[vtkusers] Using a boxwidgets transform to rotate a non-vtk 3D model?

[Totte Karlsson]

Hello,
I'm using vtk to visualize 3D models of molecules.
The actual molecular model is decoupled from vtk code, and visualization 
is implemented using a model-view kind of design.

Currently I have the following challenge. If a user wants to manipulate 
the absolute orientation of the molecule, it is done by manipulating the 
underlying model using rotation functions, like RotateX, RotateY, 
RotateAboutVector, and translation functions TranslateX, Y etc.

For now 3D rotations are simply done using two scrollbars, one 
horizontal and one vertical, causing the underlying model being rotated 
about the vtk viewUP vector and the vtk cameraPlane normal 
respectively.  This works fine, but is not so intuitive for the user.

Instead I believe allowing interaction with something like a box widget 
that encapsulates the molecule view, (with disabled handles), would be 
better.

The challenge is how to figure out how to capture the boxwidgets 
orientation in a callback, and using this information in order to 
manipulate the underlying molecular model.

For example, a boxwidget callback (from boxwidget example at 
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Widgets/BoxWidget):

class vtkMyCallback : public vtkCommand
{
     public:
         static vtkMyCallback *New()       {            return new 
vtkMyCallback;    }

     virtual void Execute(vtkObject *caller, unsigned long, void*)
     {
         vtkSmartPointer<vtkTransform> t = 
vtkSmartPointer<vtkTransform>::New();
         vtkBoxWidget *widget = reinterpret_cast<vtkBoxWidget*>(caller);
         widget->GetTransform(t);

         double* angles?? = t->GetOrientation();
         if(aMoleculeModel)
         {
             //Use some secret(!) code to manipulate orientation of a 
molecule to 'rotate' it together with the boxWidget
             aMoleculeModel->RotateZ(??);
             aMoleculeModel->RotateY(??);
             aMoleculeModel->RotateZ(??);
         }
     }
     Molecule* aMoleculeModel;

Anyone seeing how to do this or have some pointers?

Cheers,
tk