Stacked glass refracts black

[Terri Brown]

Hi guys,

 

Here's one that's stumped me for yonks, so I'd better post about it now and hope someone out there has the answer.

 

Often when I have a few sliding windows stacked together the refractive result is bizarre. As you can see on the test render below, one of the windows is slid out slightly and reveals the sea behind perfectly. The stacked ones to the right however do this bizarre thing and black the background out.

 

My sea is a plane with a sea vray dispacement mod added.

Glass settings attached, along with a screen grab of the windows.

 

Using Vray 3 with 3DS Max 2015.

 

Excuse the render - testing out camera angles for now :/

 

Please help!

 

Thanks,

T

 

[jasonstewart]

Increase max depth in refraction settings of the material would be my first suggestion.

[Terri Brown]

Hi Jason,

 

I did so - went up to 13...didn't work. How high should i go?

 

Thanks

[Terri Brown]

Please...anyone other suggestions?

 

Thanks

[jasonstewart]

Hmm must be something else then. Can you post the settings for the material?

[Terri Brown]

The settings are the same as I posted first, except that I pumped up the max depth refraction to about 13. See attached another image where it does the same thing - the glass of the window causes the balustrade outside to render black. When I hid the window glass the balustrade rendered fine. They both have the same glass material applied.

 

Strange.

 

 

Just FYI:

 

Vray 3, 3DS Max 2015, lit with an HDRi vray dome light. Irradiance Map and Light Cache for GI.

[ezequielbay]

The only thing i can tell you is that i had the same problem and couldn't solve it, must correct it in post production.

[Terri Brown]

The only thing i can tell you is that i had the same problem and couldn't solve it, must correct it in post production.

 

Well that's the route I'm forced to take, but to be honest it's frustrating and time consuming. I'm sure one of the geniuses on this forum will be able to help us

[michalfranczak]

Maybe this tutorial will help? http://www.evermotion.org/tutorials/show/8109/tip-of-the-week-advanced-refractive-material-techniques-in-vray

[NoodleLuff]

Maybe try checking override depth in global switches and upping the number?

[Tommy L]

to check if the material is reaching its max depth you can change the Exit color in the material. This is the return color at max depth (default black). If that changes the color then you have a depoth parameter, either in the globals or in the material, thats being reached/exceeded.

If it doesnt change the color then you have a refraction issue or fog or other volume effect thats preventing the object being transparent or it may be reflecting the lower half of a HDRI (which is frequently black). To test that you can put a different object in the HDRI shader, or mirror your HDRI down.

with mulitple layers of glass you have to remember that the effects/math oif transparency is cummulative. You must also remember to use sensible glass thicknesses.

IMO you should avoid fog altogether for architectural glass, the window of sweet spot is incredibly small and botht the saturation and value of the swatch have an effect on its amplitude.

[jasonstewart]

One more thing I thought you might check, make sure you don't have any reversed faces. They cause havoc with transparent materials.

[thomascoote]

2 things to try.

 

First, which has already been suggested here, in the global switches rollout set your max depth override to something like 50 and test. If that solves it you know it's Max Depth you need to tweak.

 

Second, I had this problem the other day rendering a double glazed glass wall panel with a vrayblend material on there for the frosting pattern. Fixed it by switching my VrayMtl's for Vray2sidedMtl's, default settings in the 2sided. Worked perfectly straight away.

[Terri Brown]

Hi everyone,

 

Thanks so much for the constructive replies. I had to leave this project for two weeks to move onto another one, but I'm back on it now.

 

Turns out you were all right about the global override depth switch. I upped it to 50 and voila! I always use accurate real-world measurements so I thought it was a material issue.

 

Thank you so much guys! I rendered with the original settings, then tested a section with the new override depth settings. See below:

[Terri Brown]

Just one question regarding the depth issue:

 

I don't particularly want to check override depth as it affects all my different glass materials, and produces ugly effects in other objects (like the glass table). Surely I can pump up the individual material max depth to serve the same purpose? Except it doesn't seem to work. When I pump up the window glass refraction depth to 80 it still renders black. But as soon as I tick global override depth and set it to 20 it renders fine.

As I mentioned I don't want a global setting, just the individual material.

 

Any suggestions?

Thanks

[thomascoote]

Just one question regarding the depth issue:

 

I don't particularly want to check override depth as it affects all my different glass materials, and produces ugly effects in other objects (like the glass table). Surely I can pump up the individual material max depth to serve the same purpose? Except it doesn't seem to work. When I pump up the window glass refraction depth to 80 it still renders black. But as soon as I tick global override depth and set it to 20 it renders fine.

As I mentioned I don't want a global setting, just the individual material.

 

Any suggestions?

Thanks

Did you increase the reflection aswell as refraction depth?

[Terri Brown]

Did you increase the reflection aswell as refraction depth?

 

Reflection max depth = 50, Refraction max depth = 80.

 

Still black

[thomascoote]

Reflection max depth = 50, Refraction max depth = 80.

 

Still black

I'm at a loss then sorry