attach vtk context to gcompose

src/HEP/Geant/Matter.h

@@ -59,6 +59,8 @@ private:
 class Material : public Object {
 public:
 
+    virtual const char* GetClassName() const override { return "Geant.Material"; }
+
     uLibRefMacro(G4Data,G4Material *)
 private:
     G4Material *m_G4Data;