util.Quaternion.fromLookAt = function(direction, up) {
    up = up || <0, 1, 0>;
    direction = direction.normal();

    // Orient the -z axis to be along direction.
    var firstQuat;
    if ((direction - <0, 0, -1>).lengthSquared() < 1e-08) {
        firstQuat = new util.Quaternion(0, 0, 0, 1);
    } else if ((direction - <0, 0, 1>).lengthSquared() < 1e-08) {
        firstQuat = new util.Quaternion(0, 1, 0, 0);
    } else {
        var quatAxis = <0, 0, -1>.cross(direction);
        var angle = util.acos(<0, 0, -1>.dot(direction));
        quatAxis = quatAxis.normal();
        firstQuat = new util.Quaternion(quatAxis, angle);
    }

    // Compute new up vector and orient the y axis to be along that direction.
    var secondQuat;
    if (direction != up) {
        var left = direction.cross(up);
        var newUp = left.cross(direction);
        newUp = newUp.normal();
        var quatAxis = <0, 1, 0>.cross(newUp);
        var angle = util.acos(<0, 1, 0>.dot(newUp));
        quatAxis = quatAxis.normal();
        secondQuat = new util.Quaternion(quatAxis, angle);
    } else {
        secondQuat = new util.Quaternion(0, 0, 0, 1);
    }

    return secondQuat.mul(firstQuat);
}