[Soc-2018-dev] Weekly report #10 - Implementing a Hair Shader for Cycles

Leonardo E. Segovia leonardo.segovia at cs.uns.edu.ar
Tue Jul 24 22:39:15 CEST 2018


Hey all, hi Brecht,

As regards noise and fireflies, they come from basically two places:
- Low Roughness. This compress (longitudinally) the glints so much, they
look like fireflies.
- Low Radial Roughness. These make the hair look SO soft!
- Very lightly colored hair (this one is non fixeable by us)

Possible mitigations include:
- Raising the clamp from 0.001 to 0.01 to at least have a reasonable glint
when Roughness < 0.1
- Filter Glossy

I've already uploaded a fix for the former. I'd like to discuss the
behavior of Filter Glossy.

When doing the CPU profiling that you requested, I realised that Filter
Glossy is executed after the closure setup (before closure setup =
roughness, after = logistic parameters), which means it isn't affecting the
roughness properly.
rB52a0e67fe005
<https://developer.blender.org/rB52a0e67fe0050683a888d6643ec2035bd2b3ea1c>
is the commit that includes both mitigations, however, the new
implementation is noticeably less effective. I've obtained decent results
when applying fmaxf(3*roughness to both Roughness and Radial Roughness;
you'll find a visual comparison of the fixes below. (The original picture
is up at https://framapic.org/ksZ7ftOaGvqk/gS2Cv0cjrdUg.jpg.)



I'm not sure if there is any need to strengthen Filter Glossy wrt. Radial
Roughness in this way; please let me know what you think.

Best regards,
Leonardo

El lun., 23 de jul. de 2018 a la(s) 08:16, Brecht Van Lommel (
brechtvanlommel at gmail.com) escribió:

> Hi,
>
>
>>    - The regression test suite has not been uploaded yet to SVN.
>>
>
> I've committed these as well now.
>
>
>>    - It's been asked in the BA thread if I have extra objectives for the
>>    shaders. Do you feel that more features/controls should be added?
>>
>
> More features could be good, but also part of the GSoC plan was to
> investigate optimizations for the shader, since it still is relatively slow
> / noisy.
>
> So I think you should at least profile the shader, and look into fireflies
> to see where they come from and if they are expected or not. I don't know
> if there is anything major to find, but it's worth investigating.
>
>       - I came up with controls for each of the modes (R, TT, TRT, TRRT+).
>>       - It's been also suggested to prune the UI into a "Basic" and
>>       "Advanced" mode.
>>
>
> I'd be hesitant to add features to break physical correctness and energy
> conservation so early, before people have really tested the shader. I
> rather users test it and then give us feedback saying they can't achieve
> this or that look, and then we see what the best solution is.
>
> Maybe commit it to your branch and then we can always add it later if
> there is a need for it.
>
>
>> About the GSoC project deliverables:
>>
>>    - If I read the mail correctly, Google wants us students to summarize
>>    and show off our work in a single place e.g. a blog post. How does
>> Blender
>>    handle this?
>>       - My preference would be to add a page (similar to when one
>> publishes
>>       a paper) in amyspark.me explaining the work we did. We could embed
>>       the resulting pictures, credits, etc. and the demonstration video
>> from
>>       Youtube.
>>       - As for "Get the code", perhaps I could add links to the relevant
>>       commits?
>>
>
> A webpage is fine, for the code you can link to the git branch.
>
> Thanks,
> Brecht.
>
>
> --
> Soc-2018-dev mailing list
> Soc-2018-dev at blender.org
> https://lists.blender.org/mailman/listinfo/soc-2018-dev
>


-- 
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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