liquid inside of glass breaks render passes

[itsallgoode9]

Rendering a liquid inside glass breaks ability of the render passes to correctly separate refraction and SSS from reflection. I feel like it used to work, but i might be wrong. Same thing happens with a non sss specular material, btw.

i think the image is pretty self explanatory with what is going on. Is this fixable?

[prodviz]

Mental Ray and V-Ray appear to render almost a beauty pass, for the refraction pass too.

I wonder if there is some limitation, or reason why this is the case.

[itsallgoode9]

Mental Ray and V-Ray appear to render almost a beauty pass, for the refraction pass too.

I wonder if there is some limitation, or reason why this is the case.

i mean, technically, everything is a refraction once it goes through the glass, so I can understand why it renders like this. But, like I mentioned, I swear this worked correctly at one point. could be imagining things though.

[stratified]

Hi,

In Octane, SSS is only captured on the second bounce. That means the ray needs to pierce the medium on the first bounce and scatter on the second. This happens in the liquid only case (i.e. pierce the liquid on the first bounce and scatter on the second bounce). It doesn't happen in the bottle liquid because (depending on how it's modelled), you can minimally scatter on the 3d bounce.

SSS render pass in Octane only captures on the 2nd bounce.

SSS(1).png (6.38 KiB) Viewed 4110 times

I don't think the behaviour was any different (maybe there was a bug in some development build).

I don't think there's anything special about V-ray or Mental ray's behaviour. If your scene is almost exclusively glossy and specular reflections well then the reflection pass (direct + indirect) is exactly the beauty pass. Octane does the same thing.

I hope this clears it up a bit.

cheers,
Thomas

[itsallgoode9]

what about the fact the the reflection is being combined with the refraction pass in the second example? Shouldn't those strong reflections be on the reflections pass and not the refraction pass?

That's what i'm concerned more about than the SSS not being put on its own layer. I'd just like to be able to get the liquid color in a pass without the reflections on it.

[abstrax]

what about the fact the the reflection is being combined with the refraction pass in the second example? Shouldn't those strong reflections be on the reflections pass and not the refraction pass?

That's what i'm concerned more about than the SSS not being put on its own layer. I'd just like to be able to get the liquid color in a pass without the reflections on it.

What you see there is the internal reflection at the inner glass surface, after the path has been "refracted" (is that proper English?).

[itsallgoode9]

oh!. damn. well that poses a couple more questions:

1. in real life are there 3 reflections in a liquid glass situation? Front side of the glass, inside of the glass, liquid? or are there only 2 since the liquid and glass interior kinda act as one solid surface? This is just my curiosity because it's kinda hard to actually see that in real life.

2. in the render passes, shouldn't that interior reflection be on the reflections pass and not the refraction pass? Even if it's technically considered a refraction because it's going through glass (maybe i'm wrong about that) from a usability standpoint, not having both layers of the reflections on the reflection layer, kind of breaks the usefulness of both the reflection and the refraction pass in a liquid/glass situation.

Say you have 10 flavors of juice that are different colors. if that refraction layer were completely isolated from the reflections, you could render one flavor and adjust it in post to make the other 9, without screwing up the reflections. the way it's currently setup, you can't do that. Sorry i'm always asking about super specifics situations in these glass threads!