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, 1 insertions, 4 deletions

diff --git a/intern/cycles/scene/camera.cpp b/intern/cycles/scene/camera.cpp
index eec269ab542..d9e574873bd 100644
--- a/intern/cycles/scene/camera.cpp
+++ b/intern/cycles/scene/camera.cpp
@@ -772,10 +772,7 @@ float Camera::world_to_raster_size(float3 P)
 #endif
 
     /* TODO: would it help to use more accurate differentials here? */
-    differential3 dP;
-    differential_transfer_compact(&dP, ray.dP, ray.D, ray.dD, ray.D, dist);
-
-    return max(len(dP.dx), len(dP.dy));
+    return differential_transfer_compact(ray.dP, ray.D, ray.dD, dist);
   }
 
   return res;