[vtkusers] vtkFixedPointVolumeRayCastMapper:How to see the progress of the rendering

[wassim_belhadj at topnet.tn]

Hi,

I' m using vtkFixedPointVolumeRayCastMapper and I want  to see the progress
of the rendering(Connect Observer to a QrogressBar) 

vtkFixedPointVolumeRayCastMapper has only
vtkCommand::VolumeMapperRenderStartEvent and
vtkCommand::VolumeMapperRenderEndEvent.

How can I change the  Source code of VTK ?

I could do this with VolumeRayCastMapper by modifying 
VolumeRayCastMapper_CastRays Function(I invoke an event for each image
processed).

But I have not been able to adopt these changemnts because the treatment is
not the same.

Thank you in advance