// ----------------------------------------------------------------------------
// 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);
}
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);
}