Ocean sim with foam and splashes flickering at backup interval.

[oophus]

I tried a search but I could not find a similar problem. Sorry if I missed it already.


My problem is with the backup frames in an ocean simulation of a container ship sailing at sea. All the frames of the foam and the splashes work great up until ever 15'th frame where there is a noticable difference in the sim. Looks like the opacity drops somewhat or something along those lines.



The image at the top is the problem image, and the image at the bottom is the way all the other renders are outputed. As you can see it looks like the opacity of the particles are abit lower at the backup interval.

[flipbook]

Don't know if it was fixed in the nightlies but you can set backup to 0 in the output panel and it won't do that but you obviously lose the ability to restore your sim from a backup frame.

[Svetlin.Nikolov]

Hmm, are you sure you haven't enabled motion blur, but forgotten to output velocity to the cache files?

[Ivaylo Katev]

hi, this is very common issue, the most frequent reason is the usage of the particle velocity (perhaps motion blur) in the rendering, without being exported. every 15th frame has the velocity channel for restore purposes and then the motion blur works, that makes the result different.

[oophus]

There is no motionblur in the render, but I did output the velocity channel in case I would render it out with it, but ended up doing that in post.

Edit: Scratch that. By second thought, I think I did not output a velocity channel in this sim, but I did not render with motionblur either.

[oophus]

http://www.filedropper.com/scene01

Here are a couple more frames to see it in motion.

[flipbook]

Ah yes, velocity needs outputting for foam/splash also if you use the motionblur option in the PHXfoam object, I think.

[oophus]

Ah yes, velocity needs outputting for foam/splash also if you use the motionblur option in the PHXfoam object, I think.

Maybe thats whats causing the problem. Even though I have not set the motion blur on within the camera it self, or the camera settings in the render rullout, the motionblur in the PHXFoam nodes are set to "by V-ray". Will give it a try to set it to force off.
Although if thats the case, it would still be a bug if the "by v-ray" is not turning the motion blur off since I dont have it on anywhere in the scene.

[Ivaylo Katev]

yes, if "by vray" causes motion blur without mb in vray, this is a bug. but i'm still not sure that this is the case. can you send the scene without the geometry (to make it small in size)?

[oophus]

yes, if "by vray" causes motion blur without mb in vray, this is a bug. but i'm still not sure that this is the case. can you send the scene without the geometry (to make it small in size)?

Here is the zip wih the scene.

[Ivaylo Katev]

i had a look into the scene, and didn't notice any disturbing settings, have to try it with a simulation, for now you can try the zero backup interval or export velocity workaround

[oophus]

i had a look into the scene, and didn't notice any disturbing settings, have to try it with a simulation, for now you can try the zero backup interval or export velocity workaround

Hmm, I am doing a new render now with velocity channel exported, and no backup interval, but I can still see flickering in the particles which is a bit annoying. For now this will have to do though as I don't have the time to resim and rerender, but I would appreciate it the workaround is ready for the next scene which start on monday.

I stopped the rendering and are going to put the motion blur on since its gonna render throughout the weekend anyway, to see how that goes.

Any tips I have to remember before leaving for today? Is there a preferred way on how to render the motionblur on the particles?

EDIT: For z-depth, the smoke and the foam/splash particles are returning completely white. Is there a trick for them to return the normal gray color that correspond to its surroundings?
The problem exists in the extratex-AO render as well, where its the opposite. The smoke and the foam/splash returns in a black color.

[oophus]

Did a new simulation with the backup interval at 200 frames, so I had 8 seconds of footage to take from between each 200'th frame without the huge flickering. But did some test now on frame 1600, and 1601, and the problem is still there. Frame 1600 renders a bit darker than 1599 and 1601.

EDIT: After attempt to render with motionblur, I see no difference with it forced on or off. The motion blur step in point mode have been taken from really small amounts (0,05m) to high amounts (5m) without a difference in the rendered output.

So rendering this with motionblur wont work either. And yes, I've double checked several times that the velocity checker had been switched on in the splash/mist tab and the foam.

But looking at the output section, the velocity checkmark is off. Could that be the problem? I initially though that was for fire/smoke simulation since there were the same checkmark in the splash/mist and the foam tab.

[Ivaylo Katev]

interesting. you are sure that exactly the backup interval is related to the problem? because aweek ago i was pursuing a bug appearing at every 15th frame, that was a coincidence and had no relation to the backup

[Morbid Angel]

yeah happened to me too. I've simmed without any backup intervals then it was correct. Perhaps double velocity in 15th frame?