Black areas in water mesh/materials ?

[SmokeyBear]

Working with Bifrost in Maya 2022. Current Arnold. Experiencing black areas in the fountaining water as shown in the first two images.

I have checked my Arnold settings - do have "Enable Transmit AOV's checked.

Have played around with the various Render Settings -

Camera (AA) set to "8" and experimented with maxium increase - No effect on black area.

Pushed Transmission to high values and then to max value of 10 - No Effect

Set Specular to 4, and then to max value - No Effect

In Ray Depth Area - played with all parameters, pretty much pushing them all to their max values - No Effect.

Have "System | Render Device" set on my GPU - NVidia 1080 GTX.

--------

What am I doing wrong? and "Thank You" for helpping me.

[lee_griggs]

What happens if you put a glass sphere in the scene?

How is the scene being lit?

What is in the environment to reflect/refract?

Is the transparency_depth high enough?

[SmokeyBear]

Thank you for the reply, Mr. Griggs.

To answer your good questions: the scene is being lit with the Arnold SkyDome at an intensity setting of just "1.0". In the center of the "basin" of the zinc metal bubbler, there is a brass nozzle for the water emission (although I am using a hidden cylinder that is a little larger in diameter than the brass fitting for the Bifrost liqid emittter). This is a possible source of reflections and maybe refractions through the water mesh. I have played around with the "transparency depth" and cranked it to max value without making a difference in the "black" effect.

But, your question about other sources of reflection and refraction have led me to experiment further. If I completely eliminate the "foam" - both the "foam" emitter and the "foam mesh" that is created when I add "foam" to the original Bifrost liquid, the "black" goes away. (As shown in this attached Pic 4.)

Of course, I need the foam, so I am a little puzzled as to how to overcome this issue. One thing I "think" that may be happening is that this particular scene might be corrupt. When I disabled the Bifrost foam mesh - in fact, not all of the foam mesh seems to go away. I can still see some foam mesh particles in the render, although they are not showing in the normal Viewport 2.0, nor can I "touch" them. Only the foam "particle" display appears in the Viewport. So, perhaps this scene is corrupted. I will try to rebuild this from my previous "save" of only the water, and determine if the problem still appears.

Of course, I'll report back when I've worked through this.

Thank you very much for your help so far!!!!!

Respectfully,

Forester

[SmokeyBear]

Ah, with foam once again added to the scene, the black appears again. So, foam is the cause of the problem. In this picture, I simply added the foam to my scene without actually animating the BiFrost fluids, so only a tiny bit of foam appears. That is, there are two relatively small blobs of foam positioned inside the upwelling water blob. You can see the black, in what appear to be refractions on the outer shell of the water blob.

I am also receiving an error message "mtoa.BiFrostFoam.MeshShape |Mesh not exported, it has 0 shading groups." I'm guessing that this message probably occurs because I did not advance the animation from the Frame1 starting point.

My understanding is that the most current version of Arnold (that I am using) now can use priority order for meshed liquids. But I'm not clear on how I set the shaders up to create a priority order in the scene. Perhaps establishing a priority order for rendering the shaders would help eliminate these back patches.

[SmokeyBear]

If I advance the animation, more foam mesh is created, and more black patches appear in the water blob.

[lee_griggs]

Are you using a standard_volume for the foam?

https://docs.arnoldrenderer.com/display/A5AFMUG/Legacy+Bifrost

[SmokeyBear]

Yes, I have been just accepting the "foam shader" that is automatically assigned when I tell Bifrost to create "foam."

Thank you very, very, very much Mr. Griggs. I really appreciate the time and effort you put into helping me with this. I was at a dead loss as to how to start resolving this issue. But now, I have some pieces to explore and probably can resolve these Arnold issues after a bunch of further experimentation on my part.

I was not aware of these properties of the Arnold Foam shader - and frankly, I had been puzzzled earlier as to why the foam particles were rendering as spheres, when the mesh pieces plainly were not. There is much to explore here. I'll set up some experiments where I can look at the effects of the volume foam shader versus a standard surface shader, and then dive into the parameters of each kind of shader as applied to the "foam" mesh - and the effects those have on refraction in the surrounding water mesh.

Also, some of the issue appears to have been a case of some kind of corruption in the Bifrost scene. By going back to a previous workstep, and completely re-building the Bifrost foam pieces into my scene again, at least some of the "problem" no longer exists. That is, the "black" areas now appear only as refraction areas on the outer shell of the water blobs, instead of appearing as large semi-spherical masses in the interior of the water shells - and as black inversions of the internal folds of the water shells.

I have encountered various instabilities of several kinds in this new Bifrost edition over the past week, so to find that the Arnold foam "spheres" persisted in the scene, even after I ostensibly deleted the foam elements from the Bifrost simulation setup is not too surprising. If other of your readers encounter this kind of an "Arnold problem," you might recommend systematically re-building their scenes to determine if a source of the problem really is an error in the Bifrost sim itself.For myself, starting at least a week ago, I changed practice to build up the elements of any Bifrost sim as a series of independent scenes, so that I could revert back to a clean scene earlier step if need be. This practice has already saved my fanny several times.

Thank you again - so much - for your help. I was, in fact, helpless. Your time and effort and wonderful expertise are a godsend!

[SmokeyBear]

Just to confirm, yes, it is the Arnold volume shader that is causing the black refractions on the water mesh shells.Switching the shader applied to the foam mesh to a standard surface shader more or less eliminates these black refractions. There probably are some parameter settings that I can adjust in the volume shader to help control these refractions, but I need more time to work these out.