Cycles: Added shadow terminator offset parameter.

A new user parameter can be used to shift the shadow terminator
towards the light source. With it, one can hide some of the
artifacts that appear on coarse meshes with smooth shading.

Note that this technique is not engery conserving.

This is based on the work by the Appleseed renderer team.

Differential Revision: https://developer.blender.org/D7634

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) {