Cycles: simplify handling of ray differentials

* Store compact ray differentials in ShaderData and compute full differentials
  on demand. This reduces register pressure on the GPU.
* Remove BSDF differential code that was effectively doing nothing as the
  differential orientation was discarded when making it compact.

This gives a 1-5% speedup with RTX A6000 + OptiX in our benchmarks, with the
bigger speedups in simpler scenes.

Renders appear to be identical except for the Both displacement option that
does both displacement and bump.

Differential Revision: https://developer.blender.org/D15677

1 files changed, 0 insertions, 8 deletions

diff --git a/intern/cycles/kernel/closure/bsdf_hair_principled.h b/intern/cycles/kernel/closure/bsdf_hair_principled.h
index f78a05ea212..2236bc62050 100644
--- a/intern/cycles/kernel/closure/bsdf_hair_principled.h
+++ b/intern/cycles/kernel/closure/bsdf_hair_principled.h
@@ -354,8 +354,6 @@ ccl_device int bsdf_principled_hair_sample(KernelGlobals kg,
                                            float randv,
                                            ccl_private Spectrum *eval,
                                            ccl_private float3 *omega_in,
-                                           ccl_private float3 *domega_in_dx,
-                                           ccl_private float3 *domega_in_dy,
                                            ccl_private float *pdf)
 {
   ccl_private PrincipledHairBSDF *bsdf = (ccl_private PrincipledHairBSDF *)sc;
@@ -471,12 +469,6 @@ ccl_device int bsdf_principled_hair_sample(KernelGlobals kg,
 
   *omega_in = X * sin_theta_i + Y * cos_theta_i * cosf(phi_i) + Z * cos_theta_i * sinf(phi_i);
 
-#ifdef __RAY_DIFFERENTIALS__
-  float3 N = safe_normalize(sd->I + *omega_in);
-  *domega_in_dx = (2 * dot(N, sd->dI.dx)) * N - sd->dI.dx;
-  *domega_in_dy = (2 * dot(N, sd->dI.dy)) * N - sd->dI.dy;
-#endif
-
   return LABEL_GLOSSY | ((p == 0) ? LABEL_REFLECT : LABEL_TRANSMIT);
 }