1 files changed, 29 insertions, 3 deletions

diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index dc80e67a891..4cc61e8ee71 100644
--- a/intern/cycles/kernel/closure/bsdf.h
+++ b/intern/cycles/kernel/closure/bsdf.h
@@ -97,6 +97,18 @@ ccl_device_inline float bump_shadowing_term(float3 Ng, float3 N, float3 I)
   return -g2 * g + g2 + g;
 }
 
+/* Shadow terminator workaround, taken from Appleseed.
+ * Original code is under the MIT License
+ * Copyright (c) 2019 Francois Beaune, The appleseedhq Organization */
+ccl_device_inline float shift_cos_in(float cos_in, const float frequency_multiplier)
+{
+  cos_in = min(cos_in, 1.0f);
+
+  const float angle = fast_acosf(cos_in);
+  const float val = max(cosf(angle * frequency_multiplier), 0.0f) / cos_in;
+  return val;
+}
+
 ccl_device_inline int bsdf_sample(KernelGlobals *kg,
                                   ShaderData *sd,
                                   const ShaderClosure *sc,
@@ -444,9 +456,17 @@ ccl_device_inline int bsdf_sample(KernelGlobals *kg,
       }
     }
   }
-  else if (label & LABEL_DIFFUSE) {
-    if (!isequal_float3(sc->N, sd->N)) {
-      *eval *= bump_shadowing_term((label & LABEL_TRANSMIT) ? -sd->N : sd->N, sc->N, *omega_in);
+  else {
+    /* Shadow terminator offset. */
+    const float frequency_multiplier =
+        kernel_tex_fetch(__objects, sd->object).shadow_terminator_offset;
+    if (frequency_multiplier > 1.0f) {
+      *eval *= shift_cos_in(dot(*omega_in, sc->N), frequency_multiplier);
+    }
+    if (label & LABEL_DIFFUSE) {
+      if (!isequal_float3(sc->N, sd->N)) {
+        *eval *= bump_shadowing_term((label & LABEL_TRANSMIT) ? -sd->N : sd->N, sc->N, *omega_in);
+      }
     }
   }
 
@@ -561,6 +581,12 @@ ccl_device_inline
         eval *= bump_shadowing_term(sd->N, sc->N, omega_in);
       }
     }
+    /* Shadow terminator offset. */
+    const float frequency_multiplier =
+        kernel_tex_fetch(__objects, sd->object).shadow_terminator_offset;
+    if (frequency_multiplier > 1.0f) {
+      eval *= shift_cos_in(dot(omega_in, sc->N), frequency_multiplier);
+    }
   }
   else {
     switch (sc->type) {