public static Parabola2d FromFocusAndDirectrix(Point2d focus, Line2d directrix)
{
Point2d ondir = directrix.ClosestPointInfinite(focus);
Point2d vertex = new Point2d(0.5 * (ondir.X + focus.X), 0.5 * (ondir.Y + focus.Y));
double focdist = focus.Distance(vertex);
double rot = focus.Angle(ondir) + MathUtil.Deg90;
if (focdist <= 1e-30)
{
return(null);
}
return(new Parabola2d(vertex, rot, focdist));
}
public override Point2d ClosestPoint(Point2d from)
{
if (Linear)
{
return(new Line2d(start, end).ClosestPoint(from));
}
Point2d ce = Center;
Point2d oncirc = ce.Polar(ce.Angle(from), Radius);
if (IsCirclePointOnArc(oncirc))
{
return(oncirc);
}
return(from.ClosestPoint(start, end));
}
