exports.rotate_eye_camera = rotate_eye_camera;
function rotate_eye_camera(obj, phi, theta, phi_is_abs, theta_is_abs) {
    var render = obj.render;

    // prepare delta angles
    var d_phi = phi;
    var d_theta = theta;
    if (phi_is_abs || theta_is_abs) {
        var curr_angles = get_camera_angles(obj, _vec2_tmp2);
        if (phi_is_abs)
            d_phi = -(phi - curr_angles[0]);
        if (theta_is_abs)
            d_theta = -(theta - curr_angles[1]);
    }

    if (d_phi || d_theta) {
        var rot_quat = m_quat.identity(_quat4_tmp);

        if (d_phi) {
            var quat_phi = m_quat.setAxisAngle(m_util.AXIS_Y, -d_phi/2, _quat4_tmp2);
            m_quat.multiply(rot_quat, quat_phi, rot_quat);
        }

        if (d_theta) {
            var x_world_cam = m_util.quat_to_dir(render.quat, m_util.AXIS_X, _vec3_tmp);
            var quat_theta = m_quat.setAxisAngle(x_world_cam, -d_theta/2, _quat4_tmp2);
            // NOTE: render.quat->x_world_cam->quat_theta->render.quat leads to 
            // error accumulation if quat_theta is not normalized
            m_quat.normalize(quat_theta, quat_theta);
            m_quat.multiply(rot_quat, quat_theta, rot_quat);
        }

        m_quat.multiply(rot_quat, render.quat, render.quat);
    }
}