Light leaking through solid surfaces with strong bump maps

[LudvikKoutny]

Hi,

in current job, i am very often encountering a problem where lights leak through solid surfaces with strong bump maps. It seems as if bump maps were so strong that they turn normal inside out and pick the light from other side of the surface. The thing is those bump maps are not too strong, they are exactly as strong as they need to be. I have as critical problems as lights that are inside of an enclosed box causing visible highlights on the outside of it.

Any ideas how to solve this?

[vlado]

Always use walls with thickness and it will be fine.

Best regards,
Vlado

[alexyork]

In an emergency, quickest solution is to stick a shell modifier on all your infinitely thin objects.

[LudvikKoutny]

The cube was just simplified example. Some of the objects are a bit more complex, and shell on them completely messes up the topology (corners start to self-intersect). I will just create some some planes to block out problematic areas i think... that will do the trick. Non the less, most of the other renderers i've used had some normal deviation limit or function to prevent normal turning inside, to prevent this kind of problem.

[vlado]

Non the less, most of the other renderers i've used had some normal deviation limit or function to prevent normal turning inside, to prevent this kind of problem.

That doesn't help (V-Ray has such code too). The normal doesn't really flip, but it does turn towards the light. In the absence of anything behind the plane to block the shadow ray towards the light, you get a light leak. From what I could test, both the scanline renderer and mental ray behave in the same way.

Best regards,
Vlado

[LudvikKoutny]

Nope, sorry but not true.

Here's a simple scene, which has just plane, light on the one side and camera on the other. Vray leaks even with just moderate amount of bump, while Mental Ray does not leak even with extremely overdone amount of bump. I also do not remember ever getting these problems with any Vray 2.x version. Started to encounter them only with version 3.

Scene is 3ds Max 2015 SP2 and Vray 3.00.08
Leaks.zip

EDIT: Just checked scanline. Not leaking either.

EDIT2: Forgot to attach bump bitmap Here it is:

[svetlozar.draganov]

I also do not remember ever getting these problems with any Vray 2.x version. Started to encounter them only with version 3.

This scene actually is rendered the same way in version 2.x.

[LudvikKoutny]

Yes, that may be the case. Non the less, i still feel like i haven't encountered these problems before Vray 3. It may be just that I coincidentally didn't run in this scenario before. Although i am pretty sure i didn't run into this problem using any other engine.

[vlado]

I haven't looked at your scene yet, but here is one that leaks in scanline and mr.

Best regards,
Vlado

[LudvikKoutny]

I haven't looked at your scene yet, but here is one that leaks in scanline and mr.

Best regards,
Vlado

You do realize the surface in your scene has normal flipped away from the light, right? If you flip it the correct way, it does not leak. I am not talking at messed up normals kind of scenario. I am talking about scene where normals are oriented correctly, and yet it leaks, and only in Vray

In the scene I've attached, light leaks regardless of face orientation with Vray, so i suggest you take a look at it.

[vlado]

You do realize the surface in your scene has normal flipped away from the light, right?

So? It works the same way on both sides.

In your mr scene, if you replace the Arch&Design material with a Standard material, you will get leaks too.

Anyways, no point in arguing with you especially - I do agree that the situation can probably be handled better than it is now. One more item to add to my "to do" list...

Best regards,
Vlado

[LudvikKoutny]

So? It works the same way on both sides.

Oh it does, but not in your scene, since in common settings, Fore 2-Sided option is disabled. That's what confused me, as i have it set by default in my maxstart.max.

While this may seem like minor issue, it's quite problematic. Blocking out all the leaking areas turned out to be bit more difficult than it seemed.

[vlado]

Did you get access to the stable builds? I might be able to hack something.

Best regards,
Vlado

[LudvikKoutny]

Awesome! I checked with my boss and yes, we have access to stable beta builds, as well as nightlies.

[vlado]

Ok then, check the builds on Monday and see if they work better - for V-Ray lights, at least.

Best regards,
Vlado