Cycles: reduce shadow terminator artifacts

Offset rays from the flat surface to match where they would be for a smooth
surface as specified by the normals. In the shading panel there is now a
Shading Offset (existing option) and Geometry Offset (new).

The Geometry Offset works as follows:
* 0: disabled
* 0.001: only terminated triangles (normal points to the light, geometry
  doesn't) are affected
* 0.1 (default): triangles at grazing angles are affected, and the effect
  fades out
* 1: all triangles are affected

Limitations:
* The artifact is still visible in some cases, it could be that some quads
  require to be treated specifically as quads.
* Inconsistent normals cause artifacts.
* If small objects cast shadows to a big low poly surface, the shadows can
  appear to be in a wrong place - because the surface moved slightly above
  the geometry. This can be noticed only at grazing angles to light.
* Approximated surfaces of two non-intersecting low-poly objects can overlap
  that causes off-the-wall shadows.

Generally, using one or a few levels of subdivision can get rid of artifacts
faster than before.

Differential Revision: https://developer.blender.org/D11065

2 files changed, 27 insertions, 8 deletions

diff --git a/intern/cycles/blender/addon/properties.py b/intern/cycles/blender/addon/properties.py
index cda1355eb2d..71e2f9fc3a5 100644
--- a/intern/cycles/blender/addon/properties.py
+++ b/intern/cycles/blender/addon/properties.py
@@ -1254,12 +1254,19 @@ class CyclesObjectSettings(bpy.types.PropertyGroup):
     )
 
     shadow_terminator_offset: FloatProperty(
-        name="Shadow Terminator Offset",
+        name="Shadow Terminator Shading 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,
     )
 
+    shadow_terminator_geometry_offset: FloatProperty(
+        name="Shadow Terminator Geometry Offset",
+        description="Offset rays from the surface to reduce shadow terminator artifact on low poly geometry. Only affects triangles at grazing angles to light",
+        min=0.0, max=1.0,
+        default=0.1,
+    )
+
     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 62a2fa7f036..3d990467f04 100644
--- a/intern/cycles/blender/addon/ui.py
+++ b/intern/cycles/blender/addon/ui.py
@@ -1223,20 +1223,31 @@ class CYCLES_OBJECT_PT_shading(CyclesButtonsPanel, Panel):
 
     @classmethod
     def poll(cls, context):
-        return CyclesButtonsPanel.poll(context) and (context.object)
+        if not CyclesButtonsPanel.poll(context):
+            return False
+
+        ob = context.object
+        return ob and has_geometry_visibility(ob)
+
+    def draw(self, context):
+        pass
+
+
+class CYCLES_OBJECT_PT_shading_shadow_terminator(CyclesButtonsPanel, Panel):
+    bl_label = "Shadow Terminator"
+    bl_parent_id = "CYCLES_OBJECT_PT_shading"
+    bl_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
+        flow = layout.grid_flow(row_major=False, columns=0, even_columns=True, even_rows=False, align=True)
+
         ob = context.object
         cob = ob.cycles
-
-        if has_geometry_visibility(ob):
-            col = flow.column()
-            col.prop(cob, "shadow_terminator_offset")
+        flow.prop(cob, "shadow_terminator_geometry_offset", text="Geometry Offset")
+        flow.prop(cob, "shadow_terminator_offset", text="Shading Offset")
 
 
 class CYCLES_OBJECT_PT_visibility(CyclesButtonsPanel, Panel):
@@ -2316,6 +2327,7 @@ classes = (
     CYCLES_PT_context_material,
     CYCLES_OBJECT_PT_motion_blur,
     CYCLES_OBJECT_PT_shading,
+    CYCLES_OBJECT_PT_shading_shadow_terminator,
     CYCLES_OBJECT_PT_visibility,
     CYCLES_OBJECT_PT_visibility_ray_visibility,
     CYCLES_OBJECT_PT_visibility_culling,