Edge.fromTangent constructor

Edge.fromTangent(Corner prev, Corner current)

Implementation

factory Edge.fromTangent(Corner prev, Corner current) {
  final clockwise = current.clockwise;
  final transverse = (prev.clockwise != current.clockwise);
  if (!transverse && prev.circle.radius == current.circle.radius) {
    return Edge.sameRadiusDirectTangent(prev, current);
  }

  /* Setting the bigger circle as the first and the other as second. This is
  *  important in case of the direct tangent, as we will be using the
  *  section formula to find the external point, there. */
  var (first, second) = (prev.circle.radius > current.circle.radius)
      ? (prev, current)
      : (current, prev);

  /* In case of direct tangent we will be getting the external point,
  *  Otherwise will be getting the internal point. */
  final bothRadiusAreZero =
      first.circle.radius == 0 && second.circle.radius == 0;
  final transverseFactor = (transverse ? 1 : -1);
  final commonPoint = (first.circle.center, second.circle.center)
      .pointInBetween((bothRadiusAreZero
          ? (1, transverseFactor)
          : (first.circle.radius, transverseFactor * second.circle.radius)));

  //Angle between a single direct tangent and the line joining the centres.
  final slopeDiff = Angle.fromSin(
      second.circle.radius, (second.circle.center, commonPoint).distance);

  final centerLine =
      Line.fromTwoPoints((prev.circle.center, current.circle.center));

  for (final value in const [true, false]) {
    final tangent = centerLine.rotate(commonPoint, slopeDiff, value);

    //Points of touch with the [prev] and [current] circles respectively
    final first = tangent.perpendicularFoot(prev.circle.center);
    final second = tangent.perpendicularFoot(current.circle.center);

    //Checking if according to the direction tangent is correct.
    if (areCorrectPoints(first, second, current.circle.center, clockwise)) {
      return Edge(first, second);
    }
  }

  throw PlatformException(
    code: 'NO_CORRECT_TANGENTS',
    details: 'No correct tangent found between the given two corners.',
  );
}