public void InitToIntersectionSloppy(
S2Polygon a, S2Polygon b, S1Angle vertexMergeRadius)
{
Preconditions.CheckState(NumLoops == 0);
if (!a._bound.Intersects(b._bound))
{
return;
}
// We want the boundary of A clipped to the interior of B,
// plus the boundary of B clipped to the interior of A,
// plus one copy of any directed edges that are in both boundaries.
var options = S2PolygonBuilderOptions.DirectedXor;
options.MergeDistance = vertexMergeRadius;
var builder = new S2PolygonBuilder(options);
ClipBoundary(a, false, b, false, false, true, builder);
ClipBoundary(b, false, a, false, false, false, builder);
if (!builder.AssemblePolygon(this, null))
{
// TODO (andriy): do something more meaningful here.
Debug.WriteLine("Bad directed edges");
}
}
/**
* Clip the boundary of A to the interior of B, and add the resulting edges to
* "builder". Shells are directed CCW and holes are directed clockwise, unless
* "reverseA" or "reverseB" is true in which case these directions in the
* corresponding polygon are reversed. If "invertB" is true, the boundary of A
* is clipped to the exterior rather than the interior of B. If
* "adSharedEdges" is true, then the output will include any edges that are
* shared between A and B (both edges must be in the same direction after any
* edge reversals are taken into account).
*/
private static void ClipBoundary(S2Polygon a,
bool reverseA,
S2Polygon b,
bool reverseB,
bool invertB,
bool addSharedEdges,
S2PolygonBuilder builder)
{
var bIndex = new S2PolygonIndex(b, reverseB);
bIndex.PredictAdditionalCalls(a.NumVertices);
var intersections = new List <ParametrizedS2Point>();
foreach (var aLoop in a._loops)
{
var n = aLoop.NumVertices;
var dir = (aLoop.IsHole ^ reverseA) ? -1 : 1;
var inside = b.Contains(aLoop.Vertex(0)) ^ invertB;
for (var j = (dir > 0) ? 0 : n; n > 0; --n, j += dir)
{
var a0 = aLoop.Vertex(j);
var a1 = aLoop.Vertex(j + dir);
intersections.Clear();
ClipEdge(a0, a1, bIndex, addSharedEdges, intersections);
if (inside)
{
intersections.Add(new ParametrizedS2Point(0.0, a0));
}
inside = ((intersections.Count & 0x1) == 0x1);
// assert ((b.contains(a1) ^ invertB) == inside);
if (inside)
{
intersections.Add(new ParametrizedS2Point(1.0, a1));
}
// Remove duplicates and produce a list of unique intersections.
intersections.Sort();
for (int size = intersections.Count, i = 1; i < size; i += 2)
{
builder.AddEdge(intersections[i - 1].Point, intersections[i].Point);
}
}
}
}
