closestPointToPointParameter method
point - the point for which to return a point parameter.
clampToLine - Whether to clamp the result to the range [0, 1].
Returns a point parameter based on the closest point as projected on the
line segment. If clampToLine is true, then the returned
value will be between 0 and 1.
Implementation
double closestPointToPointParameter(Vector3 point, bool clampToLine) {
  _startP.sub2(point, start);
  _startEnd.sub2(end, start);
  final startEnd2 = _startEnd.dot(_startEnd);
  final startEndStartP = _startEnd.dot(_startP);
  double t = startEndStartP / startEnd2;
  if (clampToLine) {
    t = MathUtils.clamp(t, 0, 1);
  }
  return t;
}