fog.fbs — the fog-of-war mask

Source: modules/Descent.Vtt.Protocol/schemas/fog.fbs at build time. 4 line(s) withheld — internal regions exist in the source and are removed by the scrubbing pipeline; that they exist is public, their content is not.

// ADR-092 clause 3's out-of-band fog mask message.
//
// Read schemas/README.md first; its three rules are assumed here.
//
// **Why this is not on the snapshot.** Q-010 fixes a packed chunk at 16 KiB.
// Riding the tick-driven snapshot, one chunk alone is ~320 KiB/s per viewer at
// Q-001's 20Hz — more than fifty times the entire transform payload it would be
// attached to. Its cadence is already governed separately by the
// Q-068…Q-071 ladder, so bundling it would silently re-couple two cadences §5.3
// deliberately separates.
//
// **The filter here is different in kind from the snapshot's.** A snapshot
// filter answers "may this viewer see this entity". A mask *is* the disclosure:
// the question is which party's explored set this viewer belongs to, and the
// answer is never "all of them merged". ADR-091 clause 6 is the constraint — a
// mask set exists for a party that receives one, and per-viewer masks were
// rejected because fifty independent masks were never affordable at any tier.

namespace Descent.Vtt.Protocol;

/// One chunk of fog, as a single party is permitted to see it.
///
/// The bytes are Q-010's packed form **as persisted** — `VISIBLE` already
/// stripped, per ADR-035 — so a host cannot store what it was handed and
/// resurrect a stale lit set.
table FogChunk {
  /// Cell coordinates of the chunk's origin corner.
  origin_x: int32;
  origin_y: int32;

  /// Q-010's packed chunk: 256x256 cells at 2 bits each, 16 KiB.
  ///
  /// A vector rather than a fixed-size struct because FlatBuffers has no
  /// fixed-length byte array outside a struct, and a 16 KiB struct would be
  /// copied by value at every accessor.
  packed: [ubyte];
}

/// What one viewer is sent when their party's fog advances.
///
/// **Event-driven on the mask cadence, not the tick.** The Q-068…Q-071 ladder
/// decides when a party's mask advances; this message follows that and not
/// Q-001. A viewer whose party has not advanced receives nothing rather than a
/// repeat of what they already hold.
table FogUpdate {
  /// §9.6: every packet carries this.
  protocol_version: uint32;

  /// The tick the mask was computed for.
  ///
  /// Distinct from the snapshot's `transform_tick` and routinely behind it: the
  /// tick is pipelined, geometry is dispatched fire-and-forget and consumed a
  /// tick later. A client gates rendering on the older of the two, which is what
  /// `PerViewerSnapshot.disclosure_tick` carries.
  mask_tick: int64;

  /// The chunks this viewer's party is permitted to hold.
  ///
  /// **Already filtered**, and the filter is party membership rather than
  /// entity entitlement. A viewer belonging to no party with an observer
  /// receives an empty vector — never another party's mask, and never a merge.
  chunks: [FogChunk];
}

root_type FogUpdate;

/// Identifies a fog buffer on disk or in a capture.
file_identifier "DVF1";