[vtkusers] volume rendering >1 component data

[Lauren O'Donnell]

Hi all,

I am trying out volume rendering of some characteristics of DT-MRI data,
and volume rendering (in vtk3.2) only is supported for 1 scalar component.  
So I wrote a subclass of vtkVolumeRayCastCompositeFunction to render RGBA
data by grabbing the image components rather than using lookup tables.

This is a quick solution but I can't handle shading this way, and I have a
few questions.  First, has anyone done something like this?  

Second, is there any way to "trick" the existing classes into computing
the gradient/normal information using one of the components of my data as
the scalar input?  Perhaps setting the active scalar component?

And third, is the gradient and normal information computed always? Or can
I turn it off if I don't use it?

If anyone knows a better way to go about this, please let me know.

Lauren