pointXDirectionToLine method
Returns -1 for left, 1 for right and 0 in case the point
lies on the
line and null in case the line is horizontal.
Implementation
num? pointXDirectionToLine(Coord point) {
if (slope.a == 0) return null;
final res = evaluate(point);
return (slope.a < 0) ? -res.sign : res.sign;
}