public class ParallaxCamera extends OrthographicCamera
{
   Matrix4 parallaxView     = new Matrix4 ();
   Matrix4 parallaxCombined = new Matrix4 ();
   Vector3 tmp              = new Vector3 ();
   Vector3 tmp_2            = new Vector3 ();

   public ParallaxCamera (float viewportWidth, float viewportHeight) { super (viewportWidth, viewportHeight); }

   public Matrix4 calculateMatrix (float x, float y)
   {
      update ();
      tmp.set (position);
      tmp.x *= x;
      tmp.y *= y;

      parallaxView.setToLookAt (tmp, tmp_2.set (tmp).add (direction), up);
      parallaxCombined.set (projection);
      Matrix4.mul (parallaxCombined.val, parallaxView.val);

      return parallaxCombined;
  }
}

clickPos.set (Gdx.input.getX (), Gdx.input.getY (), 0);
camera.unproject (clickPos);