foam flickering - beer animation

[jgreen3895]

Hello,

I'm a new user of Phoenix FD and for my first animation using the software I decided to try the typical "filling a glass with beer" project so I can learn some of the nuances of the software and workflow. I've attached a sample of the current animation and as you'll notice there are two flickering problems regarding the foam bubbles. I am also attaching some images so you can see some of the settings currently being used. I'm happy to upload my scene or provide any more information if needed.

https://streamable.com/jr3b4


1) The first problem has to do with the underwater bubbles. It's hard to tell what's happening at full speed, but if you compare frames 29 to 30 you'll see the problem (may need to download the video to scrub specific frames). Basically, on frame 30, a lot of the bubbles, especially the smaller ones towards at the bottom of the glass just disappear and then they re-appear on frame 31. The problem of bubbles appearing and re-appearing is happening constantly even though less noticeable on some frames. 29 to 30 is one of the more extreme examples, but it even appears to be happening from frames 28 to 29 towards the top left side of the glass just beneath the foam. These frames were rendered on a render farm using distributed rendering. I've been told by the people at the farm that they've seen this issue before and re-rendering the problematic frames will fix the problem, but I'm not totally convinced it won't happen again.

I do want to note that I do have some animation on the PHXFoam001. Specifically on the Size Threshold and Count Multiplier. I thought that could potentially be causing some jumping, but when I rendered some of the problem frames locally and compared them to the frames that were rendered distributed on the farm my results did not have this issue. And this issue also occurred on frames that didn't even have animation anyway. Any thoughts on this would be appreciated.



2) The second problem has to do with the flickering of the bubbles above the liquid. This type of flickering is more reminiscent of the type of flickering usually seen due to GI problems, but this animation actually doesn't use any GI. It's completely off (I've tried it on as well and that didn't help). My first thought was maybe the glass or glass material (not having enough refraction depth or something) might be the issue, but I've done a number of test renderings without the glass to try and isolate the issue yet still the flickering occurs. This animation is using the mode "bubbles", "rendered as geometry", "bounces 1", and "reflection cutoff 0.5". I've tried adjusting all of these settings both independently and together, but can't seem to get the flickering to stop. I've raised bounces to 100, lowered the cut off to .005, tried Cellular mode, etc. but there was still flickering.

I also lowered the Count Multiplier to .1 during some tests to get quicker results and did notice that the flickering was less. Perhaps that's just because there were less bubbles by 90%. I also want to point out that there doesn't appear to be as much flickering at the very top of the foam where it is higher than the rim of the glass. This makes me think the flickering is most apparent where the foam is densest. This is all just speculation though.

Lastly I've also tried messing with Optimize Congestion, Reflection Coloring, and Environment check boxes. Neither of those seemed to help, but I'll be honest, I'm not sure if the ladder two options were setup correctly. Not sure what type of map is supposed to go in reflection coloring (if any) and as for environment checkbox, my scene uses an HDRI map and a background image for the environment. I tried plugging those in. Not sure that's correct though.

I have no idea at this point and can't seem to find a solution to this problem. Any suggestions would be helpful.



Thanks!

[jgreen3895]

Please use the following link to see the animation.

https://streamable.com/jr3b4

***Edit...same link as 1st post. Sorry for the double post. I don't see a way to delete a post.

[georgi.zhekov]

Hello,

First things first - make sure you are using Phoenix FD's latest build.

If you have an animated Count Multiplier Phoenix will kill and create new bubbles during your animation - which is the issue you are having. My advice is to disable the animation for the Count Multiplier.

The next thing that caught my eye is that your reflection bounces are too low - generally around 5 or 8 should work better for such a scenario.

Hope this helps.

[jgreen3895]

Hello Georgi,

Thanks for your response. I am using 3.10. I am also including a link to another video to help further explain the issue. I will try disabling the animation on the count multiplayer, but I don't think that is the problem with the flickering for the underwater bubbles. The animation is only on a portion of the entire sequence and yet flickering occurs even after there is no animation on the count or size threshold. Furthermore, when testing the rendering locally the bubbles that seem to sometimes disappear were actually there so it leads me to believe this is a network/distributed rendering issue.

As for the bubbles at the top, I've tried increasing reflection bounces to the max of 100 and have tried a number of combinations adjusting all sorts of settings, but can't seem to find anything that works.

Please check out the link and let me know if you have any other thoughts. Grateful for any advice.

https://streamable.com/5iavc

Thanks!

[Svetlin.Nikolov]

Hmmm, since you are rendering only the particles Above the size threshold and you are animating the threshold so that it increases over time, this should cause the smaller particles to disappear as time progresses - wouldn't this be what is happening on frame 193?

Since we indeed had issues in the past where the count multiplier caused flickering of particles in animation, would it be possible to verify which Phoenix version the render farm uses and whether rendering goes through vrscenes - and if so, which V-Ray version the farm uses? Is it an option to run a test render locally so we can exclude an issue with the versions?

I would suggest running the render with the Bounces set to at least 6-8 - 100 is a huge value, but it should definitely be above 1. Cellular is also a must for very tightly bunched particles, or some of them would pop during animation.

Also you might try reducing the Light Cache Speedup to 0.8-0.9 or completely turning off the Phoenix Light Cache of the Particle Shader if you can afford the slowdown this is going to cause when running a test animation render.

I also notice that the foam head has some horizontal line artifacts which we need to investigate as well.

Seems like we might not have the answer to all issues, so if it's possible to send the scene and we can investigate it, this would be great.

Cheers!

[jgreen3895]

Hey Svetin,

Thank you for your input. Below is a link to download the archived scene files (it's quite large due to the cache files). The cache files may need to be re-linked, but all settings in the scene should be accurate as far as what they were when the animation was rendered.

https://drive.google.com/open?id=1CC...AyhXo-4uTaR4nA

since you are rendering only the particles Above the size threshold and you are animating the threshold so that it increases over time, this should cause the smaller particles to disappear as time progresses - wouldn't this be what is happening on frame 193?

I am going to try experimenting without the animation, but I do not think that is causing the problem. And if anything it would cause particles to appear wouldn't it? Because the animation is lowering the threshold back to 0 and the count back to 1. If you watch the video linked in my previous post though you'll see that the animation of the Size Threshold and Count Multiplier stops after frame 250, but the flickering issue still occurs on frames after 250. The animation changes are only occurring between 120 and 250. Also, I show that I rendered frame 193 locally just to check if it matched the render from the render farm and it did NOT. The local frame test looked correct. So, I'm thinking it stands to reason that somehow the distributed/network rendering on the farm caused some issues.

I've asked the render farm company and they use V-Ray 3.60.04 and Phoenix FD 3.10.00 and they've said the scene renders from 3DS Max (as opposed to vrscenes). The company is Garagefarm.net


I'll continue to try experimenting with bounces, cellular, light cache speedup (which I have no idea what it actually does), etc. As for the horizontal line artifacts, not sure I see what you mean. My biggest concern is the foam flickering above the liquid, but of course I'll need to find solutions to both problems. I greatly appreciate you taking the time to help. I feel like I'm so close to getting this all to work and just want to overcome these last few issues. If any more information is needed just let me know.

Thanks!

[jgreen3895]

Sorry if anyone had issues downloading the link. File sharing on google drive might have been set up wrong. Should be fixed now, but if there are any issues just let me know. Thanks to all who are taking their time to help me out with this issue.

[jgreen3895]

Small update...

Okay so I've been talking with the render farm company and they let me know that in regards to the 1st issue I'm having (bubbles popping in and out beneath the surface of the liquid), they re-rendered one of the problematic frames and the re-rendering seemed to produce the correct results. They believe that this issue may be due to 3DS Max having problems reading the cache (perhaps only when distributed/network rendering is happening). They think re-rendering the problematic frames could very well solve this problem. They also recommended trying vrscenes next time as well.

It seems as though right now the more concerning of the two problems is the second issue with the flickering of the foam bubbles at the top of the liquid surface. I haven't had a chance to do more local testing on this with some of the suggestions that have been mentioned here. If anyone had any ideas or finds a potential solution please let me know.

Thanks.

[Svetlin.Nikolov]

Ah, no no - vrscenes will be a less reliable solution because they are less tested with Phoenix - what I had in mind was that if they were used by the farm, then we'd know it's a different kind of problem.

We're looking at the scene right now... Will ping you when we know more.

Cheers!

[jgreen3895]

Okay thanks!

[jgreen3895]

Another quick update. Been trying some local tests and playing around with the following settings: reflection bounces, reflection cut off, cellular mode, light cache speedup, but unfortunately so far have not come across any solutions to the foam flickering. Also tried removing the animation off Count and Size Threshold on the Foam object, but had no effect whatsoever.

[georgi.zhekov]

Hey,

From our tests the scene renders differently when there is Light Cache enabled in the Particle shader and the machines used for the render have different number of cores.
So if you wish to render it with a few PCs you will need to turn off the light cache (note that this will make the renders slower).
Is there flickering on your side if you render locally on 1 machine?

[jgreen3895]

Hey Georgi,

When rendered locally, there is no flickering/bubbles popping in and out for the under the surface bubbles whether light cache is enabled or disabled. So it does sound like the 1st issue is due to rendering on multiple machines perhaps with different cores and not because of the animation on the foam count or size threshold.

Flickering for the foam bubbles above the surface still occurs when rendering locally though. Disabling light cache also drastically increases render times. Did you find this helped for the above the surface foam? Because if so, the render times become so long that I may not even be able to afford the rendering anyway, but either way, from my tests the foam flickering above the surface occurs regardless of the light cache settings anyway.

[georgi.zhekov]

Hey,
The flickering in the top part happens due to the Domelight paired with the texture that it is using. With some tweaks you can go around that.
Disable the Light cache, turn off the highlights for the foam and plug the HDRI texture in the Environment slot of the Particle shader. This will fix the flickering but will render quite slow.
If changing the lighting is an option - it's best to switch the Domelight to something else.

As for the bubbles in the liquid we are working on a fix that should solve the problem using different core count and I hope it will be in the nightlies soon.

[jgreen3895]

Hello Georgi,

Thank you for your reply. I will give this a try first chance I get and report back with results. I do just want to confirm a few things though.

1) When you say turn off the highlights do you simply mean set the "highlights strength" under cellular/bubbles/splash properties roll-out to "0"?

2) Disabling the light cache on the foam properties and plugging in the HDRI texture in the Environment slot, will, like you said, cause the rendering to be extremely slow. And I'm not just talking the frames will take 2 or 3 times longer. They'll take much much longer which might present a major problem when rendering hundreds of frames. Do you have any suggestions that wouldn't increase the rendering time by more than 2 or 3 times the initial speed?

3) Lastly, changing the lighting is an option, but I would prefer to use an HDRI though. Do you know what about this HDRI texture caused the flickering or will the flickering occur with any HDRI texture being used with the Domelight? Perhaps I could use one light for the liquid and another linked only to the foam.

Thank you for all your help thus far!