Cycles: remove ray offsetting

Remove small ray offsets that were used to avoid self intersection, and leave
that to the newly added primitive object/prim comparison. These changes together
significantly reduce artifacts on small, large or far away objects.

The balance here is that overlapping primitives are not handled well and should
be avoided (though this was already an issue). The upside is that this is
something a user has control over, whereas the other artifacts had no good
manual solution in many cases.

There is a known issue where the Blender particle system generates overlapping
objects and in turn leads to render differences between CPU and GPU. This will
be addressed separately.

Differential Revision: https://developer.blender.org/D12954

1 files changed, 14 insertions, 46 deletions

diff --git a/intern/cycles/kernel/bvh/util.h b/intern/cycles/kernel/bvh/util.h
index ea86523c0f6..39c3ecd78c0 100644
--- a/intern/cycles/kernel/bvh/util.h
+++ b/intern/cycles/kernel/bvh/util.h
@@ -21,54 +21,22 @@ CCL_NAMESPACE_BEGIN
 /* Ray offset to avoid self intersection.
  *
  * This function should be used to compute a modified ray start position for
- * rays leaving from a surface. */
-
+ * rays leaving from a surface. This is from "A Fast and Robust Method for Avoiding
+ * Self-Intersection" see https://research.nvidia.com/publication/2019-03_A-Fast-and
+ */
 ccl_device_inline float3 ray_offset(float3 P, float3 Ng)
 {
-#ifdef __INTERSECTION_REFINE__
-  const float epsilon_f = 1e-5f;
-  /* ideally this should match epsilon_f, but instancing and motion blur
-   * precision makes it problematic */
-  const float epsilon_test = 1.0f;
-  const int epsilon_i = 32;
-
-  float3 res;
-
-  /* x component */
-  if (fabsf(P.x) < epsilon_test) {
-    res.x = P.x + Ng.x * epsilon_f;
-  }
-  else {
-    uint ix = __float_as_uint(P.x);
-    ix += ((ix ^ __float_as_uint(Ng.x)) >> 31) ? -epsilon_i : epsilon_i;
-    res.x = __uint_as_float(ix);
-  }
-
-  /* y component */
-  if (fabsf(P.y) < epsilon_test) {
-    res.y = P.y + Ng.y * epsilon_f;
-  }
-  else {
-    uint iy = __float_as_uint(P.y);
-    iy += ((iy ^ __float_as_uint(Ng.y)) >> 31) ? -epsilon_i : epsilon_i;
-    res.y = __uint_as_float(iy);
-  }
-
-  /* z component */
-  if (fabsf(P.z) < epsilon_test) {
-    res.z = P.z + Ng.z * epsilon_f;
-  }
-  else {
-    uint iz = __float_as_uint(P.z);
-    iz += ((iz ^ __float_as_uint(Ng.z)) >> 31) ? -epsilon_i : epsilon_i;
-    res.z = __uint_as_float(iz);
-  }
-
-  return res;
-#else
-  const float epsilon_f = 1e-4f;
-  return P + epsilon_f * Ng;
-#endif
+  const float int_scale = 256.0f;
+  int3 of_i = make_int3((int)(int_scale * Ng.x), (int)(int_scale * Ng.y), (int)(int_scale * Ng.z));
+
+  float3 p_i = make_float3(__int_as_float(__float_as_int(P.x) + ((P.x < 0) ? -of_i.x : of_i.x)),
+                           __int_as_float(__float_as_int(P.y) + ((P.y < 0) ? -of_i.y : of_i.y)),
+                           __int_as_float(__float_as_int(P.z) + ((P.z < 0) ? -of_i.z : of_i.z)));
+  const float origin = 1.0f / 32.0f;
+  const float float_scale = 1.0f / 65536.0f;
+  return make_float3(fabsf(P.x) < origin ? P.x + float_scale * Ng.x : p_i.x,
+                     fabsf(P.y) < origin ? P.y + float_scale * Ng.y : p_i.y,
+                     fabsf(P.z) < origin ? P.z + float_scale * Ng.z : p_i.z);
 }
 
 #if defined(__KERNEL_CPU__)