Going-Commando/docs/plan/level-assets.md

Level assets

Phase 2 work record. What has been established about the four extents inside each LEVEL<n>.WAD, and what remains.

A bug found and fixed

Reading the data extent's contents exposed a defect in the Phase 1 extractor.

Level extents are declared in sector counts; the generic G/ pair table uses byte counts. The extractor routed level containers through the generic path, so LEVEL0.WAD's data extent — 6,484 sectors — was taken as 6,484 bytes. Level 0 yielded a 6,484-byte "geometry" file instead of 13,279,232 bytes. Across 27 levels that silently discarded roughly 300 MB of level content while every test still passed.

The tell was arithmetic, not a crash: the extent's own header declared an uncompressed total of 13,277,920 bytes, and the ratio against the 6,484-byte file was 2047.7× — one sector, to within rounding. A ratio that lands on 2048 is a unit error.

Fixed by extracting level containers through the typed LevelHeader instead of the generic table. Level 0 now yields:

data.bin         13,279,232   the level container's data extent
core_data.wad     9,738,678   the geometry, compressed
core_data.bin    16,969,296   the geometry, decompressed
core_index.bin       31,600   the geometry directory
gameplay.bin       659,456
sound_bank.bin   1,503,232

Lesson: a unit error is invisible to a type system and to a passing test. The check that catches it is arithmetic against an independent number the file itself declares. Any extent whose contents describe a larger structure should have that structure's own total compared against the extent.

Done: the container header

crates/gc-formats/src/level_wad.rs parses the 0x60-byte header on all 27 levels and names the four extents. See ../formats/level-wad.md for the layout and the measured invariants.

Two facts worth carrying forward:

• Sizes in this header are sector counts, unlike the generic G/*.WAD pair table where they are byte counts. Both are on the same disc.
• LEVEL21.WAD reports level id 30. Container order is not level identity.

gameplay: a compression we have not identified

This is the one genuinely puzzling result so far, and it is worth recording in full because the next attempt will otherwise repeat the work.

The extent begins:

offset 0  57 41 44   "WAD"
offset 3  79 0d 0a 0d   <- varies per level
offset 4+ <payload>

The variation is the tell. For the LZ77 WAD container the fourth byte is part of a 32-bit little-endian length; here byte 3 differs per level (0x79, 0x3a, 0xd8, 0xa9, ...) while byte 4 is a small count (13, 88, 13, 105, 163, ...) and bytes 6 and 7 are always zero.

Attempt: treat it as the known WAD LZ77 stream. Decoded all 27 levels with the decoder in wad.rs, starting after an 8-byte header. Every one produces plausible output for the first packet — 0000 0000 0000 0750 0100 0020 2b0c... looks like real level data — and then fails on all 27 with "adjacent literal packets", which the format's encoder never emits.

A uniform failure on all 27 inputs means the input is wrong, not the decoder. Ruled out:

• Bit order. The WAD container is a flag-byte packet stream, not a bit stream, so no ordering applies. Both orderings fail identically.
• Header length. Tried 8 bytes. A different skip would not fix a failure that occurs uniformly in the first few packets.
• The WAD format at all. The first packet (flag 0x00) decodes cleanly as a literal run of 18 bytes, which is why it looks plausible, but the run immediately after breaks the format's own rule. Whatever this is, it is not WAD LZ77.

Next to try, in order of cheapness:

1. Whether the payload is uncompressed and the header is a table. (len - 8) is 196..497 across the levels and divides by neither 8 nor a plausible stride, which argues against a flat pair table — but a variable-length table (counts of counts) fits that range.
2. Whether byte 4 is an entry count and bytes 5.. are records of a fixed but non-obvious width.
3. Whether the LZ77 variant differs only in the "adjacent literals" rule.

None of these is expensive to test; each is a few lines against all 27 levels at once. The right move is to write a throwaway script that tries many hypotheses across all 27 and reports which produce self-consistent results — the approach that worked for the container pair table, where "does this hold on every level" was the discriminator that the sector/byte ambiguity failed.

sound_bank: signatures found, structure unknown

+0x18  "SBlk"   present in all 27 levels
+0x24  "DAW"    present in all 27 levels

Sizes 458..833 bytes. Too small to be the level's audio; likely an index into the global AUDIO.WAD.

occlusion: smallest, and unread

2 to 25 sectors. Small enough to dump whole and stare at.

data: the real target, untouched

6,484 sectors on level 0, down to 2,102 on level 24 — 4.2 to 21.9 MB. This is the level's geometry and the largest thing in the container. Next target.

What is known from the community reference and from Insomniac's engine family: it splits into four geometry subsystems — tfrag (terrain fragments), tie (instanced environment structures), shrub (foliage) and moby (dynamic actors) — plus sky shells, collision data and textures. ReRAC's documentation of the equivalent structures in the first game is the closest reference available, though R&C2's spherical worlds change how they are used.

Order of work

1. gameplay — smallest, fully bounded, and the format is identified enough to make progress. A win here validates the approach before the large effort.
2. occlusion — tiny.
3. sound_bank — small.
4. data — the large one, and the one that decides whether anything renders.

Doing the small extents first is not just convenience: each one is a contained reverse-engineering problem that either resolves or tells us something, whereas data will keep producing ambiguous readings until we have something to check them against.

Method note

Every format question this phase has been settled the same way: write the hypothesis, test it against all 27 levels at once, and require an invariant that holds everywhere. The sector/byte ambiguity in Phase 1 survived because it happened to be correct on the one container checked by hand. The level header was fixed in a single pass because the tiling check failed immediately on levels 1, 2, 4, 7, 8, 11, 19 and 20.