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, 51 insertions, 21 deletions

diff --git a/intern/cycles/bvh/bvh_binning.cpp b/intern/cycles/bvh/bvh_binning.cpp
index b07e870d759..5ddd7349f7b 100644
--- a/intern/cycles/bvh/bvh_binning.cpp
+++ b/intern/cycles/bvh/bvh_binning.cpp
@@ -52,12 +52,35 @@ __forceinline int get_best_dimension(const float4& bestSAH)
 
 /* BVH Object Binning */
 
-BVHObjectBinning::BVHObjectBinning(const BVHRange& job, BVHReference *prims)
-: BVHRange(job), splitSAH(FLT_MAX), dim(0), pos(0)
+BVHObjectBinning::BVHObjectBinning(const BVHRange& job,
+                                   BVHReference *prims,
+                                   const BVHUnaligned *unaligned_heuristic,
+                                   const Transform *aligned_space)
+: BVHRange(job),
+  splitSAH(FLT_MAX),
+  dim(0),
+  pos(0),
+  unaligned_heuristic_(unaligned_heuristic),
+  aligned_space_(aligned_space)
 {
+	if(aligned_space_ == NULL) {
+		bounds_ = bounds();
+		cent_bounds_ = cent_bounds();
+	}
+	else {
+		/* TODO(sergey): With some additional storage we can avoid
+		 * need in re-calculating this.
+		 */
+		bounds_ = unaligned_heuristic->compute_aligned_boundbox(
+		        *this,
+		        prims,
+		        *aligned_space,
+		        &cent_bounds_);
+	}
+
 	/* compute number of bins to use and precompute scaling factor for binning */
 	num_bins = min(size_t(MAX_BINS), size_t(4.0f + 0.05f*size()));
-	scale = rcp(cent_bounds().size()) * make_float3((float)num_bins);
+	scale = rcp(cent_bounds_.size()) * make_float3((float)num_bins);
 
 	/* initialize binning counter and bounds */
 	BoundBox bin_bounds[MAX_BINS][4];	/* bounds for every bin in every dimension */
@@ -79,30 +102,34 @@ BVHObjectBinning::BVHObjectBinning(const BVHRange& job, BVHReference *prims)
 			const BVHReference& prim0 = prims[start() + i + 0];
 			const BVHReference& prim1 = prims[start() + i + 1];
 
-			int4 bin0 = get_bin(prim0.bounds());
-			int4 bin1 = get_bin(prim1.bounds());
+			BoundBox bounds0 = get_prim_bounds(prim0);
+			BoundBox bounds1 = get_prim_bounds(prim1);
+
+			int4 bin0 = get_bin(bounds0);
+			int4 bin1 = get_bin(bounds1);
 
 			/* increase bounds for bins for even primitive */
-			int b00 = (int)extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(prim0.bounds());
-			int b01 = (int)extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(prim0.bounds());
-			int b02 = (int)extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(prim0.bounds());
+			int b00 = (int)extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(bounds0);
+			int b01 = (int)extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(bounds0);
+			int b02 = (int)extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(bounds0);
 
 			/* increase bounds of bins for odd primitive */
-			int b10 = (int)extract<0>(bin1); bin_count[b10][0]++; bin_bounds[b10][0].grow(prim1.bounds());
-			int b11 = (int)extract<1>(bin1); bin_count[b11][1]++; bin_bounds[b11][1].grow(prim1.bounds());
-			int b12 = (int)extract<2>(bin1); bin_count[b12][2]++; bin_bounds[b12][2].grow(prim1.bounds());
+			int b10 = (int)extract<0>(bin1); bin_count[b10][0]++; bin_bounds[b10][0].grow(bounds1);
+			int b11 = (int)extract<1>(bin1); bin_count[b11][1]++; bin_bounds[b11][1].grow(bounds1);
+			int b12 = (int)extract<2>(bin1); bin_count[b12][2]++; bin_bounds[b12][2].grow(bounds1);
 		}
 
 		/* for uneven number of primitives */
 		if(i < ssize_t(size())) {
 			/* map primitive to bin */
 			const BVHReference& prim0 = prims[start() + i];
-			int4 bin0 = get_bin(prim0.bounds());
+			BoundBox bounds0 = get_prim_bounds(prim0);
+			int4 bin0 = get_bin(bounds0);
 
 			/* increase bounds of bins */
-			int b00 = (int)extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(prim0.bounds());
-			int b01 = (int)extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(prim0.bounds());
-			int b02 = (int)extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(prim0.bounds());
+			int b00 = (int)extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(bounds0);
+			int b01 = (int)extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(bounds0);
+			int b02 = (int)extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(bounds0);
 		}
 	}
 
@@ -151,17 +178,19 @@ BVHObjectBinning::BVHObjectBinning(const BVHRange& job, BVHReference *prims)
 		bestSAH = min(sah,bestSAH);
 	}
 
-	int4 mask = float3_to_float4(cent_bounds().size()) <= make_float4(0.0f);
+	int4 mask = float3_to_float4(cent_bounds_.size()) <= make_float4(0.0f);
 	bestSAH = insert<3>(select(mask, make_float4(FLT_MAX), bestSAH), FLT_MAX);
 
 	/* find best dimension */
 	dim = get_best_dimension(bestSAH);
 	splitSAH = bestSAH[dim];
 	pos = bestSplit[dim];
-	leafSAH	= bounds().half_area() * blocks(size());
+	leafSAH = bounds_.half_area() * blocks(size());
 }
 
-void BVHObjectBinning::split(BVHReference* prims, BVHObjectBinning& left_o, BVHObjectBinning& right_o) const
+void BVHObjectBinning::split(BVHReference* prims,
+                             BVHObjectBinning& left_o,
+                             BVHObjectBinning& right_o) const
 {
 	size_t N = size();
 
@@ -176,10 +205,12 @@ void BVHObjectBinning::split(BVHReference* prims, BVHObjectBinning& left_o, BVHO
 		prefetch_L2(&prims[start() + l + 8]);
 		prefetch_L2(&prims[start() + r - 8]);
 
-		const BVHReference& prim = prims[start() + l];
+		BVHReference prim = prims[start() + l];
+		BoundBox unaligned_bounds = get_prim_bounds(prim);
+		float3 unaligned_center = unaligned_bounds.center2();
 		float3 center = prim.bounds().center2();
 
-		if(get_bin(center)[dim] < pos) {
+		if(get_bin(unaligned_center)[dim] < pos) {
 			lgeom_bounds.grow(prim.bounds());
 			lcent_bounds.grow(center);
 			l++;
@@ -191,7 +222,6 @@ void BVHObjectBinning::split(BVHReference* prims, BVHObjectBinning& left_o, BVHO
 			r--;
 		}
 	}
-
 	/* finish */
 	if(l != 0 && N-1-r != 0) {
 		right_o = BVHObjectBinning(BVHRange(rgeom_bounds, rcent_bounds, start() + l, N-1-r), prims);