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, 92 insertions, 23 deletions

diff --git a/intern/cycles/bvh/bvh_split.cpp b/intern/cycles/bvh/bvh_split.cpp
index bf68b41021f..d0d5fbe5a7a 100644
--- a/intern/cycles/bvh/bvh_split.cpp
+++ b/intern/cycles/bvh/bvh_split.cpp
@@ -32,14 +32,18 @@ BVHObjectSplit::BVHObjectSplit(BVHBuild *builder,
                                BVHSpatialStorage *storage,
                                const BVHRange& range,
                                vector<BVHReference> *references,
-                               float nodeSAH)
+                               float nodeSAH,
+                               const BVHUnaligned *unaligned_heuristic,
+                               const Transform *aligned_space)
 : sah(FLT_MAX),
   dim(0),
   num_left(0),
   left_bounds(BoundBox::empty),
   right_bounds(BoundBox::empty),
   storage_(storage),
-  references_(references)
+  references_(references),
+  unaligned_heuristic_(unaligned_heuristic),
+  aligned_space_(aligned_space)
 {
 	const BVHReference *ref_ptr = &references_->at(range.start());
 	float min_sah = FLT_MAX;
@@ -51,12 +55,15 @@ BVHObjectSplit::BVHObjectSplit(BVHBuild *builder,
 		bvh_reference_sort(range.start(),
 		                   range.end(),
 		                   &references_->at(0),
-		                   dim);
+		                   dim,
+		                   unaligned_heuristic_,
+		                   aligned_space_);
 
 		/* sweep right to left and determine bounds. */
 		BoundBox right_bounds = BoundBox::empty;
 		for(int i = range.size() - 1; i > 0; i--) {
-			right_bounds.grow(ref_ptr[i].bounds());
+			BoundBox prim_bounds = get_prim_bounds(ref_ptr[i]);
+			right_bounds.grow(prim_bounds);
 			storage_->right_bounds[i - 1] = right_bounds;
 		}
 
@@ -64,7 +71,8 @@ BVHObjectSplit::BVHObjectSplit(BVHBuild *builder,
 		BoundBox left_bounds = BoundBox::empty;
 
 		for(int i = 1; i < range.size(); i++) {
-			left_bounds.grow(ref_ptr[i - 1].bounds());
+			BoundBox prim_bounds = get_prim_bounds(ref_ptr[i - 1]);
+			left_bounds.grow(prim_bounds);
 			right_bounds = storage_->right_bounds[i - 1];
 
 			float sah = nodeSAH +
@@ -88,16 +96,37 @@ void BVHObjectSplit::split(BVHRange& left,
                            BVHRange& right,
                            const BVHRange& range)
 {
+	assert(references_->size() > 0);
 	/* sort references according to split */
 	bvh_reference_sort(range.start(),
 	                   range.end(),
 	                   &references_->at(0),
-	                   this->dim);
+	                   this->dim,
+	                   unaligned_heuristic_,
+	                   aligned_space_);
+
+	BoundBox effective_left_bounds, effective_right_bounds;
+	const int num_right = range.size() - this->num_left;
+	if(aligned_space_ == NULL) {
+		effective_left_bounds = left_bounds;
+		effective_right_bounds = right_bounds;
+	}
+	else {
+		effective_left_bounds = BoundBox::empty;
+		effective_right_bounds = BoundBox::empty;
+		for(int i = 0; i < this->num_left; ++i) {
+			BoundBox prim_boundbox = references_->at(range.start() + i).bounds();
+			effective_left_bounds.grow(prim_boundbox);
+		}
+		for(int i = 0; i < num_right; ++i) {
+			BoundBox prim_boundbox = references_->at(range.start() + this->num_left + i).bounds();
+			effective_right_bounds.grow(prim_boundbox);
+		}
+	}
 
 	/* split node ranges */
-	left = BVHRange(this->left_bounds, range.start(), this->num_left);
-	right = BVHRange(this->right_bounds, left.end(), range.size() - this->num_left);
-
+	left = BVHRange(effective_left_bounds, range.start(), this->num_left);
+	right = BVHRange(effective_right_bounds, left.end(), num_right);
 }
 
 /* Spatial Split */
@@ -106,16 +135,31 @@ BVHSpatialSplit::BVHSpatialSplit(const BVHBuild& builder,
                                  BVHSpatialStorage *storage,
                                  const BVHRange& range,
                                  vector<BVHReference> *references,
-                                 float nodeSAH)
+                                 float nodeSAH,
+                                 const BVHUnaligned *unaligned_heuristic,
+                                 const Transform *aligned_space)
 : sah(FLT_MAX),
   dim(0),
   pos(0.0f),
   storage_(storage),
-  references_(references)
+  references_(references),
+  unaligned_heuristic_(unaligned_heuristic),
+  aligned_space_(aligned_space)
 {
 	/* initialize bins. */
-	float3 origin = range.bounds().min;
-	float3 binSize = (range.bounds().max - origin) * (1.0f / (float)BVHParams::NUM_SPATIAL_BINS);
+	BoundBox range_bounds;
+	if(aligned_space == NULL) {
+		range_bounds = range.bounds();
+	}
+	else {
+		range_bounds = unaligned_heuristic->compute_aligned_boundbox(
+		        range,
+		        &references->at(0),
+		        *aligned_space);
+	}
+
+	float3 origin = range_bounds.min;
+	float3 binSize = (range_bounds.max - origin) * (1.0f / (float)BVHParams::NUM_SPATIAL_BINS);
 	float3 invBinSize = 1.0f / binSize;
 
 	for(int dim = 0; dim < 3; dim++) {
@@ -131,8 +175,9 @@ BVHSpatialSplit::BVHSpatialSplit(const BVHBuild& builder,
 	/* chop references into bins. */
 	for(unsigned int refIdx = range.start(); refIdx < range.end(); refIdx++) {
 		const BVHReference& ref = references_->at(refIdx);
-		float3 firstBinf = (ref.bounds().min - origin) * invBinSize;
-		float3 lastBinf = (ref.bounds().max - origin) * invBinSize;
+		BoundBox prim_bounds = get_prim_bounds(ref);
+		float3 firstBinf = (prim_bounds.min - origin) * invBinSize;
+		float3 lastBinf = (prim_bounds.max - origin) * invBinSize;
 		int3 firstBin = make_int3((int)firstBinf.x, (int)firstBinf.y, (int)firstBinf.z);
 		int3 lastBin = make_int3((int)lastBinf.x, (int)lastBinf.y, (int)lastBinf.z);
 
@@ -140,7 +185,10 @@ BVHSpatialSplit::BVHSpatialSplit(const BVHBuild& builder,
 		lastBin = clamp(lastBin, firstBin, BVHParams::NUM_SPATIAL_BINS - 1);
 
 		for(int dim = 0; dim < 3; dim++) {
-			BVHReference currRef = ref;
+			BVHReference currRef(get_prim_bounds(ref),
+			                     ref.prim_index(),
+			                     ref.prim_object(),
+			                     ref.prim_type());
 
 			for(int i = firstBin[dim]; i < lastBin[dim]; i++) {
 				BVHReference leftRef, rightRef;
@@ -209,14 +257,15 @@ void BVHSpatialSplit::split(BVHBuild *builder,
 	BoundBox right_bounds = BoundBox::empty;
 
 	for(int i = left_end; i < right_start; i++) {
-		if(refs[i].bounds().max[this->dim] <= this->pos) {
+		BoundBox prim_bounds = get_prim_bounds(refs[i]);
+		if(prim_bounds.max[this->dim] <= this->pos) {
 			/* entirely on the left-hand side */
-			left_bounds.grow(refs[i].bounds());
+			left_bounds.grow(prim_bounds);
 			swap(refs[i], refs[left_end++]);
 		}
-		else if(refs[i].bounds().min[this->dim] >= this->pos) {
+		else if(prim_bounds.min[this->dim] >= this->pos) {
 			/* entirely on the right-hand side */
-			right_bounds.grow(refs[i].bounds());
+			right_bounds.grow(prim_bounds);
 			swap(refs[i--], refs[--right_start]);
 		}
 	}
@@ -231,8 +280,12 @@ void BVHSpatialSplit::split(BVHBuild *builder,
 	new_refs.reserve(right_start - left_end);
 	while(left_end < right_start) {
 		/* split reference. */
+		BVHReference curr_ref(get_prim_bounds(refs[left_end]),
+		                      refs[left_end].prim_index(),
+		                      refs[left_end].prim_object(),
+		                      refs[left_end].prim_type());
 		BVHReference lref, rref;
-		split_reference(*builder, lref, rref, refs[left_end], this->dim, this->pos);
+		split_reference(*builder, lref, rref, curr_ref, this->dim, this->pos);
 
 		/* compute SAH for duplicate/unsplit candidates. */
 		BoundBox lub = left_bounds;		// Unsplit to left:		new left-hand bounds.
@@ -240,8 +293,8 @@ void BVHSpatialSplit::split(BVHBuild *builder,
 		BoundBox ldb = left_bounds;		// Duplicate:			new left-hand bounds.
 		BoundBox rdb = right_bounds;	// Duplicate:			new right-hand bounds.
 
-		lub.grow(refs[left_end].bounds());
-		rub.grow(refs[left_end].bounds());
+		lub.grow(curr_ref.bounds());
+		rub.grow(curr_ref.bounds());
 		ldb.grow(lref.bounds());
 		rdb.grow(rref.bounds());
 
@@ -280,6 +333,17 @@ void BVHSpatialSplit::split(BVHBuild *builder,
 		            new_refs.begin(),
 		            new_refs.end());
 	}
+	if(aligned_space_ != NULL) {
+		left_bounds = right_bounds = BoundBox::empty;
+		for(int i = left_start; i < left_end - left_start; ++i) {
+			BoundBox prim_boundbox = references_->at(i).bounds();
+			left_bounds.grow(prim_boundbox);
+		}
+		for(int i = right_start; i < right_end - right_start; ++i) {
+			BoundBox prim_boundbox = references_->at(i).bounds();
+			right_bounds.grow(prim_boundbox);
+		}
+	}
 	left = BVHRange(left_bounds, left_start, left_end - left_start);
 	right = BVHRange(right_bounds, right_start, right_end - right_start);
 }
@@ -295,11 +359,13 @@ void BVHSpatialSplit::split_triangle_primitive(const Mesh *mesh,
 	Mesh::Triangle t = mesh->get_triangle(prim_index);
 	const float3 *verts = &mesh->verts[0];
 	float3 v1 = tfm ? transform_point(tfm, verts[t.v[2]]) : verts[t.v[2]];
+	v1 = get_unaligned_point(v1);
 
 	for(int i = 0; i < 3; i++) {
 		float3 v0 = v1;
 		int vindex = t.v[i];
 		v1 = tfm ? transform_point(tfm, verts[vindex]) : verts[vindex];
+		v1 = get_unaligned_point(v1);
 		float v0p = v0[dim];
 		float v1p = v1[dim];
 
@@ -339,6 +405,8 @@ void BVHSpatialSplit::split_curve_primitive(const Mesh *mesh,
 		v0 = transform_point(tfm, v0);
 		v1 = transform_point(tfm, v1);
 	}
+	v0 = get_unaligned_point(v0);
+	v1 = get_unaligned_point(v1);
 
 	float v0p = v0[dim];
 	float v1p = v1[dim];
@@ -473,6 +541,7 @@ void BVHSpatialSplit::split_reference(const BVHBuild& builder,
 	/* intersect with original bounds. */
 	left_bounds.max[dim] = pos;
 	right_bounds.min[dim] = pos;
+
 	left_bounds.intersect(ref.bounds());
 	right_bounds.intersect(ref.bounds());