double Point2d::DistanceToLine(Point2d p0, Point2d dp, bool segment) {
double m = dp.x*dp.x + dp.y*dp.y;
if(m < LENGTH_EPS*LENGTH_EPS) return VERY_POSITIVE;
// Let our line be p = p0 + t*dp, for a scalar t from 0 to 1
double t = (dp.x*(x - p0.x) + dp.y*(y - p0.y))/m;
if((t < 0 || t > 1) && segment) {
// The closest point is one of the endpoints; determine which.
double d0 = DistanceTo(p0);
double d1 = DistanceTo(p0.Plus(dp));
return min(d1, d0);
} else {
Point2d closest = p0.Plus(dp.ScaledBy(t));
return DistanceTo(closest);
}
}
