//sort point array for Grahams scan algo to find convex hull
internal static void SortedPoint2dListForGrahamScan(ref List <Point2d> ptList, int size)
{
for (int i = 1; i < size; ++i)
{
for (int j = i + 1; j < size; ++j)
{
int order = ValidateObject.CheckPointOrder(ptList[0], ptList[i], ptList[j]);
// collinear
if (order == 0)
{
if (DistanceBetweenPoints(ptList[0], ptList[0]) <= DistanceBetweenPoints(ptList[0], ptList[j]))
{
ChangePlaces(ref ptList, i, j);
}
}
else if (order == 1)
{
ChangePlaces(ref ptList, i, j);
}
}
}
}
