Vector3.SignedAngle

Parameters

Description

Returns the signed angle in degrees between from and to.

The smaller of the two possible angles between the two vectors is returned, therefore the result will never be greater than 180 degrees or smaller than -180 degrees. If you imagine the from and to vectors as lines on a piece of paper, both originating from the same point, then the axis vector would point up out of the paper. The measured angle between the two vectors would be positive in a clockwise direction and negative in an anti-clockwise direction.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public Transform target;

    void Update()
    {
        Vector3 targetDir = target.position - transform.position;
        Vector3 forward = transform.forward;
        float angle = Vector3.SignedAngle(targetDir, forward, Vector3.up);
        if (angle < -5.0F)
            print("turn left");
        else if (angle > 5.0F)
            print("turn right");
        else
            print("forward");
    }
}

See Also: Angle function.