[vtkusers] Shadow support on volume rendering

[ianl]

Hello again, apologies for (re)ressurecting my ancient thread again!

I have managed to get a bit more time to get a little further with this and
have a few more questions as a result. I have put a vtkImageCast to float
into the pipeline as suggested by David and I am now getting results that
look close to the original GPU volume mapper which is great. Additionally I
am also now able to render shadows which is really good.

It would be nice if I didn't need to do the cast as it (presumably) copies
the data again to perform the conversion to float. Did you get anywhere with
a fix for this?

What I am now aiming towards is getting an improved quality fully ray traced
volume render. Something along the lines of what is being achieved here
(pics about half way down):

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5110476/

As far as I can ascertain, I will need to use the 'pathtracer' renderer type
rather than 'scivis' to obtain more realistic ray traced results with soft
shadows and indirect illumination/ambient lighting. The results I am getting
at the moment look quite harsh and the shadows are fairly crude with scivis.

The problem I am having is that the pathtracer renderer seems to need to
have a material set for it to work, and there is no way to do this for
volumetric data actors as far as I can see (it is not a member of
vtkVolumeProperty). I guess it would probably not make sense if it was as a
medical CT volume may contain many materials (bone, soft tissue, metal
implants etc).

Does the pathtracer renderer in ospray support volumetric data? I cannot
seem to get it to render anything in paraview either, wheras the scivis
renderer in paraview shows the same sort of results I see with my pipeline.
Can you offer any guidance with how to proceed with this? Am I limited to
using something like marching cubes to extract an isosurface for, say the
skeleton, then doing a surface rendering of this to get the full ray traced
quality? Would I need to extract an isosurface for each tissue type and give
it an appropriate material? This seems a little long winded, wheras the
current volume rendering effectively does this with colour and opacity
lookup tables.

All that said, the performance is very impressive for a software renderer
and the results are a step up from the GPU renderer with regards to shadows
and quality.




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