Following code is based on the work of Craig Reynolds which I came across while reading Programming Game AI by Example by Mat Buckland . Robin Green suggests that Jitter of the Boids can be smoothened by decoupling the heading of the Boid form the velocity. I haven’t applied smoothing to the following code.
Download unity project :
GitHub : https://github.com/kalanadis/2D_FLOCKING/tree/master
Google Drive :https://drive.google.com/file/d/0ByoByqm47PspQm9oYUh6YkhIc3M/view?usp=sharing
World partitions
World is divided to a 3×4 grid for cell space partitioning (to simplify things I’ve positioned the Camera so all the x , y coordinates of the world would be +) . Steering behaviours are combined using weighted truncated running sum with prioritization .
Green lines: wall colliders,Blue lines: wall normals, Red lines: sensor antennas of the agents
The C# Script for Boid behaviour.
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
public class Agent : MonoBehaviour {
public float Agent_Radius;
private Vector2 m_Velocity;
private float m_HeadingAngle;
private Transform m_Transform
public float WanderRadius;
public float WanderDistance;
public float WanderJitter;
private Vector2 m_vWanderTarget;
private GameWorld m_GameWorld;
private int m_CurrentGrid;
private int m_NebCount;
public int SeparationWeight;
public int AlignmentWeight;
public int CohesionWeight;
public int WallAvoidanceWeight;
public int WanderWeight;
public int MaxSteeringForce;
// Use this for initialization
void Start () {
m_Transform = transform;
m_vWanderTarget = new Vector2(1,0);
m_GameWorld = GameWorld.Instance;
m_CurrentGrid = -1;
m_NebCount = 0;
}
void FixedUpdate(){
rigidbody2D.AddForce (SteeringForce());
//set heading
m_Velocity = rigidbody2D.velocity;
m_HeadingAngle = (Mathf.Atan2(m_Velocity.y,m_Velocity.x))*Mathf.Rad2Deg;
rigidbody2D.MoveRotation (m_HeadingAngle);
UpdateGrid ();
}
private void UpdateGrid(){
int x = (int)(m_Transform.position.x*0.25f);
int y = (int)(m_Transform.position.y*0.25f);
int i =((y*4)+x);
if (m_CurrentGrid != i) {
if(m_CurrentGrid!=-1)m_GameWorld.Grid[m_CurrentGrid].Remove(this);
m_CurrentGrid = i; m_GameWorld.Grid[i].Add(this);
}
}
private Vector2 SteeringForce(){
m_NebCount = 0;
Vector2 Separation=new Vector2(0,0);
Vector2 Alignment=new Vector2(0,0);
Vector2 Cohesion=new Vector2(0,0);
Vector2 SteerForce=new Vector2(0,0);
int x_0 = (int)((m_Transform.position.x-Agent_Radius)*0.25f);
if (x_0 < 0)x_0 = 0;
int y_0 = (int)((m_Transform.position.y+Agent_Radius)*0.25f);
if (y_0 > 2)y_0 = 2;
int x_1 = (int)((m_Transform.position.x+Agent_Radius)*0.25f);
if (x_1 > 3)x_1 = 3;
int y_1 = (int)((m_Transform.position.y-Agent_Radius)*0.25f);
if (y_1 < 0)y_1 = 0;
List N_lst;
Vector2 agentToTar;
float mag_of_agentToTar;
for(int i=y_1;i<=y_0;i++){
for(int j=x_0;j<=x_1;j++){
N_lst=m_GameWorld.Grid[((i*4)+j)];
foreach(Agent val in N_lst){
if(this.GetInstanceID()!=val.GetInstanceID()){
agentToTar = (Vector2)(m_Transform.position-val.transform.position) mag_of_agentToTar = agentToTar.magnitude;
//check the radius
if(mag_of_agentToTar<Agent_Radius){
m_NebCount++;
//separation
Separation += agentToTar.normalized/mag_of_agentToTar;
//sum of heading
Alignment += (Vector2)val.transform.right;
//sum of mass
Cohesion += (Vector2)val.transform.position;
}
}
} } }
if (m_NebCount > 0) {
Alignment /= m_NebCount;
Alignment -= (Vector2)m_Transform.right;
Cohesion /= m_NebCount;
Cohesion = Seek(Cohesion);
}
SteerForce += AccForce(SteerForce.magnitude,WallAvoid()*WallAvoidanceWeight)
SteerForce += AccForce(SteerForce.magnitude,Separation*SeparationWeight);
SteerForce += AccForce (SteerForce.magnitude, Cohesion*CohesionWeight);
SteerForce += AccForce(SteerForce.magnitude,Alignment*AlignmentWeight);
SteerForce += AccForce(SteerForce.magnitude,Wander ()*WanderWeight);
return SteerForce;
}
private Vector2 Seek(Vector2 targetPo){
Vector2 DesiredVelocity = (targetPo - (Vector2)m_Transform.position).normalized
return (DesiredVelocity - m_Velocity);
}
private Vector2 Wander(){
float R = Random.Range(-10f,10f);
m_vWanderTarget += (new Vector2(R,R)*WanderJitter);
m_vWanderTarget.Normalize ();
m_vWanderTarget *= WanderRadius;
Vector2 target = new Vector2 (WanderDistance,0);
target += m_vWanderTarget;
target = m_Transform.TransformPoint (target);
target = (target - (Vector2)m_Transform.position).normalized;
return (target - m_Velocity);
}
private Vector2 WallAvoid(){
int layerMask = 1 << 8; float hit_Distance=2;
Vector3 Wall_normal=new Vector3(0,0,0);
RaycastHit2D hit = Physics2D.Raycast(m_Transform.position,m_Transform.right,1,layerMask);
if (hit.collider != null){
if(hit_Distance>hit.distance){
Wall_normal = hit.collider.transform.right;
}
}
//Debug.DrawRay (m_Transform.position, m_Transform.right,Color.red);
hit=
Physics2D.Raycast(m_Transform.position,Quaternion.Euler(0,0,45)*m_Transform.right,1,layerMask);
if (hit.collider != null){
if(hit_Distance>hit.distance){
Wall_normal = hit.collider.transform.right;
}
}
//Debug.DrawRay (m_Transform.position,Quaternion.Euler(0,0,45)*m_Transform.right,Color.red);
hit = Physics2D.Raycast(m_Transform.position,Quaternion.Euler(0,0,-45)*m_Transform.right,1,layerMask);
if (hit.collider != null){
if(hit_Distance>hit.distance){
Wall_normal = hit.collider.transform.right;
}
}
/*Debug.DrawRay (m_Transform.position,Quaternion.Euler(0,0,-45)*m_Transform.right,Color.red);*/
return (Vector2)Wall_normal * hit_Distance;
}
private Vector2 AccForce(float SteeringMag,Vector2 ForceToAdd){
Vector2 returnForce = new Vector2(0,0);
float ForceToAddMag = ForceToAdd.magnitude;
float RemainingForceMag = MaxSteeringForce - SteeringMag;
if(RemainingForceMag <= 0) return returnForce;
if (ForceToAddMag < RemainingForceMag) return ForceToAdd;
else return (ForceToAdd.normalized * RemainingForceMag);
}
}
World object for Spatial Partitioning
using UnityEngine;
using System.Collections;
using System.Collections.Generic;
public class GameWorld : MonoBehaviour {
private static GameWorld m_Instance;
public static GameWorld Instance{
get{ return m_Instance; }
}
private List[] m_Grid;
public List[] Grid{
get{ return m_Grid; }
}
void Awake() {
m_Instance = this;
}
// Use this for initialization
void Start () {
m_Grid = new List[12];
for(int i=0;i<12;i++){
m_Grid[i]=new List();
}
}
}
Download unity project :
GitHub : https://github.com/kalanadis/2D_FLOCKING/tree/master
Google Drive :https://drive.google.com/file/d/0ByoByqm47PspQm9oYUh6YkhIc3M/view?usp=sharing
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