private void ComputeIntersectsForChain(int start0, int end0,
MonotoneChainEdge mce, int start1, int end1, SegmentIntersector ei)
{
Coordinate p00 = pts[start0];
Coordinate p01 = pts[end0];
Coordinate p10 = mce.pts[start1];
Coordinate p11 = mce.pts[end1];
// terminating condition for the recursion
if (end0 - start0 == 1 && end1 - start1 == 1)
{
ei.AddIntersections(e, start0, mce.e, start1);
return;
}
// nothing to do if the envelopes of these chains don't overlap
env1.Initialize(p00, p01);
env2.Initialize(p10, p11);
if (!env1.Intersects(env2))
{
return;
}
// the chains overlap, so split each in half and iterate (binary search)
int mid0 = (start0 + end0) / 2;
int mid1 = (start1 + end1) / 2;
// Assert: mid != start or end (since we checked above for end - start <= 1)
// check terminating conditions before recursing
if (start0 < mid0)
{
if (start1 < mid1)
{
ComputeIntersectsForChain(start0, mid0, mce, start1, mid1, ei);
}
if (mid1 < end1)
{
ComputeIntersectsForChain(start0, mid0, mce, mid1, end1, ei);
}
}
if (mid0 < end0)
{
if (start1 < mid1)
{
ComputeIntersectsForChain(mid0, end0, mce, start1, mid1, ei);
}
if (mid1 < end1)
{
ComputeIntersectsForChain(mid0, end0, mce, mid1, end1, ei);
}
}
}
/// <summary>
/// Performs a brute-force comparison of every segment in each Edge.
/// This has n^2 performance, and is about 100 times slower than using
/// monotone chains.
/// </summary>
private void ComputeIntersects(Edge e0, Edge e1, SegmentIntersector si)
{
ICoordinateList pts0 = e0.Coordinates;
ICoordinateList pts1 = e1.Coordinates;
for (int i0 = 0; i0 < pts0.Count - 1; i0++)
{
for (int i1 = 0; i1 < pts1.Count - 1; i1++)
{
si.AddIntersections(e0, i0, e1, i1);
}
}
}
public void ComputeIntersections(SweepLineSegment ss,
SegmentIntersector si)
{
si.AddIntersections(edge, ptIndex, ss.edge, ss.ptIndex);
}