Shadow caustics aren't 'smooth' despite smooth shading #97784

Closed
opened 2022-05-02 22:26:04 +02:00 by Tamino Fischer · 15 comments

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

**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](https://archive.blender.org/developer/F13046810/Shadow_caustics_bug.blend)
Author

Added subscriber: @Tamino-Fischer

Added subscriber: @Tamino-Fischer
Member

Added subscriber: @PratikPB2123

Added subscriber: @PratikPB2123
Member

Changed status from 'Needs Triage' to: 'Confirmed'

Changed status from 'Needs Triage' to: 'Confirmed'
Member

Added subscriber: @olivier.fx

Added subscriber: @olivier.fx
Member

Hi, thanks for the report. I can confirm.
Bug in a new feature so I'm raising the priority.
cc @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).

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

Added subscriber: @brecht

Changed status from 'Confirmed' to: 'Archived'

Changed status from 'Confirmed' to: 'Archived'

Agree we can consider this a known limitation and not a bug.

Agree we can consider this a known limitation and not a bug.

Added subscriber: @Connor-Denning

Added subscriber: @Connor-Denning

In #97784#1351285, @olivier.fx wrote:
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).

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. untitled.png 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.

> In #97784#1351285, @olivier.fx wrote: > 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). 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. ![untitled.png](https://archive.blender.org/developer/F13231630/untitled.png) 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.
Member

Added subscriber: @Alaska

Added subscriber: @Alaska
Member

In #97784#1380692, @Connor-Denning wrote:
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

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.


In #97784#1380692, @Connor-Denning wrote:
... but this looks terrible if 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.

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.

> In #97784#1380692, @Connor-Denning wrote: > 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 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. --- > In #97784#1380692, @Connor-Denning wrote: >... but this looks terrible if 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. 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.

In #97784#1380705, @Alaska wrote:

In #97784#1380692, @Connor-Denning wrote:
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

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.


In #97784#1380692, @Connor-Denning wrote:
... but this looks terrible if 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.

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.

> In #97784#1380705, @Alaska wrote: >> In #97784#1380692, @Connor-Denning wrote: >> 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 > > 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. > > --- > >> In #97784#1380692, @Connor-Denning wrote: >>... but this looks terrible if 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. > > 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.
Member

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

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
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