Spin profiles

interface SpinProfile {
  spinSpeed: number;          // deg/s at cruise
  accelerationMs: number;     // rest to cruise
  accelerationEase?: Ease;    // default 'power2.in'
  minimumSpinTime: number;    // the stop may not begin before this many ms since spin()
  minCruiseMs: number;        // nor before this long at cruise
  stopDuration: number;       // what the deceleration should take (target)
  stopEase?: Ease;            // an ease-out; default 'power3.out'
  minTurns: number;           // fewest full turns while stopping
  maxTurns: number;           // most
  skipDuration: number;       // the fast-forward on skip
}

How the stop duration is chosen#

The planner matches the ease’s start slope to the cruise speed so the hand-off is smooth. That fixes the duration for any given distance: T = distance * slope / speed. It then tries every turn count from minTurns to maxTurns and keeps the one whose T is closest to stopDuration. The actual duration is therefore near the target, not equal to it; spin:stopping reports it.

power3.out has slope 4, power2.out 3, power1.out 2, expo.out about 7. An inOut ease starts at slope 0 and is clamped with a one-time warning; use an out curve.

Eases#

Names follow the GSAP vocabulary without depending on it: none, linear, power1..4.in|out|inOut (quad, cubic, quart, quint are aliases), sine.*, expo.*, circ.*, back.in|out(1.7). Or pass a (t) => number. EASE_NAMES lists them; resolveEase(name) throws on a typo with the list.

A stop leg whose ease starts at the cruise speed lasts turns * 360 * slope / spinSpeed seconds (slope is the ease’s start slope: 3 for power2.out, 4 for power3.out, 5 for power4.out), so the planner can only choose among whole-turn durations. Keep stopDuration inside the range minTurns..maxTurns spans, or the nearest turn count wins silently; the presets are tested for it.