protected override Vector2 OnUpdateSteeringForce(float elapsedTime, Steerable movingEntity)
{
//if the evader is ahead and facing the agent then we can just seek
//for the evader's current position.
Vector2 toEvader = Evader.Position - movingEntity.Position;
float relativeHeading = Vector2.Dot(movingEntity.Forward, Evader.Forward);
if ((Vector2.Dot(toEvader, movingEntity.Forward) > 0) &&
(relativeHeading < -0.95f)) //acos(0.95)=18 degs
{
movingEntity.Target = Evader.Position + Offset;
return(SteeringHelper.Seek(elapsedTime, movingEntity));
}
//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 = toEvader.Length() / (movingEntity.MaxSpeed + Evader.Speed);
//now seek to the predicted future position of the evader
movingEntity.Target = Evader.Position + Evader.Velocity * lookAheadTime + Offset;
return(SteeringHelper.Seek(elapsedTime, movingEntity));
}
/// <summary>
/// Calculates the steering force to arrive at the target.
/// </summary>
public static Vector2 Arrive(float elapsedTime, Steerable movingEntity)
{
if (!movingEntity.Target.HasValue)
{
return(Vector2.Zero);
}
Vector2 toTarget = movingEntity.Target.Value - movingEntity.Position;
// Stop when the moving entity has passed target.
if (toTarget.Length() <= movingEntity.BoundingRadius + movingEntity.Skin + movingEntity.DecelerationRange)
{
if (movingEntity.Velocity != Vector2.Zero && Vector2.Dot(toTarget, movingEntity.Velocity) <= 0)
{
movingEntity.Target = null;
return(Vector2.Zero);
}
}
// Stop when the moving entity is close enough.
float distance = toTarget.Length();
if (distance <= movingEntity.DecelerationRange)
{
movingEntity.Target = null;
return(Vector2.Zero);
}
return(SteeringHelper.Seek(elapsedTime, movingEntity));
}
protected override Vector2 OnUpdateSteeringForce(float elapsedTime, Steerable movingEntity)
{
int count = 0;
Vector2 center = Vector2.Zero;
var boundingSphere = new BoundingSphere(new Vector3(movingEntity.Position, 0), Range);
Neighbors.FindAll(ref boundingSphere, Partners);
foreach (var partner in Partners)
{
if (partner != null && partner != movingEntity)
{
center += partner.Position;
if (++count >= SteeringHelper.MaxAffectingEntities)
{
break;
}
}
}
Partners.Clear();
if (count > 0)
{
center /= count;
movingEntity.Target = center;
return(SteeringHelper.Seek(elapsedTime, movingEntity));
}
return(Vector2.Zero);
}
protected override Vector2 OnUpdateSteeringForce(float elapsedTime, Steerable movingEntity)
{
return(SteeringHelper.Seek(elapsedTime, movingEntity));
}
