Fix T48860: Cycles SSS artifacts with spatially split BVH
authorSergey Sharybin <sergey.vfx@gmail.com>
Fri, 15 Jul 2016 12:55:37 +0000 (14:55 +0200)
committerSergey Sharybin <sergey.vfx@gmail.com>
Mon, 18 Jul 2016 08:04:20 +0000 (10:04 +0200)
The issue was caused by SSS intersection code gathering all
intersections without check for duplicated ones. This caused
situations when same intersection will be recorded twice in
the case if triangle is shared by several BVH nodes.

Usually this is handled by checking intersection distance
after sorting intersections (in shadow_blocked for example)
but for SSS we don't do such sorting and using number of
intersections to calculate various things.

Didn't find anything smarter than to check intersection
distance in triangle_intersect_subsurface().

This solves render artifacts in the cost of 1.5% slowdown
of extreme case rendering (SSS object filling in whole
FullHD screen).

Reviewers: brecht

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D2105

intern/cycles/kernel/geom/geom_triangle_intersect.h

index fc081bda525681d4d792f64825d7fdda7fed949c..720ee6a1f5c220e828bf6973c7d4b24485f2af79 100644 (file)
@@ -255,6 +255,13 @@ ccl_device_inline void triangle_intersect_subsurface(
        /* Normalize U, V, W, and T. */
        const float inv_det = 1.0f / det;
 
+       const float t = T * inv_det;
+       for(int i = min(max_hits, ss_isect->num_hits); i >= 0; --i) {
+               if(ss_isect->hits[i].t == t) {
+                       return;
+               }
+       }
+
        ss_isect->num_hits++;
        int hit;
 
@@ -277,7 +284,7 @@ ccl_device_inline void triangle_intersect_subsurface(
        isect->type = PRIMITIVE_TRIANGLE;
        isect->u = U * inv_det;
        isect->v = V * inv_det;
-       isect->t = T * inv_det;
+       isect->t = t;
 
        /* Record geometric normal. */
        /* TODO(sergey): Use float4_to_float3() on just an edges. */