Class ParametricTrajectory

§13's "custom parametric trajectory": any position function of time.

new ParametricTrajectory({
  duration: 4,
  position: (t, out) => out.set(Math.cos(t), Math.sin(t), t * 0.1),
});
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Velocity and acceleration are central differences with h = {@link CENTRAL_DIFFERENCE_STEP} (see the module note on why that value). The callback is invoked twice per velocity sample and three times per acceleration sample.

The three scratch vectors are per instance, so sampling allocates nothing when out is passed — provided the callback does not allocate either. Each callback result is copied into scratch before the next call, so a callback that ignores out and returns its own vector still produces correct differences.