Strong Shadow Catcher Flicker

[Sam67c]

Hi there,

I do a lot of rendering using the shadow catcher material, usually without issue. Recently though I've had a few scenes where the shadows have a very strong flicker that doesn't go away with more samples/UHD presision set to 4/changing the denoiser....etc

The only thing I've found that is a clear trigger for it is having any ornatrix hair objects in the scene?

Has anyone got any ideas why this would be or a workaround?

I have attached my render setting and a short clip (blacked out for IP reasons) with the shadow pass mulitiplied to more clearly show whats happening.

Thanks,
Sam

3Ds Max 2021.3 - Corona 6.1
Threadripper 3960x, 64gb ram, rtx 3070

[Sam67c]

Slight update/correction to this:

The flickering comes from the reflection in the shadow catcher material, if I set the level to 0, the flickering is gone.

It appears to be randomly alternating between reflecting the ornatrix hair or the underlying geometry?

Baking the Ornatrix hair down to a mesh or alembic does not change anything

Any help with this would be great as I'm completely out of things to try!

[Avi]

Hi,

Can you send me your scene file for a close inspection? You can upload your scene using our private uploader: https://corona-renderer.com/upload

Once you have done uploading your scene, do let me know the file name.

Looking forward to hearing back from you.

Regards,

Avi

[Sam67c]

Hi Avi,

Sorry for the delay, had to reproduce the error in a new scene.

As far as I can tell it has something to do with intersecting objects reflected in the shadow-catcher material when reflections are turned up?
I originally thought it was to do with having ornatrix hair objects intersecting (which definately seems to make it worse) but I have had similar issues with skin material objects intersecting.

I have uploaded a scene file "1620755056_AnimBox-Shadow-Flicker.zip"

The flicker is less strong in this scene but i have attached a short clip rendered from this scene to show you what I mean.

Thanks for looking at this,
Sam

[Avi]

Hi,

Thank you for sending in your file. I had a look at your file & I found that shadow flickering is happening because of broken XForms on the object. Resetting the X-form fixed the issue. However, this issue has already been resolved in Corona 7. If you use Corona 7, you won't even need to reset Xform and it renders fine.

Here you can see a breakdown of the test which I did.

https://bit.ly/3uYsRYS

I hope this solves your issue.

Thank you.

Regards,
Avi

[Sam67c]

Wow, thank you!

Very glad it's such a simple fix and even more pleased to hear it's fixed in 7.

I'll be switching to 7 as soon as a main release comes out, I've played around in the dailies and it seems great.

Thanks for your help!
Sam