Re: Help: Transparency problems. Holes in the surface! Is this a known problem and how to fix it?

Hello Bill and Eric, 

Thank you both for your feedback. Given that I am
commited to using Visad right now for our project
-since it has nice looking contours and I don't want
to have to reinvent it in Java3D I think I will
abandon using transparency and go with contours. This
in a way provides the transparency that I want without
the complications. 


Thank you both again.

Regards,

Surekha


--- Bill Hibbard <billh@xxxxxxxxxxxxx> wrote:

> Hi Surekha,
> 
> This is an old and well known problem with all
> 3-D graphics libraires that are fast enough for
> interaction. Efficient 3-D graphics libraries,
> such as Java3D, use a Z-buffer algorithm for
> depth precedence and for this to render correctly
> with multiple transparent layers the layers must
> be rendered in an ordered sorted from rear to
> front. But the sort order changes as the user
> rotates the surfaces in 3-D, and dynamically
> re-sorting as the user rotates (and dynamically
> changing the geometry used by the graphics
> library) would be too slow for interaction.
> 
> We have from time to time experimented with an
> alternate implementation of transparency, known
> as screen door transparency, available in Java3D.
> But it seems not to work (it does work in OpenGL
> and is used by Vis5D). But screen door images
> look a bit weird viewed close up, even if it did
> work in Java3D.
> 
> Bill
> 
> On Fri, 28 Oct 2005, Surekha Chandran wrote:
> 
> > I have an irregular 3D surface - a head with some
> EEG
> > signal plotted on the top of the head. I use
> > DelaunayCustom to set up the Irregular3DSet. Now
> > instead of making it an RGB ScalarMap I am using
> RGBA
> > and I want to make the whole image partially
> > transparent. There is a seconday contour plot but
> that
> > is RGB and is fine as you can see in the images
> > attached.
> >
> > Look at the images included. It is funky. When I
> > rotate the image in certain directions I find that
> > there are some wierd artifacts. It is like the
> colors
> > are painted on the inside of the head rather than
> on
> > the outside. Then there are places where I can see
> > clear triangles on the inside and holes. It does
> not
> > make any sense. Why are there holes in the colors?
> Why
> > are there light gray bands across the face when I
> know
> > I have set all the values in that area to be the
> same
> > exact gray color(the darker shade of gray).
> >
> > Please help. I looked at Test20 but it does not
> seem
> > to be describing this problem. I could not find
> any
> > similar problems in the archives.
> >
> > Thanks
> >
> > Regards,
> > Surekha
> >
> >
> >
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> 
> 



        
                
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