To add a graphics system implement 3 new classes:
 
  class G4XXX: public G4VGraphicsSystem
  class G4XXXSceneHandler: public G4VSceneHandler
  class G4XXXViewer: virtual public G4VViewer

Introduce two new environment variables G4VIS_BUILD_XXX_DRIVER and GG4VIS_USE_XXX and make the attached modifications to:

  source/visualization/management/include/MyVisManager.cc
  (similarly all examples vis managers)
  source/visualization/management/src/G4VisManager.cc
  config/G4VIS_BUILD.gmk
  config/G4VIS_USE.gmk

===================================================================
include/G4XXX.hh
===================================================================
#ifndef G4XXX_HH
#define G4XXX_HH

#include "G4VGraphicsSystem.hh"

class G4XXX: public G4VGraphicsSystem {
public:
  G4XXX ();
  virtual ~G4XXX ();
  G4VSceneHandler* CreateSceneHandler (const G4String& name = "");
  G4VViewer*  CreateViewer  (G4VSceneHandler&, const G4String& name = "");
};
#include "G4XXX.hh"
#include "G4XXXSceneHandler.hh"
#include "G4XXXViewer.hh"

#endif
===================================================================

===================================================================
include/G4XXXSceneHandler.hh
===================================================================
#ifndef G4XXXSCENEHANDLER_HH
#define G4XXXSCENEHANDLER_HH

#include "G4VSceneHandler.hh"
#include "G4Box.hh"
#include "G4Cons.hh"
#include "G4Tubs.hh"
#include "G4Trd.hh"
#include "G4Trap.hh"
#include "G4Sphere.hh"
#include "G4Para.hh"
#include "G4Torus.hh"
#include "G4Polycone.hh"
#include "G4Polyhedra.hh"

class G4VPhysicalVolume;
class G4LogicalVolume;

class G4XXXSceneHandler: public G4VSceneHandler {

public:
  G4XXXSceneHandler(G4VGraphicsSystem& system,
                      const G4String& name);
  virtual ~G4XXXSceneHandler ();
  void AddThis (const G4Box& s) {Dump (s);}
  void AddThis (const G4Cons & s) {Dump (s);}
  void AddThis (const G4Tubs& s) {Dump (s);}
  void AddThis (const G4Trd& s) {Dump (s);}
  void AddThis (const G4Trap& s) {Dump (s);}
  void AddThis (const G4Sphere& s) {Dump (s);}
  void AddThis (const G4Para& s) {Dump (s);}
  void AddThis (const G4Torus& s) {Dump (s);}
  void AddThis (const G4Polycone& s) {Dump (s);}
  void AddThis (const G4Polyhedra& s) {Dump (s);}
  void AddThis (const G4VSolid& s) {Dump (s);}
  void PreAddThis (const G4Transform3D& objectTransformation,
                   const G4VisAttributes&);
  void PostAddThis ();
  void EstablishSpecials (G4PhysicalVolumeModel&);
  G4int                GetFoundDepth          () const;
  G4VPhysicalVolume*   GetFoundVolume         () const;
  const G4Transform3D& GetFoundTransformation () const;

  ////////////////////////////////////////////////////////////////
  // Functions not used but required by the abstract interface.

  virtual void BeginPrimitives (const G4Transform3D& objectTransformation) {}
  virtual void EndPrimitives () {}
  virtual void AddPrimitive (const G4Polyline&)   {}
  virtual void AddPrimitive (const G4Text&)       {}
  virtual void AddPrimitive (const G4Circle&)     {}
  virtual void AddPrimitive (const G4Square&)     {}
  virtual void AddPrimitive (const G4Polymarker&) {}
  virtual void AddPrimitive (const G4Polyhedron&) {}
  virtual void AddPrimitive (const G4NURBS&)      {}

  static G4int GetSceneCount();

protected:
  void                 Dump (const G4VSolid&);
  static G4int         fSceneIdCount;  // Counter for Tree scene handlers.
  static G4int         fSceneCount;    // No. of extanct scene handlers.
  G4int                fCurrentDepth;  // Current depth of geom. hierarchy.
  G4VPhysicalVolume*   fpCurrentPV;    // Current physical volume.
  G4LogicalVolume*     fpCurrentLV;    // Current logical volume.
  const G4Transform3D* fpCurrentObjectTransformation;
};

#include "G4XXXSceneHandler.icc"

#endif
===================================================================

===================================================================
include/G4XXXViewer.hh
===================================================================
#ifndef G4XXXVIEWER_HH
#define G4XXXVIEWER_HH

#include "G4VViewer.hh"

class G4XXXViewer: virtual public G4VViewer {
public:
  G4XXXViewer(G4VSceneHandler&,const G4String& name);
  virtual ~G4XXXViewer();
  void SetView();
  void ClearView();
  void DrawView();
private:
  G4int fFileCount;
};

#endif
===================================================================

===================================================================
src/G4XXX.cc
===================================================================
G4XXX::G4XXX ():
  G4VGraphicsSystem ("Full Name",
                     "Nickname",
                     "A description - could run to many lines - "
                     "\n advantages, disadvantages, etc.",
                     G4VGraphicsSystem::<type>)  // See enum.
  {}

G4XXX::~G4XXX () {}

G4VSceneHandler* G4XXX::CreateSceneHandler (const G4String& name) {
  G4VSceneHandler* pScene = new G4XXXSceneHandler (*this, name);
  G4cout << G4XXXSceneHandler::GetSceneCount ()
         << ' ' << fName << " scene handlers extanct." << G4endl;
  return  pScene;
}

G4VViewer* G4XXX::CreateViewer (G4VSceneHandler& scene,
                                  const G4String& name) {
  G4VViewer* pView =
    new G4XXXViewer ((G4XXXSceneHandler&) scene, name);
  if (pView) {
    if (pView -> GetViewId () < 0) {
      G4cerr << "G4XXX::CreateViewer: error flagged by negative"
        " view id in G4XXXViewer creation."
        "\n Destroying view and returning null pointer."
           << G4endl;
      delete pView;
      pView = 0;
    }
  }
  else {
    G4cerr << "G4XXX::CreateViewer: null pointer on"
      " new G4XXXViewer." << G4endl;
  }
  return pView;
}
===================================================================

===================================================================
src/G4XXXSceneHandler.cc
===================================================================
#include "G4XXXSceneHandler.hh"

#include "G4VSolid.hh"
#include "G4PhysicalVolumeModel.hh"
#include "G4VPhysicalVolume.hh"
#include "G4LogicalVolume.hh"

G4int G4XXXSceneHandler::fSceneIdCount = 0;
// Counter for XXX scene handlers.

G4int G4XXXSceneHandler::fSceneCount = 0;
// No. of extanct scene handlers.

G4XXXSceneHandler::G4XXXSceneHandler(G4VGraphicsSystem& system,
                                         const G4String& name):
  G4VSceneHandler(system, fSceneIdCount++, name),
  fCurrentDepth                 (0),
  fpCurrentPV                   (0),
  fpCurrentLV                   (0),
  fpCurrentObjectTransformation (0)
{
  fSceneCount++;
}

G4XXXSceneHandler::~G4XXXSceneHandler () {}

void G4XXXSceneHandler::EstablishSpecials
(G4PhysicalVolumeModel& pvModel) {
  pvModel.DefinePointersToWorkingSpace (&fCurrentDepth,
                                        &fpCurrentPV,
                                        &fpCurrentLV);
}

void G4XXXSceneHandler::Dump (const G4VSolid& solid) {
  for (G4int i = 0; i < fCurrentDepth; i++ ) G4cout << "  ";
  G4cout << "\"" << fpCurrentPV -> GetName ()
         << "\", copy no. " << fpCurrentPV -> GetCopyNo ()
         << G4endl;
  return;
}
===================================================================

===================================================================
src/G4XXXViewer.cc
===================================================================
#include "G4XXXViewer.hh"

#include "G4ios.hh"
#include "g4std/strstream"

#include "G4VSceneHandler.hh"

G4XXXViewer::G4XXXViewer
(G4VSceneHandler& sceneHandler, const G4String& name):
  G4VViewer(sceneHandler, sceneHandler.IncrementViewCount(), name) {}

G4XXXViewer::~G4XXXViewer() {}

void G4XXXViewer::SetView() {}

void G4XXXViewer::ClearView() {}

void G4XXXViewer::DrawView() {
  NeedKernelVisit ();  // Always need to visit G4 kernel.
  ProcessView ();
}

===================================================================
Index: source/visualization/management/include/MyVisManager.cc
===================================================================
RCS file: /afs/cern.ch/sw/geant4/cvs/geant4/source/visualization/management/include/MyVisManager.cc,v
retrieving revision 1.5
diff -r1.5 MyVisManager.cc
67a68,71
> #ifdef G4VIS_USE_XXX
> #include "G4XXX.hh"
> #endif
> 
119a124,127
> #endif
> 
> #ifdef G4VIS_USE_XXX
>   RegisterGraphicsSystem (new G4XXX);

===================================================================
Index: source/visualization/management/src/G4VisManager.cc
===================================================================
RCS file: /afs/cern.ch/sw/geant4/cvs/geant4/source/visualization/management/src/G4VisManager.cc,v
retrieving revision 1.21
diff -r1.21 G4VisManager.cc
142a143,145
> #ifdef G4VIS_BUILD_XXX_DRIVER
>       "\n    G4VIS_USE_XXX"
> #endif
877a881,883
> #ifdef G4VIS_BUILD_XXX_DRIVER
>        << "\n  Brief description)"
> #endif
1099a1106,1118
> 		     G4VGraphicsSystem::noFunctionality) {}
> 
> #endif
> 
> #ifndef G4VIS_BUILD_XXX_DRIVER
> 
> class G4XXX: public G4VGraphicsSystem {
> public:
>   G4XXX ();
> };
> G4XXX::G4XXX ():
>   G4VGraphicsSystem ("Full name",
>                      "Mick name",

===================================================================
Index: config/G4VIS_BUILD.gmk
===================================================================
RCS file: /afs/cern.ch/sw/geant4/cvs/geant4/config/G4VIS_BUILD.gmk,v
retrieving revision 1.3
diff -r1.3 G4VIS_BUILD.gmk
80a81,85
> ifdef G4VIS_BUILD_XXX_DRIVER
>   G4VIS_BUILD = 1
>   CPPFLAGS += -DG4VIS_BUILD_XXX_DRIVER
> endif
>

===================================================================
Index: config/G4VIS_USE.gmk
===================================================================
RCS file: /afs/cern.ch/sw/geant4/cvs/geant4/config/G4VIS_USE.gmk,v
retrieving revision 1.3
diff -r1.3 G4VIS_USE.gmk
93a94,100
> ifdef G4VIS_USE_XXX
>   G4VIS_USE = 1
>   CPPFLAGS += -DG4VIS_USE_XXX
>   CPPFLAGS += -I$(G4BASE)/visualization/XXX/include
>   VISLIBS += -lG4Tree
> endif
>