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gltfpack: Accelerate deduplication pass for scenes with a lot of primitives #790

Merged
merged 4 commits into from
Oct 16, 2024
Merged

gltfpack: Accelerate deduplication pass for scenes with a lot of primitives #790

merged 4 commits into from
Oct 16, 2024

Commits on Oct 16, 2024

  1. gltfpack: Avoid searching for duplicate geometry when there's none 

    While on most scenes our strategy performs reasonably well, and we
already have some potential N^2 processing elsewhere, there are cases
where the existing N^2 algorithms in the pipeline are actually
semi-linear, because mesh merging lazily and effectively aggregates most
meshes; since deduplication is the first pass, it may actually be
quadratic in the face of a scene with a lot of meshes.

A simple fix is to track the number of occurences of each hash and only
search for duplicates for meshes where this value is >1. We could of
course implement more involved tracking but for now this works just
fine.
    @zeux
    zeux committed Oct 16, 2024
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  2. gltfpack: Switch primitive cache to std::unordered_map 

    Neither std::map nor std::unordered_map are particularly good
containers, but since we're now using unordered_map for deduplication
filtering we might as well use it for the primitive cache. This requires
a custom hash function for pair<uint64, uint64>, but our hash halves are
sufficiently decorellated that a xor suffices.
    @zeux
    zeux committed Oct 16, 2024
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  3. gltfpack: Filter duplicate nodes after merging node lists 

    This almost never comes up in practice, but occasionally scenes might
have the same geometry attached to the same nodes. This results in
counterintuitive results because we create node lists with duplicate
nodes for this, which never happened before, and end up producing more
quantization sub-nodes than necessary.

For now we can just filter these attachments out to avoid redundancy.
    @zeux
    zeux committed Oct 16, 2024
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  4. gltfpack: Work around clang-tidy report 

    clang-tidy complains that we're dividing an integer by 3 before a float
cast; this is correct as the division is exact, and a cast silences it.
    @zeux
    zeux committed Oct 16, 2024
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