Incorrect glass edge color calculation in V-Ray (comparison with Corona)

[Max_Max1]

Hi everyone,

I am rendering a glass shower panel with real geometry thickness and physical chamfers.

In Corona Renderer, the glass edge is rendered correctly with a consistent, deep green tint along the entire height. In V-Ray, however, the edge calculation seems broken — it turns gray/faded at the top instead of maintaining uniform absorption color.

Current VRayMtl settings:

• Max depth (Refraction) = 50

• Translucency = None

• Physical Chamfer modifier applied

It looks like V-Ray calculates internal refraction / volumetric absorption differently or incorrectly compared to Corona under the same conditions. Is this a known calculation bug/limitation in V-Ray, and how can I fix it to get a physically correct glass edge?

At first I thought it was the reflection, but when I completely turn off reflections in the material, nothing changes. I completely removed any intersections between the glass and other objects in V-Ray — the glass object does not intersect with anything. The smoothing groups are correct in both V-Ray and Corona, where each polygon has its own separate smoothing group ID.

In Corona, caustics rendering in glass is disabled.

1 render Vray Reflect on backside = on,
2 render Corona render.

(Renders attached below)

[maru]

Random idea: try setting Options > Cutoff to 0.0

Also, one of our users had an exactly opposite observation - Sphere thickness with shell modifier

[ChuckRT]

First of all, dont spect to have exactly same ressults from Corona to Vray, if you want to achieve it, you will have to change some settings but it will be some cases where you could see both works differently.

It seems that theres something odd with IOR which could be from Chamfer smooth, have you tried turning it off? I dont think that increasing max depth will improve anything in a simple box. Have you tried leaving everything as defaults.

[Max_Max1]

@maru Setting Options > Cutoff to 0.0 didn’t make any difference — the result remains the exact same.

@ChuckRT

1. Chamfer & Smoothing: If I turn off/remove the Chamfer completely (leaving the glass as a simple box), the result is still the same. The smoothing groups are configured correctly (each polygon has its own separate smoothing group ID, so there is no normal distortion causing IOR issues).

2. Max Depth & Defaults: Interestingly, setting Max depth to 8 (for both reflection and refraction) combined with Reflect on backside = ON actually gave me the best result so far. However, the top part of the edge is still somewhat grayish and not completely green.

[ChuckRT]

That top part was the thing making me wonder if theres something odd with refl IOR and smooth, im seeng some minor differences in the model from corona and Vray examples, could it be that you have a duplicate glass object?

Have you try using Volumetric Translucency (which is the same that Corona uses) I mean, fog color would be enough but, theres definetely something odd in your scene.

[Max_Max1]

@ChuckRT

I have the exact same feeling that something is off!

However, the geometry in both Corona and V-Ray is 100% identical, yet the rendered result is completely different. There are no duplicate glass objects in the scene.

To test this further, I even replaced the glass in V-Ray with a brand new, basic Box object with the exact same dimensions, and I still get the exact same result.

I also tried changing Translucency from None to Volumetric, but the result remained identical. Fog color on its own should definitely be enough for standard glass absorption.

I am attaching a render below showing the basic Box object rendered in V-Ray instead of the glass panel with chamfers.

[ChuckRT]

could it be a Light issue? do u mind attaching the scene, im really curious on whats happening, Ill understand if you cant share it.

[Max_Max1]

Sure, I’ll prepare the scene. I’m working in 3ds Max 2024 — will that version work for you, or should I save it as an older version?

[ChuckRT]

I use Max 26/27 so its ok in max 24, thanks

[Max_Max1]

_Vray Glass issues - Google Drive

I have added a Google Drive link.

I cleaned up the scene and removed everything unnecessary, leaving only the core setup, but the issue still persists. I also organized everything into layers. For the glass, I included both versions separately: a simple Box and the geometry with the Chamfer.

[ChuckRT]

Ok I have made some tests and I didnt notice you have a window in the left where light is entering , its causing the top part white filling with window reflection, If I move a little bit to the Left, the glass edge looks completely green.

I reset everything as default, create a new material from scratch just changing the fog color as you have and looks the same.

I recommend you to use the HDRI in a Vraydome for environment, specially in interiors, using its “Adaptive Dome” option makes faster sampling calculation (as far as I know), and using Lock texture to icon to just rotate the dome instead using offset in texture.

I think the post Maru shared to you resambles this, where Vray and Corona has different ressults with its refraction, that was my post by the way

[Max_Max1]

Alright, but if the white part at the top is just a reflection or refraction of the window, why does the exact same problem happen even when I completely turn off the HDRI or block the window with a box?

I also tried recreating the material from scratch just like you did, but that didn’t help either.

I did notice that shifting the camera fixes the edge, but the problem is that I am planning a camera animation, so this issue will definitely be visible as the camera moves.

[ChuckRT]

@Max_Max1

why does the exact same problem happen even when I completely turn off the HDRI or block the window with a box?

I did try that too and then I tried with this light only, no matter which other light you have in scene, the reflection still exist, I noticed you only have a couple of Vray Render Elements, try Refraction/Reflection/Specular Elements and take a look of its behaivior.

I dont think theres an error in the material, nor the settings, but I recommend to keep them simple, just the default ones.

Take a look into this thread that Maru shared, even recreating the same materials and lightning, Corona and Vray behaves differently. Dont spect to work exactly the same.

[Max_Max1]

@ChuckRT

I recommend you to use the HDRI in a Vraydome for environment, specially in interiors, using its “Adaptive Dome” option makes faster sampling calculation (as far as I know), and using Lock texture to icon to just rotate the dome instead using offset in texture.

I did some testing with different formats and realized that the VRayDome really doesn’t like Color Correction nodes; it seems to strictly prefer pure HDR/EXR files.

I tested 8K vs 18K maps, and the render times were absolutely identical (literally a 1-2% difference, which is just a margin of error).

But here is the interesting part: A pure HDR in the Dome Light renders in 2 minutes. However, if I plug that same HDR into 2 Color Correction nodes and then into the Dome Light, the render time shoots up to 5 minutes!

At the same time, if I put that exact same setup (HDR + 2 Color Corrections) into the standard Environment slot (8), it still renders in just 2 minutes. This seems really weird.

How can i use color correct saturation with dome light?

[Max_Max1]

I figured out why the top of the glass was looking cut off — it was the camera’s Clipping / Slice Plane! If I adjust the clipping distance, everything works correctly. Facepalm

By the way, I used the exact same V-Ray Physical Camera in Corona, and it rendered differently there.

I really wish the clipping plane would stay strictly vertical when the “Automatic vertical tilt” option is enabled.

ChuckRT Thank you so much for all your help with this!

[ChuckRT]

ohhhh thats why the ressult were different when moving the object to the left, I just check the camera once and didnt even pay attention you were using Clipping.

About automatic vertical, could it be camera resolution mod? try disabling and use Override Max resolution from vray camera, since I dont have it installed didnt saw that too.

I dont usually use HDR but If I rememeber correctly you can use it with Color Correct with no issues, but never tried using 2 at the same time, Why do u use 2 color corrections?

[ChuckRT]

Ok I did check and youre right Its not about camera resolution mode, Guess vertical still depends on target even with guess vertical, Sincerly I didnt notice this because I always set the target aligned to camera even when its turned off, I have notified as a bug or request for a modify feature.

[Max_Max1]

@ChuckRT

I dont usually use HDR but If I rememeber correctly you can use it with Color Correct with no issues, but never tried using 2 at the same time, Why do u use 2 color corrections?

I tried rendering with just a single Color Correction node and still got the same 5 minutes instead of the usual 2 minutes I get when using the Environment slot.

@ChuckRT

I dont usually use HDR but If I rememeber correctly you can use it with Color Correct with no issues, but never tried using 2 at the same time, Why do u use 2 color corrections?

As for the camera resolution, it doesn’t affect this at all — it only changes the frame resolution. The camera’s clipping plane itself remains angled, and the “Automatic vertical tilt” checkbox does not straighten or align it in any way.

Could you try rendering the scene yourself with three different setups using my environment map:

1. VRayDome with Color Correction

2. VRayDome without Color Correction

3. Standard Environment slot

I’m really curious if you’ll see the same 2x performance drop on your end as well.

[hermit.crab]

Logged as (VMAX-15850).
Linking threads.

[ChuckRT]

Sorry I didnt made the tests in your scene, instead I did it on a simple one so you can see and compare in a better way the changes between using HDR on a Dome or Environment, Ill try later in your scene.

The scene settings are mostly as default in Vray 7.2 (just changed LC subdivs from 1000 to 500 and enabled Path Guiding experimental which speed up render times)

All images done with HDR in Environment took more time than using it in a Dome. As far as I know vraydome uses better calculations and improves sampling, I even remember that environment couldt get any light info, just color and reflections, thats why vray has always needed a source light such as vraydome, maybe everything has changed since newest versions.

The ressults with dome also improves little image quality, about using Color Correct it sure takes longer time because your squeezing info from an image that its there in a minimum value because its not well calibrated or its not intended to use it that way, so I recommend the following:

1 Use Color space as Gamma inverse and use 0.5 value to get more light from the image, you would improve render time instead using CC, its not ideal but it would help.

2 Edit the image and add it a little point of white color where the light source should be, this should be the ideal to improve render times even more and asure better HDR quality.

3 You are actually using this option, to compensate light source get sun support but dont change HDR values from a CC, leave HDR as it is and use it in a Dome.

I strongly recommend to check this video from Adan Martin, that explains all of this, check all of his content, his knowledge seems infinite , its in spanish but I think you can enable subtitles.

Im uploading the simple scene in max 23 so you can compare in your machine.

HDR Dome Test.zip (209.1 KB)

Hope this helps.