OptionalfixedFixed simulation step in seconds. Default 1/60 (Appendix A).
OptionalmaximumMaximum fixed steps per step call. Default 5 (Appendix A).
OptionalonInvoked once per fixed simulation step, before onUpdate.
OptionalonInvoked once per step call, last.
OptionalonInvoked once per step call, after every fixed step of that call.
Construction options. Omitted numeric options take the Appendix A defaults.