getVelocityEstimate method

Implementation

VelocityEstimate getVelocityEstimate() {
  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).inMilliseconds.toDouble();
    final double delta = (sample.time - previousSample.time).inMilliseconds.abs().toDouble();
    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) {
    final LeastSquaresSolver xSolver = LeastSquaresSolver(time, x, w);
    final PolynomialFit xFit = xSolver.solve(2);
    if (xFit != null) {
      final LeastSquaresSolver ySolver = LeastSquaresSolver(time, y, w);
      final PolynomialFit yFit = ySolver.solve(2);
      if (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,
  );
}