Method SwapNodes

libraries/lib-track/Track.cpp:688–739

This is used when you want to swap the track at s1 with the track at s2. The complication is that the tracks are stored in a single linked list.

// The complication is that the tracks are stored in a single
// linked list.
void TrackList::SwapNodes(TrackNodePointer s1, TrackNodePointer s2)
{
   // if a null pointer is passed in, we want to know about it
   wxASSERT(!isNull(s1));
   wxASSERT(!isNull(s2));

   // Safety check...
   if (s1 == s2)
      return;

   // Be sure s1 is the earlier iterator
   {
      const auto begin = ListOfTracks::begin();
      auto d1 = std::distance(begin, s1);
      auto d2 = std::distance(begin, s2);
      if (d1 > d2)
         std::swap(s1, s2);
   }

   // For saving the removed tracks
   using Saved = ListOfTracks::value_type;
   Saved saved1, saved2;

   auto doSave = [&](Saved &saved, TrackNodePointer &s) {
      saved = *s, s = erase(s);
   };

   doSave(saved1, s1);
   // The two ranges are assumed to be disjoint but might abut
   const bool same = (s1 == s2);
   doSave(saved2, s2);
   if (same)
      // Careful, we invalidated s1 in the second doSave!
      s1 = s2;

   // Reinsert them
   auto doInsert = [&](Saved &saved, TrackNodePointer &s) {
      const auto pTrack = saved.get();
      // Insert before s, and reassign s to point at the new node before
      // old s; which is why we saved pointers in backwards order
      pTrack->SetOwner(shared_from_this(), s = insert(s, saved) );
   };
   // This does not invalidate s2 even when it equals s1:
   doInsert(saved2, s1);
   // Even if s2 was same as s1, this correctly inserts the saved1 range
   // after the saved2 range, when done after:
   doInsert(saved1, s2);

   // Now correct the Index in the tracks, and other things
   RecalcPositions(s1);
   PermutationEvent(s1);
}

bool TrackList::MoveUp(Track &t)
{