C++ AbstractVehicle::velocity方法代码示例

float
OpenSteer::SteerLibrary::
predictNearestApproachTime (const AbstractVehicle& v, 
							const AbstractVehicle& other)
{
    // imagine we are at the origin with no velocity,
    // compute the relative velocity of the other vehicle
    const float3 myVelocity = v.velocity();
    const float3 otherVelocity = other.velocity();
    const float3 relVelocity = float3_subtract(otherVelocity, myVelocity);
    const float relSpeed = float3_length(relVelocity);

    // 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
	const float3 relTangent = float3_scalar_divide(relVelocity, relSpeed);

    // find distance from its path to origin (compute offset from
    // other to us, find length of projection onto path)
    const float3 relPosition = float3_subtract(make_float3(v.position()), make_float3(other.position()));
	const float projection = float3_dot(relTangent, relPosition);

    return projection / relSpeed;
}

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);
    }

//.........这里部分代码省略.........