ReadonlyfixedConstant simulation step in seconds (§7a, §10). Appendix A default 1/60.
ReadonlysimulationDeterministic simulation clock in seconds (§9), already advanced to the end
of the step being produced — see ParticleSystem.fixedUpdate for what
that means for a §27 field's time argument.
The part of §9's
TimeStatea particle step reads.Structural, and deliberately narrow:
@fourjs/motion'sReadonlyTimeStatecarries eleven fields and this system reads two. AnyReadonlyTimeStatesatisfies it.