//------------------------------ Pursuit ---------------------------------
//
// this behavior creates a force that steers the agent towards the
// evader
//------------------------------------------------------------------------
public Vector2D Pursuit(MovingEntity evader)
{
//if the evader is ahead and facing the agent then we can just seek
//for the evader's current position.
Vector2D ToEvader = evader.Pos - m_parentMovingEntity.Pos;
double RelativeHeading = m_parentMovingEntity.Heading().Dot(evader.Heading());
if ((ToEvader.Dot(m_parentMovingEntity.Heading()) > 0) && (RelativeHeading < -0.95)) //acos(0.95)=18 degs
{
return Seek(evader.Pos);
}
//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
double LookAheadTime = ToEvader.Length() /
(m_parentMovingEntity.MaxSpeed + evader.Speed());
//now seek to the predicted future position of the evader
return Seek(evader.Pos + evader.Velocity * LookAheadTime);
}
//----------------------------- Evade ------------------------------------
//
// similar to pursuit except the agent Flees from the estimated future
// position of the pursuer
//------------------------------------------------------------------------
public Vector2D Evade(MovingEntity pursuer)
{
/* Not necessary to include the check for facing direction this time */
Vector2D ToPursuer = (pursuer.Pos - m_parentMovingEntity.Pos);
//uncomment the following two lines to have Evade only consider pursuers
//within a 'threat range'
double ThreatRange = 100.0;
if (ToPursuer.LengthSq() > ThreatRange * ThreatRange) return new Vector2D(0.0, 0.0);
//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_parentMovingEntity.MaxSpeed + pursuer.Speed());
//now flee away from predicted future position of the pursuer
return Flee(pursuer.Pos + pursuer.Velocity * LookAheadTime);
}
//------------------------- Offset Pursuit -------------------------------
//
// Produces a steering force that keeps a vehicle at a specified offset
// from a leader vehicle
//------------------------------------------------------------------------
public Vector2D OffsetPursuit(MovingEntity leader, Vector2D offset)
{
//calculate the offset's position in world space
Vector2D WorldOffsetPos = Utils.PointToWorldSpace(offset,
leader.Heading(),
leader.Side(),
leader.Pos);
Vector2D ToOffset = WorldOffsetPos - m_parentMovingEntity.Pos;
//the lookahead time is propotional to the distance between the leader
//and the pursuer; and is inversely proportional to the sum of both
//agent's velocities
double LookAheadTime = ToOffset.Length() /
(m_parentMovingEntity.MaxSpeed + leader.Speed());
//now Arrive at the predicted future position of the offset
return Arrive(WorldOffsetPos + leader.Velocity * LookAheadTime, (int)Deceleration.fast);
}
