Rounding the corners of a rectilinear polygon generated by node selection in a JTree

• download example.jar
• download src.zip
• repository

Code

public static List<Point2D> flatteningStepsOnRightSide(
    List<Point2D> list, double arc) {
  int sz = list.size();
  for (int i = 0; i < sz; i++) {
    int i1 = (i + 1) % sz;
    int i2 = (i + 2) % sz;
    int i3 = (i + 3) % sz;
    Point2D pt0 = list.get(i);
    Point2D pt1 = list.get(i1);
    Point2D pt2 = list.get(i2);
    Point2D pt3 = list.get(i3);
    double dx1 = pt2.getX() - pt1.getX();
    if (Math.abs(dx1) > 1.0e-1 && Math.abs(dx1) < arc) {
      double max = Math.max(pt0.getX(), pt2.getX());
      replace(list, i, max, pt0.getY());
      replace(list, i1, max, pt1.getY());
      replace(list, i2, max, pt2.getY());
      replace(list, i3, max, pt3.getY());
    }
  }
  return list;
}

private static void replace(List<Point2D> list, int i, double x, double y) {
  list.remove(i);
  list.add(i, new Point2D.Double(x, y));
}

/**
 * Rounding the corners of a Rectilinear Polygon.
 */
public static Path2D convertRoundedPath(List<Point2D> list, double arc) {
  double kappa = 4d * (Math.sqrt(2d) - 1d) / 3d; // = 0.55228...;
  double akv = arc - arc * kappa;
  int sz = list.size();
  Point2D pt0 = list.get(0);
  Path2D path = new Path2D.Double();
  path.moveTo(pt0.getX() + arc, pt0.getY());
  for (int i = 0; i < sz; i++) {
    Point2D prv = list.get((i - 1 + sz) % sz);
    Point2D cur = list.get(i);
    Point2D nxt = list.get((i + 1) % sz);
    double dx0 = signum(cur.getX() - prv.getX(), arc);
    double dy0 = signum(cur.getY() - prv.getY(), arc);
    double dx1 = signum(nxt.getX() - cur.getX(), arc);
    double dy1 = signum(nxt.getY() - cur.getY(), arc);
    path.curveTo(
        cur.getX() - dx0 * akv, cur.getY() - dy0 * akv,
        cur.getX() + dx1 * akv, cur.getY() + dy1 * akv,
        cur.getX() + dx1 * arc, cur.getY() + dy1 * arc);
    path.lineTo(nxt.getX() - dx1 * arc, nxt.getY() - dy1 * arc);
  }
  path.closePath();
  return path;
}

private static double signum(double v, double arc) {
  return Math.abs(v) < arc ? 0d : Math.signum(v);
}

References

• Rounding the corners of a rectilinear polygon generated by node selection in a JTree(Japanese)