/// <summary>
/// Returns true if wedge A contains wedge B. Equivalent to but faster than
/// GetWedgeRelation() == WEDGE_PROPERLY_CONTAINS || WEDGE_EQUALS.
/// REQUIRES: A and B are non-empty.
/// </summary>
public static bool WedgeContains(S2Point a0, S2Point ab1, S2Point a2, S2Point b0, S2Point b2)
{
// For A to contain B (where each loop interior is defined to be its left
// side), the CCW edge order around ab1 must be a2 b2 b0 a0. We split
// this test into two parts that test three vertices each.
return(
S2Pred.OrderedCCW(a2, b2, b0, ab1) &&
S2Pred.OrderedCCW(b0, a0, a2, ab1));
}
/// <summary>
/// Returns true if wedge A intersects wedge B. Equivalent to but faster
/// than GetWedgeRelation() != WEDGE_IS_DISJOINT.
/// REQUIRES: A and B are non-empty.
/// </summary>
/// <returns></returns>
public static bool WedgeIntersects(S2Point a0, S2Point ab1, S2Point a2, S2Point b0, S2Point b2)
{
// For A not to intersect B (where each loop interior is defined to be
// its left side), the CCW edge order around ab1 must be a0 b2 b0 a2.
// Note that it's important to write these conditions as negatives
// (!OrderedCCW(a,b,c,o) rather than Ordered(c,b,a,o)) to get correct
// results when two vertices are the same.
return(!(
S2Pred.OrderedCCW(a0, b2, b0, ab1) &&
S2Pred.OrderedCCW(b0, a2, a0, ab1)));
}
/// <summary>
/// Returns the relation from wedge A to B.
/// REQUIRES: A and B are non-empty.
/// </summary>
public static WedgeRelation GetWedgeRelation(S2Point a0, S2Point ab1, S2Point a2, S2Point b0, S2Point b2)
{
// There are 6 possible edge orderings at a shared vertex (all
// of these orderings are circular, i.e. abcd == bcda):
//
// (1) a2 b2 b0 a0: A contains B
// (2) a2 a0 b0 b2: B contains A
// (3) a2 a0 b2 b0: A and B are disjoint
// (4) a2 b0 a0 b2: A and B intersect in one wedge
// (5) a2 b2 a0 b0: A and B intersect in one wedge
// (6) a2 b0 b2 a0: A and B intersect in two wedges
//
// We do not distinguish between 4, 5, and 6.
// We pay extra attention when some of the edges overlap. When edges
// overlap, several of these orderings can be satisfied, and we take
// the most specific.
if (a0 == b0 && a2 == b2)
{
return(WedgeRelation.WEDGE_EQUALS);
}
if (S2Pred.OrderedCCW(a0, a2, b2, ab1))
{
// The cases with this vertex ordering are 1, 5, and 6,
// although case 2 is also possible if a2 == b2.
if (S2Pred.OrderedCCW(b2, b0, a0, ab1))
{
return(WedgeRelation.WEDGE_PROPERLY_CONTAINS);
}
// We are in case 5 or 6, or case 2 if a2 == b2.
return((a2 == b2)
? WedgeRelation.WEDGE_IS_PROPERLY_CONTAINED
: WedgeRelation.WEDGE_PROPERLY_OVERLAPS);
}
// We are in case 2, 3, or 4.
if (S2Pred.OrderedCCW(a0, b0, b2, ab1))
{
return(WedgeRelation.WEDGE_IS_PROPERLY_CONTAINED);
}
return(S2Pred.OrderedCCW(a0, b0, a2, ab1)
? WedgeRelation.WEDGE_IS_DISJOINT : WedgeRelation.WEDGE_PROPERLY_OVERLAPS);
}