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Making physically-based glass without weird hacks seems really hard with cycles. Does anybody have any tips they could share with me to solve this issue? I have read every single thread available on this topic, but unfortunately nothing seems to quite work.

I keep running into problems with too much refraction at glancing angles where there SHOULD be more reflection. I understand that some refraction is physically accurate and that, at certain angles, there will even be total internal refraction, but this amount of refraction seems excessive for this angle. Please see the images below.

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What I've tried so far:

(1) increased glossy and transmission light bounces to 64

(2) used light path node and math node with a mix shader to swap to a transparent shader after 20 refractions, but this seems like a cheat and I'd prefer not to use it, though it does work

(3) added a rim to the cup which surprisingly helped a lot with the excessive refractions

(4) added an edge split modifier (didn't work)

(5) changed lighting and environment (by blasting the scene with unrealistic amounts of light from all angles, the refractions start to disappear, but that's sort of a workaround)

(6) recalculated normals

If you've read this far down, I really appreciate any help that you can provide! :)

Joe
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  • This Q shows a proper cycles glass setup. – Timaroberts Jul 10 '20 at 07:37
  • @Timaroberts Thank you for your comment! Unfortunately I've seen that thread and it's more of a cycles hack. It's not accurate to use the light path node and transparent shaders like that - it also doesn't work with solid glass too well, like the base of the cup :( – Joe Jul 10 '20 at 07:59
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    The direction of refracted rays is extremely sensitive to exact shape of the profile at the rim of the glass, as you have noted in (3). Personally, that's the line I would follow, first, trusting the physics. (Run your lip around the rim of a real glass.. feel its shape) – Robin Betts Jul 10 '20 at 08:32
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    @RobinBetts Thank you, Robin! I really think you're right and this is the right way to go, but no matter what I try or how I design the rim of the cup, I can't seem to get the refraction to behave appropriately. Would you mind taking a look at the blend file and giving it a go? I'm quite stuck. – Joe Jul 11 '20 at 06:12
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    I've had a look, and the rim looks fine to me (if that's physically similar to your reference/idea), the rest is lighting and environment, which is infinitely tweakable, and would depend on exactly what you want. Do you have a reference more like what you're looking for? I found the balance between base and rim refraction could be improved with some backlighting, and balance with reflections, camera-side, , by cutting out some of the white box. You could subdivide the box and remove chunks of it to try. (and dont forget you can make area lights invisible to the camera for convenience.) – Robin Betts Jul 12 '20 at 11:24
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    @RobinBetts Thanks Robin. You're definitely right about that, but I also discovered that the problem goes away if I turn up glossy light bounces even higher than 64, around 128-256. It seems that the problem was related to too few bounces, but lighting and environment are also impacting it. – Joe Jul 16 '20 at 20:44
  • Glad you found it! .. it didn't look like that to me .. otherwise I would have mentioned it.. I had more success with balancing the lighting, but then, I couldn't be sure it was what you wanted : ) – Robin Betts Jul 16 '20 at 20:58

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