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Static external-part placement (ship::assemble_ship) is only approximate — a GN_* frame is the mount pivot, and the real offset lives in a runtime detail rig. So capture ground truth from Canary instead. Finding: the guest vertex buffer holds LOCAL coords (byte-identical to the .xpr), so capital-ship parts are placed entirely in the vertex shader. The per-part transform is in the VS float constants — c0..c2 are the WorldViewProjection rows; normalising each by its norm (= projection x/y/z scales, sy/sx = 16:9) yields the rigid WorldView (rows orthonormal, det +1). Expressing every part relative to a reference part cancels the camera: rel_p = WV_ref⁻¹·WV_p, a pure ship-space rigid transform. - examples/correlate_capture.rs: parse xenia_ship_capture.log, decode the ship's parts, match by vertex count, recover each part's ship-relative placement. - docs/re/ship-placement-runtime-capture.md: full method + the capture protocol (Canary branch capture-ship-placement, F10 hotkey) + validated e106 result. Validated on e106 (ADAN Destroyer, Stage_S01): all 7 drawn parts matched by vertex count; bdy_01/bdy_02 recovered as a PORT/STARBOARD pair (X = ∓264) that static had overlapping; engines correctly aft; extent 872×670×2181. Only brg_01 (bridge) missing — culled at that camera angle, needs a bridge-facing capture. HANDOFF: next = re-capture bridge, bake a per-ship placement table the viewer prefers over assemble_ship, then capture the cruiser / ACROPOLIS / TCAF ships. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
106 lines
5.1 KiB
Markdown
106 lines
5.1 KiB
Markdown
# Capital-ship part placement — runtime capture (ground truth)
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**Status:** pipeline working end-to-end for one ship (`e106` ADAN Destroyer);
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correlator recovers exact ship-relative transforms. Not yet baked into the viewer.
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## Problem
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Capital ships ship as **split XBG7 parts** (hull bodies, bridge, engines, turrets)
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in `hidden/resource3d/Stage_SNN.xpr`. Reconstructing the whole ship needs each
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part's placement. Static reverse-engineering of the composite scene graph
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(`e_rou_<id>`, `GN_*` frames) got the **hull right but external parts only
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approximately** — a `GN_*` frame is the mount *pivot*, and the real outboard /
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rotational offset lives in a detail sub-rig or in runtime code not recoverable
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statically. See `sylpheed-formats::ship::assemble_ship` (the static best-effort).
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## Finding
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The **guest vertex buffer holds LOCAL coordinates** — byte-identical to the
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`.xpr` (verified: `e106_bdy_04`'s first vertex `(-20.0000,153.1539,45.9997)`
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matches the decode exactly). So parts are placed **entirely in the vertex
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shader**; the buffer carries no placement. (Contrast: static *stage* geometry is
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pre-transformed into world space and byte-matches the `.xpr` at file offsets —
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that's a different case.)
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The per-part transform is in the **vertex-shader float constants**. For the ship
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shader (`vs=0xC7F781F4C1D58054`), constants `c0..c2` are the **WorldViewProjection**
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matrix rows:
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- Their norms are `(sx, sy, 1)` = the projection x/y scales; `sy/sx ≈ 1.78 = 16:9`
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aspect. Dividing each row by its norm gives the rigid **WorldView** (verified:
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normalized rows orthonormal to 1e-4, `det = +1`).
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- The camera View cancels when expressing every part relative to a reference part:
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`rel_p = WV_ref⁻¹ · WV_p` = `(Rᵀ_ref·R_p , Rᵀ_ref·(T_p − T_ref))` — a pure
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ship-space rigid transform. Applying `rel_p` to part `p`'s local geometry
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assembles the ship exactly, in the reference part's frame.
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(`c4..c14` also vary per part — likely a normal matrix / a second WVP variant /
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WorldView split; not needed, `c0..c2` suffice.)
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## Capture instrumentation
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Branch **`capture-ship-placement`** in the `xenia-canary-native` worktree (off the
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`instrument-current`-descended native branch, which already has GPU `log_draws`).
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- **F10** in the emulator window → `xe::gpu::RequestShipCaptureFrame()`.
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- Dumps the next ≤8000 draws (de-duped by vertex-buffer address) to
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**`xenia_ship_capture.log`** in the binary's dir
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(`build/bin/Linux/Release/`). Per draw:
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```
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DRAW vbase=0x… stride=… vcount=… indices=… prim=… vs=0x…
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pos: (x,y,z) … up to 64 LOCAL vertex positions (== .xpr)
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vsconst base=N: c0=(x,y,z,w) c1=… … first 48 VS float4 constants
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```
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- Files: `src/xenia/gpu/command_processor.{cc,h}` (`CaptureShipDrawForRE`,
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`RequestShipCaptureFrame`), `src/xenia/app/emulator_window.cc` (F10 key).
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- Run: `run-canary-native.sh` (HW Vulkan, interactive). Play into the mission,
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frame the ship side-on, press F10.
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## Correlator
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`sylpheed-formats/examples/correlate_capture.rs`:
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```
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SYLPHEED_ISO=… cargo run --release --example correlate_capture -- \
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<capture.log> <Stage_SNN> <ship_id> [ref_part_substr]
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```
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Parses the log, decodes the ship's base parts, matches each part to a draw by
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**vertex count** (unique per part), recovers WorldView from `c0..c2`, and prints
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each part's ship-relative transform (reference-part frame) + assembled extent.
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## Validated result — `e106` ADAN Destroyer (Mission 1 / Stage_S01, side view)
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Vertex-count → part map (all matched exactly): bdy_01/02 = 1261, bdy_03 = 815,
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bdy_04 = 1633, eng_01 = 583, eng_02 = 491, wep_02_01 = 1002, brg_01 = 202.
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Ship-relative placement (reference = `bdy_04`, aft hull):
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| part | T (ship-relative) | note |
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|---|---|---|
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| bdy_04 | (0, 0, 0) | reference, aft hull |
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| eng_01 | (131, −133, −132) | **aft** (−Z), starboard |
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| eng_02 | (0, −49, −140) | aft, centre |
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| bdy_01 | (**−264**, −150, 1165) | **port** hull, forward |
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| bdy_02 | (**+264**, −150, 1165) | **starboard** hull, forward |
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| bdy_03 | (0, −35, 1076) | forward keel/spine |
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| wep_02_01 | (0, 49, 1009) | forward weapon |
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Assembled extent **872 × 670 × 2181** (a coherent ~2181-long destroyer).
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**Key wins vs static:** `bdy_01`/`bdy_02` are a **port/starboard pair** (X = ∓264),
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which static had overlapping at one point; engines land correctly aft; the ship is
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not the 1894-tall tower the static Y put out.
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**Missing:** `brg_01` (bridge, vcount 202) was **culled/occluded** at that camera
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angle (0 draws) — needs a second capture framing the superstructure.
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## Next steps
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1. **Bridge:** re-capture with the bridge visible → fills `brg_01`.
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2. **Bake:** promote the correlator to a module; emit a per-ship placement table
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(`ship_id → [(part, R, T)]`) as a checked-in data file; have the viewer's
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`build_ship_model` prefer the captured table over `assemble_ship` when present.
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3. **Other ships:** same capture for the cruiser (`e105`, Stage_S02), ACROPOLIS
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(`f101`), TCAF cruiser/destroyer (`f105`/`f106`). One side-on F10 each.
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4. **Turrets:** the shared `e3NN`/`e4NN` gun models appear as their own draws in the
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capture too — correlate them to place turrets (static never resolved these).
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