threejs-procedural-motion-systems

Procedural Motion Systems

Semantic state is the source of truth; transforms are its presentation. Keep one writer for each position, orientation, velocity, phase, and event channel.

Process

1. Declare state and its writer

Name the observable motion, SI units, coordinate frame, stable actor identity, initial state, phase/event state, and duration contract: finite with a terminal pose plus velocity/hand-off rule, periodic with a wrap rule, or open-ended with a stop/reset policy. Assign one writer to every animated channel; clips, procedural roots, instance storage, camera rigs, and external solvers may own different channels only through an explicit layering order.

When another simulation supplies or reacts to motion, declare:

• exchanged quantities, units, frame/origin, state owner, producer, consumers, version, and publication order;
• timestamp or half-open interval, cadence, sample phase, interpolation or extrapolation, and discontinuity behavior;
• support/filter, validity, staleness, error bound, and missing-value behavior;
• rate versus interval-integrated semantics and one-way or two-way reaction ownership and order;
• GPU producer/consumer passes, resource generation, queue order, and actual completion evidence;
• immutable previous/current committed samples, stable identity, and reset, reuse, retirement, and disposal rules.

Keep frame-critical state on its owning device; schedule diagnostic readback asynchronously outside state advance and presentation.

Complete when: every animated channel has exactly one writer, one frame and unit convention, one stable identity, and a defined initial state plus finite, periodic, or open-ended duration contract; every cross-system boundary closes every applicable declaration above.

2. Choose the time model and representation

Choose by state dependence first, then actor count:

Motion	Time model	Representation
Seekable authored transform	closed form at authoritative seconds	Object3D for a few actors; vertex TSL for many
Phased authored sequence	closed form plus discrete event state	phase-local time and a replayable event log
Spring, constraint, collision, or other recurrent state	fixed step with previous/current state	CPU arrays or GPU storage selected by measured crossover
Perceptual follow	dt-correct exponential response	render-time state, explicitly non-physical