public void lookAtDirection(Vector3f direction, Vector3f up) {
        this.rotation.lookAt(direction, up);
        onFrameChange();
    }
Sets the direction the camera is facing
given a direction and an up vector.

@param direction the direction this camera is facing.
@param up the desired "up" direction for the camera (not null,
    unaffected, typically (0,1,0))
jme3-core/src/main/java/com/jme3/renderer/Camera.java