@fourjs/particles

Particle systems — deterministic CPU simulation with force fields. Part of fourJS.

Implements §27 and §36 of docs/SPECIFICATION.md; shipped in Phase 9 (§112). Simulation is seeded and deterministic: emitters burn a fixed PARTICLE_DRAWS_PER_SPAWN RNG draws per spawn slot, so the stream is a function of history.

What's here

• ParticleEmitter — spawn rate, bursts (ParticleBurst), ranges/ramps (ParticleRange, ParticleLifetimeRamp), seeded via SeededRandom (re-exported from @fourjs/core).
• ParticlePool — structure-of-arrays Float32Array storage with swap-remove; capacity is part of the deterministic contract.
• Force fields (§27) — factories uniformGravityField, dragField, windField, radialField (inverse-square), vortexField, turbulenceField (bounded hash-noise curl; honestly not divergence-free), and volumeField over box/sphere volumes.
• ParticleSystem — the fixed-step system (PRIORITY_PARTICLES = 500) advancing emitters and fields.
• ParticleRenderable — bridges to @fourjs/render's instanced particle path (PARTICLE_INSTANCE_FLOATS stride-8 interleaved instances; the ParticleDrawable contract is deliberately duck-typed — the dependency matrix forbids the edge).

100k particles + 3 fields measured at ~16.5 ms/step on CI hardware (recorded benchmark, not a 60 fps claim).

Staged / not yet implemented

• GPU compute simulation, particle-vs-physics collision, and trails.

Unit tests are colocated in tests/ per §92.

Workspace name @fourjs/particles; publishes as @danielsimonjr/fourjs-particles.