VoxelForge/Standalone/Research/WorldAssemblerM3/Linux9/REPORT.md

Linux9: LOD1 uniform-block proof

LOD1 now omits density fills only for 8-cell blocks proved uniform by the Core SurfaceWorld heightfield. It fills 924,232 samples across the 448 tiles (2,063 per tile), down from 19,208,000 (42,875 per tile): 95.2% fewer. All output hashes match the 4b1108b baseline.

Why the old gate excluded steps

git blame points to the original mesher gate: steps 2, 16 and 32 were disabled because the per-block classifier was expected to cost more than the smaller grids saved, and to preserve the old coarse-LOD latency. It gives no correctness reason at step 2; the history does not cite block edges, normal halos or skirts. Step 1 and step 8 were already enabled (step 8 is LOD2). This round enables step 2 for native SurfaceWorld tiles; steps 16/32 remain off pending a separate cost profile.

Proof and fallback

The tile and each proof box must stay inside one native SurfaceWorld stratum, with no overlapping edit. For every XY lattice point in the padded 8-cell box, Heightfield2D::classifyLatticeBox evaluates the exact ground and cap columns at the step-2 stride. For density min(z-ground, cap-z), minZ > maxGround && maxZ < minCap proves air; maxZ < minGround || minZ > maxCap proves solid. These extrema bound every discrete MC density sample; the box includes the cell samples and the one-sample normal halo (-1..+9). No nominal noise parameter is used as a bound.

Feature boxes that can add volume, edits, invalid input, mixed strata, and any Mixed/Unknown verdict stay on the exact fill path. The default FloatingIslands view does not use this Step-2 tile gate; its Unknown whole boxes (1,635) remain filled. The native classifier path is shared, and a W12 island audit also forced 9,216 uniform Step-2 candidates through fill-and-check.

The generic Heightfield2D::interval was sound but too broad here: it gave bounds [-2,883,809, 1,032,090] subvoxels around z=-2,114, so all 28,672 Step-2 blocks were Mixed. The exact lattice-column extrema produced useful verdicts instead.

Soundness sweep

The audit bypassed block skipping and explicitly evaluated every density sample in each candidate's padded block, asserting that none contradicted the verdict. It covered three SurfaceWorld seeds and one FloatingIslands audit:

Recipe / seed	Blocks checked	Density samples checked	Mixed fallbacks	Unknown	Violations
SurfaceWorld 0	27,479	36,574,549	1,193	0	0
SurfaceWorld 1	26,069	34,697,839	1,451	0	0
SurfaceWorld 17	26,954	35,875,774	1,718	0	0
SurfaceWorld total	80,502	107,148,162	4,362	0	0
FloatingIslands 0	9,216	12,266,496	0	0	0

A violation would be possible if the native density dispatch or point() stopped matching this column formula, if a new volume/edit overlay bypassed the Mixed guard, or if the padded lattice/normal halo changed without updating the proof bounds. Zero density is treated as Mixed by the audit.

W12 samples and worker time

Sample counts compare L8's SurfaceWorld profile with the final L9 profile. Worker seconds are medians of five W12 no-hash runs against linux7shared and the Clang candidate. They are per-LOD sums across workers.

LOD	L9 filled samples	Worker seconds baseline → L9	Change
0	5,316,500	2.398 → 2.395	-0.1%
1	924,232	1.213 → 0.920	-24.1%
2	932,824	0.452 → 0.456	+0.8%
3	1,858,789	0.540 → 0.549	+1.6%
4	2,085,136	1.535 → 1.545	+0.6%
5	987,696	1.378 → 1.395	+1.2%
6	658,464	2.559 → 2.564	+0.2%
7	329,232	1.134 → 1.139	+0.4%
8	1,049,427	2.055 → 2.082	+1.3%

LOD1 per tile is 42,875 → 2,063 samples.

LOD0 and LOD2–8 stayed within 1.6% of baseline worker time. LOD1's 4.064 worker-seconds in the L8 profile did not reproduce in the specified linux7shared binary's worker diagnostics: the five-run median there was 1.213 seconds. The exact-binary interleaved timing below is the comparable whole-view measure.

W12 interleaved stream time

Baseline is Standalone/bin/linux/VoxelForgeCoreHeadless-linux7shared, SHA256 fbbd468e351c8a0e00c903a7988a3765158e9400ed6a0111898da4d7f5ae6c85. Each pair used the same seed, camera, 2,553 tiles and W12 settings.

Pair	Baseline	Clang -ffp-contract=off	Delta
1	1.079 s	1.066 s	-1.2%
2	1.109 s	1.083 s	-2.3%
3	1.145 s	1.100 s	-3.9%
4	1.125 s	1.099 s	-2.3%
5	1.126 s	1.113 s	-1.2%
Median	1.125 s	1.099 s	-2.3%

Pair	Baseline	GCC 14 default	Delta
1	1.073 s	1.100 s	+2.5%
2	1.091 s	1.136 s	+4.1%
3	1.104 s	1.129 s	+2.3%
4	1.123 s	1.140 s	+1.5%
5	1.123 s	1.150 s	+2.4%
Median	1.104 s	1.136 s	+2.9%

The baseline ELF contains GCC 14 and Clang 19 objects; the candidate GCC binary is GCC-only. As a compiler-matched control, five W12 pairs against the GCC-only linux7gcc baseline measured 1.154 s → 1.116 s (-3.3%). Thus the specified-binary GCC comparison is slower, while the matched GCC control is faster; the mixed-toolchain delta cannot be attributed to this change. The Clang candidate is faster than the specified binary.

FloatingIslands seed 0 hashes match at W1/W12 for both compilers. Five W12 no-hash pairs against linux7shared gave Clang 10.836 → 11.005 s (+1.6%, pair range -0.5% to +3.0%). GCC was 11.223 → 12.618 s (+12.4%), while five compiler-matched GCC pairs against linux7gcc were 12.498 → 12.529 s (+0.25%, pair range -0.5% to +1.3%). The default island path has no measurable same-compiler slowdown; the large linux7shared GCC delta is the same toolchain mismatch.

Hashes

Every SurfaceWorld hash below matched the baseline at W1/W8/W12 for both compilers; W12 was repeated five times per compiler. FloatingIslands seed 0 matched at W1/W12 for both compilers. Per-LOD tuples are density / mesh / payload / topology.

SurfaceWorld full detail: density 0x0ee0579bd15cbbe4, mesh 0x32e5d4964d610fee, payload 0x1932b96ee4b1d910, topology 0x69743c6bad3447dc.

SurfaceWorld whole view: density 0xc10697a8f48380c7, mesh 0xe75c9119a1498cd5, payload 0x49a9a8d1835a6c8c, topology 0xedcb23288b5e8724.

SurfaceWorld exact queries (9 probes): density/unclamped 0xe4d4a8eb95b35933, detail 0xefcba20c0c70c415, collision 0xe604823a249029bf.

LOD	Density	Mesh	Payload	Topology
0	0x769f2a706d585a72	0x33eeeb39fa443816	0x645621a1d968983f	0xc2457ed905036c9d
1	0x69cc5a5c0a2c60af	0xb48335f5410c57d5	0xd15c5480162ab8ba	0xfeca1bd025823604
2	0x85deed5683a77202	0x53469895987aeea2	0xe55f8ae7e1532033	0xd5feb12a0e85c09b
3	0x6518caefb3be7e7f	0xec513c90b853a614	0xf62fa1137ff17f82	0xccf1dcf681965816
4	0x62d4be96021992f4	0xf1e4c6efcc2615a9	0x9dc5f9c88be02f33	0xfe6f55125a07c3bf
5	0x5e4a8c38b8cea6fc	0x08ee56998aaf21e5	0x541eea8558f26cc8	0x6539374a8b3336d8
6	0xe036e95b9006945b	0x624a33f941a99b02	0x81b73e14f68bdf86	0x4de4c63ce1f80a56
7	0x8ee358af56a30d8d	0x46ab3c6184048b7c	0x0a6164b7e68e80c5	0x0c26b85bb03bc831
8	0xc3458e1cbdb9c471	0x46c03d0994d75192	0x8f89fc5bde12d230	0xd16dc0cf62031898

FloatingIslands full detail: density 0x6d842d2878b08ef6, mesh 0x4b868a3184f08035, payload 0x2cedf2236788752d, topology 0xeac17d5e0cb5044a.

FloatingIslands whole view: density 0x5be4d8cde79b2a76, mesh 0x96f75041f6861b3a, payload 0x3700a516cc89d50c, topology 0x6b99948d6eab4f21.

FloatingIslands exact queries (9 probes): density/unclamped 0x61daded9c303becb, detail 0xefcba20c0c70c415, collision 0x84d37463be9b0573.

LOD	Density	Mesh	Payload	Topology
0	0xf2524906044ef994	0x15b2828701a06591	0x4cbbf7ade54321f7	0x2c0382f590d69610
1	0x71b4c8327ad91da7	0xfd2280177adb70c9	0xc6f695b969ca8573	0xb7b026366bc5b627
2	0x23925de354d86f14	0xd4b470b6aae75cab	0x38c39feddc72ca0c	0x8496f76d94d0e578
3	0x4cb68a60bc8a5103	0x30514ad73d41fd87	0x39a209d2ec7695b1	0xa2ffa199ba1e1215
4	0x0e95c8abbcf6fb37	0x966b891fbe67794a	0xf01627522109d362	0xd7bfb2fea0137c0c
5	0xf444ffed34a1bd20	0x7f3073ed3a711113	0xad32e4ea4a1b4d50	0x6fdba8d6e549193c
6	0x6a6b4f75b9583ec7	0xdbb540e17a46b981	0xe2374a66e9d12b22	0xd384b7c0c0247982
7	0x5c4e824aaa7e5f73	0x44857e6de8e89645	0xa4ac0bf1da59e406	0x94f425b0d77004c8
8	0x8ce5f96cb24bc365	0xa1406a9a6dcae02b	0x8b5e182d38fe352b	0x098f65c1a8cde739

Instrumentation, builds and limits

Removed the L8 phase/stage probes from the normal path. Kept --profile-lod-work for per-LOD density sample counts and added --audit-uniform-block-proofs; both are off by default. Normal runs do not perform the audit fill-and-check pass or sample-count aggregation. The optional LOD0 MC (1.348 worker-s) and shape compile (215 ms) were counted in L8 and not changed.

No async task or epoch path changed. The L3 FP-contract preamble/self-test, L4 FLazy, L7 shared cache, ARCHITECTURE §8.10 two-pass MC/SSE noise/clipmap-streaming invariants, and generator density output remain unchanged.

Clang 19 (-ffp-contract=off) and GCC 14 default builds used -j12; SHA256s are 0cd3f0ef993ced2c615418c6e2b37b83f57eff6d024d7d1568c30ea51490384a and 23fe40de558b1b6931469cc5e976a0e4f2ed5fb6c362bc746dcc64a38fa40e08. Peak build RSS was 901,940 KiB; highest measured runtime RSS was 623,928 KiB. Runs used CPUs 0–11, a 6 GiB address-space limit, normal priority, and the unchanged powersave governor. No run exceeded 30 minutes or remained stuck for 15 minutes.

Failed and retried runs

• The first build wrapper failed because /usr/bin/time is absent; direct builds succeeded. One RSS sampling wrapper hung on zombie handling and was interrupted; later measurements used a corrected monitor.
• Initial proof-audit commands exited 2 because the positional data file and required stream modes were missing. Corrected commands completed. The first broad global interval returned Mixed for all 28,672 blocks and was replaced by the exact lattice-column proof.
• An early all-step audit found two legacy step-8 uniform candidates whose exact filled-grid signs disagreed; the existing post-fill validator cleared them before skip. The new audit is scoped to the native step-2 proof; step 8 is unchanged.
• The first Clang retry failed to compile because SampleGridPoint was outside its lambda scope; it was corrected to call DensityAtLattice directly and rebuilt.
• The first hash comparison differed because a uniform-tile early return bypassed debug density capture. Step-2 hash runs now refill omitted samples after exercising sparse MC. A separate FloatingIslands mismatch came from changing >= 0 to > 0; the legacy >= 0 comparison was restored and both compiler hashes then matched.

Owner note: LOD1 now fills 95% fewer samples with zero proof violations, and all SurfaceWorld and FloatingIslands hashes match. The GCC W12 comparison against linux7shared is toolchain-confounded; GCC-to-GCC controls are flat or faster, while the Clang candidate is faster than the requested baseline.

Orchestrator review (Claude)

• Re-run by me, 5 interleaved W12 pairs, L1 view. Without --stream-hash (game-like): whole view L7 1.379/1.485/1.430/1.439/1.449 s vs L9 1.390/1.409/1.401/1.423/1.429 s (median 1.439 → 1.409 s, −2.1%); stream wall 1.140 → 1.112 s (−2.5%). With hashing on, the difference is inside noise (1.748 vs 1.744 s), because hashing adds ~0.3 s. The whole-view hash is identical in all runs.
• The L8 lever was inflated by L8's own instrumentation. L8's profile build reported LOD1 at 4.06 worker-s; the plain linux7shared binary spends 1.21. Per-LOD shares from instrumented builds must be re-checked on a plain build before they're ranked.
• The "baseline ELF contains GCC and Clang objects" remark is expected: crt/libstdc++ objects always come from GCC. The compiler-matched controls are the right comparison, as Luna did.
• Proof read: for native SurfaceWorld step-2 tiles the verdict uses exact column extrema over the padded block (cells plus the −1..+9 normal halo) for density min(z−ground, cap−z). Features, edits, mixed strata and Unknown verdicts all fill. The 80,502-block audit found 0 violations.