code: public Vector2f transformDirection(float x, float y, Vector2f dest) {
          return dest.set(m00 * x + m10 * y, m01 * x + m11 * y);
      }
docs: Transform/multiply the given 2D-vector <code>(x, y)</code>, as if it was a 3D-vector with z=0, 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 <code>0.0</code>, so it
  will represent a direction in 2D-space rather than a position. This method will therefore
  not take the translation part of the matrix into account.
  <p>
  In order to store the result in the same vector, use {@link #transformDirection(Vector2f)}.
  
  @see #transformDirection(Vector2f)
  
  @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