protected override Vector2 OnUpdateSteeringForce(float elapsedTime, Steerable movingEntity)
{
if (MovesPerMinute < 0f)
{
MovesPerMinute = 0f;
}
// Check if we are outside our moving range
if (Vector2.Subtract(movingEntity.Position, location).LengthSquared() > PatrolRange * PatrolRange * 1.2F)
{
timer = (float)(Random.NextDouble() * 60 / (MovesPerMinute + 0.001f));
location = movingEntity.Position;
}
// Select a random location when the timer expires
timer -= (float)elapsedTime;
if (timer < 0)
{
Vector2 target = new Vector2();
float a = (float)(Random.NextDouble() * Math.PI * 2);
float r = (float)(Random.NextDouble());
target.X = (float)(Math.Cos(a) * PatrolRange * r);
target.Y = (float)(Math.Sin(a) * PatrolRange * r);
movingEntity.Target = target + location;
timer = (float)(Random.NextDouble() * 60 / (MovesPerMinute + 0.001f));
}
return(SteeringHelper.Arrive(elapsedTime, movingEntity));
}
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)
{
// Not necessary to include the check for facing direction this time
Vector2 toPursuer = Pursuer.Position - movingEntity.Position;
//uncomment the following two lines to have Evade only consider pursuers
//within a 'threat range'
if (toPursuer.LengthSquared() > ThreatRange * ThreatRange)
{
return(Vector2.Zero);
}
//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
float LookAheadTime = toPursuer.Length() / (movingEntity.MaxSpeed + Pursuer.Speed);
//now flee away from predicted future position of the pursuer
return(SteeringHelper.Flee(elapsedTime, movingEntity, Pursuer.Position + Pursuer.Velocity * LookAheadTime));
}
protected override Vector2 OnUpdateSteeringForce(float elapsedTime, Steerable movingEntity)
{
return(SteeringHelper.Arrive(elapsedTime, movingEntity));
}
/// <summary>
/// Updates the internal state of the object based on game time.
/// </summary>
public void Update(float elapsedTime)
{
if (elapsedTime <= 0)
{
return;
}
// The max acceleration can stops the moving entity from top speed.
float MaxAcceleration = MaxSpeed / elapsedTime;
if (acceleration >= MaxAcceleration)
{
currentAcceleration = MaxAcceleration;
}
force = Vector2.Zero;
MaxForce = Acceleration;
DecelerationRange = SteeringHelper.GetDecelerateRange(this);
TargetedForward = SteeringHelper.GetTargetedForward(this);
Skin = MaxSpeed * elapsedTime * 2;
// Accumulate force of each behavior
for (int i = 0; i < Behaviors.Count; ++i)
{
Vector2 steeringForce = Behaviors.GetWeightByIndex(i) * Behaviors[i].UpdateSteeringForce(elapsedTime, this);
if (BlendMode == SteeringBehaviorBlendMode.WeightedSum)
{
if (!AccumulateForceWeightedSum(ref force, MaxForce, steeringForce))
{
break;
}
}
else if (BlendMode == SteeringBehaviorBlendMode.Solo)
{
if (!AccumulateForceSolo(ref force, MaxForce, steeringForce))
{
break;
}
}
}
if (Speed >= 0 && force == Vector2.Zero)
{
// The moving entity has fully stopped.
if (Speed == 0)
{
return;
}
// Apply friction when there is no force but the entity is still moving.
Vector2 previousVelocity = Velocity;
Velocity -= forward * MaxForce * elapsedTime;
// When the velocity has changed its direction, that indicates the moving
// entity has fully stopped.
if (Vector2.Dot(previousVelocity, Velocity) <= 0)
{
Velocity = Vector2.Zero;
Speed = 0;
return;
}
Speed = Velocity.Length();
}
else
{
// We don't multiply elapsedTime here because our force
// is calculated based on the subtracting desired speed and current speed.
Velocity += force * elapsedTime;
Speed = Velocity.Length();
if (Speed <= 0)
{
return;
}
// Turncate speed
if (Speed > MaxSpeed)
{
Velocity *= (float)(MaxSpeed / Speed);
Speed = MaxSpeed;
}
}
Debug.Assert(Speed > 0);
forward = Vector2.Normalize(Velocity);
// Update position
Vector2 newPosition;
IsStucked = DetectCollision(Position, Position + Velocity * elapsedTime, elapsedTime, out newPosition);
Position = newPosition;
}