Cycles: port curve-ray intersection from Embree for use in Cycles GPU

This keeps render results compatible for combined CPU + GPU rendering.
Peformance and quality primitives is quite different than before. There
are now two options:

* Rounded Ribbon: render hair as flat ribbon with (fake) rounded normals, for
  fast rendering. Hair curves are subdivided with a fixed number of user
  specified subdivisions.

  This gives relatively good results, especially when used with the Principled
  Hair BSDF and hair viewed from a typical distance. There are artifacts when
  viewed closed up, though this was also the case with all previous primitives
  (but different ones).

* 3D Curve: render hair as 3D curve, for accurate results when viewing hair
  close up. This automatically subdivides the curve until it is smooth.

  This gives higher quality than any of the previous primitives, but does come
  at a performance cost and is somewhat slower than our previous Thick curves.

The main problem here is performance. For CPU and OpenCL rendering performance
seems usually quite close or better for similar quality results.

However for CUDA and Optix, performance of 3D curve intersection is problematic,
with e.g. 1.45x longer render time in Koro (though there is no equivalent quality
and rounded ribbons seem fine for that scene). Any help or ideas to optimize this
are welcome.

Ref T73778

Depends on D8012

Maniphest Tasks: T73778

Differential Revision: https://developer.blender.org/D8013

1 files changed, 27 insertions, 21 deletions

diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index 4cc61e8ee71..6070fd983f5 100644
--- a/intern/cycles/kernel/closure/bsdf.h
+++ b/intern/cycles/kernel/closure/bsdf.h
@@ -119,13 +119,16 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
                                   differential3 *domega_in,
                                   float *pdf)
 {
+  /* For curves use the smooth normal, particularly for ribbons the geometric
+   * normal gives too much darkening otherwise. */
   int label;
+  const float3 Ng = (sd->type & PRIMITIVE_ALL_CURVE) ? sc->N : sd->Ng;
 
   switch (sc->type) {
     case CLOSURE_BSDF_DIFFUSE_ID:
     case CLOSURE_BSDF_BSSRDF_ID:
       label = bsdf_diffuse_sample(sc,
-                                  sd->Ng,
+                                  Ng,
                                   sd->I,
                                   sd->dI.dx,
                                   sd->dI.dy,
@@ -140,7 +143,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
 #ifdef __SVM__
     case CLOSURE_BSDF_OREN_NAYAR_ID:
       label = bsdf_oren_nayar_sample(sc,
-                                     sd->Ng,
+                                     Ng,
                                      sd->I,
                                      sd->dI.dx,
                                      sd->dI.dy,
@@ -155,7 +158,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
 #  ifdef __OSL__
     case CLOSURE_BSDF_PHONG_RAMP_ID:
       label = bsdf_phong_ramp_sample(sc,
-                                     sd->Ng,
+                                     Ng,
                                      sd->I,
                                      sd->dI.dx,
                                      sd->dI.dy,
@@ -169,7 +172,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_DIFFUSE_RAMP_ID:
       label = bsdf_diffuse_ramp_sample(sc,
-                                       sd->Ng,
+                                       Ng,
                                        sd->I,
                                        sd->dI.dx,
                                        sd->dI.dy,
@@ -184,7 +187,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
 #  endif
     case CLOSURE_BSDF_TRANSLUCENT_ID:
       label = bsdf_translucent_sample(sc,
-                                      sd->Ng,
+                                      Ng,
                                       sd->I,
                                       sd->dI.dx,
                                       sd->dI.dy,
@@ -198,7 +201,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_REFLECTION_ID:
       label = bsdf_reflection_sample(sc,
-                                     sd->Ng,
+                                     Ng,
                                      sd->I,
                                      sd->dI.dx,
                                      sd->dI.dy,
@@ -212,7 +215,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_REFRACTION_ID:
       label = bsdf_refraction_sample(sc,
-                                     sd->Ng,
+                                     Ng,
                                      sd->I,
                                      sd->dI.dx,
                                      sd->dI.dy,
@@ -226,7 +229,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_TRANSPARENT_ID:
       label = bsdf_transparent_sample(sc,
-                                      sd->Ng,
+                                      Ng,
                                       sd->I,
                                       sd->dI.dx,
                                       sd->dI.dy,
@@ -244,7 +247,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
     case CLOSURE_BSDF_MICROFACET_GGX_REFRACTION_ID:
       label = bsdf_microfacet_ggx_sample(kg,
                                          sc,
-                                         sd->Ng,
+                                         Ng,
                                          sd->I,
                                          sd->dI.dx,
                                          sd->dI.dy,
@@ -260,7 +263,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_FRESNEL_ID:
       label = bsdf_microfacet_multi_ggx_sample(kg,
                                                sc,
-                                               sd->Ng,
+                                               Ng,
                                                sd->I,
                                                sd->dI.dx,
                                                sd->dI.dy,
@@ -277,7 +280,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
     case CLOSURE_BSDF_MICROFACET_MULTI_GGX_GLASS_FRESNEL_ID:
       label = bsdf_microfacet_multi_ggx_glass_sample(kg,
                                                      sc,
-                                                     sd->Ng,
+                                                     Ng,
                                                      sd->I,
                                                      sd->dI.dx,
                                                      sd->dI.dy,
@@ -294,7 +297,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
     case CLOSURE_BSDF_MICROFACET_BECKMANN_REFRACTION_ID:
       label = bsdf_microfacet_beckmann_sample(kg,
                                               sc,
-                                              sd->Ng,
+                                              Ng,
                                               sd->I,
                                               sd->dI.dx,
                                               sd->dI.dy,
@@ -308,7 +311,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_ASHIKHMIN_SHIRLEY_ID:
       label = bsdf_ashikhmin_shirley_sample(sc,
-                                            sd->Ng,
+                                            Ng,
                                             sd->I,
                                             sd->dI.dx,
                                             sd->dI.dy,
@@ -322,7 +325,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_ASHIKHMIN_VELVET_ID:
       label = bsdf_ashikhmin_velvet_sample(sc,
-                                           sd->Ng,
+                                           Ng,
                                            sd->I,
                                            sd->dI.dx,
                                            sd->dI.dy,
@@ -336,7 +339,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_DIFFUSE_TOON_ID:
       label = bsdf_diffuse_toon_sample(sc,
-                                       sd->Ng,
+                                       Ng,
                                        sd->I,
                                        sd->dI.dx,
                                        sd->dI.dy,
@@ -350,7 +353,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_GLOSSY_TOON_ID:
       label = bsdf_glossy_toon_sample(sc,
-                                      sd->Ng,
+                                      Ng,
                                       sd->I,
                                       sd->dI.dx,
                                       sd->dI.dy,
@@ -364,7 +367,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_HAIR_REFLECTION_ID:
       label = bsdf_hair_reflection_sample(sc,
-                                          sd->Ng,
+                                          Ng,
                                           sd->I,
                                           sd->dI.dx,
                                           sd->dI.dy,
@@ -378,7 +381,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_HAIR_TRANSMISSION_ID:
       label = bsdf_hair_transmission_sample(sc,
-                                            sd->Ng,
+                                            Ng,
                                             sd->I,
                                             sd->dI.dx,
                                             sd->dI.dy,
@@ -398,7 +401,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
     case CLOSURE_BSDF_PRINCIPLED_DIFFUSE_ID:
     case CLOSURE_BSDF_BSSRDF_PRINCIPLED_ID:
       label = bsdf_principled_diffuse_sample(sc,
-                                             sd->Ng,
+                                             Ng,
                                              sd->I,
                                              sd->dI.dx,
                                              sd->dI.dy,
@@ -412,7 +415,7 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       break;
     case CLOSURE_BSDF_PRINCIPLED_SHEEN_ID:
       label = bsdf_principled_sheen_sample(sc,
-                                           sd->Ng,
+                                           Ng,
                                            sd->I,
                                            sd->dI.dx,
                                            sd->dI.dy,
@@ -485,9 +488,12 @@ ccl_device_inline
               const float3 omega_in,
               float *pdf)
 {
+  /* For curves use the smooth normal, particularly for ribbons the geometric
+   * normal gives too much darkening otherwise. */
+  const float3 Ng = (sd->type & PRIMITIVE_ALL_CURVE) ? sd->N : sd->Ng;
   float3 eval;
 
-  if (dot(sd->Ng, omega_in) >= 0.0f) {
+  if (dot(Ng, omega_in) >= 0.0f) {
     switch (sc->type) {
       case CLOSURE_BSDF_DIFFUSE_ID:
       case CLOSURE_BSDF_BSSRDF_ID: