code: public Vector2d transformPosition(double x, double y, Vector2d dest) {
          return dest.set(m00 * x + m10 * y + m20, m01 * x + m11 * y + m21);
      }
docs: Transform/multiply the given 2D-vector <code>(x, y)</code>, as if it was a 3D-vector with z=1, by
  this matrix and store the result in <code>dest</code>.
  <p>
  The given 2D-vector is treated as a 3D-vector with its z-component being 1.0, so it
  will represent a position/location in 2D-space rather than a direction.
  <p>
  In order to store the result in the same vector, use {@link #transformPosition(Vector2d)}.
  
  @see #transformPosition(Vector2d)
  @see #transform(Vector3dc, Vector3d)
  
  @param x
  the x component of the vector to transform
  @param y
  the y component of the vector to transform
  @param dest
  will hold the result
  @return dest