Open mesh: weird reflections? #41225

New Issue

Thomas Beck · 2014-07-28T19:40:19+02:00

Thomas Beck commented

2014-07-28 19:40:19 +02:00

System Information
i7 haswell, 16gb ram, nvidia gtx 560 ti oc

Blender Version
Broken: All I've tried

Short description of error
I apply a mask modifier in "vertex group" mode on an icosphere with a reflective material. I may be completely wrong but I would not expect those weird reflections to happen on the visible parts of the icosphere.

Exact steps for others to reproduce the error
Just load the supplied file and do a live preview with cycles or render...

MaskBug.blend

Greetings, Thomas

Hi @Sergey or @brecht, **System Information** i7 haswell, 16gb ram, nvidia gtx 560 ti oc **Blender Version** Broken: All I've tried **Short description of error** I apply a mask modifier in "vertex group" mode on an icosphere with a reflective material. I may be completely wrong but I would not expect those weird reflections to happen on the visible parts of the icosphere. **Exact steps for others to reproduce the error** Just load the supplied file and do a live preview with cycles or render... [MaskBug.blend](https://archive.blender.org/developer/F100048/MaskBug.blend) ![BugRender.png](https://archive.blender.org/developer/F100049/BugRender.png) Greetings, Thomas

Thomas Beck commented

2014-07-28 19:40:20 +02:00

Changed status to: 'Open'

Thomas Beck commented

2014-07-28 19:40:20 +02:00

Added subscriber: @plasmasolutions

Bastien Montagne changed title from ~~Mask modifier causes weird reflections~~ to Open mesh: weird reflections?

2014-07-28 22:10:22 +02:00

Sergey Sharybin was assigned by Bastien Montagne

2014-07-28 22:10:22 +02:00

Bastien Montagne commented

2014-07-28 22:10:22 +02:00

Added subscribers: @ThomasDinges, @mont29

Bastien Montagne commented

2014-07-28 22:11:13 +02:00

Mask modifier has nothing to see here, it’s just the opening (apply it, you get same results)… Imho those reflections are normal, but can’t be sure here.

Fasit commented

2014-07-28 23:35:13 +02:00

Added subscriber: @ygtsvtr

Fasit commented

2014-07-28 23:35:14 +02:00

I can re create this, I confirm . But the weird artifact like reflections are caused by layer weight node ; if you set the layer weight to 0.1 artifacts disappear by % 90. Also if you add a solidify modifier the artifact disappear completely. Open non-manifold mesh with glossy material with a layer weight node connect as factor creates this problem.layerweight_artifact.blend

I thought it was something like a disco ball effect at first but I'm not sure because the environment is drawn differently than it should (black areas on my file) on a non-manifold mesh. This doesn't happen on a manifold mesh with same layer weight material.

I can re create this, I confirm . But the weird artifact like reflections are caused by layer weight node ; if you set the layer weight to 0.1 artifacts disappear by % 90. Also if you add a solidify modifier the artifact disappear completely. Open non-manifold mesh with glossy material with a layer weight node connect as factor creates this problem.[layerweight_artifact.blend](https://archive.blender.org/developer/F100065/layerweight_artifact.blend) I thought it was something like a disco ball effect at first but I'm not sure because the environment is drawn differently than it should (black areas on my file) on a non-manifold mesh. This doesn't happen on a manifold mesh with same layer weight material.

Sergey Sharybin commented

2014-08-13 10:57:50 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2014-08-13 10:57:50 +02:00

Sergey Sharybin commented

2014-08-13 10:57:50 +02:00

This isn't really a bug, just a specific of how fresnel works. It uses normal direction to define the media transfer. If you're looking at the fromface in this example it'll consider light travels from the atmosphere to the sphere media. But when you're looking at he backface, it considers light travels from the sphere media to the air. This is rather correct behavior in general, so fresnel is correct in the cases when the camera itself is surrounded by the media i.e. but in this example it's not what you expect. You want it to be considered that light always travels from air to the media.

In order to make it so, you need to inverse the value of IOR used by the fresnel term. For fresnel node it's siply 1.0/IOR, for the weight layer it's 1.0-1.0 / (1.0 - blend) i believe.

Here's tweaked .blend which demonstrates MaskBug_(1).blend

Thanks for the report, but it's not a bug.

This isn't really a bug, just a specific of how fresnel works. It uses normal direction to define the media transfer. If you're looking at the fromface in this example it'll consider light travels from the atmosphere to the sphere media. But when you're looking at he backface, it considers light travels from the sphere media to the air. This is rather correct behavior in general, so fresnel is correct in the cases when the camera itself is surrounded by the media i.e. but in this example it's not what you expect. You want it to be considered that light always travels from air to the media. In order to make it so, you need to inverse the value of IOR used by the fresnel term. For fresnel node it's siply `1.0/IOR`, for the weight layer it's `1.0-1.0 / (1.0 - blend)` i believe. Here's tweaked .blend which demonstrates [MaskBug_(1).blend](https://archive.blender.org/developer/F102809/MaskBug__1_.blend) Thanks for the report, but it's not a bug.

Thomas Beck commented

2014-08-13 11:32:00 +02:00

Hi Sergey,

thanks very much for this thorough explanation - it's clear now what is happening! I'm sorry for the time you put into this altough it's no bug and I thank you very much for the example - much appreciated.

Greetings, Thomas

Hi Sergey, thanks very much for this thorough explanation - it's clear now what is happening! I'm sorry for the time you put into this altough it's no bug and I thank you very much for the example - much appreciated. Greetings, Thomas

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Open mesh: weird reflections? #41225