Ensure BSDF evals and pdfs are zero on invalid samples

Currently, the `eval` and `pdf` are not explicitly set to zero when a BSDF sample is invalid (e.g., below the upper hemisphere), when calling
`bsdf_sample` or `bsdf_eval`. It is assumed that `eval` and `pdf` are set to zero before these functions are called, which can cause problems if not.

This patch fixes this potential problem by explicitly setting `eval` and `pdf` to zero when the sampled direction is invalid.

I also added a sanity check if `eval` and `pdf` are valid (i.e., >= 0.f).
The check is activated when build in debug mode and with the `WITH_CYCLES_DEBUG` set to `ON`.

Reviewed By: brecht, sergey

Differential Revision: https://developer.blender.org/D14776

1 files changed, 3 insertions, 2 deletions

diff --git a/intern/cycles/kernel/closure/bsdf_diffuse_ramp.h b/intern/cycles/kernel/closure/bsdf_diffuse_ramp.h
index d1e31641431..aa4c091f587 100644
--- a/intern/cycles/kernel/closure/bsdf_diffuse_ramp.h
+++ b/intern/cycles/kernel/closure/bsdf_diffuse_ramp.h
@@ -93,9 +93,10 @@ ccl_device int bsdf_diffuse_ramp_sample(ccl_private const ShaderClosure *sc,
     *domega_in_dy = (2 * dot(N, dIdy)) * N - dIdy;
 #  endif
   }
-  else
+  else {
     *pdf = 0.0f;
-
+    *eval = make_float3(0.0f, 0.0f, 0.0f);
+  }
   return LABEL_REFLECT | LABEL_DIFFUSE;
 }