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Sculpt: Simplify and optimize BVH build node partitioning

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Use `std::partition` instead of implementing something similar
ourselves. This is much easier to understand, and it's also much
faster and requires less memory during the build.

I observed a change in the runtime building a 16 million face
BVH from 492 to 389 ms, a 1.27x improvement (with a Ryzen
7950x).

`std::partition` is not multithreaded. I expect there would be
some improvement from multithreading this, at least for the
first few splits.

Currently this only applies to Mesh sculpting.

Pull Request: https://projects.blender.org/blender/blender/pulls/127332
This commit is contained in:
Hans Goudey
2024-09-09 15:16:28 +02:00
committed by Hans Goudey
parent 577630d24f
commit eee34de007
1 changed files with 20 additions and 59 deletions
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79
source/blender/blenkernel/intern/pbvh.cc
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@@ -111,56 +111,24 @@ static int partition_prim_indices(MutableSpan<int> prim_indices,
return lo2;
}
static int partition_prim_indices(MutableSpan<int> face_indices,
MutableSpan<int> prim_scratch,
int lo,
int hi,
int axis,
float mid,
const Span<float3> face_centers)
static int partition_along_axis(const Span<float3> face_centers,
MutableSpan<int> faces,
const int axis,
const float middle)
{
for (int i = lo; i < hi; i++) {
prim_scratch[i - lo] = face_indices[i];
}
int lo2 = lo, hi2 = hi - 1;
int i1 = lo, i2 = 0;
while (i1 < hi) {
const int face_i = prim_scratch[i2];
const float3 &face_center = face_centers[prim_scratch[i2]];
const bool side = face_center[axis] >= mid;
while (i1 < hi && prim_scratch[i2] == face_i) {
face_indices[side ? hi2-- : lo2++] = prim_scratch[i2];
i1++;
i2++;
}
}
return lo2;
const int *split = std::partition(faces.begin(), faces.end(), [&](const int face) {
const float3 &center = face_centers[face];
return center[axis] >= middle;
});
return split - faces.begin();
}
static int partition_indices_material_faces(MutableSpan<int> face_indices,
const Span<int> material_indices,
const int lo,
const int hi)
static int partition_material_indices(const Span<int> material_indices, MutableSpan<int> faces)
{
int i = lo, j = hi;
for (;;) {
const int first = face_indices[lo];
for (; face_materials_match(material_indices, first, face_indices[i]); i++) {
/* pass */
}
for (; !face_materials_match(material_indices, first, face_indices[j]); j--) {
/* pass */
}
if (!(i < j)) {
return i;
}
std::swap(face_indices[i], face_indices[j]);
i++;
}
const int first = material_indices[faces.first()];
const int *split = std::partition(
faces.begin(), faces.end(), [&](const int face) { return material_indices[face] == first; });
return split - faces.begin();
}
/* Returns the index of the first element on the right of the partition */
@@ -274,7 +242,6 @@ static void build_nodes_recursive_mesh(const Span<int> material_indices,
const Span<float3> face_centers,
const int prim_offset,
const int prims_num,
MutableSpan<int> prim_scratch,
const int depth,
MutableSpan<int> prim_indices,
Vector<MeshNode> &nodes)
@@ -322,18 +289,15 @@ static void build_nodes_recursive_mesh(const Span<int> material_indices,
const int axis = math::dominant_axis(bounds.max - bounds.min);
/* Partition primitives along that axis */
end = partition_prim_indices(prim_indices,
prim_scratch,
prim_offset,
prim_offset + prims_num,
axis,
math::midpoint(bounds.min[axis], bounds.max[axis]),
face_centers);
end = prim_offset + partition_along_axis(face_centers,
prim_indices.slice(prim_offset, prims_num),
axis,
math::midpoint(bounds.min[axis], bounds.max[axis]));
}
else {
/* Partition primitives by material */
end = partition_indices_material_faces(
prim_indices, material_indices, prim_offset, prim_offset + prims_num - 1);
end = prim_offset +
partition_material_indices(material_indices, prim_indices.slice(prim_offset, prims_num));
}
/* Build children */
@@ -344,7 +308,6 @@ static void build_nodes_recursive_mesh(const Span<int> material_indices,
face_centers,
prim_offset,
end - prim_offset,
prim_scratch,
depth + 1,
prim_indices,
nodes);
@@ -355,7 +318,6 @@ static void build_nodes_recursive_mesh(const Span<int> material_indices,
face_centers,
end,
prim_offset + prims_num - end,
prim_scratch,
depth + 1,
prim_indices,
nodes);
@@ -423,7 +385,6 @@ std::unique_ptr<Tree> build_mesh(const Mesh &mesh)
face_centers,
0,
faces.size(),
Array<int>(pbvh->prim_indices_.size()),
0,
pbvh->prim_indices_,
nodes);