Shadow caustics aren't 'smooth' despite smooth shading #97784
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Reference: blender/blender#97784
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System Information
Operating system: Windows-10-10.0.22000-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 511.65
Blender Version
Broken: version: 3.2.0 Alpha, branch: master, commit date: 2022-04-28 19:13, hash:
308a12ac64
Worked: none
Short description of error
The shadow caustics look as if they were produced by a flat shaded model, even though the object is set to shade smooth.
Exact steps for others to reproduce the error
Add two planes, one with an ocean modifier (or any other kind of displacement) and move it up and give it a refractive material,
Set the light to caustic light, the top plane to caustic caster and the bottom to caustic reciver,
Set the top plane to shade smooth and reduce the radius of the light to see it better.
Shadow caustics bug.blend
Added subscriber: @Tamino-Fischer
Added subscriber: @PratikPB2123
Changed status from 'Needs Triage' to: 'Confirmed'
Added subscriber: @olivier.fx
Hi, thanks for the report. I can confirm.
Bug in a new feature so I'm raising the priority.
cc @olivier.fx
Hi @Tamino-Fischer and @PratikPB2123, this behavior is to be expected.
If you think of the light paths responsible for the caustics, they depend also on the position at which the interface is crossed ( = normal refraction behavior based on normal, IOR and hit point). The interface in this case is coarsely tessellated, so it's not unexpected to see some kind of discontinuity in the caustics. If you apply a subdivison modifier, these tessellation artefacts will progressively go away (as I'm sure you had noticed).
Added subscriber: @brecht
Changed status from 'Confirmed' to: 'Archived'
Agree we can consider this a known limitation and not a bug.
Added subscriber: @Connor-Denning
yeah this clearly shouldn't be Closed. took all of 30 seconds to test this guys file and up the sub divisions don't fix anything. when everything else in the software respects smooth shading your convincing no one this is reasonable, when the shadow terminator bug was fixed it stopped being reasonable to tell me to up the poly count to hid artifacts. set subdivide in his file to 7 levels and it totally fail as well. so 6 is the highest I can even go, and 8 will crash. but this looks terrible I'll I'm moving the camera ever to hid artifacts in a pathtracer then something is wrong. what happens when I need to do a close up of something with caustics on it? The answer is I can't or it's going to look terrible. If I had animation I'd have to have it hand painted out of each frame. why isn't caustics an experimental feature this doesn't work well enough to be called a feature. And if slower/less accurate it should just work like the shadow terminator it could be user adjustable.
Added subscriber: @Alaska
The report wasn't closed because it isn't a issue. It was closed because it was a known limitation and presumably it has been documented somewhere to potentially be fixed at a later date.
Cycles shadow caustics is based on a rendering technique known as "Manifold Next Event Estimation (MNEE)". MNEE is known to have limitations and artifacts, and as such it is not a general caustics solution and is not recommended for a wide variety of uses, like some of the ones you're talking about.
This is not an issue with Cycles and shadow caustics, it's mostly an issue with MNEE as a whole. Many of the same limitations will occur in other render engines with MNEE.
There are other techniques available to speed up the rendering of caustics without many of the limitations of MNEE, and work is underway to investigate implementing some of these into Cycles. So hopefully things will improve for you in the future.
Where's the documentation? I'd be happy to try to fix some of the known limitations, last I checked it wasn't in release notes. OK I found it, it's been added. https://developer.blender.org/rB1fb0247 Thankyou.
I have also documented a bunch of limitations with Cycles shadow caustics in the Blender manual: https://docs.blender.org/manual/en/latest/render/cycles/object_settings/object_data.html#shading