[Bf-cycles] Oren-Nayar model revisited

[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The description is obsolete.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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