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bbcb9c68c9
blender/intern/cycles/bvh/bvh_build.cpp
Sergey Sharybin bbcb9c68c9 Cycles: Resolve ridiculous amount of memory used by spatial split builder 
This was only visible on systems with lots of threads and root of the issue
was that we've been pre-allocating too much memory for all the threads.

Now we only pre-allocate data for the main thread and rest of the threads
does allocation on-demand.

This brings down memory usage from 36Gig to 6.9Gig when building spatial
split for the Bunny.blend file on our Intel beast.

Originally regression was happened by the threaded spacial split builder
commit.
2016-04-13 14:25:21 +02:00

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/*
* 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_binning.h"
#include "bvh_build.h"
#include "bvh_node.h"
#include "bvh_params.h"
#include "bvh_split.h"
#include "mesh.h"
#include "object.h"
#include "scene.h"
#include "curves.h"
#include "util_debug.h"
#include "util_foreach.h"
#include "util_logging.h"
#include "util_progress.h"
#include "util_stack_allocator.h"
#include "util_simd.h"
#include "util_time.h"
CCL_NAMESPACE_BEGIN
/* BVH Build Task */
class BVHBuildTask : public Task {
public:
BVHBuildTask(BVHBuild *build,
InnerNode *node,
int child,
const BVHObjectBinning& range,
int level)
: range_(range)
{
run = function_bind(&BVHBuild::thread_build_node,
build,
node,
child,
&range_,
level);
}
private:
BVHObjectBinning range_;
};
class BVHSpatialSplitBuildTask : public Task {
public:
BVHSpatialSplitBuildTask(BVHBuild *build,
InnerNode *node,
int child,
const BVHRange& range,
const vector<BVHReference>& references,
int level)
: range_(range),
references_(references.begin() + range.start(),
references.begin() + range.end())
{
range_.set_start(0);
run = function_bind(&BVHBuild::thread_build_spatial_split_node,
build,
node,
child,
&range_,
&references_,
level,
_1);
}
private:
BVHRange range_;
vector<BVHReference> references_;
};
/* Constructor / Destructor */
BVHBuild::BVHBuild(const vector<Object*>& objects_,
array<int>& prim_type_,
array<int>& prim_index_,
array<int>& prim_object_,
const BVHParams& params_,
Progress& progress_)
: objects(objects_),
prim_type(prim_type_),
prim_index(prim_index_),
prim_object(prim_object_),
params(params_),
progress(progress_),
progress_start_time(0.0)
{
spatial_min_overlap = 0.0f;
}
BVHBuild::~BVHBuild()
{
}
/* Adding References */
void BVHBuild::add_reference_mesh(BoundBox& root, BoundBox& center, Mesh *mesh, int i)
{
Attribute *attr_mP = NULL;
if(mesh->has_motion_blur())
attr_mP = mesh->attributes.find(ATTR_STD_MOTION_VERTEX_POSITION);
for(uint j = 0; j < mesh->triangles.size(); j++) {
Mesh::Triangle t = mesh->triangles[j];
BoundBox bounds = BoundBox::empty;
PrimitiveType type = PRIMITIVE_TRIANGLE;
t.bounds_grow(&mesh->verts[0], bounds);
/* motion triangles */
if(attr_mP) {
size_t mesh_size = mesh->verts.size();
size_t steps = mesh->motion_steps - 1;
float3 *vert_steps = attr_mP->data_float3();
for(size_t i = 0; i < steps; i++)
t.bounds_grow(vert_steps + i*mesh_size, bounds);
type = PRIMITIVE_MOTION_TRIANGLE;
}
if(bounds.valid()) {
references.push_back(BVHReference(bounds, j, i, type));
root.grow(bounds);
center.grow(bounds.center2());
}
}
Attribute *curve_attr_mP = NULL;
if(mesh->has_motion_blur())
curve_attr_mP = mesh->curve_attributes.find(ATTR_STD_MOTION_VERTEX_POSITION);
for(uint j = 0; j < mesh->curves.size(); j++) {
Mesh::Curve curve = mesh->curves[j];
PrimitiveType type = PRIMITIVE_CURVE;
for(int k = 0; k < curve.num_keys - 1; k++) {
BoundBox bounds = BoundBox::empty;
curve.bounds_grow(k, &mesh->curve_keys[0], bounds);
/* motion curve */
if(curve_attr_mP) {
size_t mesh_size = mesh->curve_keys.size();
size_t steps = mesh->motion_steps - 1;
float4 *key_steps = curve_attr_mP->data_float4();
for(size_t i = 0; i < steps; i++)
curve.bounds_grow(k, key_steps + i*mesh_size, bounds);
type = PRIMITIVE_MOTION_CURVE;
}
if(bounds.valid()) {
int packed_type = PRIMITIVE_PACK_SEGMENT(type, k);
references.push_back(BVHReference(bounds, j, i, packed_type));
root.grow(bounds);
center.grow(bounds.center2());
}
}
}
}
void BVHBuild::add_reference_object(BoundBox& root, BoundBox& center, Object *ob, int i)
{
references.push_back(BVHReference(ob->bounds, -1, i, 0));
root.grow(ob->bounds);
center.grow(ob->bounds.center2());
}
static size_t count_curve_segments(Mesh *mesh)
{
size_t num = 0, num_curves = mesh->curves.size();
for(size_t i = 0; i < num_curves; i++)
num += mesh->curves[i].num_keys - 1;
return num;
}
void BVHBuild::add_references(BVHRange& root)
{
/* reserve space for references */
size_t num_alloc_references = 0;
foreach(Object *ob, objects) {
if(params.top_level) {
if(!ob->mesh->is_instanced()) {
num_alloc_references += ob->mesh->triangles.size();
num_alloc_references += count_curve_segments(ob->mesh);
}
else
num_alloc_references++;
}
else {
num_alloc_references += ob->mesh->triangles.size();
num_alloc_references += count_curve_segments(ob->mesh);
}
}
references.reserve(num_alloc_references);
/* 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->is_instanced())
add_reference_mesh(bounds, center, ob->mesh, i);
else
add_reference_object(bounds, center, ob, i);
}
else
add_reference_mesh(bounds, center, ob->mesh, i);
i++;
if(progress.get_cancel()) return;
}
/* happens mostly on empty meshes */
if(!bounds.valid())
bounds.grow(make_float3(0.0f, 0.0f, 0.0f));
root = BVHRange(bounds, center, 0, references.size());
}
/* Build */
BVHNode* BVHBuild::run()
{
BVHRange root;
/* add references */
add_references(root);
if(progress.get_cancel())
return NULL;
/* init spatial splits */
if(params.top_level) {
/* NOTE: Technically it is supported by the builder but it's not really
* optimized for speed yet and not really clear yet if it has measurable
* improvement on render time. Needs some extra investigation before
* enabling spatial split for top level BVH.
*/
params.use_spatial_split = false;
}
spatial_min_overlap = root.bounds().safe_area() * params.spatial_split_alpha;
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(TaskScheduler::num_threads() + 1);
size_t num_bins = max(root.size(), (int)BVHParams::NUM_SPATIAL_BINS) - 1;
foreach(BVHSpatialStorage &storage, spatial_storage) {
storage.right_bounds.clear();
}
spatial_storage[0].right_bounds.resize(num_bins);
}
spatial_free_index = 0;
/* init progress updates */
double build_start_time;
build_start_time = progress_start_time = time_dt();
progress_count = 0;
progress_total = references.size();
progress_original_total = progress_total;
prim_type.resize(references.size());
prim_index.resize(references.size());
prim_object.resize(references.size());
/* build recursively */
BVHNode *rootnode;
if(params.use_spatial_split) {
/* Perform multithreaded spatial split build. */
rootnode = build_node(root, &references, 0, 0);
task_pool.wait_work();
}
else {
/* Perform multithreaded binning build. */
BVHObjectBinning rootbin(root, (references.size())? &references[0]: NULL);
rootnode = build_node(rootbin, 0);
task_pool.wait_work();
}
/* delete if we canceled */
if(rootnode) {
if(progress.get_cancel()) {
rootnode->deleteSubtree();
rootnode = NULL;
VLOG(1) << "BVH build cancelled.";
}
else {
/*rotate(rootnode, 4, 5);*/
rootnode->update_visibility();
}
if(rootnode != NULL) {
VLOG(1) << "BVH build statistics:\n"
<< " Build time: " << time_dt() - build_start_time << "\n"
<< " Total number of nodes: "
<< rootnode->getSubtreeSize(BVH_STAT_NODE_COUNT) << "\n"
<< " Number of inner nodes: "
<< rootnode->getSubtreeSize(BVH_STAT_INNER_COUNT) << "\n"
<< " Number of leaf nodes: "
<< rootnode->getSubtreeSize(BVH_STAT_LEAF_COUNT) << "\n"
<< " Allocation slop factor: "
<< ((prim_type.capacity() != 0)
? (float)prim_type.size() / prim_type.capacity()
: 1.0f) << "\n";
}
}
return rootnode;
}
void BVHBuild::progress_update()
{
if(time_dt() - progress_start_time < 0.25)
return;
double progress_start = (double)progress_count/(double)progress_total;
double duplicates = (double)(progress_total - progress_original_total)/(double)progress_total;
string msg = string_printf("Building BVH %.0f%%, duplicates %.0f%%",
progress_start * 100.0, duplicates * 100.0);
progress.set_substatus(msg);
progress_start_time = time_dt();
}
void BVHBuild::thread_build_node(InnerNode *inner,
int child,
BVHObjectBinning *range,
int level)
{
if(progress.get_cancel())
return;
/* build nodes */
BVHNode *node = build_node(*range, level);
/* set child in inner node */
inner->children[child] = node;
/* update progress */
if(range->size() < THREAD_TASK_SIZE) {
/*rotate(node, INT_MAX, 5);*/
thread_scoped_lock lock(build_mutex);
progress_count += range->size();
progress_update();
}
}
void BVHBuild::thread_build_spatial_split_node(InnerNode *inner,
int child,
BVHRange *range,
vector<BVHReference> *references,
int level,
int thread_id)
{
if(progress.get_cancel()) {
return;
}
/* build nodes */
BVHNode *node = build_node(*range, references, level, thread_id);
/* set child in inner node */
inner->children[child] = node;
}
bool BVHBuild::range_within_max_leaf_size(const BVHRange& range,
const vector<BVHReference>& references) const
{
size_t size = range.size();
size_t max_leaf_size = max(params.max_triangle_leaf_size, params.max_curve_leaf_size);
if(size > max_leaf_size)
return false;
size_t num_triangles = 0;
size_t num_curves = 0;
size_t num_motion_curves = 0;
for(int i = 0; i < size; i++) {
const BVHReference& ref = references[range.start() + i];
if(ref.prim_type() & PRIMITIVE_CURVE)
num_curves++;
if(ref.prim_type() & PRIMITIVE_MOTION_CURVE)
num_motion_curves++;
else if(ref.prim_type() & PRIMITIVE_ALL_TRIANGLE)
num_triangles++;
}
return (num_triangles < params.max_triangle_leaf_size) &&
(num_curves < params.max_curve_leaf_size) &&
(num_motion_curves < params.max_curve_leaf_size);
}
/* multithreaded binning builder */
BVHNode* BVHBuild::build_node(const BVHObjectBinning& range, int level)
{
size_t size = range.size();
float leafSAH = params.sah_primitive_cost * range.leafSAH;
float splitSAH = params.sah_node_cost * range.bounds().half_area() + params.sah_primitive_cost * range.splitSAH;
/* have at least one inner node on top level, for performance and correct
* visibility tests, since object instances do not check visibility flag */
if(!(range.size() > 0 && params.top_level && level == 0)) {
/* make leaf node when threshold reached or SAH tells us */
if((params.small_enough_for_leaf(size, level)) ||
(range_within_max_leaf_size(range, references) && leafSAH < splitSAH))
{
return create_leaf_node(range, references);
}
}
/* perform split */
BVHObjectBinning left, right;
range.split(&references[0], left, right);
/* create inner node. */
InnerNode *inner;
if(range.size() < THREAD_TASK_SIZE) {
/* local build */
BVHNode *leftnode = build_node(left, level + 1);
BVHNode *rightnode = build_node(right, level + 1);
inner = new InnerNode(range.bounds(), leftnode, rightnode);
}
else {
/* threaded build */
inner = new InnerNode(range.bounds());
task_pool.push(new BVHBuildTask(this, inner, 0, left, level + 1), true);
task_pool.push(new BVHBuildTask(this, inner, 1, right, level + 1), true);
}
return inner;
}
/* multithreaded spatial split builder */
BVHNode* BVHBuild::build_node(const BVHRange& range,
vector<BVHReference> *references,
int level,
int thread_id)
{
/* Update progress.
*
* TODO(sergey): Currently it matches old behavior, but we can move it to the
* task thread (which will mimic non=split builder) and save some CPU ticks
* on checking cancel status.
*/
progress_update();
if(progress.get_cancel()) {
return NULL;
}
/* Small enough or too deep => create leaf. */
if(!(range.size() > 0 && params.top_level && level == 0)) {
if(params.small_enough_for_leaf(range.size(), level)) {
progress_count += range.size();
return create_leaf_node(range, *references);
}
}
/* Perform splitting test. */
BVHSpatialStorage *storage = &spatial_storage[thread_id];
BVHMixedSplit split(this, storage, range, references, level);
if(!(range.size() > 0 && params.top_level && level == 0)) {
if(split.no_split) {
progress_count += range.size();
return create_leaf_node(range, *references);
}
}
/* Do split. */
BVHRange left, right;
split.split(this, left, right, range);
progress_total += left.size() + right.size() - range.size();
/* Create inner node. */
InnerNode *inner;
if(range.size() < THREAD_TASK_SIZE) {
/* Local build. */
/* Build left node. */
vector<BVHReference> copy(references->begin() + right.start(),
references->begin() + right.end());
right.set_start(0);
BVHNode *leftnode = build_node(left, references, level + 1, thread_id);
/* Build right node. */
BVHNode *rightnode = build_node(right, &copy, level + 1, thread_id);
inner = new InnerNode(range.bounds(), leftnode, rightnode);
}
else {
/* Threaded build. */
inner = new InnerNode(range.bounds());
task_pool.push(new BVHSpatialSplitBuildTask(this,
inner,
0,
left,
*references,
level + 1),
true);
task_pool.push(new BVHSpatialSplitBuildTask(this,
inner,
1,
right,
*references,
level + 1),
true);
}
return inner;
}
/* Create Nodes */
BVHNode *BVHBuild::create_object_leaf_nodes(const BVHReference *ref, int start, int num)
{
if(num == 0) {
BoundBox bounds = BoundBox::empty;
return new LeafNode(bounds, 0, 0, 0);
}
else if(num == 1) {
assert(start < prim_type.size());
prim_type[start] = ref->prim_type();
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, start, mid);
BVHNode *leaf1 = create_object_leaf_nodes(ref+mid, start+mid, num-mid);
BoundBox bounds = BoundBox::empty;
bounds.grow(leaf0->m_bounds);
bounds.grow(leaf1->m_bounds);
return new InnerNode(bounds, leaf0, leaf1);
}
}
BVHNode* BVHBuild::create_leaf_node(const BVHRange& range,
const vector<BVHReference>& references)
{
/* This is a bit overallocating here (considering leaf size into account),
* but chunk-based re-allocation in vector makes it difficult to use small
* size of stack storage here. Some tweaks are possible tho.
*
* NOTES:
* - If the size is too big, we'll have inefficient stack usage,
* and lots of cache misses.
* - If the size is too small, then we can run out of memory
* allowed to be used by vector.
* In practice it wouldn't mean crash, just allocator will fallback
* to heap which is slower.
* - Optimistic re-allocation in STL could jump us out of stack usage
* because re-allocation happens in chunks and size of those chunks we
* can not control.
*/
typedef StackAllocator<256, int> LeafStackAllocator;
vector<int, LeafStackAllocator> p_type[PRIMITIVE_NUM_TOTAL];
vector<int, LeafStackAllocator> p_index[PRIMITIVE_NUM_TOTAL];
vector<int, LeafStackAllocator> p_object[PRIMITIVE_NUM_TOTAL];
/* TODO(sergey): In theory we should be able to store references. */
vector<BVHReference, LeafStackAllocator> object_references;
uint visibility[PRIMITIVE_NUM_TOTAL] = {0};
/* NOTE: Keep initializtion in sync with actual number of primitives. */
BoundBox bounds[PRIMITIVE_NUM_TOTAL] = {BoundBox::empty,
BoundBox::empty,
BoundBox::empty,
BoundBox::empty};
int ob_num = 0;
/* Fill in per-type type/index array. */
for(int i = 0; i < range.size(); i++) {
const BVHReference& ref = references[range.start() + i];
if(ref.prim_index() != -1) {
int type_index = bitscan(ref.prim_type() & PRIMITIVE_ALL);
p_type[type_index].push_back(ref.prim_type());
p_index[type_index].push_back(ref.prim_index());
p_object[type_index].push_back(ref.prim_object());
bounds[type_index].grow(ref.bounds());
visibility[type_index] |= objects[ref.prim_object()]->visibility;
}
else {
object_references.push_back(ref);
ob_num++;
}
}
/* Create leaf nodes for every existing primitive.
*
* Here we write primitive types, indices and objects to a temporary array.
* This way we keep all the heavy memory allocation code outside of the
* thread lock in the case of spatial split building.
*
* TODO(sergey): With some pointer trickery we can write directly to the
* destination buffers for the non-spatial split BVH.
*/
BVHNode *leaves[PRIMITIVE_NUM_TOTAL + 1] = {NULL};
int num_leaves = 0;
size_t start_index = 0;
vector<int, LeafStackAllocator> local_prim_type,
local_prim_index,
local_prim_object;
for(int i = 0; i < PRIMITIVE_NUM_TOTAL; ++i) {
int num = (int)p_type[i].size();
local_prim_type.resize(start_index + num);
local_prim_index.resize(start_index + num);
local_prim_object.resize(start_index + num);
if(num != 0) {
assert(p_type[i].size() == p_index[i].size());
assert(p_type[i].size() == p_object[i].size());
for(int j = 0; j < num; ++j) {
const int index = start_index + j;
local_prim_type[index] = p_type[i][j];
local_prim_index[index] = p_index[i][j];
local_prim_object[index] = p_object[i][j];
}
leaves[num_leaves++] = new LeafNode(bounds[i],
visibility[i],
start_index,
start_index + num);
start_index += num;
}
}
/* Get size of new data to be copied to the packed arrays. */
const int num_new_leaf_data = start_index;
const size_t new_leaf_data_size = sizeof(int) * num_new_leaf_data;
/* Copy actual data to the packed array. */
if(params.use_spatial_split) {
spatial_spin_lock.lock();
/* We use first free index in the packed arrays and mode pointer to the
* end of the current range.
*
* This doesn't give deterministic packed arrays, but it shouldn't really
* matter because order of children in BVH is deterministic.
*/
start_index = spatial_free_index;
spatial_free_index += range.size();
/* Extend an array when needed. */
const size_t range_end = start_index + range.size();
if(prim_type.size() < range_end) {
/* Avoid extra re-allocations by pre-allocating bigger array in an
* advance.
*/
if(range_end >= prim_type.capacity()) {
float progress = (float)progress_count/(float)progress_total;
float factor = (1.0f - progress);
const size_t reserve = (size_t)(range_end + (float)range_end*factor);
prim_type.reserve(reserve);
prim_index.reserve(reserve);
prim_object.reserve(reserve);
}
prim_type.resize(range_end);
prim_index.resize(range_end);
prim_object.resize(range_end);
}
/* Perform actual data copy. */
if(new_leaf_data_size > 0) {
memcpy(&prim_type[start_index], &local_prim_type[0], new_leaf_data_size);
memcpy(&prim_index[start_index], &local_prim_index[0], new_leaf_data_size);
memcpy(&prim_object[start_index], &local_prim_object[0], new_leaf_data_size);
}
spatial_spin_lock.unlock();
}
else {
/* For the regular BVH builder we simply copy new data starting at the
* range start. This is totally thread-safe, all threads are living
* inside of their own range.
*/
start_index = range.start();
if(new_leaf_data_size > 0) {
memcpy(&prim_type[start_index], &local_prim_type[0], new_leaf_data_size);
memcpy(&prim_index[start_index], &local_prim_index[0], new_leaf_data_size);
memcpy(&prim_object[start_index], &local_prim_object[0], new_leaf_data_size);
}
}
/* So far leaves were created with the zero-based index in an arrays,
* here we modify the indices to correspond to actual packed array start
* index.
*/
for(int i = 0; i < num_leaves; ++i) {
LeafNode *leaf = (LeafNode *)leaves[i];
leaf->m_lo += start_index;
leaf->m_hi += start_index;
}
/* Create leaf node for object. */
if(num_leaves == 0 || ob_num) {
/* Only create object leaf nodes if there are objects or no other
* nodes created.
*/
const BVHReference *ref = (ob_num)? &object_references[0]: NULL;
leaves[num_leaves] = create_object_leaf_nodes(ref,
start_index + num_new_leaf_data,
ob_num);
++num_leaves;
}
if(num_leaves == 1) {
/* Simplest case: single leaf, just return it.
* In all the rest cases we'll be creating intermediate inner node with
* an appropriate bounding box.
*/
return leaves[0];
}
else if(num_leaves == 2) {
return new InnerNode(range.bounds(), leaves[0], leaves[1]);
}
else if(num_leaves == 3) {
BoundBox inner_bounds = merge(leaves[1]->m_bounds, leaves[2]->m_bounds);
BVHNode *inner = new InnerNode(inner_bounds, leaves[1], leaves[2]);
return new InnerNode(range.bounds(), leaves[0], inner);
} else {
/* Shpuld be doing more branches if more primitive types added. */
assert(num_leaves <= 5);
BoundBox inner_bounds_a = merge(leaves[0]->m_bounds, leaves[1]->m_bounds);
BoundBox inner_bounds_b = merge(leaves[2]->m_bounds, leaves[3]->m_bounds);
BVHNode *inner_a = new InnerNode(inner_bounds_a, leaves[0], leaves[1]);
BVHNode *inner_b = new InnerNode(inner_bounds_b, leaves[2], leaves[3]);
BoundBox inner_bounds_c = merge(inner_a->m_bounds, inner_b->m_bounds);
BVHNode *inner_c = new InnerNode(inner_bounds_c, inner_a, inner_b);
if(num_leaves == 5) {
return new InnerNode(range.bounds(), inner_c, leaves[4]);
}
return inner_c;
}
#undef MAX_ITEMS_PER_LEAF
}
/* Tree Rotations */
void BVHBuild::rotate(BVHNode *node, int max_depth, int iterations)
{
/* 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::rotate(BVHNode *node, int max_depth)
{
/* nothing to rotate if we reached a leaf node. */
if(node->is_leaf() || max_depth < 0)
return;
InnerNode *parent = (InnerNode*)node;
/* rotate all children first */
for(size_t c = 0; c < 2; c++)
rotate(parent->children[c], max_depth-1);
/* compute current area of all children */
BoundBox bounds0 = parent->children[0]->m_bounds;
BoundBox bounds1 = parent->children[1]->m_bounds;
float area0 = bounds0.half_area();
float area1 = bounds1.half_area();
float4 child_area = make_float4(area0, area1, 0.0f, 0.0f);
/* 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, best_target = -1, best_other = -1;
for(size_t c = 0; c < 2; c++) {
/* ignore leaf nodes as we cannot descent into */
if(parent->children[c]->is_leaf())
continue;
InnerNode *child = (InnerNode*)parent->children[c];
BoundBox& other = (c == 0)? bounds1: bounds0;
/* transpose child bounds */
BoundBox target0 = child->children[0]->m_bounds;
BoundBox target1 = child->children[1]->m_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];
if(min(cost0,cost1) < best_cost) {
best_child = (int)c;
best_other = (int)(1-c);
if(cost0 < cost1) {
best_cost = cost0;
best_target = 0;
}
else {
best_cost = cost0;
best_target = 1;
}
}
}
/* if we did not find a swap that improves the SAH then do nothing */
if(best_cost >= 0)
return;
assert(best_child == 0 || best_child == 1);
assert(best_target != -1);
/* perform the best found tree rotation */
InnerNode *child = (InnerNode*)parent->children[best_child];
swap(parent->children[best_other], child->children[best_target]);
child->m_bounds = merge(child->children[0]->m_bounds, child->children[1]->m_bounds);
}
CCL_NAMESPACE_END
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