getVelocityEstimate method

Implementation

VelocityEstimate? getVelocityEstimate() {
  // Has user recently moved since last sample?
  if (_sinceLastSample.elapsedMilliseconds > _assumePointerMoveStoppedMilliseconds) {
    return const VelocityEstimate(
      pixelsPerSecond: Offset.zero,
      confidence: 1.0,
      duration: Duration.zero,
      offset: Offset.zero,
    );
  }

  final List<double> x = <double>[];
  final List<double> y = <double>[];
  final List<double> w = <double>[];
  final List<double> time = <double>[];
  int sampleCount = 0;
  int index = _index;

  final _PointAtTime? newestSample = _samples[index];
  if (newestSample == null) {
    return null;
  }

  _PointAtTime previousSample = newestSample;
  _PointAtTime oldestSample = newestSample;

  // Starting with the most recent PointAtTime sample, iterate backwards while
  // the samples represent continuous motion.
  do {
    final _PointAtTime? sample = _samples[index];
    if (sample == null) {
      break;
    }

    final double age = (newestSample.time - sample.time).inMicroseconds.toDouble() / 1000;
    final double delta = (sample.time - previousSample.time).inMicroseconds.abs().toDouble() / 1000;
    previousSample = sample;
    if (age > _horizonMilliseconds || delta > _assumePointerMoveStoppedMilliseconds) {
      break;
    }

    oldestSample = sample;
    final Offset position = sample.point;
    x.add(position.dx);
    y.add(position.dy);
    w.add(1.0);
    time.add(-age);
    index = (index == 0 ? _historySize : index) - 1;

    sampleCount += 1;
  } while (sampleCount < _historySize);

  if (sampleCount >= _minSampleSize) {
    // Marking as "late" ensures that yFit isn't evaluated unless it's needed.
    late final PolynomialFit? xFit = LeastSquaresSolver(time, x, w).solve(2);
    late final PolynomialFit? yFit = LeastSquaresSolver(time, y, w).solve(2);

    if (xFit != null && yFit != null) {
      return VelocityEstimate( // convert from pixels/ms to pixels/s
        pixelsPerSecond: Offset(xFit.coefficients[1] * 1000, yFit.coefficients[1] * 1000),
        confidence: xFit.confidence * yFit.confidence,
        duration: newestSample.time - oldestSample.time,
        offset: newestSample.point - oldestSample.point,
      );
    }
  }

  // We're unable to make a velocity estimate but we did have at least one
  // valid pointer position.
  return VelocityEstimate(
    pixelsPerSecond: Offset.zero,
    confidence: 1.0,
    duration: newestSample.time - oldestSample.time,
    offset: newestSample.point - oldestSample.point,
  );
}