Cycles: Implement unaligned nodes BVH builder

This is a special builder type which is allowed to orient nodes to
strands direction, hence minimizing their surface area in comparison
with axis-aligned nodes. Such nodes are much more efficient for hair
rendering.

Implementation of BVH builder is based on Embree, and generally idea
there is to calculate axis-aligned SAH and oriented SAH and if SAH
of oriented node is smaller than axis-aligned SAH we create unaligned
node.

We store both aligned and unaligned nodes in the same tree (which
seems to be different from what Embree is doing) so we don't have
any any extra calculations needed to set up hair ray for BVH
traversal, hence avoiding any possible negative effect of this new
BVH nodes type.

This new builder is currently not in use, still need to make BVH
traversal code aware of unaligned nodes.

1 files changed, 74 insertions, 8 deletions

diff --git a/intern/cycles/bvh/bvh_split.h b/intern/cycles/bvh/bvh_split.h
index aea8b2565e0..dbdb51f1a5b 100644
--- a/intern/cycles/bvh/bvh_split.h
+++ b/intern/cycles/bvh/bvh_split.h
@@ -24,6 +24,7 @@
 CCL_NAMESPACE_BEGIN
 
 class BVHBuild;
+struct Transform;
 
 /* Object Split */
 
@@ -41,7 +42,9 @@ public:
 	               BVHSpatialStorage *storage,
 	               const BVHRange& range,
 	               vector<BVHReference> *references,
-	               float nodeSAH);
+	               float nodeSAH,
+	               const BVHUnaligned *unaligned_heuristic = NULL,
+	               const Transform *aligned_space = NULL);
 
 	void split(BVHRange& left,
 	           BVHRange& right,
@@ -50,6 +53,19 @@ public:
 protected:
 	BVHSpatialStorage *storage_;
 	vector<BVHReference> *references_;
+	const BVHUnaligned *unaligned_heuristic_;
+	const Transform *aligned_space_;
+
+	__forceinline BoundBox get_prim_bounds(const BVHReference& prim) const
+	{
+		if(aligned_space_ == NULL) {
+			return prim.bounds();
+		}
+		else {
+			return unaligned_heuristic_->compute_aligned_prim_boundbox(
+			        prim, *aligned_space_);
+		}
+	}
 };
 
 /* Spatial Split */
@@ -70,7 +86,9 @@ public:
 	                BVHSpatialStorage *storage,
 	                const BVHRange& range,
 	                vector<BVHReference> *references,
-	                float nodeSAH);
+	                float nodeSAH,
+	                const BVHUnaligned *unaligned_heuristic = NULL,
+	                const Transform *aligned_space = NULL);
 
 	void split(BVHBuild *builder,
 	           BVHRange& left,
@@ -87,6 +105,8 @@ public:
 protected:
 	BVHSpatialStorage *storage_;
 	vector<BVHReference> *references_;
+	const BVHUnaligned *unaligned_heuristic_;
+	const Transform *aligned_space_;
 
 	/* Lower-level functions which calculates boundaries of left and right nodes
 	 * needed for spatial split.
@@ -132,6 +152,27 @@ protected:
 	                            float pos,
 	                            BoundBox& left_bounds,
 	                            BoundBox& right_bounds);
+
+	__forceinline BoundBox get_prim_bounds(const BVHReference& prim) const
+	{
+		if(aligned_space_ == NULL) {
+			return prim.bounds();
+		}
+		else {
+			return unaligned_heuristic_->compute_aligned_prim_boundbox(
+			        prim, *aligned_space_);
+		}
+	}
+
+	__forceinline float3 get_unaligned_point(const float3& point) const
+	{
+		if(aligned_space_ == NULL) {
+			return point;
+		}
+		else {
+			return transform_point(aligned_space_, point);
+		}
+	}
 };
 
 /* Mixed Object-Spatial Split */
@@ -148,19 +189,40 @@ public:
 
 	bool no_split;
 
+	BoundBox bounds;
+
+	BVHMixedSplit() {}
+
 	__forceinline BVHMixedSplit(BVHBuild *builder,
 	                            BVHSpatialStorage *storage,
 	                            const BVHRange& range,
 	                            vector<BVHReference> *references,
-	                            int level)
+	                            int level,
+	                            const BVHUnaligned *unaligned_heuristic = NULL,
+	                            const Transform *aligned_space = NULL)
 	{
+		if(aligned_space == NULL) {
+			bounds = range.bounds();
+		}
+		else {
+			bounds = unaligned_heuristic->compute_aligned_boundbox(
+			        range,
+			        &references->at(0),
+			        *aligned_space);
+		}
 		/* find split candidates. */
-		float area = range.bounds().safe_area();
+		float area = bounds.safe_area();
 
 		leafSAH = area * builder->params.primitive_cost(range.size());
 		nodeSAH = area * builder->params.node_cost(2);
 
-		object = BVHObjectSplit(builder, storage, range, references, nodeSAH);
+		object = BVHObjectSplit(builder,
+		                        storage,
+		                        range,
+		                        references,
+		                        nodeSAH,
+		                        unaligned_heuristic,
+		                        aligned_space);
 
 		if(builder->params.use_spatial_split && level < BVHParams::MAX_SPATIAL_DEPTH) {
 			BoundBox overlap = object.left_bounds;
@@ -171,7 +233,9 @@ public:
 				                          storage,
 				                          range,
 				                          references,
-				                          nodeSAH);
+				                          nodeSAH,
+				                          unaligned_heuristic,
+				                          aligned_space);
 			}
 		}
 
@@ -181,7 +245,10 @@ public:
 		            builder->range_within_max_leaf_size(range, *references));
 	}
 
-	__forceinline void split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range)
+	__forceinline void split(BVHBuild *builder,
+	                         BVHRange& left,
+	                         BVHRange& right,
+	                         const BVHRange& range)
 	{
 		if(builder->params.use_spatial_split && minSAH == spatial.sah)
 			spatial.split(builder, left, right, range);
@@ -193,4 +260,3 @@ public:
 CCL_NAMESPACE_END
 
 #endif /* __BVH_SPLIT_H__ */
-