code: public void curveTo (final float x1,
                         final float y1,
                         final float x2,
                         final float y2,
                         final float x3,
                         final float y3) throws IOException
    {
      if (inTextMode)
      {
        throw new IllegalStateException ("Error: curveTo is not allowed within a text block.");
      }
      writeOperand (x1);
      writeOperand (y1);
      writeOperand (x2);
      writeOperand (y2);
      writeOperand (x3);
      writeOperand (y3);
      writeOperator ((byte) 'c');
    }
docs: Append a cubic Bézier curve to the current path. The curve extends from the
  current point to the point (x3, y3), using (x1, y1) and (x2, y2) as the
  Bézier control points.
  
  @param x1
  x coordinate of the point 1
  @param y1
  y coordinate of the point 1
  @param x2
  x coordinate of the point 2
  @param y2
  y coordinate of the point 2
  @param x3
  x coordinate of the point 3
  @param y3
  y coordinate of the point 3
  @throws IOException
  If the content stream could not be written.
  @throws IllegalStateException
  If the method was called within a text block.