LookRotation() make X axis face the target instead of Z

Question

I use LookRotation() in order for an object to look at another, but since I'm using 2D I would like to make the axis looking/facing the target to be X instead of Z. I have the code below currently:

Vector3 dif = targetPos - obj.position;
Quaternion angle= Quaternion.LookRotation(dif, obj.up);
obj.rotation = Quaternion.Lerp(obj.localRotation, angle, Time.deltaTime);

Now->

What I'm trying to achieve->

Thanks!

Answer 1

I've answered a few flavours of this before.

The basic idea is to chain together two rotations: one that takes the axes you want to align and points them along z+ and y+ respectively, and then the standard LookRotation to take z+ and y+ to the desired destination axes.

For a straight 3D analogue of LookRotation that positions the x+ axis instead of z+, but still treats y+ the same way as ordinary LookRotation:

Quaternion XLookRotation(Vector3 right, Vector3 up = default)
{
    if(up == default)
      up = Vector3.up;

    Quaternion rightToForward = Quaternion.Euler(0f, -90f, 0f);
    Quaternion forwardToTarget = Quaternion.LookRotation(right, up);

    return forwardToTarget * rightToForward;
}

Or, to keep an object locked in 2D with z+ forward, as in the second link above:

Quaternion XLookRotation2D(Vector3 right)
{
    Quaternion rightToUp = Quaternion.Euler(0f, 0f, 90f);
    Quaternion upToTarget = Quaternion.LookRotation(Vector3.forward, right);

    return upToTarget * rightToUp;
}