Cycles reflection and bump artifacts #46309

New Issue

Nahuel Belich · 2015-09-29T01:26:22+02:00

Nahuel Belich commented

2015-09-29 01:26:22 +02:00

System Information
win 7 x64

Blender Version
Broken: hash: 034cc85

Short description of error
Black artifacts appears when bump its used on cycles shaders,

Exact steps for others to reproduce the error

1-reflection_bump_issue.blend
2-render

NOTE: the sample file has full white environment nothing should be reflected and the light paths are all 128 but it makes no difference, changing mesh subdivisions doesn't change nothing neither.

**System Information** win 7 x64 **Blender Version** Broken: hash: 034cc85 **Short description of error** Black artifacts appears when bump its used on cycles shaders, **Exact steps for others to reproduce the error** 1-[reflection_bump_issue.blend](https://archive.blender.org/developer/F240675/reflection_bump_issue.blend) 2-render NOTE: the sample file has full white environment nothing should be reflected and the light paths are all 128 but it makes no difference, changing mesh subdivisions doesn't change nothing neither.

Nahuel Belich commented

2015-09-29 01:26:22 +02:00

Changed status to: 'Open'

Nahuel Belich commented

2015-09-29 01:26:22 +02:00

Added subscriber: @NahuelBelich

Sergey Sharybin commented

2015-09-29 11:22:11 +02:00

Added subscriber: @Sergey

Sergey Sharybin commented

2015-09-29 11:22:11 +02:00

Can confirm the issue, but currently looking into other bug so can't go into details here yet.

Aaron Carlisle commented

2015-09-29 16:54:55 +02:00

Added subscriber: @Blendify

Joshua Lotfi commented

2015-10-01 06:48:19 +02:00

Added subscriber: @jml

Lukas Stockner commented

2015-10-04 22:18:55 +02:00

Added subscriber: @LukasStockner

Lukas Stockner commented

2015-10-04 22:18:55 +02:00

The issue here is that the ray gets reflected at the bumpmapped normal, but since the bumpmap is pretty strong, the resulting outgoing ray actually goes inside the sphere, which is impossible - so the result is simply set to zero (the check is in kernel/closure/bsdf_microfacet.h:800). This is a limitation of bump mapping, Cycles handles the case correctly afaics.

Brecht Van Lommel commented

2015-10-04 22:48:55 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2015-10-04 22:48:55 +02:00

This is similar to the terminator problem, quite difficult to solve in general. There's some tricks possible like flipping the light direction vector above the geometric normal, rotating the light direction vector, tweaking the interpolated normal, ... . It should be possible to do better than returning zero, but I never figured out a really satisfactory solution for Cycles and considered this a to do item.

Nahuel Belich commented

2015-10-07 06:29:46 +02:00

to sum up, this termator thing affects reflections, refractions, bump maps or ¿can we call it shading distortion? and also shadows(actually shading not shadows per se)?
it seems to be a really big stuff not only a few things, basically affects every possible material that we could create exept volumetrics, emmit or non distorted shaders on high poly count models.
It could be possible to add some experimental feature at least to have a possibility to do a workaround using experimental stuff? or this will mess with some core functionality?
(yes i know this is not the place for feature request, im trying to understand how deep this problem is)

to sum up, this termator thing affects reflections, refractions, bump maps or ¿can we call it shading distortion? and also shadows(actually shading not shadows per se)? it seems to be a really big stuff not only a few things, basically affects every possible material that we could create exept volumetrics, emmit or non distorted shaders on high poly count models. It could be possible to add some experimental feature at least to have a possibility to do a workaround using experimental stuff? or this will mess with some core functionality? (yes i know this is not the place for feature request, im trying to understand how deep this problem is)

Thomas Dinges commented

2015-11-18 10:26:31 +01:00

Added subscriber: @ThomasDinges

Thomas Dinges commented

2015-11-18 10:26:31 +01:00

Changed status from 'Open' to: 'Archived'

Thomas Dinges closed this issue

2015-11-18 10:26:31 +01:00

Thomas Dinges self-assigned this 2015-11-18 10:26:31 +01:00

Thomas Dinges commented

2015-11-18 10:26:31 +01:00

Archiving as ToDo then, as it's similar to the Terminator problem.

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Cycles reflection and bump artifacts #46309