[Soc-2018-dev] Weekly report #04 - Implementing a Hair Shader for Cycles
Leonardo E. Segovia
leonardo.segovia at cs.uns.edu.ar
Fri Jun 8 20:34:29 CEST 2018
*(This week, I'll try and post a full-featured report instead of the
text-only version. As usual, it's posted to
https://wiki.blender.org/index.php/User:LeonardoSegovia/GSoC_2018/Reports/Week_4
<https://wiki.blender.org/index.php/User:LeonardoSegovia/GSoC_2018/Reports/Week_4>.)*
Week 4
Hi everyone! Yet another week's now gone. This is my report.
Objectives
This week, I think we've finished the Weeks 4-5 objectives:
- Test shader functionality. If working, release test build.
- Evaluate received feedback. Start bug fixes.
What's been done
- Added some documentation to the node's parameters (
rB9973c2c26f3554660546dd3452ae1234f447a00b
<http://developer.blender.org/rB9973c2c26f3554660546dd3452ae1234f447a00b>).
- Separated each mode's parameters into their own sockets.
- Melanin: rB31c3476fd31c2e497a3508e3b2390a3f9c18d945
<http://developer.blender.org/rB31c3476fd31c2e497a3508e3b2390a3f9c18d945>
- Direct coloring: rB30369e55c1458832b4057bf94a78a66fee2e15f7
<http://developer.blender.org/rB30369e55c1458832b4057bf94a78a66fee2e15f7>
- Absorption coefficient: rB8547643039a22cc998479b016660d54079851ea8
<http://developer.blender.org/rB8547643039a22cc998479b016660d54079851ea8>
- It seems that d'Eon's melanin mapping works as an absolute quantity,
not as a ratio, so I lifted the established max melanin. (
rB6d8eb3bdbceb09da8229946461eaff377e395e44
<http://developer.blender.org/rB6d8eb3bdbceb09da8229946461eaff377e395e44>)
- Added PBRT's and Benedikt Bitterli's sane defaults (
rBb891aa81094707c36504b28b40ace7996401be3c
<http://developer.blender.org/rBb891aa81094707c36504b28b40ace7996401be3c>,
rB257a7701e04db99bd5c9def75729dc07042bcb47
<http://developer.blender.org/rB257a7701e04db99bd5c9def75729dc07042bcb47>)
- What does this mean? By default, the shader should return in all
its modes brownish hair.
- I decided to follow Bitterli's defaults wrt. melanin concentration
because his reference render (in Tungsten) used pheomelanin to
achieve the
desired colors.
- Added the ability to dye hair (
rB6e8ab6d2139590c5454f146746dc8d990b4d7e84
<http://developer.blender.org/rB6e8ab6d2139590c5454f146746dc8d990b4d7e84>).
- To use it, simply set the melanin to a low quantity and then choose
the desired color.
- This ability was inspired in the new V-Ray hair shader
<https://www.chaosgroup.com/blog/v-ray-next-the-science-behind-the-new-hair-shader>.
- I don't know if the way I did it is exactly how it should work, but
it surely looks nice!
- Added Melanin and Roughness randomization (
rBf1bcaabb8ad141356aa217bd3f0b49b684a23f5b
<http://developer.blender.org/rBf1bcaabb8ad141356aa217bd3f0b49b684a23f5b>,
rBb7d540f245aa4adf48ea0481f686a46cbc812ec1
<http://developer.blender.org/rBb7d540f245aa4adf48ea0481f686a46cbc812ec1>,
rBc33fbdb9cc68bc7dd8f7e14cba9eece4d1b19e12
<http://developer.blender.org/rBc33fbdb9cc68bc7dd8f7e14cba9eece4d1b19e12>,
rB1eb55b6d12bd5741c866d0406b8e37088db01166
<http://developer.blender.org/rB1eb55b6d12bd5741c866d0406b8e37088db01166>,
rB332b2d6206c128bd7ac2474c8b80a55a1fcc64af
<http://developer.blender.org/rB332b2d6206c128bd7ac2474c8b80a55a1fcc64af>)
- This lets you add further realism by varying the properties of each
strand.
- To use it, set the "(Parameter) Randomization" factor to how much
(less) of the desired factor you wish your hairs to have. This is
implemented as a linear progression, e.g. 0 = no randomization
at all, 0.5
= hairs can have as much as 50% less melanin or roughness, 1 = completely
random up to the specified value.
- Do notice that this needs Hair Info->Random or other number source
to work.
- If you wish to disable this feature, EITHER set the Randomization
factor to 0, OR unsocket the random source and set Random to 0.5.
- Merged the latest master commits (
rB9e59a1f7b5c0aca666cda737936d9fb5621423f4
<http://developer.blender.org/rB9e59a1f7b5c0aca666cda737936d9fb5621423f4>).
- Two formatting issues were fixed.
The node now looks like this:
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-DirectColoring-week-4.png>
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-DirectColoring-week-4.png>
The node's current appearance and sockets for the Direct Coloring mode.
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-MelaninConcentration-week-4.png>
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-MelaninConcentration-week-4.png>
The node's current appearance and sockets for the Melanin Concentration
mode.
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-AbsorptionCoefficient-week-4.png>
<https://wiki.blender.org/index.php/File:ZootopiaShaderNode-AbsorptionCoefficient-week-4.png>
The node's current appearance and sockets for the Absorption Coefficient
mode.
nirved on IRC provided me with a reference scene that implements Bitterli's
"Hair Curls". These images were rendered with the following properties:
- For all hair curls:
- Offset: 2.5º
- Roughness: 0.3 azimuthal and longitudinal
- Primary Reflection Roughness: 1.0 (i.e. disabled)
- Randomness: left 0 (i.e. disabled), 1 right (i.e. fully randomized)
- Hair width: 2
- Hair strands: 1 parent, 1000 children, Simple
- Random source: Hair Info -> Random -> Modulo 0.05 -> Multiply 20
- Reduced the number of possible variations in exchange for more
distinctiveness
- For each curl:
- Dark: Melanin 0, Melanin Redness 8
- Brown: Melanin 0, Melanin Redness 3
- Red: Melanin 0, Melanin Redness 1.3
- Blond: Melanin 0, Melanin Redness 0.35
- Sampling: Branched path tracing, 784 samples (Square), max 64 bounces,
Clamp Indirect 25, and Denoised (default parameters, but enable for all
modes)
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-norandom.png>
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-norandom.png>
nirved's scene rendered with no randomized parameters.
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-10.png>
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-10.png>
nirved's scene rendered with 10% randomness.
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-25.png>
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-25.png>
nirved's scene rendered with 25% randomness.
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-50.png>
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-50.png>
nirved's scene rendered with 50% randomness.
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-100.png>
<https://wiki.blender.org/index.php/File:Nirved-HairCurls-100.png>
nirved's scene rendered with 100% randomness.
Next up
Depending on user feedback, I may change the existing melanin mapping
from *absolute
concentration* to *ratio of eu/pheomelanin* v. *concentration factor*. I
don't know what maximum should we choose or the relationship between
concentration factor and resulting absolute quantity (linear?
logarithmic?). There is no data on this in either Pharr's or d'Eon's paper.
Please note that the university has asked me to prepare a public class as
part of the examination process for my old TA post (lapsed at the end of
March, prior to GSoC). Therefore, next week I may not be available
immediately for bug fixes and new features.
If no bugs or feature requests arise in the next weeks, I'll begin
designing tests. In the BA thread there have been requests for .blend
hairstyles for this purpose -- it'll be great if you could post them!
Questions
- Do you feel the current features are sufficient and/or correct for
usage by artists?
- What would you add, change, or remove, if anything?
--
Lic. Leonardo E. Segovia
Departamento de Ciencias e Ingeniería de la Computación
Universidad Nacional del Sur
San Andrés 800 - Campus Palihue, B8000 Bahía Blanca, Argentina
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