docs(teleport): spec — retail residency + fade-cover (refutes _datLock starvation)
Live tp-probe capture refuted the handoff's _datLock-starvation hypothesis: worker BUILD is fast + uncontended (waited=0ms); the 10-14s 'long transition' is render-thread APPLY latency, and 'dropped at wrong position' is the per-frame resolve corrupting the outbound cell frame (lbX zeroed) while the player sits on an empty world. Design: priority-apply the player's dest landblock + hold-until-resident behind a retail fade cover (reuse the dormant TeleportAnimSequencer) + cell-march landblock-id hardening. Foundation-first, not a hold over slow streaming. Flood-timeslicing + 3D swirl deferred. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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# Retail-faithful teleport — priority residency + fade cover — design (2026-06-22)
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**Status:** approved design, pre-implementation.
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**Branch:** `claude/thirsty-goldberg-51bb9b`. **Baseline:** `dd2eb8b` (+ the uncommitted `tp-probe` diagnostic).
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**Supersedes the framing of:** `docs/research/2026-06-21-teleport-foundation-handoff.md` (the `_datLock`-starvation
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hypothesis is **refuted** below by direct measurement).
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> The fix makes the teleport **foundation** fast and correct first, then covers the short transit with a
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> retail-style fade. This is explicitly NOT the reverted Slice-2 hold: that band-aided slow streaming;
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> this fixes the streaming-apply so the cover is polish over a fast load, not a crutch over a slow one.
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---
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## 1. The problem, as measured (not hypothesized)
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A live capture (`ACDREAM_PROBE_TELEPORT=1`, four teleports as `+Je`) plus the ACE server log produced
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hard numbers that overturn the handoff's central hypothesis.
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**The `tp-probe` timeline for one outdoor teleport (dest landblock `0xA9B4`):**
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| Event | Timestamp (ms) | Δ from placement | Note |
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|---|---|---|---|
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| `PLACED` | 961809984 | 0 | placed the SAME tick as arrival — on an **empty** world (`lbs=0`) |
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| `BUILD 0xA9B4FFFF` | 961810156 | **+172 ms** | worker built it almost immediately; **`waited=0ms`** (no lock contention) |
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| `APPLY 0xA9B4FFFF` | 961824328 | **+14,344 ms** | render thread took **14.3 s** to apply it |
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The second outdoor teleport (`0xC6A9`) showed the same shape: `BUILD +250 ms`, `APPLY +10.7 s`. Across the
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whole session the worst `_datLock` `waited` was **74 ms** (one login landblock); every teleport-destination
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build logged `waited=0ms`.
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**Three distinct root causes (NOT one):**
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1. **`_datLock` starvation — REFUTED.** The worker is never meaningfully blocked (`waited≈0`). The bottleneck
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is the render-thread **APPLY**, not the worker BUILD. `BuildLandblockForStreaming`
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(`src/AcDream.App/Rendering/GameWindow.cs`, the `lock(_datLock)` at the build site) is fast and uncontended.
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2. **APPLY throughput — the "long transition."** A built landblock sits in the streamer outbox while the
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render thread, saturated by the synchronous unbounded CreateObject flood (`WorldSession.Tick`,
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`src/AcDream.Core.Net/WorldSession.cs:598-607`, drains the entire inbound queue per frame) and metered to
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`MaxCompletionsPerFrame = 4` (`src/AcDream.App/Streaming/StreamingController.cs:90`, applied in
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`DrainAndApply`), crawls through it. That is the 10–14 s the user feels.
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3. **Resolve-against-empty-world — the "dropped at the wrong position."** Outdoor teleports place
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immediately on an unloaded world (`TeleportArrivalRules.Decide` returns `Ready` for outdoor;
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`src/AcDream.App/World/TeleportArrivalController.cs:134-142`), so for the whole 10–14 s window the
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per-frame swept-transition cell-march runs against nothing and emits a `result.CellId` with the
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landblock-X byte **zeroed** (`0x00B40039` instead of `0xA9B40039`). The outbound encoder trusts that cell
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id verbatim (the #107 fix, `src/AcDream.App/Rendering/GameWindow.cs:7794-7807`), so ACE receives a move
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naming the wrong landblock and rejects **every** one (`MOVEMENT SPEED` → `failed transition` in the ACE
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log). The player is desynced for the entire window.
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4. **`PortalSpace` input-freeze — the "stops at the portal" (separate).** `OnTeleportStarted` sets
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`PlayerState.PortalSpace` (`GameWindow.cs:5582`); `PlayerMovementController.Update` early-returns a
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zero-movement result (`src/AcDream.App/Input/PlayerMovementController.cs:862-876`), freezing both local
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prediction and the outbound send. Independent of streaming.
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**What retail actually does (verified — ACE `Player_Location.cs:679-760`):** place the position immediately,
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set `Hidden = true; IgnoreCollisions = true`, poll every 0.1 s until `CurrentLandblock.CreateWorldObjectsCompleted`,
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then clear both. No input freeze, no position hold — collision/visibility are suppressed until the
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destination is resident, then the player materializes. The retail *client* covers the same interval with the
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portal-tunnel animation while physics keeps ticking.
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**Out of scope here (FPS):** the user observed 30–70 fps outdoors. This was a **Debug** build, which is not
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representative. The general FPS question is deferred to its own measure-in-Release pass (see §6).
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---
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## 2. Target experience (approved)
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A **retail tunnel cover**: starting a teleport plays a cover animation that hides the (now-short) load; the
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player is "in transit" — not moving in the world — and pops out at the destination once it is resident.
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Fidelity for this spec is a **fade cover** (fade-out → hold → fade-in), reusing the dormant
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`TeleportAnimSequencer`. The authentic 3D portal-swirl is deferred to a later polish pass.
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This single model resolves all three teleport symptoms at once:
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- The transit state means **no movement resolve runs against an empty world** → the cell frame cannot corrupt
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(fixes the wrong-position desync).
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- The fade **covers** the transit → the awkward freeze-in-place is gone (fixes "stops at the portal").
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- Materialization is gated on the destination being **resident**, which the foundation fix makes fast
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(fixes the "long transition").
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---
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## 3. Architecture & new sequence
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Replaces "place-immediately + `PortalSpace` freeze." Phases:
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1. **TRANSIT-IN** — `OnTeleportStarted` (`0xF751`) drives `TeleportAnimSequencer` into fade-out → cover.
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Input and outbound movement are suppressed *for the duration of transit*, but the fade covers it.
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No movement resolve runs.
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2. **AIM** — `OnLivePositionUpdated` (destination `UpdatePosition`) drops the stale source landblock,
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recenters streaming on the destination, pre-collapses if the destination is a sealed dungeon, and begins
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the arrival hold. The destination load is enqueued by the normal streaming `Tick` (unchanged; the probe
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confirmed `ENQ` fires correctly during the hold).
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3. **PRIORITY-APPLY** — when the destination landblock's completion lands in the streamer outbox, it is
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applied immediately (out-of-band of the 4/frame budget), so the player's cell becomes resident in
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~hundreds of ms instead of 10–14 s.
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4. **READY** — the arrival readiness flips when the player's **own** destination landblock terrain (+ the
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EnvCell struct for an indoor destination) is resident. Outdoor changes from "place immediately" to
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"hold-until-terrain-resident."
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5. **MATERIALIZE** — `PlaceTeleportArrival` resolves against the now-resident destination (grounds
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correctly; never takes the `NO-LANDBLOCK` verbatim branch), seeds the body's (cell, local) frame,
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fades in, exits transit → `InWorld`, sends `LoginComplete`.
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### Components
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- **A — Priority-apply** *(`src/AcDream.App/Streaming/StreamingController.cs`, small/surgical)*
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`StreamingController` gains a settable "priority landblock id" (the active teleport target). In
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`DrainAndApply`, when a priority id is set, its completion is located and applied first/out-of-band so
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the player materializes as soon as the worker finishes it (already ~170 ms). The id is cleared on
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materialize. No change to the inbound network drain. Apply remains render-thread-only.
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- **B — Arrival controller** *(`src/AcDream.App/World/TeleportArrivalController.cs` + `TeleportArrivalRules`,
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exist)* Outdoor readiness changes from unconditional `Ready` to **hold-until-terrain-resident**, using a
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**correctly-keyed** residency check (the `EncodeLandblockId` 0xFFFF form — the bug fixed at `c880973` and
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then reverted with Slice 2; do NOT reintroduce the `& 0xFFFF0000` raw-key mismatch). The controller drives
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the TAS transit and materializes on `Ready`, or loud-fails on `Impossible`/timeout. The ~10 s frame-count
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timeout is **retained as a loud safety net** (a real failure signal — worker crash / corrupt dat / OOB
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coords) but should now rarely fire because residency is fast.
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- **C — Fade cover** *(`src/AcDream.Core/World/TeleportAnimSequencer.cs`, exists, 29 tests + a render overlay)*
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Wire the dormant 7-state TAS to drive a full-screen fade overlay during transit, using its existing
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`ComputeFadeAlpha`. The overlay is a render-layer addition (a screen-space quad whose alpha the TAS
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drives). The authentic 3D swirl is explicitly NOT built here.
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- **D — Cell-march hardening** *(`src/AcDream.Core/Physics/` — the swept-transition cell-march)*
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The swept-transition path must **preserve the body's landblock id** (never emit `lbX=0`) when the swept
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position isn't covered by a resident landblock — return the body's seeded (last-known) cell rather than a
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partially-derived one. `ResolveCellId` (`PhysicsEngine.cs:330-351`) already preserves its fallback; the
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zeroing is in the swept `Transition`/`SpherePath` cell update, whose exact site is identified and fixed
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during implementation. Defense-in-depth: with the transit model the player never moves against an empty
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world on the normal path, but this also clips the #145 edge-arrival residual.
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---
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## 4. Why this is not the reverted band-aid
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The reverted Slice-2 hold (`docs/research/2026-06-21-teleport-foundation-handoff.md`) was a band-aid because
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(a) the foundation was slow, so it waited ~10 s, and (b) it force-placed on `NO-LANDBLOCK` after the timeout.
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This design is different on both counts:
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- **(a) The foundation is fixed.** Priority-apply makes the player's destination resident in ~hundreds of ms
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(the worker build is already ~170 ms; the only thing that was slow was the metered render-thread apply,
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which we now bypass for the player's own landblock).
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- **(b) Placement is on a real, grounded landblock.** Materialization resolves against a resident
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destination — never the `NO-LANDBLOCK` verbatim branch — so the cell frame is correct and outbound
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movement is accepted by ACE.
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The fade is the retail cover over a now-fast load, which is exactly what the handoff said is legitimate
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"(and only then) a retail-style visual cover is polish, not a crutch."
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---
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## 5. Error handling
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- **Destination never becomes resident** (worker crash / corrupt dat / OOB coords): the frame-count timeout
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fires, force-materializes, and logs loudly (it is a genuine failure, not normal flow). With component D,
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even a forced placement does not corrupt the outbound frame.
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- **Impossible indoor claim** (cell id outside `LandBlockInfo.NumCells`): the existing
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`IsSpawnClaimUnhydratable` → `ArrivalReadiness.Impossible` short-circuit is retained.
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- **Re-sent server position mid-transit**: `BeginArrival` is server-authoritative and resets the hold
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(existing behavior).
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---
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## 6. Scope — what this spec does NOT do
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- **CreateObject-flood timeslicing (the deferred "#2").** Even after the player materializes onto correct
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terrain, the town's *objects* (buildings, NPCs) keep flooding in synchronously, causing post-materialization
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pop-in and an FPS sag for a few seconds. Bounding `WorldSession.Tick` per frame is a real improvement that
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also helps general FPS, but it touches the inbound-drain path and is not strictly a *teleport* bug. Filed
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as a follow-up; **measure in Release first.**
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- **The authentic 3D portal-swirl** (fade cover ships now).
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- **General outdoor FPS** (30–70 in Debug — re-measure in Release before treating it as a regression/leak;
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the AP-48 unbounded-entity-map leak is a separate, already-registered concern).
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---
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## 7. Testing & acceptance
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**Unit (per layer):**
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- Priority-apply ordering — a priority id's completion is applied before the per-frame budget is spent
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(`tests/AcDream.Core.Tests/Streaming/`).
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- Outdoor + indoor readiness decision — outdoor now holds until terrain-resident; correctly-keyed lookup
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(`tests/AcDream.App.Tests/World/` + `tests/AcDream.Core.Tests/`).
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- Cell-march landblock preservation — a swept step whose position is over no resident landblock returns the
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seeded cell (correct `lbX`), never `lbX=0` (`tests/AcDream.Core.Tests/Physics/`).
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- The `TeleportAnimSequencer` keeps its 29 existing tests green.
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**Live acceptance (re-run the `tp-probe`):**
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- The destination-LB `APPLY` lands within ~1–2 frames of its `BUILD` (was +10–14 s).
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- The ACE log shows **no** `00B4…` / `MOVEMENT SPEED` / `failed transition` lines after a teleport.
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- Visual: a covered (faded) transition that pops out onto real, grounded terrain — no run-in-place stutter,
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no desync.
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- The death→lifestone building keeps its collision (component A makes the dat-static building's landblock
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resident before the player materializes; component D closes the cell-resolution residual).
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**Probe lifecycle:** the `tp-probe` (`PhysicsDiagnostics.ProbeTeleportEnabled` + the 5 log points) is the
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acceptance apparatus. It stays until the fix is verified, then is removed (it is tagged `REMOVABLE`). If it
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proves durably useful, promote it instead of removing — decide at verification time.
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---
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## 8. Divergence register impact
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- **Retire** the "outdoor teleport places immediately because streaming doesn't progress during a hold"
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divergence (the comment + behavior at `TeleportArrivalController.cs:134-142` / `GameWindow.cs:5519-5523`):
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the premise was measured false (streaming DOES progress; only APPLY was slow). The new transit-until-resident
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model is retail-faithful, so this retires a deviation rather than adding one.
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- **Add** a row for the **fade cover instead of the authentic 3D portal-swirl** (an approximation deviation,
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sibling to AP-49's fade-curve note). Cite `gmSmartBoxUI` tunnel rendering as the unported mechanism.
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- **Add** a row for the deferred CreateObject-flood timeslicing if post-materialization object pop-in is
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observed (it is an adaptation/stopgap until #2 lands).
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All register edits land in the same commits as the behavior they describe.
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---
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## 9. Retail / reference anchors
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- ACE teleport (place + `Hidden`/`IgnoreCollisions` + poll `CreateWorldObjectsCompleted`):
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`references/ACE/Source/ACE.Server/WorldObjects/Player_Location.cs:679-760`.
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- TAS decomp + the 7-state machine: `docs/research/2026-06-21-teleport-issues-handoff.md`,
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`src/AcDream.Core/World/TeleportAnimSequencer.cs`.
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- Outbound (cell, position) self-consistency (#107): `src/AcDream.App/Rendering/GameWindow.cs:7783-7807`.
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- Streaming threading + apply: `src/AcDream.App/Streaming/StreamingController.cs`,
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`src/AcDream.App/Streaming/LandblockStreamer.cs`.
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