namely the stat box. Before, I was just overloading
> > > > > the TH1::PaintStats method.
> > > > > How can I do it now ? Do I have to specify a completely different
> > > > > painter that I have to rewrite ? I looked a little bit at the code and
> > > > > found that the static member fgPainter was holding the class description
> > > > > of the current Painter. Since it is static, I cannot change it without
> > > > > changing also the painter for regular TH1.
> > > > > I suppose I'll just put regular stats off and overlay my own stat box.
> > > > >
> > > > > Any other ideas ?
> > > >
> > > > I missed one essential point, one has to add
> > > >                 fPainter->StHistogram(this) ;
> > > > statement to get:
> > > >
> > > >
> > > > class  TMyHist : public TH1 {
> > > >   public:
> > > >     TVirtualHistPainter * Painter(TVirtualHistPainter *myPainter) {
> > > >       TVirtualHistPainter * old = fPainter;
> > > >       fPainter  = myPainter;
> > > >       if (fPainter) fPainter->SetHistogram(this) ;
> > > >       return old;
> > > >     }
> > > > }
> > > >
> > > >   Afterwards you can define your own painter and attach it to your particular
> > > > histogram. This way you may use either standard or your own Painter with each
> > > > other Update step or for different TPads.
> > > >
> > > >  Another solution:
> > > >
> > > > class  TMyHist : public TH1 {
> > > >   public:
> > > >     TVirtualHistPainter * Painter(TVirtualHistPainter *myPainter) {
> > > >        delete fPainter; fPainter = 0;
> > > >       if (myPainter) {
> > > >         fPainter  = myPainter;
> > > >         fPainter->SetHistogram(this) ;
> > > >      }
> > > >       return fPainter  ;
> > > >     }
> > > > }
> > > >
> > > >                          Valery
> > >
> > > --
> > > Victor M. Perevoztchikov   perev@bnl.gov  perev@vxcern.cern.ch
> > > Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
> > > tel office : 516-344-7894; fax 516-344-4206; home 516-345-2690
> > >
> 
> -- 
> Victor M. Perevoztchikov   perev@bnl.gov  perev@vxcern.cern.ch       
> Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000
> tel office : 516-344-7894; fax 516-344-4206; home 516-345-2690
> 



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