V-Ray ignores refracted back side reflections regardless of VRayMTL setting

[LudvikKoutny]

What I find kind of curious is that in my scene that I've sent to Chaosgroup support, it happens even with simple glass material, without absorption/fog, so I think you may have found somehow related, but different problem Both of these issues may be related to refraction media detection.

[anthonyh]

I`m just using some cad that`s causing similar issues. Some normals are one way, some the other as part of the same object. On transparent objects you can see the flipped parts render differently and on the solid parts the bump normals are inverted so half the surface bumps `in` and the other bumps `out`. Since cad data can be very complex and sometimes impossible to fix by inverting specific faces without the mesh becoming corrupt it would be good if vray could handle this(maybe a material that treats normals as `double directional` somehow, I know that sounds a bit demented, I`m not the programmer ! ).
While it may be a by-product of the cad import process there doesn`t seem to be any definitive way to import cad which works under all conditions and guarantees faces all being correctly aligned. Sometimes the mesh is screwed, sometimes the normals, smoothing groups etc. I thought the double-sided option took care of this but apparently not always ?
anthonyh

[kosso_olli]

Since cad data can be very complex and sometimes impossible to fix by inverting specific faces without the mesh becoming corrupt it would be good if vray could handle this

You can always fix inverted normals in 3dsMax without breaking anything or corrupting the CAD-part, if done the right way. However, I agree that we shouldn't be worried about any of this in the first place, like in Corona. It just works, but how is the question.
Also, there are no smoothing groups on parts coming from CAD software like Catia V5, ProEngineer etc... I get the impresion that there a lot of misconceptions about how tesselated data from nurbs models is working in Max.

[anthonyh]

Well, with this mesh if I flip the normals sometimes the smoothing groups go up the wazoo. Likewise if I `detach` elements/faces the mesh goes bananas, so I have to duplicate the object and delete opposite selections to get the same effect. Probably just weird cad but I`ve seen it enough times to be an issue (a max issue). On more complex models there simply wouldn`t be enough time to go through and flip the problem faces normals even if it did work. I wonder whether it`s something to do with mirrored surfaces in the original cad(to save modelling time) and so the normals are flipped on import ? Just a guess though.

[kosso_olli]

I sent a PM to you to avoid hijacking this thread.
Anyway, I hope Chaos can find a solution to this, as it would make our lives much easier.

[Svetlozar Draganov]

OK guys, I'll make a note about that into our system.
Hopefully will find a more elegant way to render surfaces with improper normals.

[kosso_olli]

Thank you! If you need anything for testing, please ask. Have loads of stuff regarding that matter.

[Svetlozar Draganov]

I used the scene that Recon442 sent us but other samples might be also useful especially if there is a non-working version with V-Ray and working one with other render engine.
Thank you very much in advance.

[kosso_olli]

Here is a scene file illustrating the problem with the fog color. The backside of the glass has some polygons with normals flipped on purpose. The flipped normals can not be spotted in the viewport unless you know what exactly to look for. The parts with flipped normals render black, which is undesirable. It would be nice if V-Ray could render this as is without flipping the normals. This is working both in Corona and Mental Ray without problems. Just place any image into the environment background.


Regards

Oliver

fog_color_normal_error_v01.zip

[kosso_olli]

Is this issue still being looked at?

[vlado]

It's on the "to do" list, but I don't know yet when we will look into it. I don't know if it's solvable at all and we might not be able to do anything about it. For the moment, it would be best not to count on a solution other than flipping the normals correctly.

Best regards,
Vlado

[kosso_olli]

Well, you can always ask Ondra I guess. It is working there, same in Mental Ray.
I jusst hope that this knowledge transfer with Render Legion is not a one-way train for us. Right now the Corona guys get all the good stuff, it seems...

[vlado]

I have this in mind, but, like I said, it would be best not count on it.

Best regards,
Vlado

[kosso_olli]

Any news on this issue?

[kosso_olli]

It has been a while, but the problem still persists. Is there an elegant solution to this?