Cycles: BSDF eval refactor to remove separate reflection/refraction methods

Simplifies code overall to do it inside the eval function, most of the BSDFs
already compute the dot product.

The refactoring in bsdf_principled_hair_eval() was needed to avoid a HIP
compiler bug. Cause is unclear, just changing the implementation enough
is meant to sidestep it.

Ref T92571, D15286

3 files changed, 11 insertions, 19 deletions

diff --git a/intern/cycles/kernel/integrator/mnee.h b/intern/cycles/kernel/integrator/mnee.h
index a0ad7afe591..a39209bc937 100644
--- a/intern/cycles/kernel/integrator/mnee.h
+++ b/intern/cycles/kernel/integrator/mnee.h
@@ -807,7 +807,7 @@ ccl_device_forceinline bool mnee_path_contribution(KernelGlobals kg,
   float3 wo = normalize_len(vertices[0].p - sd->P, &wo_len);
 
   /* Initialize throughput and evaluate receiver bsdf * |n.wo|. */
-  surface_shader_bsdf_eval(kg, sd, wo, false, throughput, ls->shader);
+  surface_shader_bsdf_eval(kg, sd, wo, throughput, ls->shader);
 
   /* Update light sample with new position / direct.ion
    * and keep pdf in vertex area measure */
diff --git a/intern/cycles/kernel/integrator/shade_surface.h b/intern/cycles/kernel/integrator/shade_surface.h
index 7c31d673566..c766ea2a07e 100644
--- a/intern/cycles/kernel/integrator/shade_surface.h
+++ b/intern/cycles/kernel/integrator/shade_surface.h
@@ -171,7 +171,8 @@ ccl_device_forceinline void integrate_surface_direct_light(KernelGlobals kg,
 
   Ray ray ccl_optional_struct_init;
   BsdfEval bsdf_eval ccl_optional_struct_init;
-  const bool is_transmission = surface_shader_is_transmission(sd, ls.D);
+
+  const bool is_transmission = dot(ls.D, sd->N) < 0.0f;
 
 #ifdef __MNEE__
   int mnee_vertex_count = 0;
@@ -182,13 +183,15 @@ ccl_device_forceinline void integrate_surface_direct_light(KernelGlobals kg,
       const bool use_caustics = kernel_data_fetch(lights, ls.lamp).use_caustics;
       if (use_caustics) {
         /* Are we on a caustic caster? */
-        if (is_transmission && (sd->object_flag & SD_OBJECT_CAUSTICS_CASTER))
+        if (is_transmission && (sd->object_flag & SD_OBJECT_CAUSTICS_CASTER)) {
           return;
+        }
 
         /* Are we on a caustic receiver? */
-        if (!is_transmission && (sd->object_flag & SD_OBJECT_CAUSTICS_RECEIVER))
+        if (!is_transmission && (sd->object_flag & SD_OBJECT_CAUSTICS_RECEIVER)) {
           mnee_vertex_count = kernel_path_mnee_sample(
               kg, state, sd, emission_sd, rng_state, &ls, &bsdf_eval);
+        }
       }
     }
   }
@@ -207,8 +210,7 @@ ccl_device_forceinline void integrate_surface_direct_light(KernelGlobals kg,
     }
 
     /* Evaluate BSDF. */
-    const float bsdf_pdf = surface_shader_bsdf_eval(
-        kg, sd, ls.D, is_transmission, &bsdf_eval, ls.shader);
+    const float bsdf_pdf = surface_shader_bsdf_eval(kg, sd, ls.D, &bsdf_eval, ls.shader);
     bsdf_eval_mul(&bsdf_eval, light_eval / ls.pdf);
 
     if (ls.shader & SHADER_USE_MIS) {
diff --git a/intern/cycles/kernel/integrator/surface_shader.h b/intern/cycles/kernel/integrator/surface_shader.h
index 125aaae1b3f..7da81984a12 100644
--- a/intern/cycles/kernel/integrator/surface_shader.h
+++ b/intern/cycles/kernel/integrator/surface_shader.h
@@ -108,13 +108,6 @@ ccl_device_inline void surface_shader_prepare_closures(KernelGlobals kg,
 }
 
 /* BSDF */
-
-ccl_device_inline bool surface_shader_is_transmission(ccl_private const ShaderData *sd,
-                                                      const float3 omega_in)
-{
-  return dot(sd->N, omega_in) < 0.0f;
-}
-
 ccl_device_forceinline bool _surface_shader_exclude(ClosureType type, uint light_shader_flags)
 {
   if (!(light_shader_flags & SHADER_EXCLUDE_ANY)) {
@@ -141,7 +134,6 @@ ccl_device_forceinline bool _surface_shader_exclude(ClosureType type, uint light
 ccl_device_inline float _surface_shader_bsdf_eval_mis(KernelGlobals kg,
                                                       ccl_private ShaderData *sd,
                                                       const float3 omega_in,
-                                                      const bool is_transmission,
                                                       ccl_private const ShaderClosure *skip_sc,
                                                       ccl_private BsdfEval *result_eval,
                                                       float sum_pdf,
@@ -160,7 +152,7 @@ ccl_device_inline float _surface_shader_bsdf_eval_mis(KernelGlobals kg,
     if (CLOSURE_IS_BSDF_OR_BSSRDF(sc->type)) {
       if (CLOSURE_IS_BSDF(sc->type) && !_surface_shader_exclude(sc->type, light_shader_flags)) {
         float bsdf_pdf = 0.0f;
-        Spectrum eval = bsdf_eval(kg, sd, sc, omega_in, is_transmission, &bsdf_pdf);
+        Spectrum eval = bsdf_eval(kg, sd, sc, omega_in, &bsdf_pdf);
 
         if (bsdf_pdf != 0.0f) {
           bsdf_eval_accum(result_eval, sc->type, eval * sc->weight);
@@ -184,14 +176,13 @@ ccl_device_inline
     surface_shader_bsdf_eval(KernelGlobals kg,
                              ccl_private ShaderData *sd,
                              const float3 omega_in,
-                             const bool is_transmission,
                              ccl_private BsdfEval *bsdf_eval,
                              const uint light_shader_flags)
 {
   bsdf_eval_init(bsdf_eval, CLOSURE_NONE_ID, zero_spectrum());
 
   return _surface_shader_bsdf_eval_mis(
-      kg, sd, omega_in, is_transmission, NULL, bsdf_eval, 0.0f, 0.0f, light_shader_flags);
+      kg, sd, omega_in, NULL, bsdf_eval, 0.0f, 0.0f, light_shader_flags);
 }
 
 /* Randomly sample a BSSRDF or BSDF proportional to ShaderClosure.sample_weight. */
@@ -285,10 +276,9 @@ ccl_device int surface_shader_bsdf_sample_closure(KernelGlobals kg,
     bsdf_eval_init(bsdf_eval, sc->type, eval * sc->weight);
 
     if (sd->num_closure > 1) {
-      const bool is_transmission = surface_shader_is_transmission(sd, *omega_in);
       float sweight = sc->sample_weight;
       *pdf = _surface_shader_bsdf_eval_mis(
-          kg, sd, *omega_in, is_transmission, sc, bsdf_eval, *pdf * sweight, sweight, 0);
+          kg, sd, *omega_in, sc, bsdf_eval, *pdf * sweight, sweight, 0);
     }
   }