RaycastHit.normal

Description

The normal of the surface the ray hit.

// Calculate the reflection of a "laser beam" off a clicked object.

// The object from which the beam is fired. The incoming beam will
// not be visible if the camera is used for this!
var gunObj: Transform;

function Update () {
    if (Input.GetMouseButton(0)) {
        var hit: RaycastHit;
        var ray = Camera.main.ScreenPointToRay(Input.mousePosition);

        if (Physics.Raycast(ray, hit)) {
            // Find the line from the gun to the point that was clicked.
            var incomingVec = hit.point - gunObj.position;

            // Use the point's normal to calculate the reflection vector.
            var reflectVec = Vector3.Reflect(incomingVec, hit.normal);

            // Draw lines to show the incoming "beam" and the reflection.
            Debug.DrawLine(gunObj.position, hit.point, Color.red);
            Debug.DrawRay(hit.point, reflectVec, Color.green);
        }
    }
}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Transform gunObj;
    void Update() {
        if (Input.GetMouseButton(0)) {
            RaycastHit hit;
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            if (Physics.Raycast(ray, out hit)) {
                Vector3 incomingVec = hit.point - gunObj.position;
                Vector3 reflectVec = Vector3.Reflect(incomingVec, hit.normal);
                Debug.DrawLine(gunObj.position, hit.point, Color.red);
                Debug.DrawRay(hit.point, reflectVec, Color.green);
            }
        }
    }
}

See Also: Physics.Raycast, Physics.Linecast, Physics.RaycastAll.