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blender-archive/source/blender/blenkernel/BKE_volume_to_mesh.hh
Hans Goudey 16fbadde36 Mesh: Replace MLoop struct with generic attributes
Implements #102359.

Split the `MLoop` struct into two separate integer arrays called
`corner_verts` and `corner_edges`, referring to the vertex each corner
is attached to and the next edge around the face at each corner. These
arrays can be sliced to give access to the edges or vertices in a face.
Then they are often referred to as "poly_verts" or "poly_edges".

The main benefits are halving the necessary memory bandwidth when only
one array is used and simplifications from using regular integer indices
instead of a special-purpose struct.

The commit also starts a renaming from "loop" to "corner" in mesh code.

Like the other mesh struct of array refactors, forward compatibility is
kept by writing files with the older format. This will be done until 4.0
to ease the transition process.

Looking at a small portion of the patch should give a good impression
for the rest of the changes. I tried to make the changes as small as
possible so it's easy to tell the correctness from the diff. Though I
found Blender developers have been very inventive over the last decade
when finding different ways to loop over the corners in a face.

For performance, nearly every piece of code that deals with `Mesh` is
slightly impacted. Any algorithm that is memory bottle-necked should
see an improvement. For example, here is a comparison of interpolating
a vertex float attribute to face corners (Ryzen 3700x):

**Before** (Average: 3.7 ms, Min: 3.4 ms)
```
threading::parallel_for(loops.index_range(), 4096, [&](IndexRange range) {
  for (const int64_t i : range) {
    dst[i] = src[loops[i].v];
  }
});
```

**After** (Average: 2.9 ms, Min: 2.6 ms)
```
array_utils::gather(src, corner_verts, dst);
```

That's an improvement of 28% to the average timings, and it's also a
simplification, since an index-based routine can be used instead.
For more examples using the new arrays, see the design task.

Pull Request: blender/blender#104424
2023-03-20 15:55:13 +01:00

72 lines
2.1 KiB
C++

/* SPDX-License-Identifier: GPL-2.0-or-later */
#pragma once
#include "BLI_span.hh"
#include "DNA_modifier_types.h"
#ifdef WITH_OPENVDB
# include <openvdb/openvdb.h>
#endif
struct Mesh;
namespace blender::bke {
struct VolumeToMeshResolution {
VolumeToMeshResolutionMode mode;
union {
float voxel_size;
float voxel_amount;
} settings;
};
#ifdef WITH_OPENVDB
/**
* The result of converting a volume grid to mesh data, in the format used by the OpenVDB API.
*/
struct OpenVDBMeshData {
std::vector<openvdb::Vec3s> verts;
std::vector<openvdb::Vec3I> tris;
std::vector<openvdb::Vec4I> quads;
bool is_empty() const
{
return verts.empty();
}
};
struct Mesh *volume_to_mesh(const openvdb::GridBase &grid,
const VolumeToMeshResolution &resolution,
float threshold,
float adaptivity);
/**
* Convert an OpenVDB volume grid to corresponding mesh data: vertex positions and quad and
* triangle indices.
*/
struct OpenVDBMeshData volume_to_mesh_data(const openvdb::GridBase &grid,
const VolumeToMeshResolution &resolution,
float threshold,
float adaptivity);
/**
* Convert mesh data from the format provided by OpenVDB into Blender's #Mesh data structure.
* This can be used to add mesh data from a grid into an existing mesh rather than merging multiple
* meshes later on.
*/
void fill_mesh_from_openvdb_data(const Span<openvdb::Vec3s> vdb_verts,
const Span<openvdb::Vec3I> vdb_tris,
const Span<openvdb::Vec4I> vdb_quads,
int vert_offset,
int poly_offset,
int loop_offset,
MutableSpan<float3> vert_positions,
MutableSpan<MPoly> polys,
MutableSpan<int> corner_verts);
#endif
} // namespace blender::bke