Cysles: Avoid having ShaderData on the stack

This commit introduces a SSS-oriented intersection structure which is replacing
old logic of having separate arrays for just intersections and shader data and
encapsulates all the data needed for SSS evaluation.

This giver a huge stack memory saving on GPU. In own experiments it gave 25%
memory usage reduction on GTX560Ti (722MB vs. 946MB).

Unfortunately, this gave some performance loss of 20% which only happens on GPU.
This is perhaps due to different memory access pattern. Will be solved in the
future, hopefully.

Famous saying: won in memory - lost in time (which is also valid in other way
around).

1 files changed, 12 insertions, 0 deletions

diff --git a/intern/cycles/kernel/kernel_types.h b/intern/cycles/kernel/kernel_types.h
index 5ccbc1de94c..e04f500e410 100644
--- a/intern/cycles/kernel/kernel_types.h
+++ b/intern/cycles/kernel/kernel_types.h
@@ -520,6 +520,18 @@ typedef ccl_addr_space struct Intersection {
 #endif
 } Intersection;
 
+/* Subsurface Intersection result */
+
+struct SubsurfaceIntersection
+{
+	Ray ray;
+	float3 weight[BSSRDF_MAX_HITS];
+
+	int num_hits;
+	struct Intersection hits[BSSRDF_MAX_HITS];
+	float3 Ng[BSSRDF_MAX_HITS];
+};
+
 /* Primitives */
 
 typedef enum PrimitiveType {