Cycles: merging features from tomato branch.

=== BVH build time optimizations ===

* BVH building was multithreaded. Not all building is multithreaded, packing
  and the initial bounding/splitting is still single threaded, but recursive
  splitting is, which was the main bottleneck.

* Object splitting now uses binning rather than sorting of all elements, using
  code from the Embree raytracer from Intel.
  http://software.intel.com/en-us/articles/embree-photo-realistic-ray-tracing-kernels/

* Other small changes to avoid allocations, pack memory more tightly, avoid
  some unnecessary operations, ...

These optimizations do not work yet when Spatial Splits are enabled, for that
more work is needed. There's also other optimizations still needed, in
particular for the case of many low poly objects, the packing step and node
memory allocation.

BVH raytracing time should remain about the same, but BVH build time should be
significantly reduced, test here show speedup of about 5x to 10x on a dual core
and 5x to 25x on an 8-core machine, depending on the scene.

=== Threads ===

Centralized task scheduler for multithreading, which is basically the
CPU device threading code wrapped into something reusable.

Basic idea is that there is a single TaskScheduler that keeps a pool of threads,
one for each core. Other places in the code can then create a TaskPool that they
can drop Tasks in to be executed by the scheduler, and wait for them to complete
or cancel them early.

=== Normal ====

Added a Normal output to the texture coordinate node. This currently
gives the object space normal, which is the same under object animation.

In the future this might become a "generated" normal so it's also stable for
deforming objects, but for now it's already useful for non-deforming objects.

=== Render Layers ===

Per render layer Samples control, leaving it to 0 will use the common scene
setting.

Environment pass will now render environment even if film is set to transparent.

Exclude Layers" added. Scene layers (all object that influence the render,
directly or indirectly) are shared between all render layers. However sometimes
it's useful to leave out some object influence for a particular render layer.
That's what this option allows you to do.

=== Filter Glossy ===

When using a value higher than 0.0, this will blur glossy reflections after
blurry bounces, to reduce noise at the cost of accuracy. 1.0 is a good
starting value to tweak.

Some light paths have a low probability of being found while contributing much
light to the pixel. As a result these light paths will be found in some pixels
and not in others, causing fireflies. An example of such a difficult path might
be a small light that is causing a small specular highlight on a sharp glossy
material, which we are seeing through a rough glossy material. With path tracing
it is difficult to find the specular highlight, but if we increase the roughness
on the material the highlight gets bigger and softer, and so easier to find.

Often this blurring will be hardly noticeable, because we are seeing it through
a blurry material anyway, but there are also cases where this will lead to a
loss of detail in lighting.

13 files changed, 1168 insertions, 447 deletions

diff --git a/intern/cycles/bvh/CMakeLists.txt b/intern/cycles/bvh/CMakeLists.txt
index decc576fe51..131a7a1f750 100644
--- a/intern/cycles/bvh/CMakeLists.txt
+++ b/intern/cycles/bvh/CMakeLists.txt
@@ -10,17 +10,21 @@ set(INC
 
 set(SRC
 	bvh.cpp
+	bvh_binning.cpp
 	bvh_build.cpp
 	bvh_node.cpp
 	bvh_sort.cpp
+	bvh_split.cpp
 )
 
 set(SRC_HEADERS
 	bvh.h
+	bvh_binning.h
 	bvh_build.h
 	bvh_node.h
 	bvh_params.h
 	bvh_sort.h
+	bvh_split.h
 )
 
 include_directories(${INC})
diff --git a/intern/cycles/bvh/bvh.cpp b/intern/cycles/bvh/bvh.cpp
index c9bfa964332..15695dddf45 100644
--- a/intern/cycles/bvh/bvh.cpp
+++ b/intern/cycles/bvh/bvh.cpp
@@ -530,7 +530,7 @@ void RegularBVH::refit_nodes()
 {
 	assert(!params.top_level);
 
-	BoundBox bbox;
+	BoundBox bbox = BoundBox::empty;
 	uint visibility = 0;
 	refit_node(0, (pack.is_leaf[0])? true: false, bbox, visibility);
 }
@@ -572,7 +572,7 @@ void RegularBVH::refit_node(int idx, bool leaf, BoundBox& bbox, uint& visibility
 	}
 	else {
 		/* refit inner node, set bbox from children */
-		BoundBox bbox0, bbox1;
+		BoundBox bbox0 = BoundBox::empty, bbox1 = BoundBox::empty;
 		uint visibility0 = 0, visibility1 = 0;
 
 		refit_node((c0 < 0)? -c0-1: c0, (c0 < 0), bbox0, visibility0);
diff --git a/intern/cycles/bvh/bvh_binning.cpp b/intern/cycles/bvh/bvh_binning.cpp
new file mode 100644
index 00000000000..661541a8d23
--- /dev/null
+++ b/intern/cycles/bvh/bvh_binning.cpp
@@ -0,0 +1,223 @@
+/*
+ * Adapted from code copyright 2009-2011 Intel Corporation
+ * Modifications Copyright 2012, Blender Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+//#define __KERNEL_SSE__
+
+#include <stdlib.h>
+
+#include "bvh_binning.h"
+
+#include "util_algorithm.h"
+#include "util_boundbox.h"
+#include "util_types.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* SSE replacements */
+
+__forceinline void prefetch_L1 (const void* ptr) { }
+__forceinline void prefetch_L2 (const void* ptr) { }
+__forceinline void prefetch_L3 (const void* ptr) { }
+__forceinline void prefetch_NTA(const void* ptr) { }
+
+template<size_t src> __forceinline float extract(const int4& b)
+{ return b[src]; }
+template<size_t dst> __forceinline const float4 insert(const float4& a, const float b)
+{ float4 r = a; r[dst] = b; return r; }
+
+__forceinline int get_best_dimension(const float4& bestSAH)
+{
+	// return (int)__bsf(movemask(reduce_min(bestSAH) == bestSAH));
+
+	float minSAH = min(bestSAH.x, min(bestSAH.y, bestSAH.z));
+
+	if(bestSAH.x == minSAH) return 0;
+	else if(bestSAH.y == minSAH) return 1;
+	else return 2;
+}
+
+/* BVH Object Binning */
+
+BVHObjectBinning::BVHObjectBinning(const BVHRange& job, BVHReference *prims)
+: BVHRange(job), splitSAH(FLT_MAX), dim(0), pos(0)
+{
+	/* 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);
+
+	/* initialize binning counter and bounds */
+	BoundBox bin_bounds[MAX_BINS][4];	/* bounds for every bin in every dimension */
+	int4 bin_count[MAX_BINS];			/* number of primitives mapped to bin */
+
+	for(size_t i = 0; i < num_bins; i++) {
+		bin_count[i] = make_int4(0);
+		bin_bounds[i][0] = bin_bounds[i][1] = bin_bounds[i][2] = BoundBox::empty;
+	}
+
+	/* map geometry to bins, unrolled once */
+	{
+		ssize_t i;
+
+		for(i = 0; i < ssize_t(size()) - 1; i += 2) {
+			prefetch_L2(&prims[start() + i + 8]);
+
+			/* map even and odd primitive to bin */
+			BVHReference prim0 = prims[start() + i + 0];
+			BVHReference prim1 = prims[start() + i + 1];
+
+			int4 bin0 = get_bin(prim0.bounds());
+			int4 bin1 = get_bin(prim1.bounds());
+
+			/* increase bounds for bins for even primitive */
+			int b00 = extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(prim0.bounds());
+			int b01 = extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(prim0.bounds());
+			int b02 = extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(prim0.bounds());
+
+			/* increase bounds of bins for odd primitive */
+			int b10 = extract<0>(bin1); bin_count[b10][0]++; bin_bounds[b10][0].grow(prim1.bounds());
+			int b11 = extract<1>(bin1); bin_count[b11][1]++; bin_bounds[b11][1].grow(prim1.bounds());
+			int b12 = extract<2>(bin1); bin_count[b12][2]++; bin_bounds[b12][2].grow(prim1.bounds());
+		}
+
+		/* for uneven number of primitives */
+		if(i < ssize_t(size())) {
+			/* map primitive to bin */
+			BVHReference prim0 = prims[start() + i];
+			int4 bin0 = get_bin(prim0.bounds());
+
+			/* increase bounds of bins */
+			int b00 = extract<0>(bin0); bin_count[b00][0]++; bin_bounds[b00][0].grow(prim0.bounds());
+			int b01 = extract<1>(bin0); bin_count[b01][1]++; bin_bounds[b01][1].grow(prim0.bounds());
+			int b02 = extract<2>(bin0); bin_count[b02][2]++; bin_bounds[b02][2].grow(prim0.bounds());
+		}
+	}
+
+	/* sweep from right to left and compute parallel prefix of merged bounds */
+	float4 r_area[MAX_BINS];	/* area of bounds of primitives on the right */
+	float4 r_count[MAX_BINS];	/* number of primitives on the right */
+	int4 count = make_int4(0);
+
+	BoundBox bx = BoundBox::empty;
+	BoundBox by = BoundBox::empty;
+	BoundBox bz = BoundBox::empty;
+
+	for(size_t i = num_bins - 1; i > 0; i--) {
+		count = count + bin_count[i];
+		r_count[i] = blocks(count);
+
+		bx = merge(bx,bin_bounds[i][0]); r_area[i][0] = bx.half_area();
+		by = merge(by,bin_bounds[i][1]); r_area[i][1] = by.half_area();
+		bz = merge(bz,bin_bounds[i][2]); r_area[i][2] = bz.half_area();
+	}
+
+	/* sweep from left to right and compute SAH */
+	int4 ii = make_int4(1);
+	float4 bestSAH = make_float4(FLT_MAX);
+	int4 bestSplit = make_int4(-1);
+
+	count = make_int4(0);
+
+	bx = BoundBox::empty;
+	by = BoundBox::empty;
+	bz = BoundBox::empty;
+
+	for(size_t i = 1; i < num_bins; i++, ii += make_int4(1)) {
+		count = count + bin_count[i-1];
+
+		bx = merge(bx,bin_bounds[i-1][0]); float Ax = bx.half_area();
+		by = merge(by,bin_bounds[i-1][1]); float Ay = by.half_area();
+		bz = merge(bz,bin_bounds[i-1][2]); float Az = bz.half_area();
+
+		float4 lCount = blocks(count);
+		float4 lArea = make_float4(Ax,Ay,Az,Az);
+		float4 sah = lArea*lCount + r_area[i]*r_count[i];
+
+		bestSplit = select(sah < bestSAH,ii,bestSplit);
+		bestSAH = min(sah,bestSAH);
+	}
+
+	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());
+}
+
+void BVHObjectBinning::split(BVHReference* prims, BVHObjectBinning& left_o, BVHObjectBinning& right_o) const
+{
+	size_t N = size();
+
+	BoundBox lgeom_bounds = BoundBox::empty;
+	BoundBox rgeom_bounds = BoundBox::empty;
+	BoundBox lcent_bounds = BoundBox::empty;
+	BoundBox rcent_bounds = BoundBox::empty;
+
+	ssize_t l = 0, r = N-1;
+
+	while(l <= r) {
+		prefetch_L2(&prims[start() + l + 8]);
+		prefetch_L2(&prims[start() + r - 8]);
+
+		BVHReference prim = prims[start() + l];
+		float3 center = prim.bounds().center2();
+
+		if(get_bin(center)[dim] < pos) {
+			lgeom_bounds.grow(prim.bounds());
+			lcent_bounds.grow(center);
+			l++;
+		}
+		else {
+			rgeom_bounds.grow(prim.bounds());
+			rcent_bounds.grow(center);
+			swap(prims[start()+l],prims[start()+r]);
+			r--;
+		}
+	}
+
+	/* finish */
+	if(l != 0 && N-1-r != 0) {
+		right_o = BVHObjectBinning(BVHRange(rgeom_bounds, rcent_bounds, start() + l, N-1-r), prims);
+		left_o  = BVHObjectBinning(BVHRange(lgeom_bounds, lcent_bounds, start(), l), prims);
+		return;
+	}
+
+	/* object medium split if we did not make progress, can happen when all
+	   primitives have same centroid */
+	lgeom_bounds = BoundBox::empty;
+	rgeom_bounds = BoundBox::empty;
+	lcent_bounds = BoundBox::empty;
+	rcent_bounds = BoundBox::empty;
+
+	for(size_t i = 0; i < N/2; i++) {
+		lgeom_bounds.grow(prims[start()+i].bounds());
+		lcent_bounds.grow(prims[start()+i].bounds().center2());
+	}
+
+	for(size_t i = N/2; i < N; i++) {
+		rgeom_bounds.grow(prims[start()+i].bounds());
+		rcent_bounds.grow(prims[start()+i].bounds().center2());
+	}
+
+	right_o = BVHObjectBinning(BVHRange(rgeom_bounds, rcent_bounds, start() + N/2, N/2 + N%2), prims);
+	left_o  = BVHObjectBinning(BVHRange(lgeom_bounds, lcent_bounds, start(), N/2), prims);
+}
+
+CCL_NAMESPACE_END
+
diff --git a/intern/cycles/bvh/bvh_binning.h b/intern/cycles/bvh/bvh_binning.h
new file mode 100644
index 00000000000..60742157055
--- /dev/null
+++ b/intern/cycles/bvh/bvh_binning.h
@@ -0,0 +1,86 @@
+/*
+ * Adapted from code copyright 2009-2011 Intel Corporation
+ * Modifications Copyright 2012, Blender Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __BVH_BINNING_H__
+#define __BVH_BINNING_H__
+
+#include "bvh_params.h"
+
+#include "util_types.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* Single threaded object binner. Finds the split with the best SAH heuristic
+ * by testing for each dimension multiple partitionings for regular spaced
+ * partition locations. A partitioning for a partition location is computed,
+ * by putting primitives whose centroid is on the left and right of the split
+ * location to different sets. The SAH is evaluated by computing the number of
+ * blocks occupied by the primitives in the partitions. */
+
+class BVHObjectBinning : public BVHRange
+{
+public:
+	__forceinline BVHObjectBinning() {}
+	BVHObjectBinning(const BVHRange& job, BVHReference *prims);
+
+	void split(BVHReference *prims, BVHObjectBinning& left_o, BVHObjectBinning& right_o) const;
+
+	float splitSAH;	/* SAH cost of the best split */
+	float leafSAH;	/* SAH cost of creating a leaf */
+
+protected:
+	int dim;			/* best split dimension */
+	int pos;			/* best split position */
+	size_t num_bins;	/* actual number of bins to use */
+	float3 scale;		/* scaling factor to compute bin */
+
+	enum { MAX_BINS = 32 };
+	enum { LOG_BLOCK_SIZE = 2 };
+
+	/* computes the bin numbers for each dimension for a box. */
+	__forceinline int4 get_bin(const BoundBox& box) const
+	{
+		int4 a = make_int4((box.center2() - cent_bounds().min)*scale - make_float3(0.5f));
+		int4 mn = make_int4(0);
+		int4 mx = make_int4((int)num_bins-1);
+
+		return clamp(a, mn, mx);
+	}
+
+	/* computes the bin numbers for each dimension for a point. */
+	__forceinline int4 get_bin(const float3& c) const
+	{
+		return make_int4((c - cent_bounds().min)*scale - make_float3(0.5f));
+	}
+
+	/* compute the number of blocks occupied for each dimension. */
+	__forceinline float4 blocks(const int4& a) const
+	{
+		return make_float4((a + make_int4((1 << LOG_BLOCK_SIZE)-1)) >> LOG_BLOCK_SIZE);
+	}
+
+	/* compute the number of blocks occupied in one dimension. */
+	__forceinline int blocks(size_t a) const
+	{
+		return (int)((a+((1LL << LOG_BLOCK_SIZE)-1)) >> LOG_BLOCK_SIZE);
+	}
+};
+
+CCL_NAMESPACE_END
+
+#endif
+
diff --git a/intern/cycles/bvh/bvh_build.cpp b/intern/cycles/bvh/bvh_build.cpp
index 38674c2c561..c5b4f1d01ae 100644
--- a/intern/cycles/bvh/bvh_build.cpp
+++ b/intern/cycles/bvh/bvh_build.cpp
@@ -15,22 +15,36 @@
  * limitations under the License.
  */
 
+#include "bvh_binning.h"
 #include "bvh_build.h"
 #include "bvh_node.h"
 #include "bvh_params.h"
-#include "bvh_sort.h"
+#include "bvh_split.h"
 
 #include "mesh.h"
 #include "object.h"
 #include "scene.h"
 
-#include "util_algorithm.h"
+#include "util_debug.h"
 #include "util_foreach.h"
 #include "util_progress.h"
 #include "util_time.h"
 
 CCL_NAMESPACE_BEGIN
 
+/* BVH Build Task */
+
+class BVHBuildTask : public Task {
+public:
+	BVHBuildTask(InnerNode *node_, int child_, BVHObjectBinning& range_, int level_)
+	: node(node_), child(child_), level(level_), range(range_) {}
+
+	InnerNode *node;
+	int child;
+	int level;
+	BVHObjectBinning range;
+};
+
 /* Constructor / Destructor */
 
 BVHBuild::BVHBuild(const vector<Object*>& objects_,
@@ -41,10 +55,10 @@ BVHBuild::BVHBuild(const vector<Object*>& objects_,
   prim_object(prim_object_),
   params(params_),
   progress(progress_),
-  progress_start_time(0.0)
+  progress_start_time(0.0),
+  task_pool(function_bind(&BVHBuild::thread_build_node, this, _1, _2))
 {
 	spatial_min_overlap = 0.0f;
-	progress_num_duplicates = 0;
 }
 
 BVHBuild::~BVHBuild()
@@ -53,57 +67,63 @@ BVHBuild::~BVHBuild()
 
 /* Adding References */
 
-void BVHBuild::add_reference_mesh(NodeSpec& root, Mesh *mesh, int i)
+void BVHBuild::add_reference_mesh(BoundBox& root, BoundBox& center, Mesh *mesh, int i)
 {
 	for(uint j = 0; j < mesh->triangles.size(); j++) {
 		Mesh::Triangle t = mesh->triangles[j];
-		Reference ref;
+		BoundBox bounds = BoundBox::empty;
 
 		for(int k = 0; k < 3; k++) {
 			float3 pt = mesh->verts[t.v[k]];
-			ref.bounds.grow(pt);
+			bounds.grow(pt);
 		}
 
-		if(ref.bounds.valid()) {
-			ref.prim_index = j;
-			ref.prim_object = i;
-
-			references.push_back(ref);
-			root.bounds.grow(ref.bounds);
+		if(bounds.valid()) {
+			references.push_back(BVHReference(bounds, j, i));
+			root.grow(bounds);
+			center.grow(bounds.center2());
 		}
 	}
 }
 
-void BVHBuild::add_reference_object(NodeSpec& root, Object *ob, int i)
+void BVHBuild::add_reference_object(BoundBox& root, BoundBox& center, Object *ob, int i)
 {
-	Reference ref;
-
-	ref.prim_index = -1;
-	ref.prim_object = i;
-	ref.bounds = ob->bounds;
-
-	references.push_back(ref);
-	root.bounds.grow(ref.bounds);
+	references.push_back(BVHReference(ob->bounds, -1, i));
+	root.grow(ob->bounds);
+	center.grow(ob->bounds.center2());
 }
 
-void BVHBuild::add_references(NodeSpec& root)
+void BVHBuild::add_references(BVHRange& root)
 {
-	/* init root spec */
-	root.num = 0;
-	root.bounds = BoundBox();
+	/* reserve space for references */
+	size_t num_alloc_references = 0;
+
+	foreach(Object *ob, objects) {
+		if(params.top_level) {
+			if(ob->mesh->transform_applied)
+				num_alloc_references += ob->mesh->triangles.size();
+			else
+				num_alloc_references++;
+		}
+		else
+			num_alloc_references += ob->mesh->triangles.size();
+	}
+
+	references.reserve(num_alloc_references);
 
-	/* add objects */
+	/* add references from objects */
+	BoundBox bounds = BoundBox::empty, center = BoundBox::empty;
 	int i = 0;
 
 	foreach(Object *ob, objects) {
 		if(params.top_level) {
 			if(ob->mesh->transform_applied)
-				add_reference_mesh(root, ob->mesh, i);
+				add_reference_mesh(bounds, center, ob->mesh, i);
 			else
-				add_reference_object(root, ob, i);
+				add_reference_object(bounds, center, ob, i);
 		}
 		else
-			add_reference_mesh(root, ob->mesh, i);
+			add_reference_mesh(bounds, center, ob->mesh, i);
 
 		i++;
 
@@ -111,129 +131,213 @@ void BVHBuild::add_references(NodeSpec& root)
 	}
 
 	/* happens mostly on empty meshes */
-	if(!root.bounds.valid())
-		root.bounds.grow(make_float3(0.0f, 0.0f, 0.0f));
+	if(!bounds.valid())
+		bounds.grow(make_float3(0.0f, 0.0f, 0.0f));
 
-	root.num = references.size();
+	root = BVHRange(bounds, center, 0, references.size());
 }
 
 /* Build */
 
 BVHNode* BVHBuild::run()
 {
-	NodeSpec root;
+	BVHRange root;
 
 	/* add references */
 	add_references(root);
 
-	if(progress.get_cancel()) return NULL;
+	if(progress.get_cancel())
+		return NULL;
 
 	/* init spatial splits */
 	if(params.top_level) /* todo: get rid of this */
 		params.use_spatial_split = false;
 
-	spatial_min_overlap = root.bounds.area() * params.spatial_split_alpha;
+	spatial_min_overlap = root.bounds().safe_area() * params.spatial_split_alpha;
 	spatial_right_bounds.clear();
-	spatial_right_bounds.resize(max(root.num, (int)BVHParams::NUM_SPATIAL_BINS) - 1);
+	spatial_right_bounds.resize(max(root.size(), (int)BVHParams::NUM_SPATIAL_BINS) - 1);
 
 	/* init progress updates */
-	progress_num_duplicates = 0;
 	progress_start_time = time_dt();
+	progress_count = 0;
+	progress_total = references.size();
+	progress_original_total = progress_total;
+
+	prim_index.resize(references.size());
+	prim_object.resize(references.size());
 
 	/* build recursively */
-	return build_node(root, 0, 0.0f, 1.0f);
+	BVHNode *rootnode;
+
+	if(params.use_spatial_split) {
+		/* singlethreaded spatial split build */
+		rootnode = build_node(root, 0);
+	}
+	else {
+		/* multithreaded binning build */
+		BVHObjectBinning rootbin(root, &references[0]);
+		rootnode = build_node(rootbin, 0);
+		task_pool.wait();
+	}
+
+	/* delete if we cancelled */
+	if(rootnode) {
+		if(progress.get_cancel()) {
+			rootnode->deleteSubtree();
+			rootnode = NULL;
+		}
+		else if(!params.use_spatial_split) {
+			/*rotate(rootnode, 4, 5);*/
+			rootnode->update_visibility();
+		}
+	}
+
+	return rootnode;
 }
 
-void BVHBuild::progress_update(float progress_start, float progress_end)
+void BVHBuild::progress_update()
 {
 	if(time_dt() - progress_start_time < 0.25f)
 		return;
+	
+	double progress_start = (double)progress_count/(double)progress_total;
+	double duplicates = (double)(progress_total - progress_original_total)/(double)progress_total;
 
-	float duplicates = (float)progress_num_duplicates/(float)references.size();
 	string msg = string_printf("Building BVH %.0f%%, duplicates %.0f%%",
 		progress_start*100.0f, duplicates*100.0f);
 
 	progress.set_substatus(msg);
-	progress_start_time = time_dt();
+	progress_start_time = time_dt(); 
 }
 
-BVHNode* BVHBuild::build_node(const NodeSpec& spec, int level, float progress_start, float progress_end)
+void BVHBuild::thread_build_node(Task *task_, int thread_id)
 {
-	/* progress update */
-	progress_update(progress_start, progress_end);
-	if(progress.get_cancel()) return NULL;
+	if(progress.get_cancel())
+		return;
 
-	/* small enough or too deep => create leaf. */
-	if(spec.num <= params.min_leaf_size || level >= BVHParams::MAX_DEPTH)
-		return create_leaf_node(spec);
-
-	/* find split candidates. */
-	float area = spec.bounds.area();
-	float leafSAH = area * params.triangle_cost(spec.num);
-	float nodeSAH = area * params.node_cost(2);
-	ObjectSplit object = find_object_split(spec, nodeSAH);
-	SpatialSplit spatial;
-
-	if(params.use_spatial_split && level < BVHParams::MAX_SPATIAL_DEPTH) {
-		BoundBox overlap = object.left_bounds;
-		overlap.intersect(object.right_bounds);
-
-		if(overlap.area() >= spatial_min_overlap)
-			spatial = find_spatial_split(spec, nodeSAH);
-	}
+	/* build nodes */
+	BVHBuildTask *task = (BVHBuildTask*)task_;
+	BVHNode *node = build_node(task->range, task->level);
+
+	/* set child in inner node */
+	task->node->children[task->child] = node;
 
-	/* leaf SAH is the lowest => create leaf. */
-	float minSAH = min(min(leafSAH, object.sah), spatial.sah);
+	/* update progress */
+	if(task->range.size() < THREAD_TASK_SIZE) {
+		/*rotate(node, INT_MAX, 5);*/
 
-	if(minSAH == leafSAH && spec.num <= params.max_leaf_size)
-		return create_leaf_node(spec);
+		thread_scoped_lock lock(build_mutex);
 
-	/* perform split. */
-	NodeSpec left, right;
+		progress_count += task->range.size();
+		progress_update();
+	}
+}
+
+/* multithreaded binning builder */
+BVHNode* BVHBuild::build_node(const BVHObjectBinning& range, int level)
+{
+	size_t size = range.size();
+	float leafSAH = params.sah_triangle_cost * range.leafSAH;
+	float splitSAH = params.sah_node_cost * range.bounds().half_area() + params.sah_triangle_cost * range.splitSAH;
 
-	if(params.use_spatial_split && minSAH == spatial.sah)
-		do_spatial_split(left, right, spec, spatial);
-	if(!left.num || !right.num)
-		do_object_split(left, right, spec, object);
+	/* make leaf node when threshold reached or SAH tells us */
+	if(params.small_enough_for_leaf(size, level) || (size <= params.max_leaf_size && leafSAH < splitSAH))
+		return create_leaf_node(range);
+
+	/* perform split */
+	BVHObjectBinning left, right;
+	range.split(&references[0], left, right);
 
 	/* create inner node. */
-	progress_num_duplicates += left.num + right.num - spec.num;
+	InnerNode *inner;
 
-	float progress_mid = lerp(progress_start, progress_end, (float)right.num / (float)(left.num + right.num));
+	if(range.size() < THREAD_TASK_SIZE) {
+		/* local build */
+		BVHNode *leftnode = build_node(left, level + 1);
+		BVHNode *rightnode = build_node(right, level + 1);
 
-	BVHNode* rightNode = build_node(right, level + 1, progress_start, progress_mid);
-	if(progress.get_cancel()) {
-		if(rightNode) rightNode->deleteSubtree();
-		return NULL;
+		inner = new InnerNode(range.bounds(), leftnode, rightnode);
 	}
+	else {
+		/* threaded build */
+		inner = new InnerNode(range.bounds());
+
+		task_pool.push(new BVHBuildTask(inner, 0, left, level + 1), true);
+		task_pool.push(new BVHBuildTask(inner, 1, right, level + 1), true);
+	}
+
+	return inner;
+}
 
-	BVHNode* leftNode = build_node(left, level + 1, progress_mid, progress_end);
-	if(progress.get_cancel()) {
-		if(leftNode) leftNode->deleteSubtree();
+/* single threaded spatial split builder */
+BVHNode* BVHBuild::build_node(const BVHRange& range, int level)
+{
+	/* progress update */
+	progress_update();
+	if(progress.get_cancel())
 		return NULL;
+
+	/* small enough or too deep => create leaf. */
+	if(params.small_enough_for_leaf(range.size(), level)) {
+		progress_count += range.size();
+		return create_leaf_node(range);
+	}
+
+	/* splitting test */
+	BVHMixedSplit split(this, range, level);
+
+	if(split.no_split) {
+		progress_count += range.size();
+		return create_leaf_node(range);
 	}
+	
+	/* do split */
+	BVHRange left, right;
+	split.split(this, left, right, range);
+
+	progress_total += left.size() + right.size() - range.size();
+	size_t total = progress_total;
+
+	/* leaft node */
+	BVHNode *leftnode = build_node(left, level + 1);
+
+	/* right node (modify start for splits) */
+	right.set_start(right.start() + progress_total - total);
+	BVHNode *rightnode = build_node(right, level + 1);
 
-	return new InnerNode(spec.bounds, leftNode, rightNode);
+	/* inner node */
+	return new InnerNode(range.bounds(), leftnode, rightnode);
 }
 
-BVHNode *BVHBuild::create_object_leaf_nodes(const Reference *ref, int num)
+/* Create Nodes */
+
+BVHNode *BVHBuild::create_object_leaf_nodes(const BVHReference *ref, int start, int num)
 {
 	if(num == 0) {
-		BoundBox bounds;
+		BoundBox bounds = BoundBox::empty;
 		return new LeafNode(bounds, 0, 0, 0);
 	}
 	else if(num == 1) {
-		prim_index.push_back(ref[0].prim_index);
-		prim_object.push_back(ref[0].prim_object);
-		uint visibility = objects[ref[0].prim_object]->visibility;
-		return new LeafNode(ref[0].bounds, visibility, prim_index.size()-1, prim_index.size());
+		if(start == prim_index.size()) {
+			assert(params.use_spatial_split);
+
+			prim_index.push_back(ref->prim_index());
+			prim_object.push_back(ref->prim_object());
+		}
+		else {
+			prim_index[start] = ref->prim_index();
+			prim_object[start] = ref->prim_object();
+		}
+
+		uint visibility = objects[ref->prim_object()]->visibility;
+		return new LeafNode(ref->bounds(), visibility, start, start+1);
 	}
 	else {
 		int mid = num/2;
-		BVHNode *leaf0 = create_object_leaf_nodes(ref, mid); 
-		BVHNode *leaf1 = create_object_leaf_nodes(ref+mid, num-mid); 
+		BVHNode *leaf0 = create_object_leaf_nodes(ref, start, mid); 
+		BVHNode *leaf1 = create_object_leaf_nodes(ref+mid, start+mid, num-mid); 
 
-		BoundBox bounds;
+		BoundBox bounds = BoundBox::empty;
 		bounds.grow(leaf0->m_bounds);
 		bounds.grow(leaf1->m_bounds);
 
@@ -241,310 +345,136 @@ BVHNode *BVHBuild::create_object_leaf_nodes(const Reference *ref, int num)
 	}
 }
 
-BVHNode* BVHBuild::create_leaf_node(const NodeSpec& spec)
+BVHNode* BVHBuild::create_leaf_node(const BVHRange& range)
 {
 	vector<int>& p_index = prim_index;
 	vector<int>& p_object = prim_object;
-	BoundBox bounds;
-	int num = 0;
+	BoundBox bounds = BoundBox::empty;
+	int num = 0, ob_num = 0;
 	uint visibility = 0;
 
-	for(int i = 0; i < spec.num; i++) {
-		if(references.back().prim_index != -1) {
-			p_index.push_back(references.back().prim_index);
-			p_object.push_back(references.back().prim_object);
-			bounds.grow(references.back().bounds);
-			visibility |= objects[references.back().prim_object]->visibility;
-			references.pop_back();
+	for(int i = 0; i < range.size(); i++) {
+		BVHReference& ref = references[range.start() + i];
+
+		if(ref.prim_index() != -1) {
+			if(range.start() + num == prim_index.size()) {
+				assert(params.use_spatial_split);
+
+				p_index.push_back(ref.prim_index());
+				p_object.push_back(ref.prim_object());
+			}
+			else {
+				p_index[range.start() + num] = ref.prim_index();
+				p_object[range.start() + num] = ref.prim_object();
+			}
+
+			bounds.grow(ref.bounds());
+			visibility |= objects[ref.prim_object()]->visibility;
 			num++;
 		}
+		else {
+			if(ob_num < i)
+				references[range.start() + ob_num] = ref;
+			ob_num++;
+		}
 	}
 
 	BVHNode *leaf = NULL;
 	
 	if(num > 0) {
-		leaf = new LeafNode(bounds, visibility, p_index.size() - num, p_index.size());
+		leaf = new LeafNode(bounds, visibility, range.start(), range.start() + num);
 
-		if(num == spec.num)
+		if(num == range.size())
 			return leaf;
 	}
 
 	/* while there may be multiple triangles in a leaf, for object primitives
-	 * we want them to be the only one, so we  */
-	int ob_num = spec.num - num;
-	const Reference *ref = (ob_num)? &references.back() - (ob_num - 1): NULL;
-	BVHNode *oleaf = create_object_leaf_nodes(ref, ob_num);
-	for(int i = 0; i < ob_num; i++)
-		references.pop_back();
+	 * we want there to be the only one, so we keep splitting */
+	const BVHReference *ref = (ob_num)? &references[range.start()]: NULL;
+	BVHNode *oleaf = create_object_leaf_nodes(ref, range.start() + num, ob_num);
 	
 	if(leaf)
-		return new InnerNode(spec.bounds, leaf, oleaf);
+		return new InnerNode(range.bounds(), leaf, oleaf);
 	else
 		return oleaf;
 }
 
-/* Object Split */
+/* Tree Rotations */
 
-BVHBuild::ObjectSplit BVHBuild::find_object_split(const NodeSpec& spec, float nodeSAH)
+void BVHBuild::rotate(BVHNode *node, int max_depth, int iterations)
 {
-	ObjectSplit split;
-	const Reference *ref_ptr = &references[references.size() - spec.num];
-
-	for(int dim = 0; dim < 3; dim++) {
-		/* sort references */
-		bvh_reference_sort(references.size() - spec.num, references.size(), &references[0], dim);
-
-		/* sweep right to left and determine bounds. */
-		BoundBox right_bounds;
-
-		for(int i = spec.num - 1; i > 0; i--) {
-			right_bounds.grow(ref_ptr[i].bounds);
-			spatial_right_bounds[i - 1] = right_bounds;
-		}
-
-		/* sweep left to right and select lowest SAH. */
-		BoundBox left_bounds;
-
-		for(int i = 1; i < spec.num; i++) {
-			left_bounds.grow(ref_ptr[i - 1].bounds);
-			right_bounds = spatial_right_bounds[i - 1];
-
-			float sah = nodeSAH +
-				left_bounds.area() * params.triangle_cost(i) +
-				right_bounds.area() * params.triangle_cost(spec.num - i);
-
-			if(sah < split.sah) {
-				split.sah = sah;
-				split.dim = dim;
-				split.num_left = i;
-				split.left_bounds = left_bounds;
-				split.right_bounds = right_bounds;
-			}
-		}
-	}
-
-	return split;
+	/* in tested scenes, this resulted in slightly slower raytracing, so disabled
+	 * it for now. could be implementation bug, or depend on the scene */
+	if(node)
+		for(int i = 0; i < iterations; i++)
+			rotate(node, max_depth);
 }
 
-void BVHBuild::do_object_split(NodeSpec& left, NodeSpec& right, const NodeSpec& spec, const ObjectSplit& split)
+void BVHBuild::rotate(BVHNode *node, int max_depth)
 {
-	/* sort references according to split */
-	int start = references.size() - spec.num;
-	int end = references.size(); /* todo: is this right? */
-
-	bvh_reference_sort(start, end, &references[0], split.dim);
-
-	/* split node specs */
-	left.num = split.num_left;
-	left.bounds = split.left_bounds;
-	right.num = spec.num - split.num_left;
-	right.bounds = split.right_bounds;
-}
-
-/* Spatial Split */
-
-BVHBuild::SpatialSplit BVHBuild::find_spatial_split(const NodeSpec& spec, float nodeSAH)
-{
-	/* initialize bins. */
-	float3 origin = spec.bounds.min;
-	float3 binSize = (spec.bounds.max - origin) * (1.0f / (float)BVHParams::NUM_SPATIAL_BINS);
-	float3 invBinSize = 1.0f / binSize;
-
-	for(int dim = 0; dim < 3; dim++) {
-		for(int i = 0; i < BVHParams::NUM_SPATIAL_BINS; i++) {
-			SpatialBin& bin = spatial_bins[dim][i];
-
-			bin.bounds = BoundBox();
-			bin.enter = 0;
-			bin.exit = 0;
-		}
-	}
-
-	/* chop references into bins. */
-	for(unsigned int refIdx = references.size() - spec.num; refIdx < references.size(); refIdx++) {
-		const Reference& ref = references[refIdx];
-		float3 firstBinf = (ref.bounds.min - origin) * invBinSize;
-		float3 lastBinf = (ref.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);
+	/* nothing to rotate if we reached a leaf node. */
+	if(node->is_leaf() || max_depth < 0)
+		return;
+	
+	InnerNode *parent = (InnerNode*)node;
 
-		firstBin = clamp(firstBin, 0, BVHParams::NUM_SPATIAL_BINS - 1);
-		lastBin = clamp(lastBin, firstBin, BVHParams::NUM_SPATIAL_BINS - 1);
+	/* rotate all children first */
+	for(size_t c = 0; c < 2; c++)
+		rotate(parent->children[c], max_depth-1);
 
-		for(int dim = 0; dim < 3; dim++) {
-			Reference currRef = ref;
+	/* compute current area of all children */
+	BoundBox bounds0 = parent->children[0]->m_bounds;
+	BoundBox bounds1 = parent->children[1]->m_bounds;
 
-			for(int i = firstBin[dim]; i < lastBin[dim]; i++) {
-				Reference leftRef, rightRef;
+	float area0 = bounds0.half_area();
+	float area1 = bounds1.half_area();
+	float4 child_area = make_float4(area0, area1, 0.0f, 0.0f);
 
-				split_reference(leftRef, rightRef, currRef, dim, origin[dim] + binSize[dim] * (float)(i + 1));
-				spatial_bins[dim][i].bounds.grow(leftRef.bounds);
-				currRef = rightRef;
-			}
+	/* find best rotation. we pick a target child of a first child, and swap
+	 * this with an other child. we perform the best such swap. */
+	float best_cost = FLT_MAX;
+	int best_child = -1, bets_target = -1, best_other = -1;
 
-			spatial_bins[dim][lastBin[dim]].bounds.grow(currRef.bounds);
-			spatial_bins[dim][firstBin[dim]].enter++;
-			spatial_bins[dim][lastBin[dim]].exit++;
-		}
-	}
+	for(size_t c = 0; c < 2; c++) {
+		/* ignore leaf nodes as we cannot descent into */
+		if(parent->children[c]->is_leaf())
+			continue;
 
-	/* select best split plane. */
-	SpatialSplit split;
+		InnerNode *child = (InnerNode*)parent->children[c];
+		BoundBox& other = (c == 0)? bounds1: bounds0;
 
-	for(int dim = 0; dim < 3; dim++) {
-		/* sweep right to left and determine bounds. */
-		BoundBox right_bounds;
+		/* transpose child bounds */
+		BoundBox target0 = child->children[0]->m_bounds;
+		BoundBox target1 = child->children[1]->m_bounds;
 
-		for(int i = BVHParams::NUM_SPATIAL_BINS - 1; i > 0; i--) {
-			right_bounds.grow(spatial_bins[dim][i].bounds);
-			spatial_right_bounds[i - 1] = right_bounds;
-		}
+		/* compute cost for both possible swaps */
+		float cost0 = merge(other, target1).half_area() - child_area[c];
+		float cost1 = merge(target0, other).half_area() - child_area[c];
 
-		/* sweep left to right and select lowest SAH. */
-		BoundBox left_bounds;
-		int leftNum = 0;
-		int rightNum = spec.num;
+		if(min(cost0,cost1) < best_cost) {
+			best_child = (int)c;
+			best_other = (int)(1-c);
 
-		for(int i = 1; i < BVHParams::NUM_SPATIAL_BINS; i++) {
-			left_bounds.grow(spatial_bins[dim][i - 1].bounds);
-			leftNum += spatial_bins[dim][i - 1].enter;
-			rightNum -= spatial_bins[dim][i - 1].exit;
-
-			float sah = nodeSAH +
-				left_bounds.area() * params.triangle_cost(leftNum) +
-				spatial_right_bounds[i - 1].area() * params.triangle_cost(rightNum);
-
-			if(sah < split.sah) {
-				split.sah = sah;
-				split.dim = dim;
-				split.pos = origin[dim] + binSize[dim] * (float)i;
+			if(cost0 < cost1) {
+				best_cost = cost0;
+				bets_target = 0;
+			}
+			else {
+				best_cost = cost0;
+				bets_target = 1;
 			}
 		}
 	}
 
-	return split;
-}
-
-void BVHBuild::do_spatial_split(NodeSpec& left, NodeSpec& right, const NodeSpec& spec, const SpatialSplit& split)
-{
-	/* Categorize references and compute bounds.
-	 *
-	 * Left-hand side:			[left_start, left_end[
-	 * Uncategorized/split:		[left_end, right_start[
-	 * Right-hand side:			[right_start, refs.size()[ */
-
-	vector<Reference>& refs = references;
-	int left_start = refs.size() - spec.num;
-	int left_end = left_start;
-	int right_start = refs.size();
-
-	left.bounds = right.bounds = BoundBox();
-
-	for(int i = left_end; i < right_start; i++) {
-		if(refs[i].bounds.max[split.dim] <= split.pos) {
-			/* entirely on the left-hand side */
-			left.bounds.grow(refs[i].bounds);
-			swap(refs[i], refs[left_end++]);
-		}
-		else if(refs[i].bounds.min[split.dim] >= split.pos) {
-			/* entirely on the right-hand side */
-			right.bounds.grow(refs[i].bounds);
-			swap(refs[i--], refs[--right_start]);
-		}
-	}
-
-	/* duplicate or unsplit references intersecting both sides. */
-	while(left_end < right_start) {
-		/* split reference. */
-		Reference lref, rref;
-
-		split_reference(lref, rref, refs[left_end], split.dim, split.pos);
-
-		/* compute SAH for duplicate/unsplit candidates. */
-		BoundBox lub = left.bounds;		// Unsplit to left:		new left-hand bounds.
-		BoundBox rub = right.bounds;	// Unsplit to right:	new right-hand bounds.
-		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);
-		ldb.grow(lref.bounds);
-		rdb.grow(rref.bounds);
-
-		float lac = params.triangle_cost(left_end - left_start);
-		float rac = params.triangle_cost(refs.size() - right_start);
-		float lbc = params.triangle_cost(left_end - left_start + 1);
-		float rbc = params.triangle_cost(refs.size() - right_start + 1);
-
-		float unsplitLeftSAH = lub.area() * lbc + right.bounds.area() * rac;
-		float unsplitRightSAH = left.bounds.area() * lac + rub.area() * rbc;
-		float duplicateSAH = ldb.area() * lbc + rdb.area() * rbc;
-		float minSAH = min(min(unsplitLeftSAH, unsplitRightSAH), duplicateSAH);
-
-		if(minSAH == unsplitLeftSAH) {
-			/* unsplit to left */
-			left.bounds = lub;
-			left_end++;
-		}
-		else if(minSAH == unsplitRightSAH) {
-			/* unsplit to right */
-			right.bounds = rub;
-			swap(refs[left_end], refs[--right_start]);
-		}
-		else {
-			/* duplicate */
-			left.bounds = ldb;
-			right.bounds = rdb;
-			refs[left_end++] = lref;
-			refs.push_back(rref);
-		}
-	}
-
-	left.num = left_end - left_start;
-	right.num = refs.size() - right_start;
-}
+	/* if we did not find a swap that improves the SAH then do nothing */
+	if(best_cost >= 0)
+		return;
 
-void BVHBuild::split_reference(Reference& left, Reference& right, const Reference& ref, int dim, float pos)
-{
-	/* initialize references. */
-	left.prim_index = right.prim_index = ref.prim_index;
-	left.prim_object = right.prim_object = ref.prim_object;
-	left.bounds = right.bounds = BoundBox();
-
-	/* loop over vertices/edges. */
-	Object *ob = objects[ref.prim_object];
-	const Mesh *mesh = ob->mesh;
-	const int *inds = mesh->triangles[ref.prim_index].v;
-	const float3 *verts = &mesh->verts[0];
-	const float3* v1 = &verts[inds[2]];
-
-	for(int i = 0; i < 3; i++) {
-		const float3* v0 = v1;
-		int vindex = inds[i];
-		v1 = &verts[vindex];
-		float v0p = (*v0)[dim];
-		float v1p = (*v1)[dim];
-
-		/* insert vertex to the boxes it belongs to. */
-		if(v0p <= pos)
-			left.bounds.grow(*v0);
-
-		if(v0p >= pos)
-			right.bounds.grow(*v0);
-
-		/* edge intersects the plane => insert intersection to both boxes. */
-		if((v0p < pos && v1p > pos) || (v0p > pos && v1p < pos)) {
-			float3 t = lerp(*v0, *v1, clamp((pos - v0p) / (v1p - v0p), 0.0f, 1.0f));
-			left.bounds.grow(t);
-			right.bounds.grow(t);
-		}
-	}
+	/* perform the best found tree rotation */
+	InnerNode *child = (InnerNode*)parent->children[best_child];
 
-	/* intersect with original bounds. */
-	left.bounds.max[dim] = pos;
-	right.bounds.min[dim] = pos;
-	left.bounds.intersect(ref.bounds);
-	right.bounds.intersect(ref.bounds);
+	swap(parent->children[best_other], child->children[bets_target]);
+	child->m_bounds = merge(child->children[0]->m_bounds, child->children[1]->m_bounds);
 }
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/bvh/bvh_build.h b/intern/cycles/bvh/bvh_build.h
index 1fa1951d7f2..84e14632b4b 100644
--- a/intern/cycles/bvh/bvh_build.h
+++ b/intern/cycles/bvh/bvh_build.h
@@ -21,8 +21,10 @@
 #include <float.h>
 
 #include "bvh.h"
+#include "bvh_binning.h"
 
 #include "util_boundbox.h"
+#include "util_task.h"
 #include "util_vector.h"
 
 CCL_NAMESPACE_BEGIN
@@ -37,28 +39,7 @@ class Progress;
 class BVHBuild
 {
 public:
-	struct Reference
-	{
-		int prim_index;
-		int prim_object;
-		BoundBox bounds;
-
-		Reference()
-		{
-		}
-	};
-
-	struct NodeSpec
-	{
-		int num;
-		BoundBox bounds;
-
-		NodeSpec()
-		{
-			num = 0;
-		}
-	};
-
+	/* Constructor/Destructor */
 	BVHBuild(
 		const vector<Object*>& objects,
 		vector<int>& prim_index,
@@ -70,63 +51,37 @@ public:
 	BVHNode *run();
 
 protected:
+	friend class BVHMixedSplit;
+	friend class BVHObjectSplit;
+	friend class BVHSpatialSplit;
+
 	/* adding references */
-	void add_reference_mesh(NodeSpec& root, Mesh *mesh, int i);
-	void add_reference_object(NodeSpec& root, Object *ob, int i);
-	void add_references(NodeSpec& root);
+	void add_reference_mesh(BoundBox& root, BoundBox& center, Mesh *mesh, int i);
+	void add_reference_object(BoundBox& root, BoundBox& center, Object *ob, int i);
+	void add_references(BVHRange& root);
 
 	/* building */
-	BVHNode *build_node(const NodeSpec& spec, int level, float progress_start, float progress_end);
-	BVHNode *create_leaf_node(const NodeSpec& spec);
-	BVHNode *create_object_leaf_nodes(const Reference *ref, int num);
-
-	void progress_update(float progress_start, float progress_end);
-
-	/* object splits */
-	struct ObjectSplit
-	{
-		float sah;
-		int dim;
-		int num_left;
-		BoundBox left_bounds;
-		BoundBox right_bounds;
-
-		ObjectSplit()
-		: sah(FLT_MAX), dim(0), num_left(0)
-		{
-		}
-	};
-
-	ObjectSplit find_object_split(const NodeSpec& spec, float nodeSAH);
-	void do_object_split(NodeSpec& left, NodeSpec& right, const NodeSpec& spec, const ObjectSplit& split);
-
-	/* spatial splits */
-	struct SpatialSplit
-	{
-		float sah;
-		int dim;
-		float pos;
-
-		SpatialSplit()
-		: sah(FLT_MAX), dim(0), pos(0.0f)
-		{
-		}
-	};
-
-	struct SpatialBin
-	{
-		BoundBox bounds;
-		int enter;
-		int exit;
-	};
-
-	SpatialSplit find_spatial_split(const NodeSpec& spec, float nodeSAH);
-	void do_spatial_split(NodeSpec& left, NodeSpec& right, const NodeSpec& spec, const SpatialSplit& split);
-	void split_reference(Reference& left, Reference& right, const Reference& ref, int dim, float pos);
+	BVHNode *build_node(const BVHRange& range, int level);
+	BVHNode *build_node(const BVHObjectBinning& range, int level);
+	BVHNode *create_leaf_node(const BVHRange& range);
+	BVHNode *create_object_leaf_nodes(const BVHReference *ref, int start, int num);
+
+	/* threads */
+	enum { THREAD_TASK_SIZE = 4096 };
+	void thread_build_node(Task *task_, int thread_id);
+	thread_mutex build_mutex;
+
+	/* progress */
+	void progress_update();
+
+	/* tree rotations */
+	void rotate(BVHNode *node, int max_depth);
+	void rotate(BVHNode *node, int max_depth, int iterations);
 
 	/* objects and primitive references */
 	vector<Object*> objects;
-	vector<Reference> references;
+	vector<BVHReference> references;
+	int num_original_references;
 
 	/* output primitive indexes and objects */
 	vector<int>& prim_index;
@@ -138,12 +93,17 @@ protected:
 	/* progress reporting */
 	Progress& progress;
 	double progress_start_time;
-	int progress_num_duplicates;
+	size_t progress_count;
+	size_t progress_total;
+	size_t progress_original_total;
 
 	/* spatial splitting */
 	float spatial_min_overlap;
 	vector<BoundBox> spatial_right_bounds;
-	SpatialBin spatial_bins[3][BVHParams::NUM_SPATIAL_BINS];
+	BVHSpatialBin spatial_bins[3][BVHParams::NUM_SPATIAL_BINS];
+
+	/* threads */
+	TaskPool task_pool;
 };
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/bvh/bvh_node.cpp b/intern/cycles/bvh/bvh_node.cpp
index 63683bae4a3..4edfb4b70a4 100644
--- a/intern/cycles/bvh/bvh_node.cpp
+++ b/intern/cycles/bvh/bvh_node.cpp
@@ -24,6 +24,8 @@
 
 CCL_NAMESPACE_BEGIN
 
+/* BVH Node */
+
 int BVHNode::getSubtreeSize(BVH_STAT stat) const
 {
 	int cnt = 0;
@@ -59,7 +61,8 @@ int BVHNode::getSubtreeSize(BVH_STAT stat) const
 void BVHNode::deleteSubtree()
 {
 	for(int i=0;i<num_children();i++)
-		get_child(i)->deleteSubtree();
+		if(get_child(i))
+			get_child(i)->deleteSubtree();
 
 	delete this;
 }
@@ -70,12 +73,27 @@ float BVHNode::computeSubtreeSAHCost(const BVHParams& p, float probability) cons
 
 	for(int i=0;i<num_children();i++) {
 		BVHNode *child = get_child(i);
-		SAH += child->computeSubtreeSAHCost(p, probability * child->m_bounds.area()/m_bounds.area());
+		SAH += child->computeSubtreeSAHCost(p, probability * child->m_bounds.safe_area()/m_bounds.safe_area());
 	}
 
 	return SAH;
 }
 
+uint BVHNode::update_visibility()
+{
+	if(!is_leaf() && m_visibility == 0) {
+		InnerNode *inner = (InnerNode*)this;
+		BVHNode *child0 = inner->children[0];
+		BVHNode *child1 = inner->children[1];
+
+		m_visibility = child0->update_visibility()|child1->update_visibility();
+	}
+
+	return m_visibility;
+}
+
+/* Inner Node */
+
 void InnerNode::print(int depth) const
 {
 	for(int i = 0; i < depth; i++)
diff --git a/intern/cycles/bvh/bvh_node.h b/intern/cycles/bvh/bvh_node.h
index 5e0a17a1193..5c00f7b7a38 100644
--- a/intern/cycles/bvh/bvh_node.h
+++ b/intern/cycles/bvh/bvh_node.h
@@ -49,8 +49,6 @@ public:
 	virtual int num_triangles() const { return 0; }
 	virtual void print(int depth = 0) const = 0;
 
-	float getArea() const { return m_bounds.area(); }
-
 	BoundBox m_bounds;
 	uint m_visibility;
 
@@ -58,6 +56,8 @@ public:
 	int getSubtreeSize(BVH_STAT stat=BVH_STAT_NODE_COUNT) const;
 	float computeSubtreeSAHCost(const BVHParams& p, float probability = 1.0f) const;	
 	void deleteSubtree();
+
+	uint update_visibility();
 };
 
 class InnerNode : public BVHNode
@@ -66,9 +66,21 @@ public:
 	InnerNode(const BoundBox& bounds, BVHNode* child0, BVHNode* child1)
 	{
 		m_bounds = bounds;
-		m_visibility = child0->m_visibility|child1->m_visibility;
 		children[0] = child0;
 		children[1] = child1;
+
+		if(child0 && child1)
+			m_visibility = child0->m_visibility|child1->m_visibility;
+		else
+			m_visibility = 0; /* happens on build cancel */
+	}
+
+	InnerNode(const BoundBox& bounds)
+	{
+		m_bounds = bounds;
+		m_visibility = 0;
+		children[0] = NULL;
+		children[1] = NULL;
 	}
 
 	bool is_leaf() const { return false; }
diff --git a/intern/cycles/bvh/bvh_params.h b/intern/cycles/bvh/bvh_params.h
index 38093438500..0cf5e905fea 100644
--- a/intern/cycles/bvh/bvh_params.h
+++ b/intern/cycles/bvh/bvh_params.h
@@ -18,6 +18,8 @@
 #ifndef __BVH_PARAMS_H__
 #define __BVH_PARAMS_H__
 
+#include "util_boundbox.h"
+
 CCL_NAMESPACE_BEGIN
 
 /* BVH Parameters */
@@ -73,14 +75,97 @@ public:
 	}
 
 	/* SAH costs */
-	float cost(int num_nodes, int num_tris) const
+	__forceinline float cost(int num_nodes, int num_tris) const
 	{ return node_cost(num_nodes) + triangle_cost(num_tris); }
 
-	float triangle_cost(int n) const
+	__forceinline float triangle_cost(int n) const
 	{ return n*sah_triangle_cost; }
 
-	float node_cost(int n) const
+	__forceinline float node_cost(int n) const
 	{ return n*sah_node_cost; }
+
+	__forceinline bool small_enough_for_leaf(int size, int level)
+	{ return (size <= min_leaf_size || level >= MAX_DEPTH); }
+};
+
+/* BVH Reference
+ *
+ * Reference to a primitive. Primitive index and object are sneakily packed
+ * into BoundBox to reduce memory usage and align nicely */
+
+class BVHReference
+{
+public:
+	__forceinline BVHReference() {}
+
+	__forceinline BVHReference(const BoundBox& bounds_, int prim_index, int prim_object)
+	: rbounds(bounds_)
+	{
+		rbounds.min.w = __int_as_float(prim_index);
+		rbounds.max.w = __int_as_float(prim_object);
+	}
+
+	__forceinline const BoundBox& bounds() const { return rbounds; }
+	__forceinline int prim_index() const { return __float_as_int(rbounds.min.w); }
+	__forceinline int prim_object() const { return __float_as_int(rbounds.max.w); }
+
+protected:
+	BoundBox rbounds;
+};
+
+/* BVH Range
+ *
+ * Build range used during construction, to indicate the bounds and place in
+ * the reference array of a subset of pirmitives Again uses trickery to pack
+ * integers into BoundBox for alignment purposes. */
+
+class BVHRange
+{
+public:
+	__forceinline BVHRange()
+	{
+		rbounds.min.w = __int_as_float(0);
+		rbounds.max.w = __int_as_float(0);
+	}
+
+	__forceinline BVHRange(const BoundBox& bounds_, int start_, int size_)
+	: rbounds(bounds_)
+	{
+		rbounds.min.w = __int_as_float(start_);
+		rbounds.max.w = __int_as_float(size_);
+	}
+
+	__forceinline BVHRange(const BoundBox& bounds_, const BoundBox& cbounds_, int start_, int size_)
+	: rbounds(bounds_), cbounds(cbounds_)
+	{
+		rbounds.min.w = __int_as_float(start_);
+		rbounds.max.w = __int_as_float(size_);
+	}
+
+	__forceinline void set_start(int start_) { rbounds.min.w = __int_as_float(start_); }
+
+	__forceinline const BoundBox& bounds() const { return rbounds; }
+	__forceinline const BoundBox& cent_bounds() const { return cbounds; }
+	__forceinline int start() const { return __float_as_int(rbounds.min.w); }
+	__forceinline int size() const { return __float_as_int(rbounds.max.w); }
+	__forceinline int end() const { return start() + size(); }
+
+protected:
+	BoundBox rbounds;
+	BoundBox cbounds;
+};
+
+/* BVH Spatial Bin */
+
+struct BVHSpatialBin
+{
+	BoundBox bounds;
+	int enter;
+	int exit;
+
+	__forceinline BVHSpatialBin()
+	{
+	}
 };
 
 CCL_NAMESPACE_END
diff --git a/intern/cycles/bvh/bvh_sort.cpp b/intern/cycles/bvh/bvh_sort.cpp
index ee4531a4843..bef384be592 100644
--- a/intern/cycles/bvh/bvh_sort.cpp
+++ b/intern/cycles/bvh/bvh_sort.cpp
@@ -32,23 +32,23 @@ public:
 		dim = dim_;
 	}
 
-	bool operator()(const BVHBuild::Reference& ra, const BVHBuild::Reference& rb)
+	bool operator()(const BVHReference& ra, const BVHReference& rb)
 	{
-		float ca = ra.bounds.min[dim] + ra.bounds.max[dim];
-		float cb = rb.bounds.min[dim] + rb.bounds.max[dim];
+		float ca = ra.bounds().min[dim] + ra.bounds().max[dim];
+		float cb = rb.bounds().min[dim] + rb.bounds().max[dim];
 
 		if(ca < cb) return true;
 		else if(ca > cb) return false;
-		else if(ra.prim_object < rb.prim_object) return true;
-		else if(ra.prim_object > rb.prim_object) return false;
-		else if(ra.prim_index < rb.prim_index) return true;
-		else if(ra.prim_index > rb.prim_index) return false;
+		else if(ra.prim_object() < rb.prim_object()) return true;
+		else if(ra.prim_object() > rb.prim_object()) return false;
+		else if(ra.prim_index() < rb.prim_index()) return true;
+		else if(ra.prim_index() > rb.prim_index()) return false;
 
 		return false;
 	}
 };
 
-void bvh_reference_sort(int start, int end, BVHBuild::Reference *data, int dim)
+void bvh_reference_sort(int start, int end, BVHReference *data, int dim)
 {
 	sort(data+start, data+end, BVHReferenceCompare(dim));
 }
diff --git a/intern/cycles/bvh/bvh_sort.h b/intern/cycles/bvh/bvh_sort.h
index f0676948146..ba35ba3fae7 100644
--- a/intern/cycles/bvh/bvh_sort.h
+++ b/intern/cycles/bvh/bvh_sort.h
@@ -20,7 +20,7 @@
 
 CCL_NAMESPACE_BEGIN
 
-void bvh_reference_sort(int start, int end, BVHBuild::Reference *data, int dim);
+void bvh_reference_sort(int start, int end, BVHReference *data, int dim);
 
 CCL_NAMESPACE_END
 
diff --git a/intern/cycles/bvh/bvh_split.cpp b/intern/cycles/bvh/bvh_split.cpp
new file mode 100644
index 00000000000..263c5834428
--- /dev/null
+++ b/intern/cycles/bvh/bvh_split.cpp
@@ -0,0 +1,293 @@
+/*
+ * Adapted from code copyright 2009-2010 NVIDIA Corporation
+ * Modifications Copyright 2011, Blender Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "bvh_build.h"
+#include "bvh_split.h"
+#include "bvh_sort.h"
+
+#include "mesh.h"
+#include "object.h"
+
+#include "util_algorithm.h"
+
+CCL_NAMESPACE_BEGIN
+
+/* Object Split */
+
+BVHObjectSplit::BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH)
+: sah(FLT_MAX), dim(0), num_left(0), left_bounds(BoundBox::empty), right_bounds(BoundBox::empty)
+{
+	const BVHReference *ref_ptr = &builder->references[range.start()];
+	float min_sah = FLT_MAX;
+
+	for(int dim = 0; dim < 3; dim++) {
+		/* sort references */
+		bvh_reference_sort(range.start(), range.end(), &builder->references[0], dim);
+
+		/* 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());
+			builder->spatial_right_bounds[i - 1] = right_bounds;
+		}
+
+		/* sweep left to right and select lowest SAH. */
+		BoundBox left_bounds = BoundBox::empty;
+
+		for(int i = 1; i < range.size(); i++) {
+			left_bounds.grow(ref_ptr[i - 1].bounds());
+			right_bounds = builder->spatial_right_bounds[i - 1];
+
+			float sah = nodeSAH +
+				left_bounds.safe_area() * builder->params.triangle_cost(i) +
+				right_bounds.safe_area() * builder->params.triangle_cost(range.size() - i);
+
+			if(sah < min_sah) {
+				min_sah = sah;
+
+				this->sah = sah;
+				this->dim = dim;
+				this->num_left = i;
+				this->left_bounds = left_bounds;
+				this->right_bounds = right_bounds;
+			}
+		}
+	}
+}
+
+void BVHObjectSplit::split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range)
+{
+	/* sort references according to split */
+	bvh_reference_sort(range.start(), range.end(), &builder->references[0], this->dim);
+
+	/* 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);
+
+}
+
+/* Spatial Split */
+
+BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH)
+: sah(FLT_MAX), dim(0), pos(0.0f)
+{
+	/* initialize bins. */
+	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++) {
+		for(int i = 0; i < BVHParams::NUM_SPATIAL_BINS; i++) {
+			BVHSpatialBin& bin = builder->spatial_bins[dim][i];
+
+			bin.bounds = BoundBox::empty;
+			bin.enter = 0;
+			bin.exit = 0;
+		}
+	}
+
+	/* chop references into bins. */
+	for(unsigned int refIdx = range.start(); refIdx < range.end(); refIdx++) {
+		const BVHReference& ref = builder->references[refIdx];
+		float3 firstBinf = (ref.bounds().min - origin) * invBinSize;
+		float3 lastBinf = (ref.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);
+
+		firstBin = clamp(firstBin, 0, BVHParams::NUM_SPATIAL_BINS - 1);
+		lastBin = clamp(lastBin, firstBin, BVHParams::NUM_SPATIAL_BINS - 1);
+
+		for(int dim = 0; dim < 3; dim++) {
+			BVHReference currRef = ref;
+
+			for(int i = firstBin[dim]; i < lastBin[dim]; i++) {
+				BVHReference leftRef, rightRef;
+
+				split_reference(builder, leftRef, rightRef, currRef, dim, origin[dim] + binSize[dim] * (float)(i + 1));
+				builder->spatial_bins[dim][i].bounds.grow(leftRef.bounds());
+				currRef = rightRef;
+			}
+
+			builder->spatial_bins[dim][lastBin[dim]].bounds.grow(currRef.bounds());
+			builder->spatial_bins[dim][firstBin[dim]].enter++;
+			builder->spatial_bins[dim][lastBin[dim]].exit++;
+		}
+	}
+
+	/* select best split plane. */
+	for(int dim = 0; dim < 3; dim++) {
+		/* sweep right to left and determine bounds. */
+		BoundBox right_bounds = BoundBox::empty;
+
+		for(int i = BVHParams::NUM_SPATIAL_BINS - 1; i > 0; i--) {
+			right_bounds.grow(builder->spatial_bins[dim][i].bounds);
+			builder->spatial_right_bounds[i - 1] = right_bounds;
+		}
+
+		/* sweep left to right and select lowest SAH. */
+		BoundBox left_bounds = BoundBox::empty;
+		int leftNum = 0;
+		int rightNum = range.size();
+
+		for(int i = 1; i < BVHParams::NUM_SPATIAL_BINS; i++) {
+			left_bounds.grow(builder->spatial_bins[dim][i - 1].bounds);
+			leftNum += builder->spatial_bins[dim][i - 1].enter;
+			rightNum -= builder->spatial_bins[dim][i - 1].exit;
+
+			float sah = nodeSAH +
+				left_bounds.safe_area() * builder->params.triangle_cost(leftNum) +
+				builder->spatial_right_bounds[i - 1].safe_area() * builder->params.triangle_cost(rightNum);
+
+			if(sah < this->sah) {
+				this->sah = sah;
+				this->dim = dim;
+				this->pos = origin[dim] + binSize[dim] * (float)i;
+			}
+		}
+	}
+}
+
+void BVHSpatialSplit::split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range)
+{
+	/* Categorize references and compute bounds.
+	 *
+	 * Left-hand side:			[left_start, left_end[
+	 * Uncategorized/split:		[left_end, right_start[
+	 * Right-hand side:			[right_start, refs.size()[ */
+
+	vector<BVHReference>& refs = builder->references;
+	int left_start = range.start();
+	int left_end = left_start;
+	int right_start = range.end();
+	int right_end = range.end();
+	BoundBox left_bounds = BoundBox::empty;
+	BoundBox right_bounds = BoundBox::empty;
+
+	for(int i = left_end; i < right_start; i++) {
+		if(refs[i].bounds().max[this->dim] <= this->pos) {
+			/* entirely on the left-hand side */
+			left_bounds.grow(refs[i].bounds());
+			swap(refs[i], refs[left_end++]);
+		}
+		else if(refs[i].bounds().min[this->dim] >= this->pos) {
+			/* entirely on the right-hand side */
+			right_bounds.grow(refs[i].bounds());
+			swap(refs[i--], refs[--right_start]);
+		}
+	}
+
+	/* duplicate or unsplit references intersecting both sides. */
+	while(left_end < right_start) {
+		/* split reference. */
+		BVHReference lref, rref;
+
+		split_reference(builder, lref, rref, refs[left_end], this->dim, this->pos);
+
+		/* compute SAH for duplicate/unsplit candidates. */
+		BoundBox lub = left_bounds;		// Unsplit to left:		new left-hand bounds.
+		BoundBox rub = right_bounds;	// Unsplit to right:	new right-hand bounds.
+		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());
+		ldb.grow(lref.bounds());
+		rdb.grow(rref.bounds());
+
+		float lac = builder->params.triangle_cost(left_end - left_start);
+		float rac = builder->params.triangle_cost(right_end - right_start);
+		float lbc = builder->params.triangle_cost(left_end - left_start + 1);
+		float rbc = builder->params.triangle_cost(right_end - right_start + 1);
+
+		float unsplitLeftSAH = lub.safe_area() * lbc + right_bounds.safe_area() * rac;
+		float unsplitRightSAH = left_bounds.safe_area() * lac + rub.safe_area() * rbc;
+		float duplicateSAH = ldb.safe_area() * lbc + rdb.safe_area() * rbc;
+		float minSAH = min(min(unsplitLeftSAH, unsplitRightSAH), duplicateSAH);
+
+		if(minSAH == unsplitLeftSAH) {
+			/* unsplit to left */
+			left_bounds = lub;
+			left_end++;
+		}
+		else if(minSAH == unsplitRightSAH) {
+			/* unsplit to right */
+			right_bounds = rub;
+			swap(refs[left_end], refs[--right_start]);
+		}
+		else {
+			/* duplicate */
+			left_bounds = ldb;
+			right_bounds = rdb;
+			refs[left_end++] = lref;
+			refs.insert(refs.begin() + right_end, rref);
+			right_end++;
+		}
+	}
+
+	left = BVHRange(left_bounds, left_start, left_end - left_start);
+	right = BVHRange(right_bounds, right_start, right_end - right_start);
+}
+
+void BVHSpatialSplit::split_reference(BVHBuild *builder, BVHReference& left, BVHReference& right, const BVHReference& ref, int dim, float pos)
+{
+	/* initialize boundboxes */
+	BoundBox left_bounds = BoundBox::empty;
+	BoundBox right_bounds = BoundBox::empty;
+
+	/* loop over vertices/edges. */
+	Object *ob = builder->objects[ref.prim_object()];
+	const Mesh *mesh = ob->mesh;
+	const int *inds = mesh->triangles[ref.prim_index()].v;
+	const float3 *verts = &mesh->verts[0];
+	const float3* v1 = &verts[inds[2]];
+
+	for(int i = 0; i < 3; i++) {
+		const float3* v0 = v1;
+		int vindex = inds[i];
+		v1 = &verts[vindex];
+		float v0p = (*v0)[dim];
+		float v1p = (*v1)[dim];
+
+		/* insert vertex to the boxes it belongs to. */
+		if(v0p <= pos)
+			left_bounds.grow(*v0);
+
+		if(v0p >= pos)
+			right_bounds.grow(*v0);
+
+		/* edge intersects the plane => insert intersection to both boxes. */
+		if((v0p < pos && v1p > pos) || (v0p > pos && v1p < pos)) {
+			float3 t = lerp(*v0, *v1, clamp((pos - v0p) / (v1p - v0p), 0.0f, 1.0f));
+			left_bounds.grow(t);
+			right_bounds.grow(t);
+		}
+	}
+
+	/* intersect with original bounds. */
+	left_bounds.max[dim] = pos;
+	right_bounds.min[dim] = pos;
+	left_bounds.intersect(ref.bounds());
+	right_bounds.intersect(ref.bounds());
+
+	/* set referecnes */
+	left = BVHReference(left_bounds, ref.prim_index(), ref.prim_object());
+	right = BVHReference(right_bounds, ref.prim_index(), ref.prim_object());
+}
+
+CCL_NAMESPACE_END
+
diff --git a/intern/cycles/bvh/bvh_split.h b/intern/cycles/bvh/bvh_split.h
new file mode 100644
index 00000000000..1f4befbe8e2
--- /dev/null
+++ b/intern/cycles/bvh/bvh_split.h
@@ -0,0 +1,110 @@
+/*
+ * Adapted from code copyright 2009-2010 NVIDIA Corporation
+ * Modifications Copyright 2011, Blender Foundation.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef __BVH_SPLIT_H__
+#define __BVH_SPLIT_H__
+
+#include "bvh_build.h"
+#include "bvh_params.h"
+
+CCL_NAMESPACE_BEGIN
+
+class BVHBuild;
+
+/* Object Split */
+
+class BVHObjectSplit
+{
+public:
+	float sah;
+	int dim;
+	int num_left;
+	BoundBox left_bounds;
+	BoundBox right_bounds;
+
+	BVHObjectSplit() {}
+	BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH);
+
+	void split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range);
+};
+
+/* Spatial Split */
+
+class BVHSpatialSplit
+{
+public:
+	float sah;
+	int dim;
+	float pos;
+
+	BVHSpatialSplit() : sah(FLT_MAX), dim(0), pos(0.0f) {}
+	BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH);
+
+	void split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range);
+	void split_reference(BVHBuild *builder, BVHReference& left, BVHReference& right, const BVHReference& ref, int dim, float pos);
+};
+
+/* Mixed Object-Spatial Split */
+
+class BVHMixedSplit
+{
+public:
+	BVHObjectSplit object;
+	BVHSpatialSplit spatial;
+
+	float leafSAH;
+	float nodeSAH;
+	float minSAH;
+
+	bool no_split;
+
+	__forceinline BVHMixedSplit(BVHBuild *builder, const BVHRange& range, int level)
+	{
+		/* find split candidates. */
+		float area = range.bounds().safe_area();
+
+		leafSAH = area * builder->params.triangle_cost(range.size());
+		nodeSAH = area * builder->params.node_cost(2);
+
+		object = BVHObjectSplit(builder, range, nodeSAH);
+
+		if(builder->params.use_spatial_split && level < BVHParams::MAX_SPATIAL_DEPTH) {
+			BoundBox overlap = object.left_bounds;
+			overlap.intersect(object.right_bounds);
+
+			if(overlap.safe_area() >= builder->spatial_min_overlap)
+				spatial = BVHSpatialSplit(builder, range, nodeSAH);
+		}
+
+		/* leaf SAH is the lowest => create leaf. */
+		minSAH = min(min(leafSAH, object.sah), spatial.sah);
+		no_split = (minSAH == leafSAH && range.size() <= builder->params.max_leaf_size);
+	}
+
+	__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);
+		if(!left.size() || !right.size())
+			object.split(builder, left, right, range);
+	}
+};
+
+CCL_NAMESPACE_END
+
+#endif /* __BVH_SPLIT_H__ */
+