float BVH4i::sah (NodeRef& node, const BBox3f& bounds)
{
float f = bounds.empty() ? 0.0f : area(bounds);
if (node.isNode())
{
Node* n = node.node(nodePtr());
for (size_t c=0; c<4; c++)
f += sah(n->child(c),n->bounds(c));
return f;
}
else
{
size_t num; node.leaf(triPtr(),num);
return f*num;
}
}
// pick best split plane among all possible splits
float Bvh::pickBestSplit( unsigned& axis , float& split_pos , Bvh_Node* node , unsigned _start , unsigned _end )
{
BBox inner;
for( unsigned i = _start ; i < _end ; i++ )
inner.Union( m_bvhpri[i].m_centroid );
unsigned tri_num = _end - _start;
axis = inner.MaxAxisId();
float min_sah = FLT_MAX;
// distribute the triangles into bins
unsigned bin[BVH_SPLIT_COUNT];
BBox bbox[BVH_SPLIT_COUNT];
BBox rbox[BVH_SPLIT_COUNT-1];
memset( bin , 0 , sizeof( unsigned ) * BVH_SPLIT_COUNT );
float split_start = inner.m_Min[axis];
float split_delta = inner.Delta(axis) * BVH_INV_SPLIT_COUNT;
float inv_split_delta = 1.0f / split_delta;
for( unsigned i = _start ; i < _end ; i++ ){
int index = (int)((m_bvhpri[i].m_centroid[axis] - split_start) * inv_split_delta);
index = min( index , (int)(BVH_SPLIT_COUNT - 1) );
bin[index]++;
bbox[index].Union( m_bvhpri[i].GetBBox() );
}
rbox[BVH_SPLIT_COUNT-2].Union( bbox[BVH_SPLIT_COUNT-1] );
for( int i = BVH_SPLIT_COUNT-3; i >= 0 ; i-- )
rbox[i] = Union( rbox[i+1] , bbox[i+1] );
unsigned left = bin[0];
BBox lbox = bbox[0];
float pos = split_delta + split_start ;
for( unsigned i = 0 ; i < BVH_SPLIT_COUNT - 1 ; i++ ){
float sah_value = sah( left , tri_num - left , lbox , rbox[i] , node->bbox );
if( sah_value < min_sah ){
min_sah = sah_value;
split_pos = pos;
}
left += bin[i+1];
lbox.Union( bbox[i+1] );
pos += split_delta;
}
return min_sah;
}
float BVH4i::sah (NodeRef& node, BBox3fa bounds)
{
float f = bounds.empty() ? 0.0f : area(bounds);
if (node.isNode())
{
Node* n = node.node(nodePtr());
for (size_t c=0; c<BVH4i::N; c++)
if (n->child(c) != BVH4i::invalidNode)
f += sah(n->child(c),n->bounds(c));
return f;
}
else
{
unsigned int num; node.leaf(triPtr(),num);
return f*num;
}
}
float BVH4i::sah () {
return sah(root,bounds)/area(bounds);
}
