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, 44 insertions, 3 deletions

diff --git a/intern/cycles/bvh/bvh_node.h b/intern/cycles/bvh/bvh_node.h
index d476fb917ed..f2965a785e6 100644
--- a/intern/cycles/bvh/bvh_node.h
+++ b/intern/cycles/bvh/bvh_node.h
@@ -31,6 +31,14 @@ enum BVH_STAT {
 	BVH_STAT_TRIANGLE_COUNT,
 	BVH_STAT_CHILDNODE_COUNT,
 	BVH_STAT_QNODE_COUNT,
+	BVH_STAT_ALIGNED_COUNT,
+	BVH_STAT_UNALIGNED_COUNT,
+	BVH_STAT_ALIGNED_INNER_COUNT,
+	BVH_STAT_UNALIGNED_INNER_COUNT,
+	BVH_STAT_ALIGNED_INNER_QNODE_COUNT,
+	BVH_STAT_UNALIGNED_INNER_QNODE_COUNT,
+	BVH_STAT_ALIGNED_LEAF_COUNT,
+	BVH_STAT_UNALIGNED_LEAF_COUNT,
 };
 
 class BVHParams;
@@ -38,16 +46,41 @@ class BVHParams;
 class BVHNode
 {
 public:
-	BVHNode()
+	BVHNode() : m_is_unaligned(false),
+	            m_aligned_space(NULL)
 	{
 	}
 
-	virtual ~BVHNode() {}
+	virtual ~BVHNode()
+	{
+		delete m_aligned_space;
+	}
+
 	virtual bool is_leaf() const = 0;
 	virtual int num_children() const = 0;
 	virtual BVHNode *get_child(int i) const = 0;
 	virtual int num_triangles() const { return 0; }
 	virtual void print(int depth = 0) const = 0;
+	bool is_unaligned() const { return m_is_unaligned; }
+
+	inline void set_aligned_space(const Transform& aligned_space)
+	{
+		m_is_unaligned = true;
+		if (m_aligned_space == NULL) {
+			m_aligned_space = new Transform(aligned_space);
+		}
+		else {
+			*m_aligned_space = aligned_space;
+		}
+	}
+
+	inline Transform get_aligned_space() const
+	{
+		if(m_aligned_space == NULL) {
+			return transform_identity();
+		}
+		return *m_aligned_space;
+	}
 
 	BoundBox m_bounds;
 	uint m_visibility;
@@ -58,12 +91,20 @@ public:
 	void deleteSubtree();
 
 	uint update_visibility();
+
+	bool m_is_unaligned;
+
+	// TODO(sergey): Can be stored as 3x3 matrix, but better to have some
+	// utilities and type defines in util_transform first.
+	Transform *m_aligned_space;
 };
 
 class InnerNode : public BVHNode
 {
 public:
-	InnerNode(const BoundBox& bounds, BVHNode* child0, BVHNode* child1)
+	InnerNode(const BoundBox& bounds,
+	          BVHNode* child0,
+	          BVHNode* child1)
 	{
 		m_bounds = bounds;
 		children[0] = child0;