float3
OpenSteer::SteerLibrary::
steerForWander (const AbstractVehicle& v, float dt)
{
// random walk WanderSide and WanderUp between -1 and +1
const float speed = 12 * dt; // maybe this (12) should be an argument?
WanderSide = scalarRandomWalk (WanderSide, speed, -1, +1);
WanderUp = scalarRandomWalk (WanderUp, speed, -1, +1);
// return a pure lateral steering vector: (+/-Side) + (+/-Up)
return float3_add(float3_scalar_multiply(v.side(), WanderSide), float3_scalar_multiply(v.up(), WanderUp));
}
OpenSteer::Vec3
OpenSteer::Obstacle::PathIntersection::
steerToAvoidIfNeeded (const AbstractVehicle& vehicle,
const float minTimeToCollision) const
{
// if nearby intersection found, steer away from it, otherwise no steering
const float minDistanceToCollision = minTimeToCollision * vehicle.speed();
if (intersect && (distance < minDistanceToCollision))
{
// compute avoidance steering force: take the component of
// steerHint which is lateral (perpendicular to vehicle's
// forward direction), set its length to vehicle's maxForce
Vec3 lateral = steerHint.perpendicularComponent (vehicle.forward ());
if (lateral == Vec3::zero)
lateral = vehicle.side ();
return lateral.normalize () * vehicle.maxForce ();
}
else
{
return Vec3::zero;
}
}
float3
OpenSteer::SteerLibrary::
steerToAvoidNeighbors (const AbstractVehicle& v,
const float minTimeToCollision,
const AVGroup& others)
{
// first priority is to prevent immediate interpenetration
const float3 separation = steerToAvoidCloseNeighbors (v, 0, others);
if (!float3_equals(separation, float3_zero()))
return separation;
// otherwise, go on to consider potential future collisions
float steer = 0;
AbstractVehicle* 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;
// xxx solely for annotation
float3 xxxThreatPositionAtNearestApproach;
float3 xxxOurPositionAtNearestApproach;
// for each of the other vehicles, determine which (if any)
// pose the most immediate threat of collision.
for (AVIterator i = others.begin(); i != others.end(); i++)
{
AbstractVehicle& other = **i;
if (&other != &v)
{
// avoid when future positions are this close (or less)
const float collisionDangerThreshold = v.radius() * 2;
// predicted time until nearest approach of "this" and "other"
const float time = predictNearestApproachTime (v, other);
// If the time is in the future, sooner than any other
// threatened collision...
if ((time >= 0) && (time < minTime))
{
// if the two will be close enough to collide,
// make a note of it
if (computeNearestApproachPositions (v, other, time)
< collisionDangerThreshold)
{
minTime = time;
threat = &other;
xxxThreatPositionAtNearestApproach
= hisPositionAtNearestApproach;
xxxOurPositionAtNearestApproach
= ourPositionAtNearestApproach;
}
}
}
}
// if a potential collision was found, compute steering to avoid
if (threat != NULL)
{
// parallel: +1, perpendicular: 0, anti-parallel: -1
float parallelness = float3_dot(make_float3(v.forward()), make_float3(threat->forward()));
float angle = 0.707f;
if (parallelness < -angle)
{
// anti-parallel "head on" paths:
// steer away from future threat position
float3 offset = float3_subtract(xxxThreatPositionAtNearestApproach, make_float3(v.position()));
float sideDot = float3_dot(offset, v.side());
steer = (sideDot > 0) ? -1.0f : 1.0f;
}
else
{
if (parallelness > angle)
{
// parallel paths: steer away from threat
float3 offset = float3_subtract(make_float3(threat->position()), make_float3(v.position()));
float sideDot = float3_dot(offset, v.side());
steer = (sideDot > 0) ? -1.0f : 1.0f;
}
else
{
// perpendicular paths: steer behind threat
// (only the slower of the two does this)
if (threat->speed() <= v.speed())
{
float sideDot = float3_dot(v.side(), threat->velocity());
steer = (sideDot > 0) ? -1.0f : 1.0f;
}
}
}
annotateAvoidNeighbor (*threat,
steer,
xxxOurPositionAtNearestApproach,
xxxThreatPositionAtNearestApproach);
}
return float3_scalar_multiply(v.side(), steer);
}