Cycles: Fix three numerical issues in the fresnel, normal map and Beckmann code

- In fresnel_dielectric, the differentials calculation sometimes divided by zero.
- When the normal map was (0.5, 0.5, 0.5), the code would try to normalize a zero vector. Now, it just uses the regular normal as a fallback.
- The approximate error function used in Beckmann sampling sometimes overflowed to inf while calculating r^16. The final value is 1 - 1/r^16, however,
  so now it just returns 1 if the computation would overflow otherwise.

1 files changed, 1 insertions, 1 deletions

diff --git a/intern/cycles/kernel/closure/bsdf_util.h b/intern/cycles/kernel/closure/bsdf_util.h
index 89b1998d1ce..b0c5280b6cb 100644
--- a/intern/cycles/kernel/closure/bsdf_util.h
+++ b/intern/cycles/kernel/closure/bsdf_util.h
@@ -80,7 +80,7 @@ ccl_device float fresnel_dielectric(
 		return 1; // total internal reflection
 	}
 	else {
-		float dnp = sqrtf(arg);
+		float dnp = max(sqrtf(arg), 1e-7f);
 		float nK = (neta * cos)- dnp;
 		*T = -(neta * I)+(nK * Nn);
 #ifdef __RAY_DIFFERENTIALS__