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re: the proven offsets ARE candidates -- these mis-anchors are selection failures

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debug_vertex_run_starts exposes the anchor scan's candidate list: Stage_S01 has
15710 stride-24 starts and all three capture-proven offsets (0x3c55d8 twin,
0x40e418 bridge, 0x44a32c eng_02_l) are among them. anchor_pool_mesh takes the
first that validates, so an earlier lookalike wins. Scoped to the current
decoder's e106 cases; does not overturn the residual-51 finding.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
This commit is contained in:
Claude (auto-RE)
2026-08-12 02:11:41 +00:00
parent 26f1bdf6fd
commit 76a433f75c
4 changed files with 65 additions and 17 deletions
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10
crates/sylpheed-formats/examples/shared_vbase_check.rs
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@@ -154,7 +154,12 @@ fn main() {
let n: usize = m.meshes.iter().map(|s| s.positions.len()).sum();
by_count.entry(n).or_default().push(m.name.clone());
}
println!("{:<12} {:>7} {:<44} our resources with that vcount", "file offset", "vcount", "claimed by our decode");
// Is a capture-proven offset even a candidate the scan considers?
// Absent ⇒ the run scan misses it; present ⇒ selection picked another.
let starts: BTreeSet<usize> =
sylpheed_formats::mesh::debug_vertex_run_starts(&bytes, 24).into_iter().collect();
eprintln!("{} stride-24 candidate starts in this container", starts.len());
println!("{:<12} {:>7} {:>9} {:<44} our resources with that vcount", "file offset", "vcount", "candidate", "claimed by our decode");
for (off, vcount) in &drawn {
let who = ours
.get(off)
@@ -173,7 +178,8 @@ fn main() {
.next_back()
.map(|(o, v)| format!("{} @ -0x{:x}", v[0].0, off - o))
.unwrap_or_default();
println!("0x{off:<10x} {vcount:>7} {who:<44} {same:<34} {near}");
let cand = if starts.contains(off) { "yes" } else { "NO" };
println!("0x{off:<10x} {vcount:>7} {cand:>9} {who:<44} {same:<34} {near}");
}
return;
}

21
crates/sylpheed-formats/src/mesh.rs
View File

@@ -613,6 +613,27 @@ impl Xbg7Model {
}
}
/// Diagnostic: the candidate vertex-buffer starts the stage anchor scan will
/// consider for a given `stride`, for one container. A runtime capture names the
/// offsets the engine really drew from (see `examples/shared_vbase_check.rs`), so
/// asking whether a proven offset is in this list separates the two possible
/// root causes of a mis-anchor: **absent** ⇒ the run scan misses it, **present**
/// ⇒ the scan sees it and the selection picks another.
pub fn debug_vertex_run_starts(bytes: &[u8], stride: usize) -> Vec<usize> {
if bytes.len() < 16 || &bytes[..4] != b"XPR2" {
return Vec::new();
}
let mut cur = Cursor::new(bytes);
let Ok(header) = Xpr2Header::read(&mut cur) else {
return Vec::new();
};
let data_base = header.header_size as usize;
if data_base >= bytes.len() {
return Vec::new();
}
vertex_run_starts(bytes, data_base, stride)
}
/// Scan the data section for offsets that begin a `stride`-sized unit-normal
/// vertex run (NORMAL is `f16×4` at vertex offset +12). A run *start* is an
/// offset whose normal is unit while the preceding stride slot's is not — i.e.

30
docs/re/captures/stage-s01-capture-truth-offsets.txt
View File

@@ -1,15 +1,15 @@
file offset vcount claimed by our decode our resources with that vcount
0x38788 181 — NOBODY — none
0x4b8b8 93 — NOBODY — none
0xb6574 41 — NOBODY n042_bdy_m e007_bdy_01 @ -0x24864
0xdbbac 77 — NOBODY — none _rou_e010_break @ -0x5050
0x133da0 76 — NOBODY e303_wep_01_m, n041_bdy_l _rou_e010_break @ -0x407bc
0x162840 60 — NOBODY — none _rou_e010_break @ -0x6f25c
0x3b3ee8 119 e106_bdy_01_l(119), e106_bdy_02_l(119) e106_bdy_01_l, e106_bdy_02_l e106_bdy_01_l @ -0x0
0x3c55d8 119 — NOBODY e106_bdy_01_l, e106_bdy_02_l e106_bdy_01_m @ -0x104e8
0x3dd2c4 146 e106_bdy_03_l(146) e106_bdy_03_l e106_bdy_03_l @ -0x0
0x40763c 179 e106_bdy_04_l(179) e106_bdy_04_l e106_bdy_04_l @ -0x0
0x40e418 51 — NOBODY e106_brg_01_b_02, e106_brg_01_l e106_brg_01_b_02 @ -0x5d0
0x444ccc 58 e106_eng_01_l(58) e106_eng_01_l e106_eng_01_l @ -0x0
0x44a32c 44 — NOBODY e106_eng_02_l e106_eng_02 @ -0x35b8
0x45705c 82 e106_wep_02_01_l(82) e106_wep_02_01_l e106_wep_02_01_l @ -0x0
file offset vcount candidate claimed by our decode our resources with that vcount
0x38788 181 NO — NOBODY — none
0x4b8b8 93 NO — NOBODY — none
0xb6574 41 NO — NOBODY n042_bdy_m e007_bdy_01 @ -0x24864
0xdbbac 77 NO — NOBODY — none _rou_e010_break @ -0x5050
0x133da0 76 NO — NOBODY e303_wep_01_m, n041_bdy_l _rou_e010_break @ -0x407bc
0x162840 60 NO — NOBODY — none _rou_e010_break @ -0x6f25c
0x3b3ee8 119 yes e106_bdy_01_l(119), e106_bdy_02_l(119) e106_bdy_01_l, e106_bdy_02_l e106_bdy_01_l @ -0x0
0x3c55d8 119 yes — NOBODY e106_bdy_01_l, e106_bdy_02_l e106_bdy_01_m @ -0x104e8
0x3dd2c4 146 yes e106_bdy_03_l(146) e106_bdy_03_l e106_bdy_03_l @ -0x0
0x40763c 179 yes e106_bdy_04_l(179) e106_bdy_04_l e106_bdy_04_l @ -0x0
0x40e418 51 yes — NOBODY e106_brg_01_b_02, e106_brg_01_l e106_brg_01_b_02 @ -0x5d0
0x444ccc 58 yes e106_eng_01_l(58) e106_eng_01_l e106_eng_01_l @ -0x0
0x44a32c 44 yes — NOBODY e106_eng_02_l e106_eng_02 @ -0x35b8
0x45705c 82 yes e106_wep_02_01_l(82) e106_wep_02_01_l e106_wep_02_01_l @ -0x0

21
docs/re/structures/xbg7-mesh.md
View File

@@ -653,6 +653,27 @@ could not: `0x3b3ee8` stays with whichever twin we already decode there, and the
other twin must move to `0x3c55d8`. The invariant is checkable without a capture
— *mirrored twins must decode to X-reflected buffers, never identical ones*.
**4. Root cause, for these three: selection, not the run scan.**
`mesh::debug_vertex_run_starts` exposes the candidate list the anchor scan works
from. `Stage_S01` yields **15 710** stride-24 candidate starts, and **all three
capture-proven offsets are in it** — `0x3c55d8` (the mirrored twin), `0x40e418`
(the drawn bridge buffer) and `0x44a32c` (`eng_02_l`). The scan sees the right
offsets; `anchor_pool_mesh` walks the list in ascending order and takes the first
that validates, so an earlier lookalike wins — our bridge resources sit `0x5d0`
before the buffer the engine drew.
This is scoped: it says the *current* decoder's e106 mis-anchors are selection
failures. It does not overturn the earlier finding that the residual 51 *under
the withdrawn neighbourhood fix* had no validating candidate at all — a different
population, and the two can both be true.
What the twins suggest as the fix: selection is **per-resource and greedy**, so
two resources can and do claim one buffer while a validating buffer sits unused.
An assignment that is distinct by construction — each candidate used at most once
— resolves the twin case by shape rather than by heuristic. Whether the proven
offsets actually validate for their resources is the next thing to test; if they
do, distinctness alone is the fix.
Not settled: `e106_brg_01_b_02` ≡ `e106_brg_01_l` (51 verts). A second 51-vertex
`vbase` exists in the logs but is **not** from this container, and the container
holds three near-identical 51-vertex runs, so the pair has no oracle yet.