class TGLScenePad: public TVirtualViewer3D, public TGLScene

 Constructor.

 Scale and rotate a histo object to mimic placement in canvas.

 Iterate over pad-primitves and import them.

 Override of virtual TVirtualViewer3D::ObjectPaint().
 Special handling of 2D/3D histograms to activate Timur's
 histo-painters.

 Entry point for requesting update of scene's contents from
 gl-viewer.

 Entry point for updating scene contents via VirtualViewer3D
 interface.
 For now this is handled by TGLViewer as it remains
 the 'Viewer3D' of given pad.

 Start building of the scene.
 Old contents is dropped, unless smart-refresh is in active. Then
 the object supporting it are kept in a cache and possibly reused.

 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture.

 End building of the scene.
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add an object to the viewer, using internal physical IDs
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add an object to the scene, using an external physical ID
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Open new composite container.
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture.

 Close composite container
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add composite operation used to combine objects added via AddObject
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Validate if the passed 'buffer' contains all sections we require to add object.
 Returns Int_t combination of TBuffer::ESection flags still required - or
 TBuffer3D::kNone if buffer is valid.
 If 'includeRaw' is kTRUE check for kRaw/kRawSizes - skip otherwise.
 See base/src/TVirtualViewer3D.cxx for description of viewer architecture

 Create and return a new TGLLogicalShape from the supplied buffer

 Create and return a new TGLPhysicalShape with id 'ID', using
 'buffer' placement information (translation etc), and bound to
 suppled 'logical'

 Build and return composite shape mesh

 Try to construct an appropriate logical-shape sub-class based
 on id'class, following convention that SomeClassGL is a suitable
 renderer for class SomeClass.

 void SetPad(TVirtualPad* p) { fPad = p; /* also need to drop contents */ }

 TVirtualViewer3D interface

 For now handled by viewer