iRay Water Shader - Help needed

AndyS

Hi,

while converting a small waterpond setup to jRay, I experienced a strange behaviour of the refraction / dispersion handling of the render engine. I got the impression, that the renderer is not able to determine uniquely what side of a surfce belongs to the less dense or more dense medium.

So far the calculation of the rays from i.e. air into water seems to be OK. But the way back fails.

In the setup I applyed the iRay water shader preset to the surface of my little waterpond. As long as the light entered my scene in a really steep angle, I can see the ground of the pond. As I lowered the angle for the light, the pond suddenly appeared almost black.

So I did some tests, which you see in the attached pictures. I compared the results of the 3Delight render engine (left) with that of iRay (right).

First the refraction and reflection. After intoducing some small waves I detected those dark areas. That let to the comparison of the underwater-view in the second part. Here I saw that the total reflection, which appears from a distinct angle, was missing for the iRay render. And you see that the "back"-refraction (from water out to the air) is handled in the wrong way.
Please don't be irritated by the effect of less light transmission with increasing depth of the water. For 3Delight I used the special Ubervolume shader of omnifreaker. But iRay can handle it very easily by itself.

Or are there any special parameters of the water shader, which have to be altered ???
The iRay water shader is part of the DAZ 4.8 standard installation.

The last picture shows the limit angle where you can / can not look to the ground due to the wrong handling of the "back"-refraction with iRay.

I hope, somebody can help. Or I have to wait for an update with that bug solved.

Yours
Andy

Rashad Carter

Two questions.
1. What were your settings for Caustics in the 3Delight versions? 2. Is the water model a mere 2d plane or is it a fully 3d object with volume?

mjc1016

Geometry is critical in any PBR...simple flat planes just don't cut it, when it comes to things like liquids. Trying to apply formulas that are working on the assumption that the item in question is a 'volume' of water does odd things. In other words, in a PBR, like Iray, a simple one poly thick plane is just a 2 dimensional construct of no thickness...unless it's the boundary of a volume.

AndyS

Hi,

thanks for the answers.
Yes, I tried with caustics setting - no change.
Caustics only added a lot of little white spots all over the scene. Even those areas where reflected and scattered light never can reach. Looked like a blizzard.

And yes, instead of the simple plane, which worked perfect with 3Delight, I used a cube. - Same effect: no change of the odd behaviour.

Andy