measureFps.ts

type FpsCallback = (fps: number) => void;

function measureFps() {
  const _deltaArr: number[] = [];
  let _time = 0;
  let _isRunning = false;
  let _callback: FpsCallback;

  const measure = () => {
    if (!_isRunning) return;

    const now = performance.now();
    _deltaArr.push(now - _time);
    _time = now;

    while (_deltaArr.length > 50) _deltaArr.shift();

    if (_callback) {
      const sum = _deltaArr.reduce((a, b) => a + b, 0);
      const avg = 1 / (sum / _deltaArr.length / 1000);

      _callback(Math.round(avg));
    }

    requestAnimationFrame(measure);
  };

  return {
    isRunning: () => _isRunning,
    start: (callback: FpsCallback) => {
      if (_isRunning) return;
      _callback = callback;
      _time = performance.now() - 1;
      _isRunning = true;
      _deltaArr.length = 0;
      requestAnimationFrame(measure);
    },
    stop: () => {
      _isRunning = false;
      _deltaArr.length = 0;
    },
  };
}