[vtkusers] multiple volumes rendering

[Amy Squillacote]

Hi Eugen,

Allowing overlapping volume rendering is a difficult problem. In VTK, 
rendering is done per actor / volume. In order to render overlapping 
volumes, you'd have to be rendering the overlapping volumes at the same 
time. There is also the problem that you can have different transfer 
functions per volume, and even if the transfer functions were the same, 
you'd have different scalar values at the same 3D location. You'd get a 
different color and opacity for a given pixel, and you'd have to specify 
how these different colors/opacities should be combined.

Hopefully this gives you an idea why this is a difficult problem and why 
this is not supported in VTK. If your volumes are completely overlapping 
and lie on the same grid, you could first combine them into a single 
volume and then volume render the multi-component volume. However, from 
reading your previous post, I see that you do not find this approach 
acceptable.

As for why you may not have gotten a response to your initial e-mail, 
please keep in mind that this e-mail list has far more traffic during 
the week, and you only asked your initial question two days ago.

- Amy

eugen wrote:
> Hi!
>
> I've already asked about overlapping multiple volumes rendering (Sat 
> Jun 9 10:24:33 EDT 2007), but got no answer, so this is just a second, 
> but shorter try:-)
>
> Why is it that complicated to introduce overlapping multiple volumes 
> rendering in vtk, that no one has done it before?
> Where to start if one want to add overlapping multiple volumes 
> rendering (with 3D texture mapping) to vtk?
>
> Maybe I'm missing something and vtk already is capable of overlapping 
> multiple volumes rendering...
>
> Please, can someone give me a hint?
>
>
> Thanks it advance!!!
>
> Eugen
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-- 
Amy Squillacote
Kitware, Inc.
28 Corporate Drive
Clifton Park, NY 12065
Phone: (518) 371-3971 x106