[vtkusers] Shadow of 2D Actor when using VolumeRayCastCompositeFunction

[Lisa Avila]

Hello David,

You seem to have answered your own question!  Yes, during interaction a 
lower resolution image is generated. This means the geometry zbuffer is 
subsampled - leading to the "shadow" effect you mentioned. Turning off 
intermixing only "solves" the problem in that geometry is not intermixed 
with the volume (geometry/volume appearance will only be correct if the 
geometry does not intersect the volume).

Lisa




At 12:02 AM 2/18/2002, David Netherway wrote:
>The problem seems not be with an offset of the z buffer image but with the
>coarse rendering for interaction.
>
>The projection of the 1 pixel wide 2d actor has a width equal to the coarse
>sampling pixel size used for interaction. Sometimes the
>last render is left in a coarsely sampled mode and the "shadow" appears.
>
>David
>
>----- Original Message -----
>From: "David Netherway" <david.netherway at adelaide.edu.au>
>To: <vtkusers at public.kitware.com>
>Sent: Monday, February 18, 2002 12:30 PM
>Subject: Re: [vtkusers] Shadow of 2D Actor when using
>VolumeRayCastCompositeFunction
>
>
> > If a "renWin Render" is issued through the vtkInteract console the shadow
> > goes away.
> >
> > I am using vtk4 from about  8th or 9th Feb.
> >
> > Thanks, David
> >
> > ----- Original Message -----
> > From: "David Netherway" <david.netherway at adelaide.edu.au>
> > To: <vtkusers at public.kitware.com>
> > Sent: Monday, February 18, 2002 12:03 PM
> > Subject: [vtkusers] Shadow of 2D Actor when using
> > VolumeRayCastCompositeFunction
> >
> >
> > > Hello Vtk Users,
> > >
> > > On top of my ray cast image I have inserted a cross using 2D actors. But
>I
> > > get a shadow offset from the cross. See attached sample code. The shadow
> > > does not always appear but if you move the volume a few times (say, 5)
>you
> > > should see the problem.
> > >
> > > For ray casting with imbedded geometry there is early termination using
> > the
> > > z buffer. The problem may be related to an image offset between the z
> > buffer
> > > and the 2D actor position. I have not yet tracked it down. If you turn
>off
> > > the early ray termination using
> > > volumeMapper SetIntermixIntersectingGeometry 0
> > >
> > > The problem goes away.
> > >
> > > Does anyone recognise the problem and have a solution?
> > >
> > > Thanks, David
> > >
> > >
> >
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