Goal
I am designing a boid system using Unity. I deal with the awareness radius by adding a boid to the "Swarm" list when it enters a collider. In order to find the force for each boid, I need to cycle through the swarm list, access the "Boid" class, and retrieve velocity and position.
Problem
The Boid classes from each swarm entity are added to a new list, and passed to the physics controller. However, a NullReferenceException is thrown at line 96, and I don't understand why that variable would be null. As far as I know, accessing a populated Enumerable<Boid> using foreach should have variables within.
NullReferenceException: Object reference not set to an instance of an object Boid.Alignment (System.Collections.Generic.IEnumerable`1[T] boids) (at Assets/Scripts/Boid.cs:96) Boid.Update () (at Assets/Scripts/Boid.cs:42)
After testing, it seems it is thrown when accessing any part of the new list of Boids.
Why does my new list contain no data? Is there a better way to handle a 2D implementation of boids in a 3D space? Is there a resource I can use to better understand Linq?
P.S. I am very new to using Linq systems, and most of this code is taken from this video and this Unity project script
Code
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;
public class Boid : MonoBehaviour
{
// Global Variables
public Boid_Settings settings;
// Local Variables
public Rigidbody body;
public Vector2 acceleration;
public Vector2 velocity
{
get
{ return new Vector2(body.velocity.x, body.velocity.z); }
set
{ body.velocity = new Vector3(value.x, body.velocity.y, value.y); }
}
public Vector2 position
{
get
{ return new Vector2(transform.position.x, transform.position.z); }
}
public List<GameObject> swarm = new List<GameObject>();
public List<GameObject> targets = new List<GameObject>();
// Functions
private void Start()
{
float angle = Random.Range(0, 2 * Mathf.PI);
transform.rotation = Quaternion.Euler(new Vector3(0, 0, angle));
velocity = new Vector2(Mathf.Cos(angle), Mathf.Sin(angle));
}
private void Update()
{
IEnumerable<Boid> boids = swarm.Select(o => o.GetComponent<Boid>()).ToList(); //Line 40
Vector2 alignment = Alignment(boids); //LINE 42
Vector2 separation = Separation(boids);
Vector2 cohesion = Cohesion(boids);
acceleration = settings.alignmentWeight * alignment + settings.cohesionWeight * cohesion + settings.seperationWeight * separation;
UpdatePhysics();
}
// Entity Awareness Assignment
private void OnTriggerEnter(Collider collider)
{
if (collider.CompareTag("Zombie"))
{ swarm.Add(collider.gameObject); }
else if (collider.CompareTag("Player") || collider.CompareTag("Lure"))
{ targets.Add(collider.gameObject); }
}
private void OnTriggerExit(Collider collider)
{
if (collider.CompareTag("Zombie"))
{ swarm.Remove(collider.gameObject); }
else if (collider.CompareTag("Player") || collider.CompareTag("Lure"))
{
targets.Remove(collider.gameObject);
StartCoroutine(LingerTarget(collider.gameObject));
}
}
IEnumerator LingerTarget(GameObject target)
{
targets.Add(target);
yield return new WaitForSeconds(settings.lingerTime);
targets.Remove(target);
}
// Core Boid Logic
public void UpdatePhysics()
{
// Apply the acceleration, and then limit the speed to the maximum.
Vector2 UncappedVelocity = velocity + acceleration;
velocity = ApplyLimit(UncappedVelocity, settings.maxSpeed);
float angle = Mathf.Atan2(velocity.y, velocity.x) * Mathf.Rad2Deg;
body.transform.rotation = Quaternion.Euler(new Vector3(0, 0, angle));
}
private Vector2 Alignment(IEnumerable<Boid> boids)
{
Vector2 velocity = Vector2.zero;
if (!boids.Any()) return velocity;
foreach (Boid boid in boids)
{ velocity += boid.velocity; } //LINE 96
velocity /= boids.Count();
Vector2 steer = Steer(velocity.normalized * settings.maxSpeed);
return steer;
}
private Vector2 Cohesion(IEnumerable<Boid> boids)
{
if (!boids.Any()) return Vector2.zero;
Vector2 sumPositions = Vector2.zero;
foreach (Boid boid in boids)
{ sumPositions += boid.position; }
Vector2 average = sumPositions / boids.Count();
Vector2 direction = average - position;
Vector2 steer = Steer(direction.normalized * settings.maxSpeed);
return steer;
}
private Vector2 Separation(IEnumerable<Boid> boids)
{
Vector2 direction = Vector2.zero;
boids = boids.Where(o => Vector3.Distance(o.transform.position, position) <= settings.avoidanceRadius);
if (!boids.Any()) return direction;
foreach (Boid boid in boids)
{
Vector2 difference = position - boid.position;
direction += difference.normalized / difference.magnitude;
}
direction /= boids.Count();
Vector2 steer = Steer(direction.normalized * settings.maxSpeed);
return steer;
}
private Vector2 Steer(Vector2 desired)
{
Vector2 steer = desired - velocity;
steer = ApplyLimit(steer, settings.maxSteerForce);
return steer;
}
// Calculation Helpers
private Vector2 ApplyLimit(Vector2 baseVector, float limit)
{
if (baseVector.sqrMagnitude > limit * limit)
{ baseVector = baseVector.normalized * limit; }
return baseVector;
}
}
The Boid_Settings Module:
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
[CreateAssetMenu]
public class Boid_Settings : ScriptableObject
{
// Boid
public float maxSpeed = 5;
public float avoidanceRadius = 1;
public float maxSteerForce = 3;
public float lingerTime = 2.5f;
public float alignmentWeight = 1;
public float cohesionWeight = 1;
public float seperationWeight = 1;
public float targetWeight = 1;
// Spawner
public float awarenessRadius = 2.5f;
}
Context Pictures
Proof the boid classes have data to be read
Unity Enviroment & Boid.cs Attachment
Unity Boid Boid.body Component
Each Boid finds two swarm mates when the game is run
