UHD Cache precomp issue

[Jpjapers]

Im having an issue with a previously fine file whereby the UHD Cache precomp stage seemingly doesnt finish in either interactive nor production rendering. Last try at a 2k image i stopped it after 90 minutes.
There have been some small changes to the file since i last rendered but these were purely positional changes to objects in the scene and switching to a slightly different camera angle.

I tried merging to a new file but the issue persists. Ive tried hiding various selections of objects to narrow down a problematic object but still nothing.
Its having an extremely low UHD Cache success rate in the low single digits according to the VFB but in a previous save version it is around 25%.

Its an exterior scene, lit with a HDRI. Lots of translucent vegetation and some water in the right side of the image.

Any ideas how i can further troubleshoot this file as currently it just will not render and reverting to an older save loses quite a bit of work.

[TomG]

Just thoughts on troubleshooting steps

- If you load the old scene, it still calculates fine? (in case it is an update to Corona or some other plugin, and not a scene change, that has caused the issue)

- What happens if you use the 4K cache instead of the UHD?

- You can force a minidump, which if you want to send in a ticket will basically let us see what the software was doing at the time,https://support.chaos.com/hc/en-us/articles/4649117083409-How-to-report-issues-3ds-Max for forcing a crash

- I know you did some object hiding, but what about hiding everything leaving the HDRI and a new cube, does it work then? Then add objects back in groups?

- What happens with a Material Override set to a default Physical Material? Might pin it down to some translucency or volume textures.

- Thinking of volume textures, anything that uses a volume (including the absorption etc in a standard Phys Mat) is applied only to enclosed objects, and not to single sided things like planes? (Remembering that on a plane, Corona has no idea where the volume stops, which can "embed" the camera inside a volume)

[Jpjapers]

Just thoughts on troubleshooting steps

- If you load the old scene, it still calculates fine? (in case it is an update to Corona or some other plugin, and not a scene change, that has caused the issue)

- What happens if you use the 4K cache instead of the UHD?

- You can force a minidump, which if you want to send in a ticket will basically let us see what the software was doing at the time,https://support.chaos.com/hc/en-us/articles/4649117083409-How-to-report-issues-3ds-Max for forcing a crash

- I know you did some object hiding, but what about hiding everything leaving the HDRI and a new cube, does it work then? Then add objects back in groups?

- What happens with a Material Override set to a default Physical Material? Might pin it down to some translucency or volume textures.

- Thinking of volume textures, anything that uses a volume (including the absorption etc in a standard Phys Mat) is applied only to enclosed objects, and not to single sided things like planes? (Remembering that on a plane, Corona has no idea where the volume stops, which can "embed" the camera inside a volume)

The material override was a great idea that I hadn't thought of.

That narrowed it down to a material issue. I disabled the override and disabled displacement it got to rendering fairly quickly so i thought theres clearly a rogue material somewhere.
Couldnt find anything odd so went back to randomly hiding things.

I thought i found the problem object. When i hide the object the scene renders and the success rate increases significantly.
But when i apply a new blank material to the object the problem doesnt go away. Also the object in question renders fine when isolated.

The object in question or its material hasnt been altered for a dozen or so versions of this file either.

I then tried hiding half the scene but kept the problem object visible and the scene renders fine.
Im wondering if this is some sort of memory issue. I have 128gb in my system and using about half of it.

Since this scene was successfully rendered i have updated to 12.1 from 12.0

Ill do some further digging but i will try and send a minidump as this is looking like a very hard issue to troubleshoot without seeing internal workings.

[TomG]

TY for the extra info! If the scene is shareable (perhaps it can be shortened to the problem object and another object or two, enough that the problem occurs, but reduced so that nothing NDA breaking is involved), you can send it in by ticket for us to look at https://support.chaos.com/requests/new - otherwise nothing springs to mind for me at the moment based on the description :(

[Jpjapers]

TY for the extra info! If the scene is shareable (perhaps it can be shortened to the problem object and another object or two, enough that the problem occurs, but reduced so that nothing NDA breaking is involved), you can send it in by ticket for us to look at https://support.chaos.com/requests/new - otherwise nothing springs to mind for me at the moment based on the description :(

Ive reopened the original file this morning and its rendering fine. Very very strange.
If it happens again and i can strip the file down to a problem object ill send it over.

[TomG]

Ugh - well, hurray it's working, but ugh for unknown random issues where you never know if they will pop up again. If it does, we'll be here to sort it out!

[Jpjapers]

I submitted the scene on the support portal a few days ago

ID 326017

Ive noticed that if its getting stuck on the UHD pass isolate an object and then render it with IR, then stop it and start the render it tends to actually start rendering.

[Jpjapers]

I believe i have solved this.

The culprit appears to be a Corona Decal that was created in corona 12.0. Im using 12.1 now.

The decal had a corona material applied and was purely being used for displacement. If I hid the decal, the UHD/4K Cache would work as expected.
If i unhid it during IR, The render would continue as expected. But if i tried to begin a render IR or production, with it visible. The UHD Cache wouldnt complete.

This makes sense as to why both a material override or disabling displacement globally would fix the issue.
Replacing the decal with a new one with the same settings and same material applied appears to have fixed the issue.

This suggests to me that there is a potential bug in decals created with v12 but migrated to v12.1.

I will see if this still happens when the scene is simplified and if so ill send it on the support ticket.

[Aram Avetisyan]

It does sound like a bug.
If you manage to get to the simplified version of the scene, and exact issue still appears, please send it over. Thanks in advance.

[Jpjapers]

I tried simplifying the scene and tried merging those pieces to a new file but i couldnt replicate it.
This file however has been through a handful of different saves with the issue still presenting until i replaced the decal.