Cycles: BSDF changes in preparation of path guiding

* Return roughness and IOR for BSDF sampling
* Add functions to query IOR and label for given BSDF
* Default IOR to 1.0 instead of 0.0 for BSDFs that don't use it
* Ensure pdf >= 0.0 in case of numerical precision issues

Ref T92571, D15286

13 files changed, 396 insertions, 33 deletions

diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index f0b28ff77c4..d202018be9a 100644
--- a/intern/cycles/kernel/closure/bsdf.h
+++ b/intern/cycles/kernel/closure/bsdf.h
@@ -105,7 +105,9 @@ ccl_device_inline int bsdf_sample(KernelGlobals kg,
                                   float randv,
                                   ccl_private Spectrum *eval,
                                   ccl_private float3 *omega_in,
-                                  ccl_private float *pdf)
+                                  ccl_private float *pdf,
+                                  ccl_private float2 *sampled_roughness,
+                                  ccl_private float *eta)
 {
   /* For curves use the smooth normal, particularly for ribbons the geometric
    * normal gives too much darkening otherwise. */
@@ -115,78 +117,131 @@ ccl_device_inline int bsdf_sample(KernelGlobals kg,
   switch (sc->type) {
     case CLOSURE_BSDF_DIFFUSE_ID:
       label = bsdf_diffuse_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
 #if defined(__SVM__) || defined(__OSL__)
     case CLOSURE_BSDF_OREN_NAYAR_ID:
       label = bsdf_oren_nayar_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
 #  ifdef __OSL__
     case CLOSURE_BSDF_PHONG_RAMP_ID:
-      label = bsdf_phong_ramp_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_phong_ramp_sample(
+          sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness);
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_DIFFUSE_RAMP_ID:
       label = bsdf_diffuse_ramp_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
 #  endif
     case CLOSURE_BSDF_TRANSLUCENT_ID:
       label = bsdf_translucent_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_REFLECTION_ID:
-      label = bsdf_reflection_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_reflection_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, eta);
+      *sampled_roughness = zero_float2();
       break;
     case CLOSURE_BSDF_REFRACTION_ID:
-      label = bsdf_refraction_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_refraction_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, eta);
+      *sampled_roughness = zero_float2();
       break;
     case CLOSURE_BSDF_TRANSPARENT_ID:
       label = bsdf_transparent_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = zero_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_MICROFACET_GGX_ID:
     case CLOSURE_BSDF_MICROFACET_GGX_FRESNEL_ID:
     case CLOSURE_BSDF_MICROFACET_GGX_CLEARCOAT_ID:
     case CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID:
-      label = bsdf_microfacet_ggx_sample(kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_microfacet_ggx_sample(
+          kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness, eta);
       break;
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_ID:
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_FRESNEL_ID:
-      label = bsdf_microfacet_multi_ggx_sample(
-          kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, &sd->lcg_state);
+      label = bsdf_microfacet_multi_ggx_sample(kg,
+                                               sc,
+                                               Ng,
+                                               sd->I,
+                                               randu,
+                                               randv,
+                                               eval,
+                                               omega_in,
+                                               pdf,
+                                               &sd->lcg_state,
+                                               sampled_roughness,
+                                               eta);
       break;
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_ID:
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_FRESNEL_ID:
-      label = bsdf_microfacet_multi_ggx_glass_sample(
-          kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, &sd->lcg_state);
+      label = bsdf_microfacet_multi_ggx_glass_sample(kg,
+                                                     sc,
+                                                     Ng,
+                                                     sd->I,
+                                                     randu,
+                                                     randv,
+                                                     eval,
+                                                     omega_in,
+                                                     pdf,
+                                                     &sd->lcg_state,
+                                                     sampled_roughness,
+                                                     eta);
       break;
     case CLOSURE_BSDF_MICROFACET_BECKMANN_ID:
     case CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID:
       label = bsdf_microfacet_beckmann_sample(
-          kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+          kg, sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness, eta);
       break;
     case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
-      label = bsdf_ashikhmin_shirley_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_ashikhmin_shirley_sample(
+          sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness);
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
       label = bsdf_ashikhmin_velvet_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_DIFFUSE_TOON_ID:
       label = bsdf_diffuse_toon_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_GLOSSY_TOON_ID:
       label = bsdf_glossy_toon_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      // double check if this is valid
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_HAIR_REFLECTION_ID:
-      label = bsdf_hair_reflection_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_hair_reflection_sample(
+          sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness);
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_HAIR_TRANSMISSION_ID:
-      label = bsdf_hair_transmission_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      label = bsdf_hair_transmission_sample(
+          sc, Ng, sd->I, randu, randv, eval, omega_in, pdf, sampled_roughness);
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_HAIR_PRINCIPLED_ID:
-      label = bsdf_principled_hair_sample(kg, sc, sd, randu, randv, eval, omega_in, pdf);
+      label = bsdf_principled_hair_sample(
+          kg, sc, sd, randu, randv, eval, omega_in, pdf, sampled_roughness, eta);
       break;
     case CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID:
       label = bsdf_principled_diffuse_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
     case CLOSURE_BSDF_PRINCIPLED_SHEEN_ID:
       label = bsdf_principled_sheen_sample(sc, Ng, sd->I, randu, randv, eval, omega_in, pdf);
+      *sampled_roughness = one_float2();
+      *eta = 1.0f;
       break;
 #endif
     default:
@@ -226,6 +281,246 @@ ccl_device_inline int bsdf_sample(KernelGlobals kg,
   return label;
 }
 
+ccl_device_inline void bsdf_roughness_eta(const KernelGlobals kg,
+                                          ccl_private const ShaderClosure *sc,
+                                          ccl_private float2 *roughness,
+                                          ccl_private float *eta)
+{
+  bool refractive = false;
+  float alpha = 1.0f;
+  switch (sc->type) {
+    case CLOSURE_BSDF_DIFFUSE_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+#ifdef __SVM__
+    case CLOSURE_BSDF_OREN_NAYAR_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+#  ifdef __OSL__
+    case CLOSURE_BSDF_PHONG_RAMP_ID:
+      alpha = phong_ramp_exponent_to_roughness(((ccl_private const PhongRampBsdf *)sc)->exponent);
+      *roughness = make_float2(alpha, alpha);
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_DIFFUSE_RAMP_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+#  endif
+    case CLOSURE_BSDF_TRANSLUCENT_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_REFLECTION_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = zero_float2();
+      *eta = bsdf->ior;
+      break;
+    }
+    case CLOSURE_BSDF_REFRACTION_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = zero_float2();
+      // do we need to inverse eta??
+      *eta = bsdf->ior;
+      break;
+    }
+    case CLOSURE_BSDF_TRANSPARENT_ID:
+      *roughness = zero_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_MICROFACET_GGX_ID:
+    case CLOSURE_BSDF_MICROFACET_GGX_FRESNEL_ID:
+    case CLOSURE_BSDF_MICROFACET_GGX_CLEARCOAT_ID:
+    case CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+      refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
+      *eta = refractive ? 1.0f / bsdf->ior : bsdf->ior;
+      break;
+    }
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_ID:
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_FRESNEL_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+      *eta = bsdf->ior;
+      break;
+    }
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_ID:
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_FRESNEL_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+      *eta = bsdf->ior;
+      break;
+    }
+    case CLOSURE_BSDF_MICROFACET_BECKMANN_ID:
+    case CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+      refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID;
+      *eta = refractive ? 1.0f / bsdf->ior : bsdf->ior;
+    } break;
+    case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      *roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+      *eta = 1.0f;
+      break;
+    }
+    case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_DIFFUSE_TOON_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_GLOSSY_TOON_ID:
+      // double check if this is valid
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_HAIR_REFLECTION_ID:
+      *roughness = make_float2(((ccl_private HairBsdf *)sc)->roughness1,
+                               ((ccl_private HairBsdf *)sc)->roughness2);
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_HAIR_TRANSMISSION_ID:
+      *roughness = make_float2(((ccl_private HairBsdf *)sc)->roughness1,
+                               ((ccl_private HairBsdf *)sc)->roughness2);
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_HAIR_PRINCIPLED_ID:
+      alpha = ((ccl_private PrincipledHairBSDF *)sc)->m0_roughness;
+      *roughness = make_float2(alpha, alpha);
+      *eta = ((ccl_private PrincipledHairBSDF *)sc)->eta;
+      break;
+    case CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+    case CLOSURE_BSDF_PRINCIPLED_SHEEN_ID:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+#endif
+    default:
+      *roughness = one_float2();
+      *eta = 1.0f;
+      break;
+  }
+}
+
+ccl_device_inline int bsdf_label(const KernelGlobals kg,
+                                 ccl_private const ShaderClosure *sc,
+                                 const float3 omega_in)
+{
+  /* For curves use the smooth normal, particularly for ribbons the geometric
+   * normal gives too much darkening otherwise. */
+  int label;
+  switch (sc->type) {
+    case CLOSURE_BSDF_DIFFUSE_ID:
+    case CLOSURE_BSSRDF_BURLEY_ID:
+    case CLOSURE_BSSRDF_RANDOM_WALK_ID:
+    case CLOSURE_BSSRDF_RANDOM_WALK_FIXED_RADIUS_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+#ifdef __SVM__
+    case CLOSURE_BSDF_OREN_NAYAR_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+#  ifdef __OSL__
+    case CLOSURE_BSDF_PHONG_RAMP_ID:
+      label = LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_DIFFUSE_RAMP_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+#  endif
+    case CLOSURE_BSDF_TRANSLUCENT_ID:
+      label = LABEL_TRANSMIT | LABEL_DIFFUSE;
+      break;
+    case CLOSURE_BSDF_REFLECTION_ID:
+      label = LABEL_REFLECT | LABEL_SINGULAR;
+      break;
+    case CLOSURE_BSDF_REFRACTION_ID:
+      label = LABEL_TRANSMIT | LABEL_SINGULAR;
+      break;
+    case CLOSURE_BSDF_TRANSPARENT_ID:
+      label = LABEL_TRANSMIT | LABEL_TRANSPARENT;
+      break;
+    case CLOSURE_BSDF_MICROFACET_GGX_ID:
+    case CLOSURE_BSDF_MICROFACET_GGX_FRESNEL_ID:
+    case CLOSURE_BSDF_MICROFACET_GGX_CLEARCOAT_ID:
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_ID:
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_FRESNEL_ID:
+    case CLOSURE_BSDF_MICROFACET_BECKMANN_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      label = (bsdf->alpha_x * bsdf->alpha_y <= 1e-7f) ? LABEL_REFLECT | LABEL_SINGULAR :
+                                                         LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    }
+    case CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID:
+    case CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID: {
+      ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+      label = (bsdf->alpha_x * bsdf->alpha_y <= 1e-7f) ? LABEL_TRANSMIT | LABEL_SINGULAR :
+                                                         LABEL_TRANSMIT | LABEL_GLOSSY;
+      break;
+    }
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_ID:
+    case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_FRESNEL_ID:
+      label = (bsdf_is_transmission(sc, omega_in)) ? LABEL_TRANSMIT | LABEL_GLOSSY :
+                                                     LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
+      label = LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+    case CLOSURE_BSDF_DIFFUSE_TOON_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+    case CLOSURE_BSDF_GLOSSY_TOON_ID:
+      label = LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_HAIR_REFLECTION_ID:
+      label = LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_HAIR_TRANSMISSION_ID:
+      label = LABEL_TRANSMIT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_HAIR_PRINCIPLED_ID:
+      if (is_transmission)
+        label = LABEL_TRANSMIT | LABEL_GLOSSY;
+      else
+        label = LABEL_REFLECT | LABEL_GLOSSY;
+      break;
+    case CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+    case CLOSURE_BSDF_PRINCIPLED_SHEEN_ID:
+      label = LABEL_REFLECT | LABEL_DIFFUSE;
+      break;
+#endif
+    default:
+      label = LABEL_NONE;
+      break;
+  }
+
+  /* Test if BSDF sample should be treated as transparent for background. */
+  if (label & LABEL_TRANSMIT) {
+    float threshold_squared = kernel_data.background.transparent_roughness_squared_threshold;
+
+    if (threshold_squared >= 0.0f) {
+      if (bsdf_get_specular_roughness_squared(sc) <= threshold_squared) {
+        label |= LABEL_TRANSMIT_TRANSPARENT;
+      }
+    }
+  }
+  return label;
+}
+
 #ifndef __KERNEL_CUDA__
 ccl_device
 #else
diff --git a/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h b/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h
index 75995262030..cfe1ced43f2 100644
--- a/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h
+++ b/intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h
@@ -137,9 +137,11 @@ ccl_device int bsdf_ashikhmin_shirley_sample(ccl_private const ShaderClosure *sc
                                              float randv,
                                              ccl_private Spectrum *eval,
                                              ccl_private float3 *omega_in,
-                                             ccl_private float *pdf)
+                                             ccl_private float *pdf,
+                                             ccl_private float2 *sampled_roughness)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
+  *sampled_roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
   float3 N = bsdf->N;
   int label = LABEL_REFLECT | LABEL_GLOSSY;
 
diff --git a/intern/cycles/kernel/closure/bsdf_hair.h b/intern/cycles/kernel/closure/bsdf_hair.h
index a29f7c444ae..69c05813982 100644
--- a/intern/cycles/kernel/closure/bsdf_hair.h
+++ b/intern/cycles/kernel/closure/bsdf_hair.h
@@ -155,13 +155,15 @@ ccl_device int bsdf_hair_reflection_sample(ccl_private const ShaderClosure *sc,
                                            float randv,
                                            ccl_private Spectrum *eval,
                                            ccl_private float3 *omega_in,
-                                           ccl_private float *pdf)
+                                           ccl_private float *pdf,
+                                           ccl_private float2 *sampled_roughness)
 {
   ccl_private const HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
   float offset = bsdf->offset;
   float3 Tg = bsdf->T;
   float roughness1 = bsdf->roughness1;
   float roughness2 = bsdf->roughness2;
+  *sampled_roughness = make_float2(roughness1, roughness2);
   float Iz = dot(Tg, I);
   float3 locy = normalize(I - Tg * Iz);
   float3 locx = cross(locy, Tg);
@@ -206,13 +208,15 @@ ccl_device int bsdf_hair_transmission_sample(ccl_private const ShaderClosure *sc
                                              float randv,
                                              ccl_private Spectrum *eval,
                                              ccl_private float3 *omega_in,
-                                             ccl_private float *pdf)
+                                             ccl_private float *pdf,
+                                             ccl_private float2 *sampled_roughness)
 {
   ccl_private const HairBsdf *bsdf = (ccl_private const HairBsdf *)sc;
   float offset = bsdf->offset;
   float3 Tg = bsdf->T;
   float roughness1 = bsdf->roughness1;
   float roughness2 = bsdf->roughness2;
+  *sampled_roughness = make_float2(roughness1, roughness2);
   float Iz = dot(Tg, I);
   float3 locy = normalize(I - Tg * Iz);
   float3 locx = cross(locy, Tg);
diff --git a/intern/cycles/kernel/closure/bsdf_hair_principled.h b/intern/cycles/kernel/closure/bsdf_hair_principled.h
index 2236bc62050..d0a44c65d52 100644
--- a/intern/cycles/kernel/closure/bsdf_hair_principled.h
+++ b/intern/cycles/kernel/closure/bsdf_hair_principled.h
@@ -354,10 +354,15 @@ ccl_device int bsdf_principled_hair_sample(KernelGlobals kg,
                                            float randv,
                                            ccl_private Spectrum *eval,
                                            ccl_private float3 *omega_in,
-                                           ccl_private float *pdf)
+                                           ccl_private float *pdf,
+                                           ccl_private float2 *sampled_roughness,
+                                           ccl_private float *eta)
 {
   ccl_private PrincipledHairBSDF *bsdf = (ccl_private PrincipledHairBSDF *)sc;
 
+  *sampled_roughness = make_float2(bsdf->m0_roughness, bsdf->m0_roughness);
+  *eta = bsdf->eta;
+
   float3 Y = float4_to_float3(bsdf->extra->geom);
 
   float3 X = safe_normalize(sd->dPdu);
diff --git a/intern/cycles/kernel/closure/bsdf_microfacet.h b/intern/cycles/kernel/closure/bsdf_microfacet.h
index 04d5ca90bfd..f29897bc55d 100644
--- a/intern/cycles/kernel/closure/bsdf_microfacet.h
+++ b/intern/cycles/kernel/closure/bsdf_microfacet.h
@@ -541,12 +541,18 @@ ccl_device int bsdf_microfacet_ggx_sample(KernelGlobals kg,
                                           float randv,
                                           ccl_private Spectrum *eval,
                                           ccl_private float3 *omega_in,
-                                          ccl_private float *pdf)
+                                          ccl_private float *pdf,
+                                          ccl_private float2 *sampled_roughness,
+                                          ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
   float alpha_x = bsdf->alpha_x;
   float alpha_y = bsdf->alpha_y;
   bool m_refractive = bsdf->type == CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID;
+
+  *sampled_roughness = make_float2(alpha_x, alpha_y);
+  *eta = m_refractive ? 1.0f / bsdf->ior : bsdf->ior;
+
   float3 N = bsdf->N;
   int label;
 
@@ -952,7 +958,9 @@ ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals kg,
                                                float randv,
                                                ccl_private Spectrum *eval,
                                                ccl_private float3 *omega_in,
-                                               ccl_private float *pdf)
+                                               ccl_private float *pdf,
+                                               ccl_private float2 *sampled_roughness,
+                                               ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
   float alpha_x = bsdf->alpha_x;
@@ -961,6 +969,9 @@ ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals kg,
   float3 N = bsdf->N;
   int label;
 
+  *sampled_roughness = make_float2(alpha_x, alpha_y);
+  *eta = m_refractive ? 1.0f / bsdf->ior : bsdf->ior;
+
   float cosNO = dot(N, I);
   if (cosNO > 0) {
     float3 X, Y, Z = N;
diff --git a/intern/cycles/kernel/closure/bsdf_microfacet_multi.h b/intern/cycles/kernel/closure/bsdf_microfacet_multi.h
index 9402ce11f7a..34115749611 100644
--- a/intern/cycles/kernel/closure/bsdf_microfacet_multi.h
+++ b/intern/cycles/kernel/closure/bsdf_microfacet_multi.h
@@ -462,6 +462,12 @@ ccl_device Spectrum bsdf_microfacet_multi_ggx_eval_reflect(ccl_private const Sha
     *pdf = mf_ggx_aniso_pdf(localI, localO, make_float2(bsdf->alpha_x, bsdf->alpha_y));
   else
     *pdf = mf_ggx_pdf(localI, localO, bsdf->alpha_x);
+
+  if (*pdf <= 0.f) {
+    *pdf = 0.f;
+    return make_float3(0.f, 0.f, 0.f);
+  }
+
   return mf_eval_glossy(localI,
                         localO,
                         true,
@@ -483,7 +489,9 @@ ccl_device int bsdf_microfacet_multi_ggx_sample(KernelGlobals kg,
                                                 ccl_private Spectrum *eval,
                                                 ccl_private float3 *omega_in,
                                                 ccl_private float *pdf,
-                                                ccl_private uint *lcg_state)
+                                                ccl_private uint *lcg_state,
+                                                ccl_private float2 *sampled_roughness,
+                                                ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
 
@@ -511,6 +519,9 @@ ccl_device int bsdf_microfacet_multi_ggx_sample(KernelGlobals kg,
 
   bool use_fresnel = (bsdf->type == CLOSURE_BSDF_MICROFACET_MULTI_GGX_FRESNEL_ID);
 
+  *eta = bsdf->ior;
+  *sampled_roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+
   bool is_aniso = (bsdf->alpha_x != bsdf->alpha_y);
   if (is_aniso)
     make_orthonormals_tangent(Z, bsdf->T, &X, &Y);
@@ -541,6 +552,7 @@ ccl_device int bsdf_microfacet_multi_ggx_sample(KernelGlobals kg,
     *pdf = mf_ggx_aniso_pdf(localI, localO, make_float2(bsdf->alpha_x, bsdf->alpha_y));
   else
     *pdf = mf_ggx_pdf(localI, localO, bsdf->alpha_x);
+  *pdf = fmaxf(0.f, *pdf);
   *eval *= *pdf;
 
   return LABEL_REFLECT | LABEL_GLOSSY;
@@ -598,6 +610,7 @@ bsdf_microfacet_multi_ggx_glass_eval_transmit(ccl_private const ShaderClosure *s
   float3 localO = make_float3(dot(omega_in, X), dot(omega_in, Y), dot(omega_in, Z));
 
   *pdf = mf_glass_pdf(localI, localO, bsdf->alpha_x, bsdf->ior);
+  kernel_assert(*pdf >= 0.f);
   return mf_eval_glass(localI,
                        localO,
                        false,
@@ -634,6 +647,7 @@ bsdf_microfacet_multi_ggx_glass_eval_reflect(ccl_private const ShaderClosure *sc
   float3 localO = make_float3(dot(omega_in, X), dot(omega_in, Y), dot(omega_in, Z));
 
   *pdf = mf_glass_pdf(localI, localO, bsdf->alpha_x, bsdf->ior);
+  kernel_assert(*pdf >= 0.f);
   return mf_eval_glass(localI,
                        localO,
                        true,
@@ -655,13 +669,18 @@ ccl_device int bsdf_microfacet_multi_ggx_glass_sample(KernelGlobals kg,
                                                       ccl_private Spectrum *eval,
                                                       ccl_private float3 *omega_in,
                                                       ccl_private float *pdf,
-                                                      ccl_private uint *lcg_state)
+                                                      ccl_private uint *lcg_state,
+                                                      ccl_private float2 *sampled_roughness,
+                                                      ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
 
   float3 X, Y, Z;
   Z = bsdf->N;
 
+  *eta = bsdf->ior;
+  *sampled_roughness = make_float2(bsdf->alpha_x, bsdf->alpha_y);
+
   if (bsdf->alpha_x * bsdf->alpha_y < 1e-7f) {
     float3 R, T;
     bool inside;
@@ -696,6 +715,7 @@ ccl_device int bsdf_microfacet_multi_ggx_glass_sample(KernelGlobals kg,
                           use_fresnel,
                           bsdf->extra->cspec0);
   *pdf = mf_glass_pdf(localI, localO, bsdf->alpha_x, bsdf->ior);
+  kernel_assert(*pdf >= 0.f);
   *eval *= *pdf;
 
   *omega_in = X * localO.x + Y * localO.y + Z * localO.z;
diff --git a/intern/cycles/kernel/closure/bsdf_phong_ramp.h b/intern/cycles/kernel/closure/bsdf_phong_ramp.h
index 4236e77ae6c..a50df0b397d 100644
--- a/intern/cycles/kernel/closure/bsdf_phong_ramp.h
+++ b/intern/cycles/kernel/closure/bsdf_phong_ramp.h
@@ -79,6 +79,11 @@ ccl_device float3 bsdf_phong_ramp_eval_transmit(ccl_private const ShaderClosure
   return make_float3(0.0f, 0.0f, 0.0f);
 }
 
+ccl_device_inline float phong_ramp_exponent_to_roughness(float exponent)
+{
+  return sqrt(1.0f / ((exponent + 2.0f) / 2.0f));
+}
+
 ccl_device int bsdf_phong_ramp_sample(ccl_private const ShaderClosure *sc,
                                       float3 Ng,
                                       float3 I,
@@ -86,11 +91,14 @@ ccl_device int bsdf_phong_ramp_sample(ccl_private const ShaderClosure *sc,
                                       float randv,
                                       ccl_private Spectrum *eval,
                                       ccl_private float3 *omega_in,
-                                      ccl_private float *pdf)
+                                      ccl_private float *pdf,
+                                      ccl_private float2 *sampled_roughness)
 {
   ccl_private const PhongRampBsdf *bsdf = (ccl_private const PhongRampBsdf *)sc;
   float cosNO = dot(bsdf->N, I);
   float m_exponent = bsdf->exponent;
+  const float m_roughness = phong_ramp_exponent_to_roughness(m_exponent);
+  *sampled_roughness = make_float2(m_roughness, m_roughness);
 
   if (cosNO > 0) {
     // reflect the view vector
diff --git a/intern/cycles/kernel/closure/bsdf_reflection.h b/intern/cycles/kernel/closure/bsdf_reflection.h
index 5e6c6cdcde6..798bcfaf9e7 100644
--- a/intern/cycles/kernel/closure/bsdf_reflection.h
+++ b/intern/cycles/kernel/closure/bsdf_reflection.h
@@ -43,10 +43,12 @@ ccl_device int bsdf_reflection_sample(ccl_private const ShaderClosure *sc,
                                       float randv,
                                       ccl_private Spectrum *eval,
                                       ccl_private float3 *omega_in,
-                                      ccl_private float *pdf)
+                                      ccl_private float *pdf,
+                                      ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
   float3 N = bsdf->N;
+  *eta = bsdf->ior;
 
   // only one direction is possible
   float cosNO = dot(N, I);
diff --git a/intern/cycles/kernel/closure/bsdf_refraction.h b/intern/cycles/kernel/closure/bsdf_refraction.h
index e680a9617db..34836206ddf 100644
--- a/intern/cycles/kernel/closure/bsdf_refraction.h
+++ b/intern/cycles/kernel/closure/bsdf_refraction.h
@@ -43,10 +43,13 @@ ccl_device int bsdf_refraction_sample(ccl_private const ShaderClosure *sc,
                                       float randv,
                                       ccl_private Spectrum *eval,
                                       ccl_private float3 *omega_in,
-                                      ccl_private float *pdf)
+                                      ccl_private float *pdf,
+                                      ccl_private float *eta)
 {
   ccl_private const MicrofacetBsdf *bsdf = (ccl_private const MicrofacetBsdf *)sc;
   float m_eta = bsdf->ior;
+
+  *eta = 1.0f / m_eta;
   float3 N = bsdf->N;
 
   float3 R, T;
diff --git a/intern/cycles/kernel/integrator/shade_surface.h b/intern/cycles/kernel/integrator/shade_surface.h
index c19f56a9b70..7c31d673566 100644
--- a/intern/cycles/kernel/integrator/shade_surface.h
+++ b/intern/cycles/kernel/integrator/shade_surface.h
@@ -357,8 +357,18 @@ ccl_device_forceinline int integrate_surface_bsdf_bssrdf_bounce(
   float3 bsdf_omega_in ccl_optional_struct_init;
   int label;
 
-  label = surface_shader_bsdf_sample_closure(
-      kg, sd, sc, rand_bsdf, &bsdf_eval, &bsdf_omega_in, &bsdf_pdf);
+  float2 bsdf_sampled_roughness = make_float2(1.0f, 1.0f);
+  float bsdf_eta = 1.0f;
+
+  label = surface_shader_bsdf_sample_closure(kg,
+                                             sd,
+                                             sc,
+                                             rand_bsdf,
+                                             &bsdf_eval,
+                                             &bsdf_omega_in,
+                                             &bsdf_pdf,
+                                             &bsdf_sampled_roughness,
+                                             &bsdf_eta);
 
   if (bsdf_pdf == 0.0f || bsdf_eval_is_zero(&bsdf_eval)) {
     return LABEL_NONE;
diff --git a/intern/cycles/kernel/integrator/surface_shader.h b/intern/cycles/kernel/integrator/surface_shader.h
index 64b5556f7e9..125aaae1b3f 100644
--- a/intern/cycles/kernel/integrator/surface_shader.h
+++ b/intern/cycles/kernel/integrator/surface_shader.h
@@ -267,7 +267,9 @@ ccl_device int surface_shader_bsdf_sample_closure(KernelGlobals kg,
                                                   const float2 rand_bsdf,
                                                   ccl_private BsdfEval *bsdf_eval,
                                                   ccl_private float3 *omega_in,
-                                                  ccl_private float *pdf)
+                                                  ccl_private float *pdf,
+                                                  ccl_private float2 *sampled_roughness,
+                                                  ccl_private float *eta)
 {
   /* BSSRDF should already have been handled elsewhere. */
   kernel_assert(CLOSURE_IS_BSDF(sc->type));
@@ -276,7 +278,8 @@ ccl_device int surface_shader_bsdf_sample_closure(KernelGlobals kg,
   Spectrum eval = zero_spectrum();
 
   *pdf = 0.0f;
-  label = bsdf_sample(kg, sd, sc, rand_bsdf.x, rand_bsdf.y, &eval, omega_in, pdf);
+  label = bsdf_sample(
+      kg, sd, sc, rand_bsdf.x, rand_bsdf.y, &eval, omega_in, pdf, sampled_roughness, eta);
 
   if (*pdf != 0.0f) {
     bsdf_eval_init(bsdf_eval, sc->type, eval * sc->weight);
diff --git a/intern/cycles/kernel/osl/closures_setup.h b/intern/cycles/kernel/osl/closures_setup.h
index f8d68444f90..96c551b9951 100644
--- a/intern/cycles/kernel/osl/closures_setup.h
+++ b/intern/cycles/kernel/osl/closures_setup.h
@@ -428,7 +428,7 @@ ccl_device void osl_closure_microfacet_multi_ggx_setup(
   bsdf->N = ensure_valid_reflection(sd->Ng, sd->I, closure->N);
   bsdf->alpha_x = closure->alpha_x;
   bsdf->alpha_y = bsdf->alpha_x;
-  bsdf->ior = 0.0f;
+  bsdf->ior = 1.0f;
 
   bsdf->extra = extra;
   bsdf->extra->color = rgb_to_spectrum(closure->color);
@@ -510,7 +510,7 @@ ccl_device void osl_closure_microfacet_multi_ggx_aniso_setup(
   bsdf->N = ensure_valid_reflection(sd->Ng, sd->I, closure->N);
   bsdf->alpha_x = closure->alpha_x;
   bsdf->alpha_y = closure->alpha_y;
-  bsdf->ior = 0.0f;
+  bsdf->ior = 1.0f;
 
   bsdf->extra = extra;
   bsdf->extra->color = rgb_to_spectrum(closure->color);
diff --git a/intern/cycles/kernel/svm/closure.h b/intern/cycles/kernel/svm/closure.h
index 2d91b014f60..d18f2cc0854 100644
--- a/intern/cycles/kernel/svm/closure.h
+++ b/intern/cycles/kernel/svm/closure.h
@@ -31,7 +31,7 @@ ccl_device void svm_node_glass_setup(ccl_private ShaderData *sd,
     else {
       bsdf->alpha_y = 0.0f;
       bsdf->alpha_x = 0.0f;
-      bsdf->ior = 0.0f;
+      bsdf->ior = eta;
       sd->flag |= bsdf_reflection_setup(bsdf);
     }
   }
@@ -542,7 +542,7 @@ ccl_device_noinline int svm_node_closure_bsdf(KernelGlobals kg,
       float roughness = sqr(param1);
 
       bsdf->N = N;
-      bsdf->ior = 0.0f;
+      bsdf->ior = 1.0f;
       bsdf->extra = NULL;
 
       if (data_node.y == SVM_STACK_INVALID) {