Cycles: Wrap spatial split storage into own structure

This has following advantages:

- Localizes all the run-time storage into a single structure,
  which could easily be extended further.

- Storage could be created per-thread, so once builder is
  threaded we wouldn't have any conflicts between threads.

- Global nature of the storage avoids memory re-allocation
  on the runtime, keeping builder as fast as possible.

Currently it's just API changes, which don't affect user at all.

intern/cycles/bvh/bvh_build.cpp

@@ -230,8 +230,23 @@ BVHNode* BVHBuild::run()
 	}
 
 	spatial_min_overlap = root.bounds().safe_area() * params.spatial_split_alpha;
-	spatial_right_bounds.clear();
+
-	spatial_right_bounds.resize(max(root.size(), (int)BVHParams::NUM_SPATIAL_BINS) - 1);
+	if(params.use_spatial_split) {
+		/* NOTE: The API here tries to be as much ready for multi-threaded build
+		 * as possible, but at the same time it tries not to introduce any
+		 * changes in behavior for until all refactoring needed for threading is
+		 * finished.
+		 *
+		 * So we currently allocate single storage for now, which is only used by
+		 * the only thread working on the spatial BVH build.
+		 */
+		spatial_storage.resize(1);
+		size_t num_bins = max(root.size(), (int)BVHParams::NUM_SPATIAL_BINS) - 1;
+		foreach(BVHSpatialStorage &storage, spatial_storage) {
+			storage.spatial_right_bounds.clear();
+			storage.spatial_right_bounds.resize(num_bins);
+		}
+	}
 
 	/* init progress updates */
 	double build_start_time;
@@ -407,7 +422,7 @@ BVHNode* BVHBuild::build_node(const BVHRange& range, int level)
 	}
 
 	/* splitting test */
-	BVHMixedSplit split(this, range, level);
+	BVHMixedSplit split(this, &spatial_storage[0], range, level);
 
 	if(!(range.size() > 0 && params.top_level && level == 0)) {
 		if(split.no_split) {

intern/cycles/bvh/bvh_build.h

@@ -114,8 +114,7 @@ protected:
 
 	/* spatial splitting */
 	float spatial_min_overlap;
-	vector<BoundBox> spatial_right_bounds;
+	vector<BVHSpatialStorage> spatial_storage;
-	BVHSpatialBin spatial_bins[3][BVHParams::NUM_SPATIAL_BINS];
 
 	/* threads */
 	TaskPool task_pool;

intern/cycles/bvh/bvh_params.h

@@ -175,6 +175,18 @@ struct BVHSpatialBin
 	}
 };
 
+/* BVH Spatial Storage
+ *
+ * The idea of this storage is have thread-specific storage for the spatial
+ * splitters. We can pre-allocate this storage in advance and avoid heavy memory
+ * operations during split process.
+ */
+
+struct BVHSpatialStorage {
+	vector<BoundBox> spatial_right_bounds;
+	BVHSpatialBin spatial_bins[3][BVHParams::NUM_SPATIAL_BINS];
+};
+
 CCL_NAMESPACE_END
 
 #endif /* __BVH_PARAMS_H__ */

intern/cycles/bvh/bvh_split.cpp

@@ -28,8 +28,16 @@ CCL_NAMESPACE_BEGIN
 
 /* Object Split */
 
-BVHObjectSplit::BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH)
+BVHObjectSplit::BVHObjectSplit(BVHBuild *builder,
-: sah(FLT_MAX), dim(0), num_left(0), left_bounds(BoundBox::empty), right_bounds(BoundBox::empty)
+                               BVHSpatialStorage *storage,
+                               const BVHRange& range,
+                               float nodeSAH)
+: sah(FLT_MAX),
+  dim(0),
+  num_left(0),
+  left_bounds(BoundBox::empty),
+  right_bounds(BoundBox::empty),
+  storage_(storage)
 {
 	const BVHReference *ref_ptr = &builder->references[range.start()];
 	float min_sah = FLT_MAX;
@@ -43,7 +51,7 @@ BVHObjectSplit::BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float n
 
 		for(int i = range.size() - 1; i > 0; i--) {
 			right_bounds.grow(ref_ptr[i].bounds());
-			builder->spatial_right_bounds[i - 1] = right_bounds;
+			storage_->spatial_right_bounds[i - 1] = right_bounds;
 		}
 
 		/* sweep left to right and select lowest SAH. */
@@ -51,7 +59,7 @@ BVHObjectSplit::BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float n
 
 		for(int i = 1; i < range.size(); i++) {
 			left_bounds.grow(ref_ptr[i - 1].bounds());
-			right_bounds = builder->spatial_right_bounds[i - 1];
+			right_bounds = storage_->spatial_right_bounds[i - 1];
 
 			float sah = nodeSAH +
 				left_bounds.safe_area() * builder->params.primitive_cost(i) +
@@ -83,8 +91,14 @@ void BVHObjectSplit::split(BVHBuild *builder, BVHRange& left, BVHRange& right, c
 
 /* Spatial Split */
 
-BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH)
+BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder,
-: sah(FLT_MAX), dim(0), pos(0.0f)
+                                 BVHSpatialStorage *storage,
+                                 const BVHRange& range,
+                                 float nodeSAH)
+: sah(FLT_MAX),
+  dim(0),
+  pos(0.0f),
+  storage_(storage)
 {
 	/* initialize bins. */
 	float3 origin = range.bounds().min;
@@ -93,7 +107,7 @@ BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float
 
 	for(int dim = 0; dim < 3; dim++) {
 		for(int i = 0; i < BVHParams::NUM_SPATIAL_BINS; i++) {
-			BVHSpatialBin& bin = builder->spatial_bins[dim][i];
+			BVHSpatialBin& bin = storage_->spatial_bins[dim][i];
 
 			bin.bounds = BoundBox::empty;
 			bin.enter = 0;
@@ -119,13 +133,13 @@ BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float
 				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());
+				storage_->spatial_bins[dim][i].bounds.grow(leftRef.bounds());
 				currRef = rightRef;
 			}
 
-			builder->spatial_bins[dim][lastBin[dim]].bounds.grow(currRef.bounds());
+			storage_->spatial_bins[dim][lastBin[dim]].bounds.grow(currRef.bounds());
-			builder->spatial_bins[dim][firstBin[dim]].enter++;
+			storage_->spatial_bins[dim][firstBin[dim]].enter++;
-			builder->spatial_bins[dim][lastBin[dim]].exit++;
+			storage_->spatial_bins[dim][lastBin[dim]].exit++;
 		}
 	}
 
@@ -135,8 +149,8 @@ BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float
 		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);
+			right_bounds.grow(storage_->spatial_bins[dim][i].bounds);
-			builder->spatial_right_bounds[i - 1] = right_bounds;
+			storage_->spatial_right_bounds[i - 1] = right_bounds;
 		}
 
 		/* sweep left to right and select lowest SAH. */
@@ -145,13 +159,13 @@ BVHSpatialSplit::BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float
 		int rightNum = range.size();
 
 		for(int i = 1; i < BVHParams::NUM_SPATIAL_BINS; i++) {
-			left_bounds.grow(builder->spatial_bins[dim][i - 1].bounds);
+			left_bounds.grow(storage_->spatial_bins[dim][i - 1].bounds);
-			leftNum += builder->spatial_bins[dim][i - 1].enter;
+			leftNum += storage_->spatial_bins[dim][i - 1].enter;
-			rightNum -= builder->spatial_bins[dim][i - 1].exit;
+			rightNum -= storage_->spatial_bins[dim][i - 1].exit;
 
 			float sah = nodeSAH +
 				left_bounds.safe_area() * builder->params.primitive_cost(leftNum) +
-				builder->spatial_right_bounds[i - 1].safe_area() * builder->params.primitive_cost(rightNum);
+				storage_->spatial_right_bounds[i - 1].safe_area() * builder->params.primitive_cost(rightNum);
 
 			if(sah < this->sah) {
 				this->sah = sah;

intern/cycles/bvh/bvh_split.h

@@ -37,9 +37,18 @@ public:
 	BoundBox right_bounds;
 
 	BVHObjectSplit() {}
-	BVHObjectSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH);
+	BVHObjectSplit(BVHBuild *builder,
+	               BVHSpatialStorage *storage,
+	               const BVHRange& range,
+	               float nodeSAH);
 
-	void split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range);
+	void split(BVHBuild *builder,
+	           BVHRange& left,
+	           BVHRange& right,
+	           const BVHRange& range);
+
+protected:
+	BVHSpatialStorage *storage_;
 };
 
 /* Spatial Split */
@@ -52,7 +61,10 @@ public:
 	float pos;
 
 	BVHSpatialSplit() : sah(FLT_MAX), dim(0), pos(0.0f) {}
-	BVHSpatialSplit(BVHBuild *builder, const BVHRange& range, float nodeSAH);
+	BVHSpatialSplit(BVHBuild *builder,
+	                BVHSpatialStorage *storage,
+	                const BVHRange& range,
+	                float nodeSAH);
 
 	void split(BVHBuild *builder, BVHRange& left, BVHRange& right, const BVHRange& range);
 	void split_reference(BVHBuild *builder,
@@ -63,6 +75,8 @@ public:
 	                     float pos);
 
 protected:
+	BVHSpatialStorage *storage_;
+
 	/* Lower-level functions which calculates boundaries of left and right nodes
 	 * needed for spatial split.
 	 *
@@ -123,7 +137,10 @@ public:
 
 	bool no_split;
 
-	__forceinline BVHMixedSplit(BVHBuild *builder, const BVHRange& range, int level)
+	__forceinline BVHMixedSplit(BVHBuild *builder,
+	                            BVHSpatialStorage *storage,
+	                            const BVHRange& range,
+	                            int level)
 	{
 		/* find split candidates. */
 		float area = range.bounds().safe_area();
@@ -131,14 +148,14 @@ public:
 		leafSAH = area * builder->params.primitive_cost(range.size());
 		nodeSAH = area * builder->params.node_cost(2);
 
-		object = BVHObjectSplit(builder, range, nodeSAH);
+		object = BVHObjectSplit(builder, storage, 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);
+				spatial = BVHSpatialSplit(builder, storage, range, nodeSAH);
 		}
 
 		/* leaf SAH is the lowest => create leaf. */