public Coordinates Tangent(PointOnPath pt)
{
// assert that we're looking at the same segment
Debug.Assert(Equals(pt.segment));
// short circuit for near the start/end point
if (pt.pt.ApproxEquals(cb.P0, 0.001))
{
return(cb.dBdt(0).Normalize());
}
else if (pt.pt.ApproxEquals(cb.P3, 0.001))
{
return(cb.dBdt(1).Normalize());
}
else
{
// find the t-value in the general case
double tvalue = cb.FindT(pt.dist);
return(cb.dBdt(tvalue).Normalize());
}
}