Cycles: Fix multiscattering Oren-Nayar at glancing angles, update tests

intern/cycles/kernel/closure/bsdf_oren_nayar.h

@@ -24,6 +24,10 @@ static_assert(sizeof(ShaderClosure) >= sizeof(OrenNayarBsdf), "OrenNayarBsdf is
 
 ccl_device_inline float bsdf_oren_nayar_G(const float cosTheta)
 {
+  if (cosTheta < 1e-6f) {
+    /* The tan(theta) term starts to act up at low cosTheta, so fall back to Taylor expansion. */
+    return (M_PI_2_F - 2.0f / 3.0f) - cosTheta;
+  }
   const float sinTheta = sin_from_cos(cosTheta);
   const float theta = safe_acosf(cosTheta);
   return sinTheta * (theta - 2.0f / 3.0f - sinTheta * cosTheta) +

tests/data

@@ -1 +1 @@
-Subproject commit 2b31a6bd1059cd85df2a2cd14b1345d24a3147d3
+Subproject commit e5964c9b2df4d85d2f50a7d38807e4fa2d02128a