7 files changed, 68 insertions, 3 deletions
diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index c91e210bbd8..da18ac7c693 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -1205,6 +1205,13 @@ class CyclesObjectSettings(bpy.types.PropertyGroup):
         default=1.0,
     )
 
+    shadow_terminator_offset: FloatProperty(
+        name="Shadow Terminator Offset",
+        description="Push the shadow terminator towards the light to hide artifacts on low poly geometry",
+        min=0.0, max=1.0,
+        default=0.0,
+    )
+
     is_shadow_catcher: BoolProperty(
         name="Shadow Catcher",
         description="Only render shadows on this object, for compositing renders into real footage",
diff --git a/intern/cycles/blender/addon/ui.py b/intern/cycles/blender/addon/ui.py
index a15daee706f..7a339e71197 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -1209,6 +1209,27 @@ def has_geometry_visibility(ob):
     return ob and ((ob.type in {'MESH', 'CURVE', 'SURFACE', 'FONT', 'META', 'LIGHT'}) or
                     (ob.instance_type == 'COLLECTION' and ob.instance_collection))
 
+class CYCLES_OBJECT_PT_shading(CyclesButtonsPanel, Panel):
+    bl_label = "Shading"
+    bl_context = "object"
+    bl_options = {'DEFAULT_CLOSED'}
+
+    @classmethod
+    def poll(cls, context):
+        return  CyclesButtonsPanel.poll(context) and (context.object)
+
+    def draw(self, context):
+        layout = self.layout
+        layout.use_property_split = True
+
+        flow = layout.grid_flow(row_major=False, columns=0, even_columns=True, even_rows=False, align=False)
+        layout = self.layout
+        ob = context.object
+        cob = ob.cycles
+
+        if has_geometry_visibility(ob):
+            col = flow.column()
+            col.prop(cob, "shadow_terminator_offset")
 
 class CYCLES_OBJECT_PT_visibility(CyclesButtonsPanel, Panel):
     bl_label = "Visibility"
@@ -2268,6 +2289,7 @@ classes = (
     CYCLES_CAMERA_PT_dof_aperture,
     CYCLES_PT_context_material,
     CYCLES_OBJECT_PT_motion_blur,
+    CYCLES_OBJECT_PT_shading,
     CYCLES_OBJECT_PT_visibility,
     CYCLES_OBJECT_PT_visibility_ray_visibility,
     CYCLES_OBJECT_PT_visibility_culling,
diff --git a/intern/cycles/blender/blender_object.cpp b/intern/cycles/blender/blender_object.cpp
index a461982a538..c28586d0f63 100644
--- a/intern/cycles/blender/blender_object.cpp
+++ b/intern/cycles/blender/blender_object.cpp
@@ -238,6 +238,12 @@ Object *BlenderSync::sync_object(BL::Depsgraph &b_depsgraph,
     object_updated = true;
   }
 
+  float shadow_terminator_offset = get_float(cobject, "shadow_terminator_offset");
+  if (shadow_terminator_offset != object->shadow_terminator_offset) {
+    object->shadow_terminator_offset = shadow_terminator_offset;
+    object_updated = true;
+  }
+
   /* sync the asset name for Cryptomatte */
   BL::Object parent = b_ob.parent();
   ustring parent_name;
diff --git a/intern/cycles/kernel/closure/bsdf.h b/intern/cycles/kernel/closure/bsdf.h
index dc80e67a891..a70a6bfbba1 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 +456,16 @@ 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 +580,11 @@ 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) {
diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 304835a1685..630d00a4e71 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -1480,6 +1480,9 @@ typedef struct KernelObject {
 
   float cryptomatte_object;
   float cryptomatte_asset;
+
+  float shadow_terminator_offset;
+  float pad1, pad2, pad3;
 } KernelObject;
 static_assert_align(KernelObject, 16);
 
diff --git a/intern/cycles/render/object.cpp b/intern/cycles/render/object.cpp
index 90a1d90019d..61deef4cd76 100644
--- a/intern/cycles/render/object.cpp
+++ b/intern/cycles/render/object.cpp
@@ -101,6 +101,7 @@ NODE_DEFINE(Object)
   SOCKET_POINT(dupli_generated, "Dupli Generated", make_float3(0.0f, 0.0f, 0.0f));
   SOCKET_POINT2(dupli_uv, "Dupli UV", make_float2(0.0f, 0.0f));
   SOCKET_TRANSFORM_ARRAY(motion, "Motion", array<Transform>());
+  SOCKET_FLOAT(shadow_terminator_offset, "Terminator Offset", 0.0f);
 
   SOCKET_BOOLEAN(is_shadow_catcher, "Shadow Catcher", false);
 
@@ -534,6 +535,7 @@ void ObjectManager::device_update_object_transform(UpdateObjectTransformState *s
   uint32_t hash_asset = util_murmur_hash3(ob->asset_name.c_str(), ob->asset_name.length(), 0);
   kobject.cryptomatte_object = util_hash_to_float(hash_name);
   kobject.cryptomatte_asset = util_hash_to_float(hash_asset);
+  kobject.shadow_terminator_offset = 1.0f / (1.0f - 0.5f * ob->shadow_terminator_offset);
 
   /* Object flag. */
   if (ob->use_holdout) {
diff --git a/intern/cycles/render/object.h b/intern/cycles/render/object.h
index 7c84c2de4fb..ac9b4c331f5 100644
--- a/intern/cycles/render/object.h
+++ b/intern/cycles/render/object.h
@@ -59,6 +59,7 @@ class Object : public Node {
   bool hide_on_missing_motion;
   bool use_holdout;
   bool is_shadow_catcher;
+  float shadow_terminator_offset;
 
   float3 dupli_generated;
   float2 dupli_uv;