Bump mapping not visible behind refraction

[LudvikKoutny]

Hi,

I have hard time setting up car headlights that are made of two sheets of glass with no thickness. Front sheet has normal facing forward, back sheet backwards, and back sheet of glass has a bump map. Whenever I render two sheets together, bump mapping is not visible through the front sheet of glass. Also, changing normal orientation of the back sheet does not have any effect on the issue.

Here's how it looks in the viewport (blue=front, red=back):

Here's how it renders:

Here's how back sheet only renders:

Here's back sheet moved slightly sideways to show how bump becomes invisible through refraction.

V-Ray 3.40.03 and Max 2016 SP3

Any help appreciated.

[LarsSonparsson]

Why don't you create some thickness to the front lens?
Because I don't think that the bump is invisible, but the whole object is invisible through the front lens with your current setup.

[Vizioen]

Just guessing but did you increase, refraction, reflection, depth and reflect on backside?

[kosso_olli]

As far as I know, this was never working. What I do is to collapse both parts into one object and then mapping only the backside with the bitmap. That way the front and back part share the same material, but only the back side is bumped. Just like the lens would be in reality. The reason it doesn't work is because there are 2 different materials assigned to the objects. The way I understand is that the rays hit the front part and travel "infinitely far" through the object, because there is no backside for the ray to exit the material.
If you want you can upload these two parts and I will take a look.

[LudvikKoutny]

LarsSonparsson:

I need refraction to happen between front flat surface and back bumpy surface. I do not want two separate glass objects, that would give me different result which I am not after. And no, the visibility through the lens is not an issue. If I replace bumped back wall with actual displaced geometry, it works:



Vizioen:

Yep, I've got global override enabled and set to 25

[LudvikKoutny]

As far as I know, this was never working. What I do is to collapse both parts into one object and then mapping only the backside with the bitmap. That way the front and back part share the same material, but only the back side is bumped. Just like the lens would be in reality. The reason it doesn't work is because there are 2 different materials assigned to the objects. The way I understand is that the rays hit the front part and travel "infinitely far" through the object, because there is no backside for the ray to exit the material.
If you want you can upload these two parts and I will take a look.

Yep, you were right. V-Ray decides refractive media based on same material. That's a bit confusing, but good to know. Thanks!

[kosso_olli]

Here is the scene file to the setup I mentioned:

lens_setup_v01.zip

[LudvikKoutny]

Here is the scene file to the setup I mentioned:

[ATTACH]33782[/ATTACH]

Yep, thanks I already knew what you meant. I am using VrayMultisub map to assign bump map per face ID. That works

[Vizioen]

So a brick wall bump wouldn't be visible behind refraction?

[kosso_olli]

If the transparent object is single sided, then probably not (or very distorted, black, fish-tank-effect etc). If it has thickness however, it will be fine.