code: public PathBuilder cubicTo(Point2d cp1, Point2d cp2, Point2d ep) {
          add(new CubicTo(cp1, cp2, ep));
          return this;
      }
docs: Make a cubic curve in the path, with two control points.
  
  @param cp1 the first control point
  @param cp2 the second control point
  @param ep the end point of the curve
  @return  a reference to this builder