Cycles hair shader reflects incorrectly for meshes #45058

New Issue

Kevin Hays · 2015-06-13T09:07:03+02:00

Kevin Hays commented

2015-06-13 09:07:03 +02:00

System Information
OS: Windows 7 64 bit
Graphics Card: nvidia geforce 560ti

Blender Version
Broken: 2.75 Release candidate bff8b5d

Short description of error
Adding a hair shader to a plane makes the reflections look triangulated.

Exact steps for others to reproduce the error
Add a sun lamp and plane, then give the plane a hair shader with the default settings. I noticed if you triangulate the plane, separate one of the faces, and move the the vertices counter-clockwise, the reflections look correct.
HairShaderBug.blend

**System Information** OS: Windows 7 64 bit Graphics Card: nvidia geforce 560ti **Blender Version** Broken: 2.75 Release candidate bff8b5d **Short description of error** Adding a hair shader to a plane makes the reflections look triangulated. **Exact steps for others to reproduce the error** Add a sun lamp and plane, then give the plane a hair shader with the default settings. I noticed if you triangulate the plane, separate one of the faces, and move the the vertices counter-clockwise, the reflections look correct. [HairShaderBug.blend](https://archive.blender.org/developer/F190702/HairShaderBug.blend)

Kevin Hays commented

2015-06-13 09:07:03 +02:00

Changed status to: 'Open'

Kevin Hays commented

2015-06-13 09:07:03 +02:00

Added subscriber: @KevinHays

Bastien Montagne commented

2015-06-13 10:13:01 +02:00

Added subscriber: @mont29

Bastien Montagne commented

2015-06-13 10:13:01 +02:00

Looks like there is something going wrong with winding here indeed…

Sergey Sharybin was assigned by Bastien Montagne

2015-06-13 10:13:31 +02:00

Bastien Montagne commented

2015-06-13 10:13:31 +02:00

Added subscribers: @ThomasDinges, @MartijnBerger

Thomas Dinges commented

2015-06-14 16:19:42 +02:00

Serious question. Why would you use a "Hair" shader on regular geometry?
I am not sure we have a bug here.

Serious question. Why would you use a "Hair" shader on regular geometry? I am not sure we have a bug here.

Kevin Hays commented

2015-06-14 21:16:44 +02:00

In #45058#315569, @ThomasDinges wrote:
Serious question. Why would you use a "Hair" shader on regular geometry?
I am not sure we have a bug here.

I'm trying to make a detailed feather and I'm using a plane to approximate the barbule strands between the barb strands
http://www.peteducation.com/images/articles/ill_feather_barb.gif

> In #45058#315569, @ThomasDinges wrote: > Serious question. Why would you use a "Hair" shader on regular geometry? > I am not sure we have a bug here. I'm trying to make a detailed feather and I'm using a plane to approximate the barbule strands between the barb strands http://www.peteducation.com/images/articles/ill_feather_barb.gif ![featherCycles.png](https://archive.blender.org/developer/F191661/featherCycles.png)

Brecht Van Lommel commented

2015-06-14 22:08:46 +02:00

Added subscriber: @brecht

Brecht Van Lommel commented

2015-06-14 22:08:47 +02:00

I guess the problem is that tangent used by the hair shader is not smooth for triangles? Curves have a smooth default tangent, but triangles do not, for that you would need to use a Tangent node with a UV map. But the Hair BSDF does not have a tangent input, so that's not possible right now.

I guess the solution would be to add a tangent input for the Hair BSDF, or to make the Hair BSDF use the default UV map to create a tangent for triangles, or to just consider this not supported.

I guess the problem is that tangent used by the hair shader is not smooth for triangles? Curves have a smooth default tangent, but triangles do not, for that you would need to use a Tangent node with a UV map. But the Hair BSDF does not have a tangent input, so that's not possible right now. I guess the solution would be to add a tangent input for the Hair BSDF, or to make the Hair BSDF use the default UV map to create a tangent for triangles, or to just consider this not supported.

Sergey Sharybin commented

2015-06-14 22:15:25 +02:00

@brecht, that's exactly it. Think supporting such configurations will be nice to have and started working on it, but then got bounced to other work. Well, more code next week :)

Julian Eisel commented

2015-06-28 22:29:46 +02:00

Added subscriber: @JulianEisel

Julian Eisel commented

2015-06-28 22:29:46 +02:00

This sounds like a todo?

Sergey Sharybin commented

2015-07-21 14:58:03 +02:00

Changed status from 'Open' to: 'Archived'

Sergey Sharybin closed this issue

2015-07-21 14:58:03 +02:00

Sergey Sharybin commented

2015-07-21 14:58:03 +02:00

It is more a TODO yes. I've got patch for this tho (D1428), but it needs some additional review (especially from artists) before we can merge it.

@KevinHays, so thanks for the report, but archiving it now and suggesting you to test D1428.

It is more a TODO yes. I've got patch for this tho ([D1428](https://archive.blender.org/developer/D1428)), but it needs some additional review (especially from artists) before we can merge it. @KevinHays, so thanks for the report, but archiving it now and suggesting you to test [D1428](https://archive.blender.org/developer/D1428).

blender-admin commented

2015-10-11 16:43:30 +02:00

This issue was referenced by 3f4c0612fe

This issue was referenced by 3f4c0612fedf9d135d72c428e2433c890edb0412

Sergey Sharybin commented

2015-10-11 16:57:30 +02:00

Changed status from 'Archived' to: 'Resolved'

blender-admin commented

2015-10-21 07:18:39 +02:00

This issue was referenced by blender/cycles@ddcd92fd73

This issue was referenced by blender/cycles@ddcd92fd7305053ccdf79af8e04511952bce1466

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Cycles hair shader reflects incorrectly for meshes #45058