A walk-up curve with a long slow start read as lag: check a filmstrip, not only the arrival time

// A cubic bezier from (0,0) to (1,1), as CSS cubic-bezier(), sampled once into a table.
function sampledEase(x1: number, y1: number, x2: number, y2: number, n = 96) {
  const bez = (t: number, a: number, b: number) => 3 * (1 - t) * (1 - t) * t * a + 3 * (1 - t) * t * t * b + t * t * t;
  const table = new Float32Array(n + 1);
  for (let i = 0; i <= n; i++) {
    let lo = 0, hi = 1;
    for (let k = 0; k < 24; k++) { const t = (lo + hi) / 2; if (bez(t, x1, x2) < i / n) lo = t; else hi = t; }
    table[i] = bez((lo + hi) / 2, y1, y2);
  }
  return (u: number) => {
    const p = Math.min(1, Math.max(0, u)) * n, i = Math.min(n - 1, Math.floor(p));
    return table[i] + (table[i + 1] - table[i]) * (p - i);
  };
}
// before: sampledEase(0.5, 0, 0.14, 1)
const walkEase = sampledEase(0.36, 0.04, 0.16, 1);
// The walk up: u = (msSinceClick - 60) / 1230