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.

2 files changed, 53 insertions, 3 deletions

diff --git a/intern/cycles/render/mesh.cpp b/intern/cycles/render/mesh.cpp
index 4e1e36d7658..24cfb477600 100644
--- a/intern/cycles/render/mesh.cpp
+++ b/intern/cycles/render/mesh.cpp
@@ -73,6 +73,37 @@ void Mesh::Curve::bounds_grow(const int k, const float3 *curve_keys, const float
 	bounds.grow(upper, mr);
 }
 
+void Mesh::Curve::bounds_grow(const int k,
+                              const float3 *curve_keys,
+                              const float *curve_radius,
+                              const Transform& aligned_space,
+                              BoundBox& bounds) const
+{
+	float3 P[4];
+
+	P[0] = curve_keys[max(first_key + k - 1,first_key)];
+	P[1] = curve_keys[first_key + k];
+	P[2] = curve_keys[first_key + k + 1];
+	P[3] = curve_keys[min(first_key + k + 2, first_key + num_keys - 1)];
+
+	P[0] = transform_point(&aligned_space, P[0]);
+	P[1] = transform_point(&aligned_space, P[1]);
+	P[2] = transform_point(&aligned_space, P[2]);
+	P[3] = transform_point(&aligned_space, P[3]);
+
+	float3 lower;
+	float3 upper;
+
+	curvebounds(&lower.x, &upper.x, P, 0);
+	curvebounds(&lower.y, &upper.y, P, 1);
+	curvebounds(&lower.z, &upper.z, P, 2);
+
+	float mr = max(curve_radius[first_key + k], curve_radius[first_key + k + 1]);
+
+	bounds.grow(lower, mr);
+	bounds.grow(upper, mr);
+}
+
 /* Mesh */
 
 NODE_DEFINE(Mesh)
@@ -522,7 +553,11 @@ void Mesh::pack_curves(Scene *scene, float4 *curve_key_co, float4 *curve_data, s
 	}
 }
 
-void Mesh::compute_bvh(SceneParams *params, Progress *progress, int n, int total)
+void Mesh::compute_bvh(DeviceScene * /*dscene*/,
+                       SceneParams *params,
+                       Progress *progress,
+                       int n,
+                       int total)
 {
 	if(progress->get_cancel())
 		return;
@@ -553,6 +588,7 @@ void Mesh::compute_bvh(SceneParams *params, Progress *progress, int n, int total
 			BVHParams bparams;
 			bparams.use_spatial_split = params->use_bvh_spatial_split;
 			bparams.use_qbvh = params->use_qbvh;
+			bparams.use_unaligned_nodes = false;
 
 			delete bvh;
 			bvh = BVH::create(bparams, objects);
@@ -1186,6 +1222,7 @@ void MeshManager::device_update_bvh(Device *device, DeviceScene *dscene, Scene *
 	bparams.top_level = true;
 	bparams.use_qbvh = scene->params.use_qbvh;
 	bparams.use_spatial_split = scene->params.use_bvh_spatial_split;
+	bparams.use_unaligned_nodes = false;
 
 	delete bvh;
 	bvh = BVH::create(bparams, scene->objects);
@@ -1399,6 +1436,7 @@ void MeshManager::device_update(Device *device, DeviceScene *dscene, Scene *scen
 		if(mesh->need_update) {
 			pool.push(function_bind(&Mesh::compute_bvh,
 			                        mesh,
+			                        dscene,
 			                        &scene->params,
 			                        &progress,
 			                        i,
diff --git a/intern/cycles/render/mesh.h b/intern/cycles/render/mesh.h
index bc3d30af499..0aea55544f2 100644
--- a/intern/cycles/render/mesh.h
+++ b/intern/cycles/render/mesh.h
@@ -72,7 +72,15 @@ public:
 
 		int num_segments() { return num_keys - 1; }
 
-		void bounds_grow(const int k, const float3 *curve_keys, const float *curve_radius, BoundBox& bounds) const;
+		void bounds_grow(const int k,
+		                 const float3 *curve_keys,
+		                 const float *curve_radius,
+		                 BoundBox& bounds) const;
+		void bounds_grow(const int k,
+		                 const float3 *curve_keys,
+		                 const float *curve_radius,
+		                 const Transform& aligned_space,
+		                 BoundBox& bounds) const;
 	};
 
 	Curve get_curve(size_t i) const
@@ -172,7 +180,11 @@ public:
 	                size_t vert_offset,
 	                size_t tri_offset);
 	void pack_curves(Scene *scene, float4 *curve_key_co, float4 *curve_data, size_t curvekey_offset);
-	void compute_bvh(SceneParams *params, Progress *progress, int n, int total);
+	void compute_bvh(DeviceScene *dscene,
+	                 SceneParams *params,
+	                 Progress *progress,
+	                 int n,
+	                 int total);
 
 	bool need_attribute(Scene *scene, AttributeStandard std);
 	bool need_attribute(Scene *scene, ustring name);