Reading it

There are three ways to read a flight, from cheapest to dearest.

In a frame, without renderingCopy Anchor Link

useFlightFrame calls back every frame with the flight's values, as useFrame does. Use it for anything that moves with the flight: a camera's shake, a sound's pitch, a gauge needle drawn in the scene.

useFlightFrame((flight) => {
  engine_sound.playbackRate = 0.6 + flight.throttle * 0.4;
  needle.current.rotation.z = -flight.mach * Math.PI;
});

The second argument is the callback's priority, as useFrame's. A tracked flight is written at −1, so anything at 0 or later reads this frame's.

By handCopy Anchor Link

useFlightStore gives the Flight itself. Its values is one object for its whole life, written in place, so it can be held and read whenever:

const flight = useFlightStore();
const values = flight?.values;

useFrame(() => {
  if (values && values.mach > 1) {
    boom();
  }
});

Don't write to values. Write with flight.set, so the speeds and the air that follow are worked out and the effects hear of it.

flight.version counts the writes. Remember the last one you read at, and you can skip your own work when nothing changed, as the effects do.

In the UICopy Anchor Link

useFlight selects from the flight and renders when the selection changes:

const Hud = () => {
  const mach = useFlight((v) => v.mach.toFixed(2), { hz: 10 });
  const altitude = useFlight((v) => Math.round(v.altitudeM / 10) * 10);

  return (
    <div>
      M {mach} · {altitude} m
    </div>
  );
};

• hz caps the renders a second. A value that moves every frame would otherwise render every frame: give it one. The last change in a gap is never dropped.
• Round what you select. A selection that does not change does not render, so rounding the altitude to 10 m renders when it crosses one.
• equal compares two selections, Object.is by default. A selector that builds an object every time renders on every write unless you give one.

Outside any provider, useFlight reads a default flight at rest, so a HUD renders before its scene has loaded.

What it knowsCopy Anchor Link

Beyond what is written, a flight works out:

flight.air is the whole moist air, with the vapour pressure and the mixing ratio too. See The atmosphere.

Next, engines.