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Cycles: Fix for transmissive microfacet sampling 

This is an alternate fix for T40964 which resolves bad handling of
caustics reported in T45609.

There were too much transmission rays being discarded by the original
fix, which caused by caustic light being totally disabled. There is
still some room for investigation why exactly original paper didn't
work that well, could be caused by the way how the pdf is calculated.

In any case current results seems rather correct now.
This commit is contained in:
Sergey Sharybin 2015-07-31 13:43:36 +02:00
parent 55fead4767
commit 12b7850d4f
Notes: blender-bot 2023-02-14 08:49:50 +01:00 
Referenced by issue #45641, VSE MetaStrip cut crash
Referenced by issue #45609, The "Filter Glossy" option is broken, makes refractive caustics harder to sample rather than easier.
1 changed files with 2 additions and 10 deletions
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12
intern/cycles/kernel/closure/bsdf_microfacet.h
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@ -382,10 +382,6 @@ ccl_device float3 bsdf_microfacet_ggx_eval_transmit(const ShaderClosure *sc, con
float cosHO = dot(Ht, I);
float cosHI = dot(Ht, omega_in);
/* those situations makes chi+ terms in eq. 33, 34 be zero */
if(dot(Ht, N) <= 0.0f || cosHO * cosNO <= 0.0f || cosHI * cosNI <= 0.0f)
return make_float3(0.0f, 0.0f, 0.0f);
float D, G1o, G1i;
/* eq. 33: first we calculate D(m) with m=Ht: */
@ -412,7 +408,7 @@ ccl_device float3 bsdf_microfacet_ggx_eval_transmit(const ShaderClosure *sc, con
* pdf = pm * (m_eta * m_eta) * fabsf(cosHI) / Ht2 */
float common = D * (m_eta * m_eta) / (cosNO * Ht2);
float out = G * fabsf(cosHI * cosHO) * common;
*pdf = G1o * cosHO * fabsf(cosHI) * common;
*pdf = G1o * fabsf(cosHO * cosHI) * common;
return make_float3(out, out, out);
}
@ -735,10 +731,6 @@ ccl_device float3 bsdf_microfacet_beckmann_eval_transmit(const ShaderClosure *sc
float cosHO = dot(Ht, I);
float cosHI = dot(Ht, omega_in);
/* those situations makes chi+ terms in eq. 25, 27 be zero */
if(dot(Ht, N) <= 0.0f || cosHO * cosNO <= 0.0f || cosHI * cosNI <= 0.0f)
return make_float3(0.0f, 0.0f, 0.0f);
/* eq. 25: first we calculate D(m) with m=Ht: */
float alpha2 = alpha_x * alpha_y;
float cosThetaM = min(dot(N, Ht), 1.0f);
@ -764,7 +756,7 @@ ccl_device float3 bsdf_microfacet_beckmann_eval_transmit(const ShaderClosure *sc
* pdf = pm * (m_eta * m_eta) * fabsf(cosHI) / Ht2 */
float common = D * (m_eta * m_eta) / (cosNO * Ht2);
float out = G * fabsf(cosHI * cosHO) * common;
*pdf = G1o * cosHO * fabsf(cosHI) * common;
*pdf = G1o * fabsf(cosHO * cosHI) * common;
return make_float3(out, out, out);
}