Crazy artifacts with animated fog volume + camera moving into fog volume

[Spatial]

Hey guys!

This scene is using:
- Phoenix FD ocean tex on a plane for the water surface
- A VrayEnvironmentFog contained within a mesh gizmo to simulate the muddy/murky water (note: this fog mesh gizmo is animated to move right as the camera moves left)

As the camera moves into the fog volume, I'm getting some epic artifacting and was wondering what it could be and how to solve it.
The artifacts do disappear once the camera is 100% inside the fog volume



short video of issue:
https://vimeo.com/383894840
pass: foggy


Render settings are pretty standard with Vray Next 4.30.01

Using Bucket 3/6 for this render
GI settings:



Fog Settings:


Any ideas how to fix? Render times are already 30 mins per frame on a 32 core threadripper

Cheers!

[Philip Shounev]

Hello,

I couldn't replicate this one in a fresh scene. Would it be possible to send over your scene to philip.shounev@chaosgroup.com for a closer look?

Best,
Philip

[^Lele^]

Reset the GI settings to default and try again.
Specifically, do *not* use the LC in animation/camera path mode (i.e. follow the tooltips' suggestions exactly), and see if those issues disappear.

[Spatial]

Thanks for replying Lele. I tried resetting GI as suggested and set to Still and single frame Light cache.
It didn't effect the outcome at all unfortunately even if cranking the subdivs really high.

Just now while trying all sorts of random GI settings combinations I found I could make the artifacts disappear only by enabling "use camera path" in light cache settings as well as set the mode to "progressive path tracing"
This solution is noisy as hell though requiring excessively high subdiv values up in the 20,000+ range. This makes render times pretty crazy.

I might have to bite that bullet though if there's no other solution. (IF the output looks exactly the same as the main render that is)
It's a weird one!

I will package up the max file and send through Philip, thanks

[^Lele^]

Ah, it's been a while since i heard of PPT, eheh.
I even delivered a job with it (an elevator cabin) in, herm, 2005.

Do send a scene over, support will definitely want to see it.

[Philip Shounev]

Thanks for packing up the scene. It turned out that the aforementioned artifacts are related to the fog gizmo custom geometry, for which I've made a note for our developers to look into and investigate further ( issue ID: VMAX-9468 ). Remodeling the fog gizmo geometry is the suggested workaround, as it seems to resolve the problem with the artifacts.

Best,
Philip

[Spatial]

Thanks for looking into that Philip.

Could you elaborate on "remodeling the fog gizmo geometry?"
My scene requires a specific shape for the fog to conform to as I need to composite live actors into that semi circular cutout.
Are you saying it currently only works with a box?

Thanks again
KG

[Philip Shounev]

You could preserve the form of the current gizmo with its circular cutout. F.e. this can be achieved by selecting the upper border of the gizmo geometry, then from the edit poly menu / Edit Edges section use "Create Shape From Selection". Then add a shell modifier to the newly created spline. The idea is to generate a quad-based topology of the newly created geometry (for some reason the "diagonal" edges that were connecting the circular cutout and the corners of the old gizmo geometry lead to those above mentioned issues).

[Spatial]

Ah, thank you Philip, that's an easy fix

[Spatial]

Update: I quaded up the fog gizmo mesh and am still experiencing the issue on one frame now haha. I believe it's just as the camera passes through the gizmo and then its fine once inside the volume,

My aforementioned method of trying progressive path tracing does not match the main render visually at all by the way. (The fog is a lot thicker) so that fix doesn't work in this scenario.

After trying every possible combination of settings I'm reduced to cutting that frame out for now until a fix or workaround is implemented.I do have a lot of other scenes to render using this same technique so fingers crossed it doesn't rear its head again.

[Philip Shounev]

Would it be possible to pack up the updated version of the scene, along with the problematic frame, since I can't reproduce it on my end?

[Spatial]

Will do Philip. I tried again to make a clean gizmo with a fresh shape and shell again but no cigar. Will email through asap

[Philip Shounev]

Thanks again for the provided scene and apologies for the inconveniences. I've made an additional note about the matter with higher priority - indeed there seems to be an odd issue in this exact frame as the camera passes by the edge of the circular cutout, which needs to be investigated further.

Best,
Philip