[Paraview] Opacity problem with Paraview 3.1/3.2

[Berk Geveci]

Hi Tom,

I don't think bug 2347 is causing what you are observing. The whole
opacity thing is a long story but I will try to summarize it:

1) OpenGL requires polygons to be rendered in a sorted order (back to
front, http://www.opengl.org/resources/faq/technical/transparency.htm)
for correct transparency

2) By default, VTK does not render polygons in a sorted order because
sorting has to be done for each camera position and is potentially
very expensive for large models

3) VTK supports an algorithm called depth peeling
(http://www.vtk.org/Wiki/VTK/Depth_Peeling) to deal with this issue.
This algorithm works fairly well for many cases

4) Depth peeling requires certain extensions that are not available on
all graphic cards

5) Transparency would work well if your card supports all extensions
listed here: http://www.vtk.org/Wiki/VTK/Depth_Peeling. I believe the
latest version of Mesa also works.

You have a high-end nVidia and depth peeling should work on it. I will
see if we can figure out why it is not working. I have a colleague
with a 8 series card.

-berk


On 11/2/07, Thomas D. Uram <turam at mcs.anl.gov> wrote:
>
> We're seeing a problem with opacity with very basic models in Paraview
> 3.1 and 3.2.  Using the stock cylinder source and setting the opacity to
> 0.5, we're getting this:
>
>     http://www.mcs.anl.gov/~turam/paraview/pv-snap01.jpg
>
> Note that the opacity is applied to the polygons inconsistently.  When
> rotating the model, some opaque polygons become transparent, and
> transparent polygons become opaque.  When setting opacity to 0, the
> entire model becomes transparent.
>
> I found some seemingly related reports that reference bug 2347:
>
>     http://www.paraview.org/Bug/view.php?id=2347
>
> which includes patches for 2.6 which have been applied in the 3.x code,
> and a later reference to more work that will be done.
>
> Is this a known problem encountered by others?  Should we suspect a
> machine/graphics configuration problem?  Is it likely related to the
> proposed fixes in bug 2347?
>
>
> Tom Uram
>
>
> Details:
> Paraview:  3.1, 3.2
> Platform:  Ubuntu Linux 7.04
> Graphics card:  nVidia 8800 GTX (latest driver, 100.14.19)
> Additional details on request.
>
>
> _______________________________________________
> ParaView mailing list
> ParaView at paraview.org
> http://www.paraview.org/mailman/listinfo/paraview
>