NanoVDB: CUDA connected-components labeling for ValueOnIndex grids - #2261
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Add nanovdb::tools::cuda::ConnectedComponents, which labels the active voxels
of a NanoVDB ValueOnIndex grid by 6-connectivity: two active voxels share a
label iff they are connected through a path of adjacent active voxels. The
public getVoxelLabelsAndCount() returns a per-active-voxel dense component id
in [0,N) plus the component count N.
The implementation is hierarchical:
- per-leaf Shiloach-Vishkin union-find in shared memory (one block per leaf),
yielding each leaf-local component's voxel Mask<3> and six face bitmasks;
- cross-leaf edge detection by intersecting touching face masks over +X/+Y/+Z
neighbours;
- a global lock-free union-find over the resulting component graph.
Also add the ex_connected_components_cuda example (rasterize an .obj to a
narrow band via MeshToGrid, drop the sqrt(3)/2-voxel surface shell via
PruneGrid, then label; a CPU union-find oracle verifies the result) and a
ConnectedComponentsMultiSphere unit test.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: Efty Sifakis <esifakis@nvidia.com>
…-voxels Accept one or more .obj files (concatenated into a single mesh) and add a --discard-surface-voxels switch: by default label the full narrow band (one component per closed surface), or prune the sqrt(3)/2-voxel barrier shell first when the switch is given. --voxel-size / --band-width replace the old positional args. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> Signed-off-by: JaeHyun Lee <jaehlee@nvidia.com>
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Summary
Adds
nanovdb::tools::cuda::ConnectedComponents— a CUDA connected-components labeling of theactive voxels of a NanoVDB
ValueOnIndexgrid (6-connectivity). Two active voxels share a labeliff they are connected through a path of adjacent active voxels. The public
getVoxelLabelsAndCount()returns a per-active-voxel dense component id in[0, N)plus thecomponent count
N.Algorithm
Hierarchical, exploiting the 8³ leaf structure:
leaf-local component's voxel
Mask<3>and six face bitmasks.neighbours (each undirected boundary visited once).
class's minimum slot, so the result is order-independent.
Also included
ex_connected_components_cuda— rasterizes an.objto a narrow band (MeshToGrid), drops the√3/2-voxel surface shell (
PruneGrid), then labels; a CPU union-find oracle independentlyverifies the GPU component count and per-voxel partition.
ConnectedComponentsMultiSphereunit test (analytic ground truth: N separated spheres → 2Nshells; overlapping pair → 2).
pendingchanges/entry.Notes
MeshToGrid,PruneGrid,voxelsToGrid) + CUB;no new third-party dependencies, no OpenVDB requirement for the example.
master.Opening as a draft to run CI and for review.
🤖 Generated with Claude Code