Building a Mutable Set

Figure 2: Outline of the Bentley-Ottmann algorithm

C          = collection of all non-vertical line segments.
ScanSet    = sorted collection of x-values of all segment endpoints.
ActiveSegs = sorted subcollection of segments from C which are
             intersected by the current scanline.

for (each x_c in ScanSet)
  Reorder ActiveSegs based on x_c
  for each segment s in C
    if (x_c is the left endpoint of s)
      insert s into ActiveSegs
      report any new intersections created and update ScanSet
  for each segment s in ActiveSegs
    if (x_c is the right endpoint of s)
      remove s from ActiveSegs
      report any new intersections created and update ScanSet
    else // x_c is a point of intersection of two or more segments in
            ActiveSegs reverse the order of the segments that
            intersect s at this point report any new intersections
            created and update ScanSet