Manually update rotation of only Y-axis on Agent

Question

I have some code to manage to rotation of my Navmesh agents:

if (Agent.isActiveAndEnabled && Agent.hasPath)
        {
            if (Agent.velocity.sqrMagnitude > Mathf.Epsilon)
            {
                transform.rotation = Quaternion.LookRotation(Agent.velocity.normalized);
            }
        }

It's causing my some issues with some odd rotations on the x/z axis for 1-2 frames every now and then, is there some way I can get this exact behaviour but only modify the y-axis?

Answer 1

If your agents are always oriented vertically, this is reasonably straightforward. Just project your velocity into the horizontal plane, and look toward that. This can always be accomplished with a pure yaw, no pitch/roll required:

var projected = Agent.velocity;
projected.y = 0f;

if(!Mathf.Approximately(projected.sqrMagnitude, 0f))    
    transform.rotation = Quaternion.LookRotation(projected);

The if check just declines to rotate if the agent has stopped or is travelling purely vertically, which helps avoid a sudden snap to 0-degrees in those cases. Instead, we'll just keep our current yaw.

If your agent can be aligned arbitrarily, then you can use this technique explained in existing answers to locally yaw to face your velocity while keeping your current/desired local up vector fixed.