Vector3.Dot

Description

Dot Product of two vectors.

The dot product is a float value equal to the magnitudes of the two vectors multiplied together and then multiplied by the cosine of the angle between them.

For normalized vectors Dot returns 1 if they point in exactly the same direction, -1 if they point in completely opposite directions and zero if the vectors are perpendicular.

// detects if other transform is behind this object

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour
{
    public Transform other;

    void Update()
    {
        if (other)
        {
            Vector3 forward = transform.TransformDirection(Vector3.forward);
            Vector3 toOther = other.position - transform.position;

            if (Vector3.Dot(forward, toOther) < 0)
            {
                print("The other transform is behind me!");
            }
        }
    }
}