Foam artifacts

[Steve_Green]

Hi,

I've just been having a play with the foam object, but more to use as a viscous liquid sim.

I'm getting artifacts in the render (there's a single VRay area light)

I'm not sure what options to try to reduce the flickering - any suggestions?

Thanks,

Steve

https://dl.dropboxusercontent.com/u/2230663/foam.mp4

[Ivaylo Katev]

can you post a movie? the flickering is usual for the GI , but you didn't mention to use GI.

[Ivaylo Katev]

well, i assumed that the movie is a kind of signature
so, this looks as GI issue or light cache issue. by default the light cache of the foam is on. however, the foam looks strange, single bubbles not connected with the other, but following the movement. is there any liquid ?

[Steve_Green]

Yeah, it's a liquid with quite high viscosity. Light cache was on but GI was not turned on for the scene, just a single VRay Area light.

Yeah I noticed the 'floating bubbles' as well.

I tried turning Light cache off, but I seemed to get lines/blocks in the render.

Rendered in VRay 3 with the latest 2.2 build of PhoenixFD.

Thanks,

Steve

[Ivaylo Katev]

that's an unexpected behavior, usually any artifacts disappear if the lc is turned off.
can you post an image with these line/block artifacts?

[Steve_Green]

Hi,

thanks - sadly no, I don't have the iteration of that file any more, I'm just trying another one with LC off and a Vray Shadow Mapped light, I'll see how that turns out...

Cheers

Steve

[Steve_Green]

https://dl.dropboxusercontent.com/u/...3/foam%202.mp4

Is the new version, it's a lot better - still noise there though, not sure if really whacking up the image samples would cure it or if it's something else.

I'm not sure if there's a solution for the floating bits - it's not an especially fine grid (about 200x200x160)

[Ivaylo Katev]

as i see the flickering is in the internal areas, can you show the phxfoam settings?
let me explain more about the flickering, understanding the process may help you to avoid it.
so, very big part of the raytracing is dedicated to the light calculation, and that's why we use light cache and it is enabled by default. the foam light cache uses the lighting at the bubble center for the entire bubble and any change of the lighting in this point affects the entire bubble, it becomes brighter or darker.
the area lights are sampled in random points, and rays are traced toward these points. usually it's not a big problem, because the result lighting is the same regardless of the sampling points, however if you have some obstacles (the other bubbles in your case), each area light sampling may produce quite different result, depending on the count of the rays that hit an obstacle. in this case you need significantly more subdivisions (ray count) to have the same quality as if no obstacles are present.
the line artifact you mentioned may be a symptom for correlation of the random sampling points, that is not good and we have to investigate it. for now you can increase the light subdivisions, if the render times are still acceptable.

[Steve_Green]

Hi, thanks

I've attached the settings anyway, but I'll look at the light subdivisions.

TBH the non-light cache version is OK(ish), it gives a bit of a feel that the foam is popping.

I was more curious if there was a solution.

Regards,

Steve

[Ivaylo Katev]

you can try also the option "optimize bad systems", by default it is enabled because if you have too many bubbles in small area, this may produce very long render times, but the most foam simulations are ok. this option can cause flickering because it affects the foam size even if the bubbles are at acceptable distance.

[Ivaylo Katev]

one more possible flickering cause - the liquid is invisible, but the option "liquid" is enabled and if you have particles at the liquid surface, they may be rendered differently in every frame, because small change in the position can put the particle from inside to outside state.

[Steve_Green]

Thanks, will give those options a try!

Cheers

[Steve_Green]

OK, I've managed to get the line artifacts back.

I've included the Max 2013 scene (without the sim cache)

It appears differently on every frame in an animation.

[Ivaylo Katev]

thanks for the scene, this helps a lot

[Steve_Green]

You're welcome!