[Paraview-developers] Backface Styling bug?

[Felipe Bordeu Weldt]

Thanks for the explanations and I understand the complexity of the problem.

I use the front/back culling technique to make border of my objects darker, like in cel shading rendering ( https://en.wikipedia.org/wiki/Cel_shading ). Any idea to get the same effect in Paraview??


Felipe



Le 11 sept. 2015 à 15:02, Ken Martin <ken.martin at kitware.com> a écrit :

> Unfortunately this is a real issue and the fix is sort of ugly/painful
> unless I am missing something. The issue is that the new backend converts
> quads/polygons into triangles as quads and polygons are deprecated in later
> versions of OpenGL. Plus triangles are fast as they each have just 3 verts
> and can be counted on to have three verts etc. :-) But when you render
> wireframe you do not want to use the same IBO because if your original data
> was a quad, showing triangle wireframes would be misleading. So we build a
> different IBO that constructs the boundary edges as lines.  Lines do not
> get front/back culled by OpenGL. The reason we do not use triangle_fans is
> that without the primitive restart index support (not available in OpenGL
> 2.1 or ES 2.0/3.0/3.1) you (or the driver) have to essentially make a draw
> call per primitive which is slow. Plus glPolygonMode is not in OpenGL ES so
> it would not work on iOS/Android anyhow. So ... edge visibility or
> wireframe when combined with front/back culling is not working and off the
> top of my head I cannot think of a universal solution other than performing
> the culling on the CPU and sending a new IBO up every frame, yuck.
> 
> 
> 
> Ken
> 
> 
> 
> Ken Martin PhD
> 
> Chairman & CFO
> 
> Kitware Inc.
> 
> 28 Corporate Drive
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> 
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> 
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> 
> *From:* Paraview-developers [mailto:paraview-developers-bounces at paraview.org]
> *On Behalf Of *Joachim Pouderoux
> *Sent:* Friday, September 11, 2015 5:52 AM
> *To:* Felipe Bordeu
> *Cc:* ParaView Developers
> *Subject:* Re: [Paraview-developers] Backface Styling bug?
> 
> 
> 
> Not totally sure but it could be related to Ken's current merge request:
> https://gitlab.kitware.com/vtk/vtk/merge_requests/643
> 
> Support of OpenGL2 backend in PV is not yet complete by the way. PV4.4 is
> still base on the legacy backend.
> 
> Regards,
> 
> 
> 
> 
> *Joachim Pouderoux*
> 
> *PhD, Technical Expert*
> *Kitware SAS <http://www.kitware.fr>*
> 
> 
> 
> 2015-09-11 11:24 GMT+02:00 Felipe Bordeu <felipe.bordeu at ec-nantes.fr>:
> 
> 
> Signé partie PGP
> hi I don't know if this is a bug of paraview or vtk.
> 
> 1) make a simple Arrow source
> 2) change the view to Surface With Edges.
> 3) change the "Backface Representation" to "Cull Frontface"
> 
> only the back surfaces are rendered (as expected ), but ALL the edge are
> rendered.
> 
> Using the 4.4.0-RC2 64bit on linux and using "
> VTK_RENDERING_BACKEND            OpenGL2"
> 
> In Paraview 4.3.1 (binary from web) only the back edges and surface are
> rendered (as expected).
> 
> Felipe
> 
> 
> 
> --
> Felipe Bordeu Weldt
> Ingénieur de Recherche
> -------------------------------------
> Tél. : 33 (0)2 40 37 16 57
> Fax. : 33 (0)2 40 74 74 06
> Felipe.Bordeu at ec-nantes.fr
> Institut GeM - UMR CNRS 6183
> École Centrale Nantes
> 1 Rue de La Noë, 44321 Nantes, FRANCE
> -------------------------------------
> 
> 
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