A structural stream specifies the structure of a realm’s objects — what exists, of what type, parented where — and typically varies slowly over time. It is one of the two stream kinds the Scene Composition Protocol uses; the other, the parameter stream, carries the values that change quickly.
Why the split#
The two kinds have opposite delivery needs. Structural records are comparatively rare, but nothing else can be interpreted without them, and a missed one cannot be papered over by extrapolation — a node that never learned an object exists cannot render it. Parameter records are the reverse: high rate, individually disposable, stale within a frame. Separating them lets a node fetch the structure of a newly-visible BVH partition once and then track only its parameters, and lets each kind be delivered on the terms it actually needs.
A late-joining node must obtain the current structure before the parameter stream means anything at all, which makes the structural stream the natural home for a baseline — a full description a subscriber can start from, rather than a delta against a state it never had. Since every node is ephemeral and peers join constantly, this is the common case rather than an edge case. How baselines are produced, how often, and by whom is not yet specified.
External links#
Similar concepts and prior art:
- Delta encoding — baseline-plus-changes, the general form
- Netcode on Wikipedia
- Snapshot Interpolation — Gaffer on Games, on baselines and deltas in practice
- glTF scenes and nodes — the kind of static structure a baseline resembles