void ShipEnemy::avoid(const float minTimeToCollision,						std::vector<Object*> others){    float steer = 0;    Object* threat = NULL;    // Time (in seconds) until the most immediate collision threat found    // so far.  Initial value is a threshold: don't look more than this    // many frames into the future.    float minTime = minTimeToCollision;    // for each of the other vehicles, determine which (if any)    // pose the most immediate threat of collision.	for (std::vector<Object*>::iterator i = others.begin(); i != others.end(); i++){        Object* other = *i;        if (other != this && other->mBody){	            // avoid when future positions are this close (or less)			float collisionDangerThreshold = GetRadius() * 2;            // predicted time until nearest approach of "this" and "other"            float time = predictNearestApproachTime (other);            // If the time is in the future, sooner than any other            // threatened collision...            if ((time >= 0) && (time < minTime)){                if (computeNearestApproachPositions (other, time)                    < collisionDangerThreshold){                    minTime = time;                    threat = other;                }            }        }    }	b2Vec2 side = GetDirection3();	side.Normalize();	side = b2Vec2(side.y,-side.x);    // if a potential collision was found, compute steering to avoid    if (threat != NULL){		b2Vec2 direction = GetDirection3();		b2Vec2 otherDirection = threat->GetDirection3();        // parallel: +1, perpendicular: 0, anti-parallel: -1        float parallelness = b2Dot(direction, otherDirection);        float angle = 0.707f;        if (parallelness < -angle){            // anti-parallel "head on" paths:            // steer away from future threat position            b2Vec2 offset = hisPositionAtNearestApproach - GetPosition();            float sideDot = b2Dot(offset,side);			steer = (sideDot > 0) ? -1.0f : 1.0f;        }        else{            if (parallelness > angle){                // parallel paths: steer away from threat                b2Vec2 offset = threat->GetPosition() - GetPosition();				float sideDot = b2Dot(offset,side);				steer = (sideDot > 0) ? -1.0f : 1.0f;            }            else{                // perpendicular paths: steer behind threat                // (only the slower of the two does this)                if (threat->GetSpeed() <= GetSpeed()){                    float sideDot = b2Dot(side, otherDirection);					steer = (sideDot > 0) ? -1.0f : 1.0f;                }            }        }    }	b2Vec2 result = side;	result *= steer;	if(steer != 0)		targetPoint = result + GetPosition() + GetDirection3();}float ShipEnemy::predictNearestApproachTime (Object *other){    b2Vec2 myVelocity = GetVelocity();    b2Vec2 otherVelocity = other->GetVelocity();    b2Vec2 relVelocity = otherVelocity - myVelocity;    float relSpeed = relVelocity.Length();    // for parallel paths, the vehicles will always be at the same distance,    // so return 0 (aka "now") since "there is no time like the present"    if (relSpeed == 0)		return 0;    // Now consider the path of the other vehicle in this relative    // space, a line defined by the relative position and velocity.    // The distance from the origin (our vehicle) to that line is    // the nearest approach.    // Take the unit tangent along the other vehicle's path    b2Vec2 relTangent = relVelocity;	relTangent.x /= relSpeed;	relTangent.y /= relSpeed;    // find distance from its path to origin (compute offset from    // other to us, find length of projection onto path)    b2Vec2 relPosition = GetPosition() - other->GetPosition();    float projection = b2Dot(relTangent,relPosition);	float time = projection / relSpeed;    return time;}float ShipEnemy::computeNearestApproachPositions (Object *other,                                 float time){	b2Vec2 position = GetPosition();	b2Vec2 direction = GetDirection3();	float speed = GetSpeed();	b2Vec2 otherPosition = other->GetPosition();	b2Vec2 otherDirection = other->GetDirection3();	float otherSpeed = other->GetSpeed();	b2Vec2 myTravel = direction;	myTravel *= speed * time;	b2Vec2 otherTravel = otherDirection;	otherTravel *= otherSpeed * time;	b2Vec2 myFinal = position + myTravel;    b2Vec2 otherFinal = otherPosition + otherTravel;    ourPositionAtNearestApproach = myFinal;    hisPositionAtNearestApproach = otherFinal;	float distance = (myFinal - otherFinal).Length();    return distance;}