/// <summary>
///
/// </summary>
/// <param name="searchEnv"></param>
/// <param name="start0"></param>
/// <param name="end0"></param>
/// <param name="mcs"></param>
private void ComputeSelect(Envelope searchEnv, int start0, int end0, MonotoneChainSelectAction mcs)
{
var p0 = _pts[start0];
var p1 = _pts[end0];
// terminating condition for the recursion
if (end0 - start0 == 1)
{
mcs.Select(this, start0);
return;
}
// nothing to do if the envelopes don't overlap
if (!searchEnv.Intersects(p0, p1))
{
return;
}
// the chains overlap, so split each in half and iterate (binary search)
int mid = (start0 + end0) / 2;
// Assert: mid != start or end (since we checked above for end - start <= 1)
// check terminating conditions before recursing
if (start0 < mid)
{
ComputeSelect(searchEnv, start0, mid, mcs);
}
if (mid < end0)
{
ComputeSelect(searchEnv, mid, end0, mcs);
}
}
/// <summary>
/// Determine all the line segments in the chain whose envelopes overlap
/// the searchEnvelope, and process them.
/// </summary>
/// <remarks>
/// The monotone chain search algorithm attempts to optimize
/// performance by not calling the select action on chain segments
/// which it can determine are not in the search envelope.
/// However, it *may* call the select action on segments
/// which do not intersect the search envelope.
/// This saves on the overhead of checking envelope intersection
/// each time, since clients may be able to do this more efficiently.
/// </remarks>
/// <param name="searchEnv">The search envelope</param>
/// <param name="mcs">The select action to execute on selected segments</param>
public void Select(Envelope searchEnv, MonotoneChainSelectAction mcs)
{
ComputeSelect(searchEnv, _start, _end, mcs);
}