public SteeringBehavior(MovingEntity entity)
{
for (int i = 0; i < m_Feelers.Length; i++)
m_Feelers[i] = new Vector2();
Walls = new List<Wall2D>();
m_Entity = entity;
}
internal void CheckBounds(MovingEntity movingEntity)
{
if (movingEntity.Position.X > Width)
movingEntity.Position = new Vector2(Width, movingEntity.Position.Y);
if (movingEntity.Position.Y > Height)
movingEntity.Position = new Vector2(movingEntity.Position.X, Height);
if (movingEntity.Position.X < 0)
movingEntity.Position = new Vector2(0, movingEntity.Position.Y);
if (movingEntity.Position.Y < 0)
movingEntity.Position = new Vector2(movingEntity.Position.X,0);
}
public Vector2 Calculate(MovingEntity entity)
{
m_SteeringForce = Vector2.Zero;
m_SteeringForce += CalculateWeightedSum(entity);
return m_SteeringForce;
}
private Vector2 Wander(MovingEntity entity)
{
m_WanderTarget = Vector2.Zero;
//this behavior is dependent on the update rate, so this line must
//be included when using time independent framerate.
double JitterThisTimeSlice = m_WanderJitter * entity.TimeElapsed.TotalSeconds;
//first, add a small random vector to the target's position
m_WanderTarget += new Vector2((float)(RandomClamped() * JitterThisTimeSlice),
(float)(RandomClamped() * JitterThisTimeSlice));
//reproject this new vector back on to a unit circle
m_WanderTarget.Normalize();
//increase the length of the vector to the same as the radius
//of the wander circle
m_WanderTarget *= m_WanderRadius;
//move the target into a position WanderDist in front of the agent
Vector2 target = m_WanderTarget + new Vector2(m_WanderDistance, 0);
//project the target into world space
target = PointToWorldSpace(target,
entity.Heading,
entity.Side,
entity.Position);
//and steer towards it
return target - entity.Position;
}
Vector2 Pursuit(MovingEntity evader)
{
//if the evader is ahead and facing the agent then we can just seek
//for the evader's current position.
Vector2 toEvader = evader.Position - m_Entity.Position;
double relativeHeading = Vector2.Dot(m_Entity.Heading, evader.Heading);
double direction = Vector2.Dot(toEvader, m_Entity.Heading);
if ( direction > 0 && relativeHeading < -0.95) //acos(0.95)=18 degs
{
return Seek(evader.Position);
}
//Not considered ahead so we predict where the evader will be.
//the lookahead time is propotional to the distance between the evader
//and the pursuer; and is inversely proportional to the sum of the
//agent's velocities
float LookAheadTime = (float)(toEvader.Length() /
(m_Entity.MaxSpeed + evader.Speed));
//now seek to the predicted future position of the evader
return Seek(evader.Position + Vector2.Multiply(evader.Velocity, LookAheadTime));
}
Vector2 Evade(MovingEntity pursuer)
{
/* Not necessary to include the check for facing direction this time */
Vector2 ToPursuer = pursuer.Position - m_Entity.Position;
//uncomment the following two lines to have Evade only consider pursuers
//within a 'threat range'
const double ThreatRange = 100.0;
if (ToPursuer.LengthSquared() > ThreatRange * ThreatRange)
return new Vector2();
//the lookahead time is propotional to the distance between the pursuer
//and the pursuer; and is inversely proportional to the sum of the
//agents' velocities
double LookAheadTime = ToPursuer.Length() / (m_Entity.MaxSpeed + pursuer.Speed);
//now flee away from predicted future position of the pursuer
return Flee(pursuer.Position + pursuer.Velocity * (float)LookAheadTime);
}
public Vector2 CalculateWeightedSum(MovingEntity entity)
{
Vector2 force = Vector2.Zero;
if(entity.Behavior.HasFlag(BehaviorType.Pursuit))
force += Pursuit(Target);
if (entity.Behavior.HasFlag(BehaviorType.Seek))
force += Seek(Target != null ? Target.Position : entity.TargetPosition);
if (entity.Behavior.HasFlag(BehaviorType.Evade))
force += Evade(Pursuer);
if (entity.Behavior.HasFlag(BehaviorType.Arrive))
force += Arrive(Target != null ? Target.Position : entity.TargetPosition, Deceleration.normal);
if (entity.Behavior.HasFlag(BehaviorType.Wander))
force += Wander(Target); //broken random numbers are not random
if (entity.Behavior.HasFlag(BehaviorType.Wall_avoidance))
force += WallAvoidance(Walls);
return force;
}
public void SetTarget(MovingEntity target)
{
m_Steering.Target = target;
}
public void SetPursuer(MovingEntity pursuer)
{
m_Steering.Pursuer = pursuer;
}
