Author Topic: Translucent plastic silicone tubing material, what is a good approach?  (Read 2654 times)

2020-09-08, 22:24:40
Reply #15

SharpEars

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Hey! I mentioned in my first post that I removed some stuff for sharing. The geometry you are missing is from a model on GrabCAD, I can post a link tomorrow. Obviously, I can't redistribute the data, but you can download yourself, and there are many other well suited models over there.

The HDR used for lighting my test scene came from hdrihaven, these again are public domain but I decided to remove it nonetheless... will post a link, too.

Glad you found it useful!! It's really very sensitive to lighting but I think the general parameters are acceptable. Then again, lots are left to play with and I had a hard time deciding which exact settings to go with. But that's the beauty of the scattering feature.
The only thing that's odd is how much scattering differs with caustics with exactly the same settings. I'm not sure what's going on there.

Your machine sounds about 10 times faster than mine :D

Yeah, I noticed that as well. The caustic completely change the material's appearance. I think I almost prefer the version without them, but since caustics are supposed to add realism, I am trying to work them in to my material.

That said, our materials are somewhat different, although based on the same principles. I suppose you can judge for yourself once I get this render done.

2020-09-09, 10:14:19
Reply #16

pokoy

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So here's the updated zip containing Max files for 2020, 2018, 2016 and 2014 with Corona v5, plus a screenshot of the material setup (all colors black/white except for absorption and scattering).

The HDR used for lighting the example was this one:
https://hdrihaven.com/hdri/?c=indoor&h=aft_lounge

The missing geometry is something I can't trace back anymore so I can't provide a source, unfortunately. There are tons of good CAD models suited perfectly for this over at grabCAD.com

2020-09-09, 19:11:21
Reply #17

SharpEars

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So looks like I won't be posting comparison images of our materials, because at least with Corona 6/3ds max, the caustics appear to be "broken." The image can never clear, I tried doing region renders on small regions to be sure.

The photons being shot into the scene for caustics are large, there aren't enough of them, and there is no or not enough interpolation between them, causing large bright spots (and I don't mean fireflies, those could be removed with denoising) to be present in the scene and never clear. The denoisers are useless for this, because they only clear small "pixel size" noise, not large bright caustic photon splotches (see attached image for a better description of this effect in general, this is not what I am seeing specifically, just an example that illustrates what bad photon handling looks like, although in the sample image shown it was done intentionally).

I tried toggling adaptive caustics mode, even tried playing with the developer/experimental caustics settings, including maxing out the number of photons (per pass?) to 99,000 and playing with _many_ permutations of the other settings - well as many as time would allow, since rendering with caustics on is as slow as watching Pluto rotate around the sun, and I did want results some time this century, especially given that the hardware I am using, although not a 64/128 core threadripper, is far faster than what 99.99% of people are using (Skylake X 18/36 cores at a fixed 4.9 GHz with -1 AVX2 (also fixed) and custom loop direct [cold plate to actual silicon die - no IHS] water cooling to keep temps ≪90 ℃ while using AVX2 full blast, like Corona does). Nothing helped, the caustics mode is completely useless for this scene and Corona does not allow enough control over photon settings to fix it, not to mention that having to twiddle with these is reminiscent of trying to get caustics to work in VRay/RedShift/Corona Physical, etc..., with the million knobs you have to turn to get caustics right (or to appear at all in the scene!).

We love Corona for its simplicity when it comes to render settings - its greatest selling point! But, as this scene clearly shows that the caustics simply do not work for a scene like this. I don't know if this is a bug, a deficiency in the specific algorithm that the Corona team chose to use for caustics, or what.

If someone from the Corona team wants the 3ds Max Sample scene that demos caustics completely failing due to very poor caustic photon handling/calculations, I can post it as an attachment. It is just a variant of the scene already posted in this thread by pokoy with some tweaks.

Or is this a known issue with caustics - that they just don't work for some scenes with partially transparent objects? I mean the scene is not overly complex, by any means and the lighting is trivial, with two area lights.

« Last Edit: 2020-09-09, 19:27:45 by SharpEars »

2020-09-09, 22:14:21
Reply #18

pokoy

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You should definitely let the devs know - best through a support request - that caustics failed in your scene.
I have just rendered my scene for 3 hours with caustics and it did work like expected - in v5, that is, and with HDR lighting, so that's a different setup - so make sure to provide the scene to the developers and see if they can figure out what went wrong. I could do the same in v6 tomorrow, just to test if v6 in general works differently.

2020-09-10, 01:22:24
Reply #19

SharpEars

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I believe that the reason you are not seeing the photon issue is possibly due to rendering at fairly low resolutions. Try a high resolution render with a region select (of say one of the lower coils), so it finishes in a reasonable amount of time and see if you see the issue.

I'll post an image to show what I am getting, soon - trying a few more attempts to get to the bottom of it.

2020-09-10, 09:08:04
Reply #20

GeorgeK

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You should definitely let the devs know - best through a support request - that caustics failed in your scene.
I have just rendered my scene for 3 hours with caustics and it did work like expected - in v5, that is, and with HDR lighting, so that's a different setup - so make sure to provide the scene to the developers and see if they can figure out what went wrong. I could do the same in v6 tomorrow, just to test if v6 in general works differently.
I believe that the reason you are not seeing the photon issue is possibly due to rendering at fairly low resolutions. Try a high resolution render with a region select (of say one of the lower coils), so it finishes in a reasonable amount of time and see if you see the issue.

I'll post an image to show what I am getting, soon - trying a few more attempts to get to the bottom of it.

I Will be checking this right away in case there is an issue.

Please submit a ticket or upload an archive of your scene, thanks
« Last Edit: 2020-09-10, 10:13:45 by GeorgeK »
For solutions and troubleshooting please visit - [link]
Please submit your tickets here - [link]

2020-09-10, 11:43:27
Reply #21

pokoy

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I believe that the reason you are not seeing the photon issue is possibly due to rendering at fairly low resolutions. Try a high resolution render with a region select (of say one of the lower coils), so it finishes in a reasonable amount of time and see if you see the issue.

I'll post an image to show what I am getting, soon - trying a few more attempts to get to the bottom of it.

The scene seems to render fine here with v6.
I now see that you mention using region rendering - I think this is generally not supported and can cause unexpected results with caustics.

2021-05-04, 19:29:20
Reply #22

kadir

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thanks for the share
i did a test with some tweak to achieve the look I wanted