How can I raycast between two moving objects in Unity?

Question

How can I raycast between two moving objects?

I want to raycast from a moving enemy to a moving player. I dont know how to actually code to make the direction work.

using UnityEngine;
using System.Collections;

public class Enemy_Manage_Two : MonoBehaviour {

    public GameObject player;

    // Use this for initialization
    void Start () { }

    // Update is called once per frame
    void Update () {

        player = GameObject.FindGameObjectWithTag ("Player");
        //Debug.Log (player.transform.position + " " + transform.position);

        Ray ray = new Ray (transform.position, player.transform.position);
        RaycastHit hit;

        Debug.DrawRay (transform.position, player.transform.position,
            Color.red);

        if(Physics.Raycast(ray, out hit)) {
            gameObject.renderer.material.color = Color.blue;
        } else {
            gameObject.renderer.material.color = Color.white;
        }
    }
}

Answer 1

http://docs.unity3d.com/ScriptReference/Ray.html

This shows us that ray takes 2 parameters; an origin( the place the ray is being cast from ), and a direction. This is where your code is wrong, you pass in the enemy position for an origin, and pass in the player's position for the direction.

A direction should be a normalised vector. To get the direction from one point to another, you must subtract the origin position from the target position and then normalise. So, your code would end up like this:

Vector3 direction = ( player.transform.position - transform.position ).normalized;
Ray     ray       = new Ray( transform.position, direction );

We get the vector difference between the player and the enemy( the vector between the player and enemy ), then we normalise so the vector is of unity length and only describes a direction. Using that and an origin, Ray can figure out that it must shoot from origin towards direction.

Answer 2

Subtract to get the position difference:

/**
 *  Show ray between two points 
 */
void ShowRayBetweenPoints (Vector3 p1, Vector3 p2)
{
    Debug.DrawRay (p1, (p2 - p1), Color.yellow);
}