/// <summary>
/// sort sites on y, then x, coord also change each site's _siteIndex to
/// match its new position in the list so the _siteIndex can be used to
/// identify the site for nearest-neighbor queries
/// </summary>
/// <param name="s1"></param>
/// <param name="s2"></param>
/// <returns></returns>
private static double Compare(Site s1, Site s2)
{
int returnValue = FortunesAlgorithm.CompareByYThenX(s1, s2);
// swap _siteIndex values if necessary to match new ordering:
int tempIndex;
if (returnValue == -1)
{
if (s1._siteIndex > s2._siteIndex)
{
tempIndex = s1._siteIndex;
s1._siteIndex = s2._siteIndex;
s2._siteIndex = tempIndex;
}
}
else if (returnValue == 1)
{
if (s2._siteIndex > s1._siteIndex)
{
tempIndex = s2._siteIndex;
s2._siteIndex = s1._siteIndex;
s1._siteIndex = tempIndex;
}
}
return(returnValue);
}
/// <summary>
/// This is the only way to make a Vertex
/// </summary>
/// <param name="halfedge0"></param>
/// <param name="halfedge1"></param>
/// <returns></returns>
public static Vertex Intersect(Halfedge halfedge0, Halfedge halfedge1)
{
Edge edge0, edge1, edge;
Halfedge halfedge;
double determinant, intersectionX, intersectionY;
bool rightOfSite;
edge0 = halfedge0.edge;
edge1 = halfedge1.edge;
if (edge0 == null || edge1 == null)
{
return(null);
}
if (edge0.RightSite == edge1.RightSite)
{
return(null);
}
determinant = edge0.a * edge1.b - edge0.b * edge1.a;
if (-1.0e-10 < determinant && determinant < 1.0e-10)
{
// the edges are parallel
return(null);
}
intersectionX = (edge0.c * edge1.b - edge1.c * edge0.b) / determinant;
intersectionY = (edge1.c * edge0.a - edge0.c * edge1.a) / determinant;
if (FortunesAlgorithm.CompareByYThenX(edge0.RightSite, edge1.RightSite) < 0)
{
halfedge = halfedge0;
edge = edge0;
}
else
{
halfedge = halfedge1;
edge = edge1;
}
rightOfSite = intersectionX >= edge.RightSite.X;
if ((rightOfSite && halfedge.leftRight == LR.Left) ||
(!rightOfSite && halfedge.leftRight == LR.Right))
{
return(null);
}
return(Vertex.Create(intersectionX, intersectionY));
}
