FW: [vtkusers] Blending two volumes

[Lisa Avila]

Hello John,




>Aha! OK then I'll have to abandon the lookup table I guess and map
>scalars through a normal lookup table the hard way. Is there a better
>way of doing it?

Asking the piecewise function or color transfer function for each value 
would be the simplest way to do it, but definitely not efficient.

> > No - the ray caster in VolView 2.0 is not derived from the
> > VTK ray caster.
>
>Does this mean you've just created a new ray cast mapper, or are you not
>using vtk at all? From the comments below it sounds like a new mapper is
>required for proper blending of volumes

VolView is built on top of VTK - the VolView volume mappers are subclasses 
of vtkVolumeMapper.


> > >3) I'd like to be able to move cross hairs etc around on the image
>
> > yes - memory issues. There is no single depth map for volume
>
>Hmm. Yes I confused myself here. Actually, I really only want to move
>cross hairs in an overlay plane, so simply recopying the rendered image
>ought to be fine. Someone else on the list was asking almost the same
>question so putting in a facility to disable the rerender if the volumes
>are not modified and instead recopy the saved buffer might be feasible.

I believe Amy may have done some recent work for adding a zoom box in this 
manner to an interactor - I am not sure if this was VTK or ParaView work, 
but you could use the same concept.


>May I ask how you've apporached the problem in your new renderer?

We support vtkImageData with multiple components rather than separate field 
arrays.

>Is there any easy mechanism for terminating rays that can be injected in
>a consistent manner? I'm not sure if the existing ray caster terminates
>rays, but it'd be nice to integrate this.

The VTK ray cast mapper (and the VolView one) do early ray termination 
because they blend as they sample. If you switch to a "sample first then 
blend" method you won't be able to early terminate the sampling.


>PS. Can a volumepro card do any kind of clever blending for two volumes

Yes, but you have to do this from VLI - VTK does not support it in the 
vtkVolumeProMapper.

Lisa