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4DCodeBench-synthetic-liquid-cache

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4DCodeBench synthetic — liquid solver caches

Mantaflow bakes for the liquid scenes of 4DCodeBench/4DCodeBench-synthetic, reduced to the grids the evaluation actually reads. Access is granted case by case.

What is here

One folder per case. Each holds cache/, named to match the "cache" key in that world's solver/manifest.json, plus a CACHE.json recording the frames present, the grids kept and dropped, and a per-file md5.

<case>/
  CACHE.json
  cache/
    config/config_%04d.uni
    data/fluid_data_%04d.vdb

Installing one

  1. Take <case>/world.h5 from 4DCodeBench/4DCodeBench-synthetic and unpack it.
  2. Put this repo's <case>/cache/ at world/solver/cache/ — the sibling of manifest.json, named as its cache key says.
  3. check_world(world/) passes.

What was removed, and what that costs

The bake directories total 89.1 GB. Only velocity, and phi where the bake has it, are read by tools/export/mantaflow.py and tools/export/liquid_tracks_ref.py; the other ten grids are not read by anything. Keeping only those is lossless — the dense arrays are byte-identical before and after — and brings the set to 4.36 GB.

The one real loss is the FLIP particle cloud (particles), 33 GB on its own. Nothing in the evaluation reads it. Dropping it disables liquid_tracks_ref.py --snap, and it means Blender cannot resume or re-render the liquid from these files. They are for track extraction. The full bakes are retained offline.

There is no lossy version and there should not be. Perturbing the velocity field to int8 — under half a voxel in the median — moves a minority of advected tracers by 34 m on a 130-frame take of dam_break, a full domain diagonal. Cached flow at this resolution amplifies any error you introduce, so the lossless guarantee is load-bearing.

Caveats

  • Files were rewritten by OpenVDB 10.0.1 (file format 224; Blender 5.2 wrote 225). Grid contents are bit-identical; the container bytes are not. CACHE.json carries md5s of what is here.
  • Frame coverage is not always the clip length — slit_spillway_plunge_basin has 300 cache frames against a 302-frame clip. Read frames_present rather than inferring it.
  • liquid_jet_free_surface_splash and poured_water_glass_filling_splash come from the complete bakes held offline; their config/ is partial or absent, which affects only Blender's own bookkeeping, not the grids.
  • mantaflow.py reads phi, and nine of the twelve bakes were made with cache_type = "ALL" and contain no phi grid at all. That generator cannot run on them. liquid_tracks_ref.py, which needs only velocity, runs on all twelve.
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