/// <summary>
/// Visits all pairs of crossing edges in the given S2ShapeIndex, terminating
/// early if the given EdgePairVisitor function returns false (in which case
/// VisitCrossings returns false as well). "type" indicates whether all
/// crossings should be visited, or only interior crossings.
///
/// If "need_adjacent" is false, then edge pairs of the form (AB, BC) may
/// optionally be ignored (even if the two edges belong to different edge
/// chains). This option exists for the benefit of FindSelfIntersection(),
/// which does not need such edge pairs (see below).
/// </summary>
private static bool VisitCrossings(S2ShapeIndex index, CrossingType type, bool need_adjacent, EdgePairVisitor visitor)
{
// TODO(ericv): Use brute force if the total number of edges is small enough
// (using a larger threshold if the S2ShapeIndex is not constructed yet).
var count = index.GetEnumerableCount();
for (var pos = 0; pos < count; pos++)
{
var shape_edges = new ShapeEdgeVector();
var icell = index.GetIndexCell(pos);
var indexCell = icell.Value.Item2;
GetShapeEdges(index, indexCell, shape_edges);
if (!VisitCrossings(shape_edges, type, need_adjacent, visitor))
{
return(false);
}
}
return(true);
}
/// <summary>
/// Given a vector of edges within an S2ShapeIndexCell, visit all pairs of
/// crossing edges (of the given CrossingType).
/// </summary>
private static bool VisitCrossings(ShapeEdgeVector shape_edges, CrossingType type, bool need_adjacent, EdgePairVisitor visitor)
{
var min_crossing_sign = type == CrossingType.INTERIOR ? 1 : 0;
var num_edges = shape_edges.Count;
for (int i = 0; i + 1 < num_edges; i++)
{
var a = shape_edges[i];
var j = i + 1;
// A common situation is that an edge AB is followed by an edge BC. We
// only need to visit such crossings if "need_adjacent" is true (even if
// AB and BC belong to different edge chains).
if (!need_adjacent && a.V1 == shape_edges[j].V0)
{
j++;
if (j >= num_edges)
{
break;
}
}
var crosser = new S2EdgeCrosser(a.V0, a.V1);
for (; j < num_edges; j++)
{
var b = shape_edges[j];
if (crosser.C == S2Point.Empty || crosser.C != b.V0)
{
crosser.RestartAt(b.V0);
}
var sign = crosser.CrossingSign(b.V1);
if (sign >= min_crossing_sign)
{
if (!visitor(a, b, sign == 1))
{
return(false);
}
}
}
}
return(true);
}
// Visits all crossings of any edge in "a_edges" with any edge in "b_edges".
private bool VisitEdgesEdgesCrossings(ShapeEdgeVector a_edges, ShapeEdgeVector b_edges)
{
// Test all edges of "a_edges" against all edges of "b_edges".
foreach (var a in a_edges)
{
var crosser = new S2EdgeCrosser(a.V0, a.V1);
foreach (var b in b_edges)
{
if (crosser.C == S2Point.Empty || crosser.C != b.V0)
{
crosser.RestartAt(b.V0);
}
int sign = crosser.CrossingSign(b.V1);
if (sign >= min_crossing_sign_)
{
if (!VisitEdgePair(a, b, sign == 1))
{
return(false);
}
}
}
}
return(true);
}
/// <summary>
/// Returns a vector containing all edges in the given S2ShapeIndexCell vector.
/// (The result is returned as an output parameter so that the same storage can
/// be reused, rather than allocating a new temporary vector each time.)
/// </summary>
private static void GetShapeEdges(S2ShapeIndex index, List <S2ShapeIndexCell> cells, ShapeEdgeVector shape_edges)
{
shape_edges.Clear();
foreach (var cell in cells)
{
AppendShapeEdges(index, cell, shape_edges);
}
}
/// <summary>
/// Returns a vector containing all edges in the given S2ShapeIndexCell.
/// (The result is returned as an output parameter so that the same storage can
/// be reused, rather than allocating a new temporary vector each time.)
/// </summary>
private static void GetShapeEdges(S2ShapeIndex index, S2ShapeIndexCell cell, ShapeEdgeVector shape_edges)
{
shape_edges.Clear();
AppendShapeEdges(index, cell, shape_edges);
}
/// <summary>
/// Appends all edges in the given S2ShapeIndexCell to the given vector.
/// </summary>
private static void AppendShapeEdges(S2ShapeIndex index, S2ShapeIndexCell cell, ShapeEdgeVector shape_edges)
{
for (int s = 0; s < cell.NumClipped(); ++s)
{
var clipped = cell.Clipped(s);
var shape = index.Shape(clipped.ShapeId);
var num_edges = clipped.NumEdges;
for (int i = 0; i < num_edges; i++)
{
shape_edges.Add(new ShapeEdge(shape, clipped.Edge(i)));
}
}
}
