[Paraview] Disabling polygon offset (z-fighting prevention) in Paraview

[Utkarsh Ayachit]

Ken,

Offsetting the points/lines handles the cases when people try to
render two overlapping datasets: one as surface and other as
wireframe, and they don't necessarily want to show surface with edges
(say they want scalar coloring for both surface and the wireframe). I
believe Jean Favre has several such use cases.

Utkarsh

On Mon, Oct 26, 2009 at 1:18 PM, Moreland, Kenneth <kmorel at sandia.gov> wrote:
> Utkarsh,
>
> After reading this question from Olumide, I noticed that ParaView now turns
> on ZShift for lines and points (vtkProcessModule.cxx, 198-199).  I don’t
> know why this is.  This effect is turned off when drawing surface+edges
> (vtkOpenGLCoincidentTopologyResolutionPainter.cxx, 56-58) because it
> automatically switches to offsetting the polygons the polygons back
> (vtkOpenGLRepresentationPainter.cxx, 79-85).  Should we remove those two
> lines from vtkProcessModule.cxx?
>
> -Ken
>
>
> On 10/26/09 12:53 AM, "Olumide" <50295 at web.de> wrote:
>
> Hi -
>
> I use Paraview not for visualizing datasets, but for inspecting
> polygonal meshes and the operations I perform on them. My work involves
> computing various points and line segments on meshes, and I use
> VTK/Paraview to see if the points and line segments are where they ought
> to be (if not, I conclude that there's a bug in my code and then proceed
> to hunt it down).
>
> <Digression>
> Why I use VTK for this task: VTK is the the only publicly available 3d
> graphics file format I'm aware of that explicitly supports and points,
> lines, and meshes, and has a viewer for viewing these entities. Most
> other 3d graphics file formats either support surfaces alone or have no
> ready-made viewers.
> </Digression>
>
> Lately however, upon closer inspection, I've noticed that many of the
> points and line segments that I compute appear to hover above the mesh
> they are computed from and never quite touch it, and points never seem
> to lie on the line segments they are supposed to. For example, see:
> http://i17.photobucket.com/albums/b52/videohead/SurfaceError.png
> (note that the yellow line segment hover above the blue surface in the
> horizon)
>
> After much experimentation, debugging and consultation, I now suspect
> that this is caused by polygon offset in Paraview, designed to prevent
> z-fighting. I would therefore like to know:
>
> (i.) if my suspicion is correct i.e. Paraview implement polygon offset
> for preventing z-fighting in this case
>
> (ii.) if the above is true, how polygon offset can be disabled without
> recompiling the source
>
> Thanks,
>
> - Olumide
>
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>    ****      Kenneth Moreland
>     ***      Sandia National Laboratories
> ***********
> *** *** ***  email: kmorel at sandia.gov
> **  ***  **  phone: (505) 844-8919
>     ***      web:   http://www.cs.unm.edu/~kmorel
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