[vtkusers] Combining volumes and transparent

Pixton, John JPixton at continuum-corp.com
Wed Sep 12 15:54:09 EDT 2001

Jiro -

I can't explain your problem, but there are limitations to the VP 500 board
may not be aware of.

First, the VolumePro 500 board works by producing a single 2D image from the
in its memory.  The image must then be combined in some way with the scene.
OpenInventor did was to assign depth values at every pixel.  This means that
each pixel either contains an RGBA color from this produced 2D image (if the
depth test succeeds) or it contains a pixel from the scene (if it doesn't),
but it isn't possible to combine them.  The VP 500 board itself cannot
accurately blend geometry and volume, although some people
have argued that the visualizations produced are good enough for their

I haven't used VTK's VPro mapper, but I it will face a similar issue.
Surely transparent
geometry within the volume will present a problem to the VP500 ...

But ...

I spoke with Frank Baker from TeraRecon (Bought RTViz from Mitsubishi, same
product) just yesterday.  The VolumePro 1000 board is in its final debugging
phase.  VP 1000 has a redesigned architecture to accomodate correct blending
of volume and geometry.  You'll need to upgrade when it becomes available to
get accurate blending of volume and geometry, especially blending
transparent geometry.  They should be in production in 
a month or so.

If you need perspective rendering, you'll have to wait for the next version
of VolumePro,
expected to be released Jan 2002.

Hope this helps,


-----Original Message-----
From: Jiro Inoue [mailto:inoue at cs.queensu.ca]
Sent: Monday, September 10, 2001 10:28 AM
To: vtkusers at public.kitware.com
Subject: [vtkusers] Combining volumes and transparent

I have multiple vtkActors and vtkVolumes set as inputs to a single
vtkRenderer. I'm using volumepro 500 hardware with the vtkVolumeProMapper
for my volumes and vtkPolyDataMapper for the actors. My problem is that my
actors have transparency (opacity of 0.2), which works fine until I
introduce a volume into the scene. As soon as the volume is placed in the
scene, all of my actors become fully opaque - the volume on the other hand
maintains the correct opacity characteristics.
Has anybody else seen this? Any insights?


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