private static double CompareDistance(CartesianCoordinates referencePoint, CartesianCoordinates a, CartesianCoordinates b)
{
var distA = (referencePoint.X - a.X) * (referencePoint.X - a.X) + (referencePoint.Y - a.Y) * (referencePoint.Y - a.Y);
var distB = (referencePoint.X - b.X) * (referencePoint.X - b.X) + (referencePoint.Y - b.Y) * (referencePoint.Y - b.Y);
return(distA - distB);
}
public static void SortForNonSelfIntersectingPolygon(this List <CartesianCoordinates> points)
{
var refX = points.Select(_ => _.X).Max();
var refY = points.Where(_ => _.X == refX).Select(_ => _.Y).Min();
var referencePoint = new CartesianCoordinates(refX, refY);
points.Sort((CartesianCoordinates a, CartesianCoordinates b) => CompareAngle(referencePoint, a, b));
}
private static int CompareAngle(CartesianCoordinates referencePoint, CartesianCoordinates a, CartesianCoordinates b)
{
var left = IsLeft(referencePoint, a, b);
var compareDistance = CompareDistance(referencePoint, a, b);
if (left == 0)
{
return(compareDistance == 0 ? 0 : compareDistance > 0 ? 1 : -1);
}
return(left == 0 ? 0 : left > 0 ? 1 : -1);
}
private static double IsLeft(CartesianCoordinates referencePoint, CartesianCoordinates a, CartesianCoordinates b)
{
return((a.X - referencePoint.X) * (b.Y - referencePoint.Y) - (b.X - referencePoint.X) * (a.Y - referencePoint.Y));
}