/**
* Indexing structure to efficiently clipEdge() of a polygon. This is an
* abstract class because we need to use if for both polygons (for
* initToIntersection() and friends) and for sets of lists of points (for
* initToSimplified()).
*
* Usage -- in your subclass, create an array of vertex counts for each loop
* in the loop sequence and pass it to this constructor. Overwrite
* edgeFromTo(), calling decodeIndex() and use the resulting two indices to
* access your accessing vertices.
*/
private static void AddIntersection(S2Point a0,
S2Point a1,
S2Point b0,
S2Point b1,
bool addSharedEdges,
int crossing, System.Collections.Generic.ICollection <ParametrizedS2Point> intersections)
{
if (crossing > 0)
{
// There is a proper edge crossing.
var x = S2EdgeUtil.GetIntersection(a0, a1, b0, b1);
var t = S2EdgeUtil.GetDistanceFraction(x, a0, a1);
intersections.Add(new ParametrizedS2Point(t, x));
}
else if (S2EdgeUtil.VertexCrossing(a0, a1, b0, b1))
{
// There is a crossing at one of the vertices. The basic rule is simple:
// if a0 equals one of the "b" vertices, the crossing occurs at t=0;
// otherwise, it occurs at t=1.
//
// This has the effect that when two symmetric edges are encountered (an
// edge an its reverse), neither one is included in the output. When two
// duplicate edges are encountered, both are included in the output. The
// "addSharedEdges" flag allows one of these two copies to be removed by
// changing its intersection parameter from 0 to 1.
double t = (a0 == b0 || a0 == b1) ? 0 : 1;
if (!addSharedEdges && a1 == b1)
{
t = 1;
}
intersections.Add(new ParametrizedS2Point(t, t == 0 ? a0 : a1));
}
}
/**
* This method is equivalent to the S2EdgeUtil.edgeOrVertexCrossing() method
* defined below. It is similar to robustCrossing, but handles cases where
* two vertices are identical in a way that makes it easy to implement
* point-in-polygon containment tests.
*/
public bool EdgeOrVertexCrossing(S2Point d)
{
// We need to copy c since it is clobbered by robustCrossing().
var c2 = new S2Point(c[0], c[1], c[2]);
var crossing = RobustCrossing(d);
if (crossing < 0)
{
return(false);
}
if (crossing > 0)
{
return(true);
}
return(S2EdgeUtil.VertexCrossing(a, b, c2, d));
}