acdream had no ambient system: StartAmbient minted a handle and played
nothing. Retail's is a weighted-accumulation + timer-queue engine, not
looping voices. On every objcell change (24 m) CellManager::ChangePosition
rebuilds per-sound weights over the 3x3 landblock ring x 64 land cells
each, decoding each cell's terrain word through the region file's
terrain -> scene -> AmbientSTBDesc chain; playback is a min-heap of
absolute deadlines drained from the frame tick, where each pop fires a
one-shot and re-arms.
A continuous bed (base_chance == 0) is non-positional, crossfaded by its
share of the TOTAL weight, and re-fired every min_rate seconds — that
rate is the author's intended loop period, and re-firing is how retail
fakes a sustained bed with no looping voice, re-rolling the variant and
the crossfade each time. An intermittent one keeps its authored volume,
plays at a random accumulated compass bearing at min + (max-min)*t^2,
and is dice-gated. Indoors is silent by design: CEnvCell's contributor is
a folded ret and EnvCell carries no sound data.
The Opus review caught four bugs before this landed, one fatal:
- Cell offsets were built in ABSOLUTE world coordinates and differenced
against the listener's STREAMED-frame position, so every one of 576
offsets came out ~32 km, every contribution was culled, and the whole
feature was silent with nothing logged. Offsets are now landblock-local
the way Position::get_offset builds them, and the streamed-frame
position is carried separately for playback, where it belongs.
- The cell's weight was added to the shared denominator once per
DESCRIPTOR instead of once per CELL, dividing every bed's crossfade by
the table's entry count — enough to push a typical authored volume
under the 0.03 audibility floor.
- The drain used where retail's UseTime is strictly
below, so a descriptor authored with a zero rate re-armed at the same
instant and spun the frame forever.
- Arming only enqueued; retail's UpdatePlayQueue PLAYS and then re-arms,
so a newly audible ambient was silent for a full period after the
crossing that made it audible.
Also: beds now go through retail's single 16-voice priority pool rather
than acdream's UI pool (retail has one pool; parking beds in the UI pool
let an A4 portal cue chop one mid-wave and discarded the authored
priority), and CalcDir's in-block test is XY-only, since CalcWeight
includes Z on purpose and CalcDir excludes it on purpose.
Two behaviours are knowingly incomplete and registered rather than
guessed at slice end: TS-66 (sky-lit interiors should keep the outdoor
set) and TS-67 (contribution weight is computed in-plane). Retires TS-29.
The frame-loop hook is a typed IAmbientFramePhase, not a callback — the
first attempt used an Action<float> and the architecture guard
ExtractedUpdateOwners_DoNotRetainAnonymousCallbacks correctly rejected it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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