[HOU-2366] Explicit UV in Bump

[david.anastacio]

Hi,

There seems to be an issue when using the explicit UV node for getting a rest position and then using that in a Bump. But when debugging the noise where the explicit UV is used the noise is getting correctly mapped.
This happens on both V-Ray 4.3 and 5.

In this example I exaggerated the noise show the issue.


Noise using "objectUV" as the uvwGen of the noise:


Noise using "UV named" as the uvwGen of the noise:


Noise using "Explicit UV" as the uvwGen of the noise, bump stops working:


Debugging the noise that uses the Explicit UV node shows that the noise is actually working:


Best,
David.

[LeoYfver]

Can confirm. just had the same issue.

Regards Alexis

[Gosho.Genchev]

Hey David, Alexis,

Thank you for the heads up - I've reproduced the issue on my end and have informed the dev team. I'll get back with more info as soon as I know more.

Best regards!

[vlado]

I will fix this, but keep in mind that I would strongly recommend against using UVs in this way. It is much better to use named UVs than using explicit UVs. This is because currently using explicit UVs disables texture filtering for the textures that use that node. This means that tiled .tx files will be loaded at full resolution and will require more time to sample properly.

Best regards,
Vlado

[david.anastacio]

I will fix this, but keep in mind that I would strongly recommend against using UVs in this way. It is much better to use named UVs than using explicit UVs. This is because currently using explicit UVs disables texture filtering for the textures that use that node. This means that tiled .tx files will be loaded at full resolution and will require more time to sample properly.

Best regards,
Vlado

Hi vlado, and Gosho.Genchev,

That's is very good information to be aware.
Using named UVs are an option yes, but the geometry might not always have UVs and deforming (which was my case), so using a "rest" position attribute to drive the procedural maps is necessary. Even if the geometry has UVs there is still value in using the "rest" position with explicitUV, as this will result in an even size distribution of the procedural maps across the model, unlike the UVs (depending on the UVs distribuition of course).

Could this be fixed and eventually also make it work with the filtering? For the use case I was trying it the filtering is not an issue since it's only used with procedural maps, I don't see myself using it with textures (.tx .exr).

Best,
David.

[Gosho.Genchev]

Hey David,

I might be grossly misuderstanding you here but I'll go ahead and ask - using the rest position as UVs will basically give you a flat snapshot of your geometry, as if seen from the +Z axis, e.g. :



Excuse me for being thick here - I'm just wondering if using the TriPlanar texture together with the Object Properties -> Reference Mesh options would make things simpler ?

Thank you!

[david.anastacio]

Hey David,

I might be grossly misuderstanding you here but I'll go ahead and ask - using the rest position as UVs will basically give you a flat snapshot of your geometry, as if seen from the +Z axis, e.g. :



Excuse me for being thick here - I'm just wondering if using the TriPlanar texture together with the Object Properties -> Reference Mesh options would make things simpler ?

Thank you!

Hmmm, that's not expected result.

I was trying to use it has a UVWgen of a 3D noise map, and that does not generate the result you described, it's correctly mapped across a round surface. See my example bellow.



You can also find this technique described here by yourself: https://forums.chaosgroup.com/forum/...r-bercon-noise
This works even if the noise map is set to 2D (Dimensions), so it's not only in 3D noises.

Tri-Planar with a reference mesh, that's only available in V-Ray 5, and we currently don't use V-Ray 5 in production (not ready yet).

Best,
David.

[Gosho.Genchev]

Ah, alright, I see.

Thank you for explaining, David.

Best regards!

[vlado]

Even if the geometry has UVs there is still value in using the "rest" position with explicitUV, as this will result in an even size distribution of the procedural maps across the model, unlike the UVs (depending on the UVs distribuition of course).

You can totally use the "rest" position attribute in a named UV generator. For V-Ray, mapping channels have three components (U, V and W) and they can be used to drive procedural textures as well.

Could this be fixed and eventually also make it work with the filtering?

Yes, I've made a note about it, but it will take a while.

Best regards,
Vlado

[david.anastacio]

Ah, alright, I see.

Thank you for explaining, David.

Best regards!

No problem, thanks for looking into this

You can totally use the "rest" position attribute in a named UV generator. For V-Ray, mapping channels have three components (U, V and W) and they can be used to drive procedural textures as well.

Ok, that's a great point, I was under the impression after reading the post from Gosho that the "explicitUV" was a requirement. Thanks for the clarification.

Yes, I've made a note about it, but it will take a while.

Thanks.

Best,
David.