[Bf-cycles] Oren-Nayar model revisited

[Aurel W.]

Hi Yasuhiro,

I couldn't investigate this in detail now, but looks plausible at first sight.

aurel

On 23 February 2012 10:11, Thomas Dinges <blender at dingto.org> wrote:
> I removed the comments, thanks. :)
>
> Regards,
> Thomas
>
> Am 23.02.2012 02:43, schrieb Yasuhiro Fujii:
>> Thank you very much for speedy committing.
>>
>> Also, please remove the comments in the head of bsdf_oren_nayar.h?
>> The description is obsolete.
>>
>> -- Yasuhiro Fujii
>>
>> On Thu, Feb 23, 2012 at 12:04 AM, Brecht Van Lommel
>> <brechtvanlommel at pandora.be>  wrote:
>>> Thanks, seems to be working well, and the code is simpler too.
>>> Committed to svn now.
>>>
>>> Brecht.
>>>
>>> On Tue, Feb 21, 2012 at 3:17 PM, Yasuhiro Fujii
>>> <y-fujii at mimosa-pudica.net>  wrote:
>>>> Hi all,
>>>>
>>>> A few month ago, I implemented a Oren-Nayar model for cycles.  It has a little
>>>> wider range of roughness parameter, I noticed that it sometimes generates bad
>>>> results. For example, The dark rings are appeared on the spheres.
>>>> Essentially, it is caused a bad approximation of O-N model.
>>>>
>>>> In the original paper, Oren and Nayar have proposed two approximate functions
>>>> (I call them full O-N and qualitative O-N, respectively). Qualitative O-N is
>>>> well known and widely used in CG community but full O-N is less used. I think
>>>> full O-N is too complex.
>>>>
>>>> So I developed a tiny improvement of qualitative O-N.  It has the same
>>>> simplicity as qualitative O-N but yields very similar result as full O-N.
>>>>
>>>> The detail are described at:
>>>> http://mimosa-pudica.net/improved-oren-nayar.html
>>>>
>>>> The implementation for cycles is very simple:
>>>>
>>>> __device float3 bsdf_oren_nayar_get_intensity(const ShaderClosure *sc,
>>>> float3 n, float3 v, float3 l)
>>>> {
>>>>     float nl = max(dot(n, l), 0.0f);
>>>>     float nv = max(dot(n, v), 0.0f);
>>>>     float t = dot(l, v) - nl * nv;
>>>>     if (t>  0.0f)
>>>>         t /= max(nl, nv) + FLT_MIN;
>>>>     float is = nl * (sc->data0 + sc->data1 * t);
>>>>     return make_float3(is, is, is);
>>>> }
>>>>
>>>> __device void bsdf_oren_nayar_setup(ShaderData *sd, ShaderClosure *sc,
>>>> float sigma)
>>>> {
>>>>     sc->type = CLOSURE_BSDF_OREN_NAYAR_ID;
>>>>     sd->flag |= SD_BSDF | SD_BSDF_HAS_EVAL;
>>>>
>>>>     sigma = clamp(sigma, 0.0f, 1.0f);
>>>>     float div = 1.0f / (M_PI_F + ((3.0f * M_PI_F - 4.0f) / 6.0f) * sigma);
>>>>
>>>>     sc->data0 =  1.0f * div;
>>>>     sc->data1 = sigma * div;
>>>> }
>>>>
>>>> I've used this model in practice for 2, 3 month and no problems are
>>>> found at the moment.
>>>> I'd be happy if this improvement is reviewed.
>>>>
>>>> -- Yasuhiro Fujii
>>>> _______________________________________________
>>>> Bf-cycles mailing list
>>>> Bf-cycles at blender.org
>>>> http://lists.blender.org/mailman/listinfo/bf-cycles
>>> _______________________________________________
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>>> http://lists.blender.org/mailman/listinfo/bf-cycles
>> _______________________________________________
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>
>
> --
> Thomas Dinges
> Blender Developer, Artist and Musician
>
> www.dingto.org
>
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