[vtkusers] vtkFixedPointVolumeRayCastMapper features

[Lisa Avila]

Hi Mario,

For your first problem: I am unaware of this. Can you cause it on one of 
the VTK data sets? If so, can you send me the code that causes it so I can 
try it?

On the second issue - yes, the vtkFixedPointVolumeRayCastMapper does use 
its own code for generating gradients since the gradient estimator is not 
able to process multicomponent data. Originally, the 
vtkFixedPointVolumeRayCastMapper relied on a specific gradient encoding 
since it used to interpolate normals (Phong-style shading) but that turned 
out to be too unstable so it interpolates shaded value (just like the 
standard ray cast mapper). So - it should be possible to expand the 
gradient estimator to handle multi component data, switch the 
vtkFixedPointVolumeRayCastMapper over to using this, and then everything 
will run faster on a multiprocessor system (although keep in mind that the 
code in the fixed point mapper tries harder to get a gradient in 
homogeneous regions - looking out at larger distances until it finds one 
with a sufficient magnitude - now that we are not interpolating gradients 
perhaps this is not necessary....).

Lisa


At 08:53 AM 9/28/2005, Mario Medved wrote:
>Hi,
>
>I was experimenting with vtkFixedPointVolumeRayCastMapper which is great,
>but I noticed 2 problems/features:
>
>1. MIP blend mode causes black spots over some images. I think this is due
>space leaping, since vtkVolumeRayCastMapper does not have these problems.
>
>2. When the shading is turned on, the gradient estimator works slower then
>in vtkVolumeRayCastMapper. On larger volumes this can be very lengthy
>operation. I checked the source code and there is just block of code for
>calculating gradient values directly without any multiprocessor support.
>vtkVolumeRayCastMapper uses gradient estimator object which does all
>calculations with miltiproc support, but I am not sure why this code is not
>used in vtkFixedPointVolumeRayCastMapper.
>
>If anyone solved these problems, please let mo know, so I do not rediscover
>hot water.
>
>Thanks,
>Mario
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