Revert "Cycles: Fix inconsistency in Ng handling between Microfacets and other closures"

This reverts commit a6015e1411 in the
blender-v4.5-release branch to work around HIP compiler issues. It will
remain in the main branch.

Ref blender/blender#139836

intern/cycles/kernel/closure/bsdf.h

@@ -532,15 +532,18 @@ ccl_device_inline
     case CLOSURE_BSDF_MICROFACET_GGX_ID:
     case CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID:
     case CLOSURE_BSDF_MICROFACET_GGX_GLASS_ID:
-      eval = bsdf_microfacet_ggx_eval(kg, sc, sd->wi, wo, pdf);
+      /* For consistency with eval() this should be using sd->Ng, but that causes
+       * artifacts (see shadow_terminator_metal test). Needs deeper investigation
+       * for how to solve this. */
+      eval = bsdf_microfacet_ggx_eval(kg, sc, sd->N, sd->wi, wo, pdf);
       break;
     case CLOSURE_BSDF_MICROFACET_BECKMANN_ID:
     case CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID:
     case CLOSURE_BSDF_MICROFACET_BECKMANN_GLASS_ID:
-      eval = bsdf_microfacet_beckmann_eval(kg, sc, sd->wi, wo, pdf);
+      eval = bsdf_microfacet_beckmann_eval(kg, sc, sd->N, sd->wi, wo, pdf);
       break;
     case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
-      eval = bsdf_ashikhmin_shirley_eval(sc, sd->wi, wo, pdf);
+      eval = bsdf_ashikhmin_shirley_eval(sc, sd->N, sd->wi, wo, pdf);
       break;
     case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
       eval = bsdf_ashikhmin_velvet_eval(sc, sd->wi, wo, pdf);

intern/cycles/kernel/closure/bsdf_ashikhmin_shirley.h

@@ -46,11 +46,13 @@ ccl_device_inline float bsdf_ashikhmin_shirley_roughness_to_exponent(const float
 }
 
 ccl_device_forceinline Spectrum bsdf_ashikhmin_shirley_eval(const ccl_private ShaderClosure *sc,
+                                                            const float3 Ng,
                                                             const float3 wi,
                                                             const float3 wo,
                                                             ccl_private float *pdf)
 {
   const ccl_private MicrofacetBsdf *bsdf = (const ccl_private MicrofacetBsdf *)sc;
+  const float cosNgO = dot(Ng, wo);
   const float3 N = bsdf->N;
 
   float NdotI = dot(N, wi);
@@ -58,7 +60,9 @@ ccl_device_forceinline Spectrum bsdf_ashikhmin_shirley_eval(const ccl_private Sh
 
   float out = 0.0f;
 
-  if (fmaxf(bsdf->alpha_x, bsdf->alpha_y) <= 1e-4f || (NdotI < 0.0f) || (NdotO < 0.0f)) {
+  if ((cosNgO < 0.0f) || fmaxf(bsdf->alpha_x, bsdf->alpha_y) <= 1e-4f ||
+      !(NdotI > 0.0f && NdotO > 0.0f))
+  {
     *pdf = 0.0f;
     return zero_spectrum();
   }
@@ -204,13 +208,6 @@ ccl_device int bsdf_ashikhmin_shirley_sample(const ccl_private ShaderClosure *sc
   /* reflect wi on H to get wo */
   *wo = -wi + (2.0f * HdotI) * H;
 
-  /* Check hemisphere. */
-  if (dot(Ng, *wo) < 0.0f) {
-    *pdf = 0.0f;
-    *eval = zero_spectrum();
-    return LABEL_NONE;
-  }
-
   if (fmaxf(bsdf->alpha_x, bsdf->alpha_y) <= 1e-4f) {
     /* Some high number for MIS. */
     *pdf = 1e6f;
@@ -219,7 +216,7 @@ ccl_device int bsdf_ashikhmin_shirley_sample(const ccl_private ShaderClosure *sc
   }
   else {
     /* leave the rest to eval */
-    *eval = bsdf_ashikhmin_shirley_eval(sc, wi, *wo, pdf);
+    *eval = bsdf_ashikhmin_shirley_eval(sc, Ng, wi, *wo, pdf);
   }
 
   return label;

intern/cycles/kernel/closure/bsdf_microfacet.h

@@ -564,6 +564,7 @@ ccl_device_forceinline int bsdf_microfacet_eval_flag(const ccl_private Microface
 template<MicrofacetType m_type>
 ccl_device Spectrum bsdf_microfacet_eval(KernelGlobals kg,
                                          const ccl_private ShaderClosure *sc,
+                                         const float3 Ng,
                                          const float3 wi,
                                          const float3 wo,
                                          ccl_private float *pdf)
@@ -577,6 +578,7 @@ ccl_device Spectrum bsdf_microfacet_eval(KernelGlobals kg,
   const float3 N = bsdf->N;
   const float cos_NI = dot(N, wi);
   const float cos_NO = dot(N, wo);
+  const float cos_NgO = dot(Ng, wo);
 
   const float alpha_x = bsdf->alpha_x;
   const float alpha_y = bsdf->alpha_y;
@@ -586,10 +588,11 @@ ccl_device Spectrum bsdf_microfacet_eval(KernelGlobals kg,
   /* Check whether the pair of directions is valid for evaluation:
    * - Incoming direction has to be in the upper hemisphere (Cycles convention)
    * - Specular cases can't be evaluated, only sampled.
+   * - The outgoing direction has to be the in the same hemisphere w.r.t. both normals.
    * - Purely reflective closures can't have refraction.
    * - Purely refractive closures can't have reflection.
    */
-  if ((cos_NI <= 0) || !bsdf_microfacet_eval_flag(bsdf) ||
+  if ((cos_NI <= 0) || !bsdf_microfacet_eval_flag(bsdf) || ((cos_NgO < 0.0f) != is_transmission) ||
       (is_transmission && !has_transmission) || (!is_transmission && !has_reflection))
   {
     return zero_spectrum();
@@ -729,16 +732,7 @@ ccl_device int bsdf_microfacet_sample(KernelGlobals kg,
 
   /* Compute actual reflected or refracted direction. */
   *wo = do_refract ? refract_angle(wi, H, cos_HO, m_inv_eta) : 2.0f * cos_HI * H - wi;
-
-  /* Ensure that the sampled direction lies in the correct hemisphere.
-   * Note that the check against Ng is only performed in the sampling code, not the evaluation.
-   * This is technically inconsistent, but required in order to avoid shadow terminator artifacts
-   * on smooth geometry (which we'd get if we checked Ng in evaluation) while ensuring that
-   * sampling doesn't return supposed reflection rays going into the geometry and vice versa.
-   * The same is done for other closures as well. */
-  const float cos_NO = dot(N, *wo);
-  const float cos_NgO = dot(Ng, *wo);
-  if ((cos_NgO < 0) != do_refract || (cos_NO < 0) != do_refract) {
+  if ((dot(Ng, *wo) < 0) != do_refract) {
     return LABEL_NONE;
   }
 
@@ -982,12 +976,13 @@ ccl_device void bsdf_microfacet_blur(ccl_private ShaderClosure *sc, const float
 
 ccl_device Spectrum bsdf_microfacet_ggx_eval(KernelGlobals kg,
                                              const ccl_private ShaderClosure *sc,
+                                             const float3 Ng,
                                              const float3 wi,
                                              const float3 wo,
                                              ccl_private float *pdf)
 {
   const ccl_private MicrofacetBsdf *bsdf = (const ccl_private MicrofacetBsdf *)sc;
-  return bsdf->energy_scale * bsdf_microfacet_eval<MicrofacetType::GGX>(kg, sc, wi, wo, pdf);
+  return bsdf->energy_scale * bsdf_microfacet_eval<MicrofacetType::GGX>(kg, sc, Ng, wi, wo, pdf);
 }
 
 ccl_device int bsdf_microfacet_ggx_sample(KernelGlobals kg,
@@ -1048,11 +1043,12 @@ ccl_device int bsdf_microfacet_beckmann_glass_setup(ccl_private MicrofacetBsdf *
 
 ccl_device Spectrum bsdf_microfacet_beckmann_eval(KernelGlobals kg,
                                                   const ccl_private ShaderClosure *sc,
+                                                  const float3 Ng,
                                                   const float3 wi,
                                                   const float3 wo,
                                                   ccl_private float *pdf)
 {
-  return bsdf_microfacet_eval<MicrofacetType::BECKMANN>(kg, sc, wi, wo, pdf);
+  return bsdf_microfacet_eval<MicrofacetType::BECKMANN>(kg, sc, Ng, wi, wo, pdf);
 }
 
 ccl_device int bsdf_microfacet_beckmann_sample(KernelGlobals kg,

intern/cycles/kernel/closure/bsdf_sheen.h

@@ -65,10 +65,19 @@ ccl_device Spectrum bsdf_sheen_eval(const ccl_private ShaderClosure *sc,
   const float a = bsdf->transformA;
   const float b = bsdf->transformB;
 
+  if (dot(N, wo) <= 0.0f) {
+    *pdf = 0.0f;
+    return zero_spectrum();
+  }
+
   const float3 localO = to_local(wo, T, B, N);
+  if (localO.z <= 0.0f) {
+    *pdf = 0.0f;
+    return zero_spectrum();
+  }
 
   const float lenSqr = sqr(a * localO.x + b * localO.z) + sqr(a * localO.y) + sqr(localO.z);
-  const float val = M_1_PI_F * fmaxf(localO.z, 0.0f) * sqr(a / lenSqr);
+  const float val = M_1_PI_F * localO.z * sqr(a / lenSqr);
 
   *pdf = val;
   return make_spectrum(val);