Curve segment hair not smooth when set to thick #58065

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omgold · 2018-11-26T17:41:37+01:00

omgold commented

2018-11-26 17:41:37 +01:00

I find that the geometry of hair is no longer smoothly rendered when switching from 'Ribbons' to 'Thick' (using curve segments for both). The hair seems to actually be a smooth curve for Ribbons (first image), but line segments (of the given curve subdivision level) for 'Thick' (second image).

Also the normals become discontinuous as can be seen from the image (shader is setup to display the normals as colors).

broken-thick-hair.blend

Blender version: 2.79b, Hash 32432d91bbe, Arch Linux package 17:2.79.b.git3.32432d91-11

I find that the geometry of hair is no longer smoothly rendered when switching from 'Ribbons' to 'Thick' (using curve segments for both). The hair seems to actually be a smooth curve for Ribbons (first image), but line segments (of the given curve subdivision level) for 'Thick' (second image). Also the normals become discontinuous as can be seen from the image (shader is setup to display the normals as colors). [broken-thick-hair.blend](https://archive.blender.org/developer/F5726701/broken-thick-hair.blend) ![hair-ribbons.png](https://archive.blender.org/developer/F5726710/hair-ribbons.png) ![hair-thick.png](https://archive.blender.org/developer/F5726713/hair-thick.png) Blender version: 2.79b, Hash 32432d91bbe, Arch Linux package 17:2.79.b.git3.32432d91-11

omgold commented

2018-11-26 17:41:37 +01:00

Added subscriber: @omgold

Bastien Montagne commented

2018-11-29 11:02:05 +01:00

Added subscribers: @brecht, @mont29

Brecht Van Lommel was assigned by Bastien Montagne

2018-11-29 11:02:05 +01:00

Bastien Montagne commented

2018-11-29 11:02:05 +01:00

@brecht, guess that one is for you to check? ;)

Brecht Van Lommel commented

2018-11-29 14:22:35 +01:00

Changed status from 'Open' to: 'Archived'

Brecht Van Lommel closed this issue

2018-11-29 14:22:35 +01:00

Brecht Van Lommel commented

2018-11-29 14:22:35 +01:00

The hair curve primitive is optimized for performance, not so much for exact results when viewing hair under a microscope.

It might be possible to improve render quality or precision, but we do not consider this a bug.

The hair curve primitive is optimized for performance, not so much for exact results when viewing hair under a microscope. It might be possible to improve render quality or precision, but we do not consider this a bug.

omgold commented

2018-11-29 14:35:00 +01:00

I fear I can't follow you there. Why is the curve smooth for ribbons? Why is it called curve at all, then, when it is effectively line segments with an extra subdivision option?

Also the issue about the discontinuous normal quickly becomes visible from larger distances, when using shaders other than hair (which hide the issue better, than e.g. diffuse or glossy). It requires a very fine subdivision to go away.

I fear I can't follow you there. Why is the curve smooth for ribbons? Why is it called curve at all, then, when it is effectively line segments with an extra subdivision option? Also the issue about the discontinuous normal quickly becomes visible from larger distances, when using shaders other than hair (which hide the issue better, than e.g. diffuse or glossy). It requires a very fine subdivision to go away.

omgold commented

2018-11-29 14:51:45 +01:00

Here is an example. Straight, uncombed hair, diffuse material:

hait-diffuse.blend

It basically means thick curve segments are unusable for anything other than hair shaders.

Here is an example. Straight, uncombed hair, diffuse material: ![hair-diffuse.jpg](https://archive.blender.org/developer/F5756517/hair-diffuse.jpg) [hait-diffuse.blend](https://archive.blender.org/developer/F5756526/hait-diffuse.blend) It basically means thick curve segments are unusable for anything other than hair shaders.

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Curve segment hair not smooth when set to thick #58065