// XXX 4-23-03: Temporary work around (see comment above)
//
// Checks for intersection of the given spherical obstacle with a
// volume of "likely future vehicle positions": a cylinder along the
// current path, extending minTimeToCollision seconds along the
// forward axis from current position.
//
// If they intersect, a collision is imminent and this function returns
// a steering force pointing laterally away from the obstacle's center.
//
// Returns a zero vector if the obstacle is outside the cylinder
//
// xxx couldn't this be made more compact using localizePosition?
Vector3 steerToAvoid(Vehicle v, float minTimeToCollision)
{
// minimum distance to obstacle before avoidance is required
float minDistanceToCollision = minTimeToCollision * v.Speed;
float minDistanceToCenter = minDistanceToCollision + radius;
// contact distance: sum of radii of obstacle and vehicle
float totalRadius = radius + v.Radius;
// obstacle center relative to vehicle position
Vector3 localOffset = center - v.Position;
// distance along vehicle's forward axis to obstacle's center
float forwardComponent = Vector3.Dot(localOffset, v.Forward);
Vector3 forwardOffset = forwardComponent * v.Forward;
// offset from forward axis to obstacle's center
Vector3 offForwardOffset = localOffset - forwardOffset;
// test to see if sphere overlaps with obstacle-free corridor
bool inCylinder = offForwardOffset.magnitude < totalRadius;
bool nearby = forwardComponent < minDistanceToCenter;
bool inFront = forwardComponent > 0;
// if all three conditions are met, steer away from sphere center
if (inCylinder && nearby && inFront)
{
return offForwardOffset * -1;
}
else
{
return Vector3.zero;
}
}
// constructor
public tokenType(Vehicle parentObject, BruteForceProximityDatabase pd)
{
// store pointer to our associated database and the object this
// token represents, and store this token on the database's vector
bfpd = pd;
tParentObject = parentObject;
bfpd.group.Add(this);
}
// type for the "tokens" manipulated by this spatial database
//typedef AbstractTokenForProximityDatabase<ContentType> tokenType;
// allocate a token to represent a given client object in this database
public virtual AbstractTokenForProximityDatabase allocateToken(Vehicle parentObject)
{
return new AbstractTokenForProximityDatabase();
}
// ----------------------------------------------------------------------------
// evasion of another vehicle
public Vector3 steerForEvasion ( Vehicle menace, float maxPredictionTime)
{
// offset from this to menace, that distance, unit vector toward menace
Vector3 offset = menace.Position - Position;
float distance = offset.magnitude;
float roughTime = distance / menace.Speed;
float predictionTime = ((roughTime > maxPredictionTime) ?
maxPredictionTime :
roughTime);
Vector3 target = menace.predictFuturePosition (predictionTime);
return steerForFlee (target);
}
// allocate a token to represent a given client object in this database
//public override tokenType allocateToken (Object parentObject)
public override AbstractTokenForProximityDatabase allocateToken(Vehicle parentObject)
{
tokenType tToken=new tokenType (parentObject, this);
return (AbstractTokenForProximityDatabase)tToken;
}
// ----------------------------------------------------------------------------
// pursuit of another vehicle (& version with ceiling on prediction time)
public Vector3 steerForPursuit (Vehicle quarry)
{
return steerForPursuit (quarry, float.MaxValue);
}
public Vector3 steerForPursuit (Vehicle quarry, float maxPredictionTime)
{
// offset from this to quarry, that distance, unit vector toward quarry
Vector3 offset = quarry.Position - Position;
float distance = offset.magnitude;
Vector3 unitOffset = offset / distance;
// how parallel are the paths of "this" and the quarry
// (1 means parallel, 0 is pependicular, -1 is anti-parallel)
float parallelness = Vector3.Dot(Forward, quarry.Forward);
// how "forward" is the direction to the quarry
// (1 means dead ahead, 0 is directly to the side, -1 is straight back)
float forwardness = Vector3.Dot(Forward, unitOffset);
float directTravelTime = distance / Speed;
int f = intervalComparison (forwardness, -0.707f, 0.707f);
int p = intervalComparison (parallelness, -0.707f, 0.707f);
float timeFactor = 0; // to be filled in below
Color color = Color.black; // to be filled in below (xxx just for debugging)
// Break the pursuit into nine cases, the cross product of the
// quarry being [ahead, aside, or behind] us and heading
// [parallel, perpendicular, or anti-parallel] to us.
switch (f)
{
case +1:
switch (p)
{
case +1: // ahead, parallel
timeFactor = 4;
color = Color.black;
break;
case 0: // ahead, perpendicular
timeFactor = 1.8f;
color = Color.gray;
break;
case -1: // ahead, anti-parallel
timeFactor = 0.85f;
color = Color.white;
break;
}
break;
case 0:
switch (p)
{
case +1: // aside, parallel
timeFactor = 1;
color = Color.red;
break;
case 0: // aside, perpendicular
timeFactor = 0.8f;
color = Color.yellow;
break;
case -1: // aside, anti-parallel
timeFactor = 4;
color = Color.green;
break;
}
break;
case -1:
switch (p)
{
case +1: // behind, parallel
timeFactor = 0.5f;
color = Color.cyan;
break;
case 0: // behind, perpendicular
timeFactor = 2;
color = Color.blue;
break;
case -1: // behind, anti-parallel
timeFactor = 2;
color = Color.magenta;
break;
}
break;
}
// estimated time until intercept of quarry
float et = directTravelTime * timeFactor;
// xxx experiment, if kept, this limit should be an argument
float etl = (et > maxPredictionTime) ? maxPredictionTime : et;
// estimated position of quarry at intercept
Vector3 target = quarry.predictFuturePosition (etl);
// annotation
#if DEBUG
annotationLine (Position,
target,
gaudyPursuitAnnotation ? color : Color.gray);
#endif
return steerForSeek (target);
}
// ----------------------------------------------------------------------------
// used by boid behaviors: is a given vehicle within this boid's neighborhood?
bool inBoidNeighborhood ( Vehicle other, float minDistance, float maxDistance, float cosMaxAngle)
{
if (other == this)
{
return false;
}
else
{
Vector3 offset = other.Position - Position;
float distanceSquared = offset.sqrMagnitude;
// definitely in neighborhood if inside minDistance sphere
if (distanceSquared < (minDistance * minDistance))
{
return true;
}
else
{
// definitely not in neighborhood if outside maxDistance sphere
if (distanceSquared > (maxDistance * maxDistance))
{
return false;
}
else
{
// otherwise, test angular offset from forward axis
Vector3 unitOffset = offset / (float) System.Math.Sqrt (distanceSquared);
float forwardness = Vector3.Dot(Forward, unitOffset);
return forwardness > cosMaxAngle;
}
}
}
}
// Given the time until nearest approach (predictNearestApproachTime)
// determine position of each vehicle at that time, and the distance
// between them
float computeNearestApproachPositions(Vehicle other, float time,
ref Vector3 ourPosition,
ref Vector3 hisPosition)
{
Vector3 myTravel = Forward * Speed * time;
Vector3 otherTravel = other.Forward * other.Speed * time;
ourPosition = Position + myTravel;
hisPosition = other.Position + otherTravel;
return Vector3.Distance(ourPosition, hisPosition);
}
// Given two vehicles, based on their current positions and velocities,
// determine the time until nearest approach
//
// XXX should this return zero if they are already in contact?
float predictNearestApproachTime (Vehicle other)
{
// imagine we are at the origin with no velocity,
// compute the relative velocity of the other vehicle
Vector3 myVelocity = Velocity;
Vector3 otherVelocity = other.Velocity;
Vector3 relVelocity = otherVelocity - myVelocity;
float relSpeed = relVelocity.magnitude;
// 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
Vector3 relTangent = relVelocity / relSpeed;
// find distance from its path to origin (compute offset from
// other to us, find length of projection onto path)
Vector3 relPosition = Position - other.Position;
float projection = Vector3.Dot(relTangent, relPosition);
return projection / relSpeed;
}
// called when steerToAvoidNeighbors decides steering is required
// (default action is to do nothing, layered classes can overload it)
public virtual void annotateAvoidNeighbor ( Vehicle vehicle, float steer, Vector3 position, Vector3 threatPosition)
{
Debug.DrawLine(Position, vehicle.Position, Color.red); // Neighbor position
Debug.DrawLine(Position, position, Color.green); // Position we're aiming for
}
// called when steerToAvoidCloseNeighbors decides steering is required
// (default action is to do nothing, layered classes can overload it)
public virtual void annotateAvoidCloseNeighbor(Vehicle otherVehicle, Vector3 component)
{
Debug.DrawLine(Position, otherVehicle.Position, Color.red);
Debug.DrawRay (Position, component*3, Color.yellow);
}
