Re-work layering in possibly debatable ways. Sketchy docs in doc/layering.

git-svn-id: svn://localhost/ardour2/branches/3.0@11088 d708f5d6-7413-0410-9779-e7cbd77b26cf

1 files changed, 392 insertions, 309 deletions

diff --git a/libs/ardour/playlist.cc b/libs/ardour/playlist.cc
index 641aeff012..f2084fda0c 100644
--- a/libs/ardour/playlist.cc
+++ b/libs/ardour/playlist.cc
@@ -30,6 +30,7 @@
 
 #include "pbd/convert.h"
 #include "pbd/failed_constructor.h"
+#include "pbd/stacktrace.h"
 #include "pbd/stateful_diff_command.h"
 #include "pbd/xml++.h"
 
@@ -320,8 +321,8 @@ Playlist::init (bool hide)
 	_frozen = false;
 	layer_op_counter = 0;
 	freeze_length = 0;
-	_explicit_relayering = false;
 	_combine_ops = 0;
+	_relayer_suspended = false;
 
 	_session.history().BeginUndoRedo.connect_same_thread (*this, boost::bind (&Playlist::begin_undo, this));
 	_session.history().EndUndoRedo.connect_same_thread (*this, boost::bind (&Playlist::end_undo, this));
@@ -487,6 +488,8 @@ Playlist::notify_region_moved (boost::shared_ptr<Region> r)
 {
 	Evoral::RangeMove<framepos_t> const move (r->last_position (), r->length (), r->position ());
 
+	/* We could timestamp the region's layer op here, but we're doing it in region_bounds_changed */
+
 	if (holding_state ()) {
 
 		pending_range_moves.push_back (move);
@@ -503,6 +506,8 @@ Playlist::notify_region_moved (boost::shared_ptr<Region> r)
 void
 Playlist::notify_region_start_trimmed (boost::shared_ptr<Region> r)
 {
+	timestamp_layer_op (LayerOpBoundsChange, r);
+
 	if (r->position() >= r->last_position()) {
 		/* trimmed shorter */
 		return;
@@ -526,6 +531,8 @@ Playlist::notify_region_start_trimmed (boost::shared_ptr<Region> r)
 void
 Playlist::notify_region_end_trimmed (boost::shared_ptr<Region> r)
 {
+	timestamp_layer_op (LayerOpBoundsChange, r);
+
 	if (r->length() < r->last_length()) {
 		/* trimmed shorter */
 	}
@@ -552,6 +559,8 @@ Playlist::notify_region_added (boost::shared_ptr<Region> r)
 	   as though it could be.
 	*/
 
+	timestamp_layer_op (LayerOpAdd, r);
+
 	if (holding_state()) {
 		pending_adds.insert (r);
 		pending_contents_change = true;
@@ -560,6 +569,7 @@ Playlist::notify_region_added (boost::shared_ptr<Region> r)
 		pending_contents_change = false;
 		RegionAdded (boost::weak_ptr<Region> (r)); /* EMIT SIGNAL */
 		ContentsChanged (); /* EMIT SIGNAL */
+		relayer (r);
 	}
 }
 
@@ -577,34 +587,35 @@ Playlist::flush_notifications (bool from_undo)
 
 	in_flush = true;
 
+	/* We have:
+
+	   pending_bounds:  regions whose bounds position and/or length changes
+	   pending_removes: regions which were removed
+	   pending_adds:    regions which were added
+	   pending_length:  true if the playlist length might have changed
+	   pending_contents_change: true if there was almost any change in the playlist
+	   pending_range_moves: details of periods of time that have been moved about (when regions have been moved)
+
+	*/
+
 	if (!pending_bounds.empty() || !pending_removes.empty() || !pending_adds.empty()) {
 		regions_changed = true;
 	}
 
-	/* we have no idea what order the regions ended up in pending
-	   bounds (it could be based on selection order, for example).
-	   so, to preserve layering in the "most recently moved is higher"
-	   model, sort them by existing layer, then timestamp them.
-	*/
-
-	// RegionSortByLayer cmp;
-	// pending_bounds.sort (cmp);
+	/* Make a list of regions that need relayering */
+	RegionList regions_to_relayer;
 
 	for (RegionList::iterator r = pending_bounds.begin(); r != pending_bounds.end(); ++r) {
-		if (_session.config.get_layer_model() == MoveAddHigher) {
-			timestamp_layer_op (*r);
-		}
+		regions_to_relayer.push_back (*r);
 		dependent_checks_needed.insert (*r);
 	}
 
 	for (s = pending_removes.begin(); s != pending_removes.end(); ++s) {
 		remove_dependents (*s);
-		// cerr << _name << " sends RegionRemoved\n";
 		RegionRemoved (boost::weak_ptr<Region> (*s)); /* EMIT SIGNAL */
 	}
 
 	for (s = pending_adds.begin(); s != pending_adds.end(); ++s) {
-		 // cerr << _name << " sends RegionAdded\n";
 		 /* don't emit RegionAdded signal until relayering is done,
 		    so that the region is fully setup by the time
 		    anyone hear's that its been added
@@ -613,18 +624,14 @@ Playlist::flush_notifications (bool from_undo)
 	 }
 
 	 if (regions_changed || pending_contents_change) {
-		 if (!in_set_state) {
-			 relayer ();
-		 }
 		 pending_contents_change = false;
-		 // cerr << _name << " sends 5 contents change @ " << get_microseconds() << endl;
 		 ContentsChanged (); /* EMIT SIGNAL */
-		 // cerr << _name << "done contents change @ " << get_microseconds() << endl;
 	 }
 
 	 for (s = pending_adds.begin(); s != pending_adds.end(); ++s) {
 		 (*s)->clear_changes ();
 		 RegionAdded (boost::weak_ptr<Region> (*s)); /* EMIT SIGNAL */
+		 regions_to_relayer.push_back (*s);
 	 }
 
 	 for (s = dependent_checks_needed.begin(); s != dependent_checks_needed.end(); ++s) {
@@ -639,6 +646,10 @@ Playlist::flush_notifications (bool from_undo)
 		 RegionsExtended (pending_region_extensions);
 	 }
 
+	 if (!regions_to_relayer.empty ()) {
+		 relayer (regions_to_relayer);
+	 }
+
 	 clear_pending ();
 
 	 in_flush = false;
@@ -741,18 +752,11 @@ Playlist::flush_notifications (bool from_undo)
 
 	 region->set_position (position);
 
-	 timestamp_layer_op (region);
-
 	 regions.insert (upper_bound (regions.begin(), regions.end(), region, cmp), region);
 	 all_regions.insert (region);
 
 	 possibly_splice_unlocked (position, region->length(), region);
 
-	 if (!holding_state ()) {
-		 /* layers get assigned from XML state, and are not reset during undo/redo */
-		 relayer ();
-	 }
-
 	 /* we need to notify the existence of new region before checking dependents. Ick. */
 
 	 notify_region_added (region);
@@ -812,7 +816,6 @@ Playlist::flush_notifications (bool from_undo)
 			 possibly_splice_unlocked (pos, -distance);
 
 			 if (!holding_state ()) {
-				 relayer ();
 				 remove_dependents (region);
 			 }
 
@@ -865,11 +868,20 @@ Playlist::flush_notifications (bool from_undo)
 	 }
  }
 
+/** Go through each region on the playlist and cut them at start and end, removing the section between
+ *  start and end if cutting == true.  Regions that lie entirely within start and end are always
+ *  removed.
+ */
  void
  Playlist::partition_internal (framepos_t start, framepos_t end, bool cutting, RegionList& thawlist)
  {
 	 RegionList new_regions;
 
+	 /* Don't relayer regions that are created during this operation; leave them
+	    on the same region as the original.
+	 */
+	 suspend_relayer ();
+
 	 {
 		 RegionLock rlock (this);
 
@@ -948,7 +960,7 @@ Playlist::flush_notifications (bool from_undo)
 					 plist.add (Properties::start, current->start() + (pos2 - pos1));
 					 plist.add (Properties::length, pos3 - pos2);
 					 plist.add (Properties::name, new_name);
-					 plist.add (Properties::layer, regions.size());
+					 plist.add (Properties::layer, current->layer());
 					 plist.add (Properties::automatic, true);
 					 plist.add (Properties::left_of_split, true);
 					 plist.add (Properties::right_of_split, true);
@@ -967,7 +979,7 @@ Playlist::flush_notifications (bool from_undo)
 				 plist.add (Properties::start, current->start() + (pos3 - pos1));
 				 plist.add (Properties::length, pos4 - pos3);
 				 plist.add (Properties::name, new_name);
-				 plist.add (Properties::layer, regions.size());
+				 plist.add (Properties::layer, current->layer());
 				 plist.add (Properties::automatic, true);
 				 plist.add (Properties::right_of_split, true);
 
@@ -1005,7 +1017,7 @@ Playlist::flush_notifications (bool from_undo)
 					 plist.add (Properties::start, current->start() + (pos2 - pos1));
 					 plist.add (Properties::length, pos4 - pos2);
 					 plist.add (Properties::name, new_name);
-					 plist.add (Properties::layer, regions.size());
+					 plist.add (Properties::layer, current->layer());
 					 plist.add (Properties::automatic, true);
 					 plist.add (Properties::left_of_split, true);
 
@@ -1048,7 +1060,7 @@ Playlist::flush_notifications (bool from_undo)
 					 plist.add (Properties::start, current->start());
 					 plist.add (Properties::length, pos3 - pos1);
 					 plist.add (Properties::name, new_name);
-					 plist.add (Properties::layer, regions.size());
+					 plist.add (Properties::layer, current->layer());
 					 plist.add (Properties::automatic, true);
 					 plist.add (Properties::right_of_split, true);
 
@@ -1095,6 +1107,8 @@ Playlist::flush_notifications (bool from_undo)
 	 for (RegionList::iterator i = new_regions.begin(); i != new_regions.end(); ++i) {
 		 check_dependents (*i, false);
 	 }
+
+	 resume_relayer ();
  }
 
  boost::shared_ptr<Playlist>
@@ -1370,18 +1384,6 @@ Playlist::flush_notifications (bool from_undo)
 	 add_region_internal (left, region->position());
 	 add_region_internal (right, region->position() + before);
 
-	 uint64_t orig_layer_op = region->last_layer_op();
-	 for (RegionList::iterator i = regions.begin(); i != regions.end(); ++i) {
-		 if ((*i)->last_layer_op() > orig_layer_op) {
-			 (*i)->set_last_layer_op( (*i)->last_layer_op() + 1 );
-		 }
-	 }
-
-	 left->set_last_layer_op ( orig_layer_op );
-	 right->set_last_layer_op ( orig_layer_op + 1);
-
-	 layer_op_counter++;
-
 	 finalize_split_region (region, left, right);
 
 	 remove_region_internal (region);
@@ -1467,6 +1469,8 @@ Playlist::flush_notifications (bool from_undo)
 
 	 if (what_changed.contains (Properties::position)) {
 
+		 timestamp_layer_op (LayerOpBoundsChange, region);
+		 
 		 /* remove it from the list then add it back in
 		    the right place again.
 		 */
@@ -1506,13 +1510,8 @@ Playlist::flush_notifications (bool from_undo)
 		 if (holding_state ()) {
 			 pending_bounds.push_back (region);
 		 } else {
-			 if (_session.config.get_layer_model() == MoveAddHigher) {
-				 /* it moved or changed length, so change the timestamp */
-				 timestamp_layer_op (region);
-			 }
-
 			 notify_contents_changed ();
-			 relayer ();
+			 relayer (region);
 			 check_dependents (region, false);
 		 }
 	 }
@@ -1572,10 +1571,6 @@ Playlist::flush_notifications (bool from_undo)
 		 notify_region_start_trimmed (region);
 	 }
 
-	 /* don't notify about layer changes, since we are the only object that can initiate
-	    them, and we notify in ::relayer()
-	 */
-
 	 if (what_changed.contains (our_interests)) {
 		 save = true;
 	 }
@@ -2134,6 +2129,7 @@ Playlist::flush_notifications (bool from_undo)
 		 return -1;
 	 }
 
+	 suspend_relayer ();
 	 freeze ();
 
 	 plist = node.properties();
@@ -2195,9 +2191,7 @@ Playlist::flush_notifications (bool from_undo)
 			}
 
 			add_region (region, region->position(), 1.0);
-			
-			// So that layer_op ordering doesn't get screwed up
-			region->set_last_layer_op( region->layer());
+
 			region->resume_property_changes ();
 
 		}
@@ -2218,6 +2212,7 @@ Playlist::flush_notifications (bool from_undo)
 		
 	thaw ();
 	notify_contents_changed ();
+	resume_relayer ();
 
 	in_set_state--;
 	first_set_state = false;
@@ -2345,289 +2340,253 @@ Playlist::set_edit_mode (EditMode mode)
 	_edit_mode = mode;
 }
 
-/********************
- * Region Layering
- ********************/
-
+/** Relayer a region.  See the other relayer() methods for commentary. */
 void
-Playlist::relayer ()
+Playlist::relayer (boost::shared_ptr<Region> region)
 {
-	/* never compute layers when changing state for undo/redo or setting from XML */
-
-	if (in_update || in_set_state) {
+	if (_relayer_suspended) {
 		return;
 	}
+	
+	RegionList r;
+	r.push_back (region);
+	relayer (r);
+}
 
-	bool changed = false;
-
-	/* Build up a new list of regions on each layer, stored in a set of lists
-	   each of which represent some period of time on some layer.  The idea
-	   is to avoid having to search the entire region list to establish whether
-	   each region overlaps another */
-
-	/* how many pieces to divide this playlist's time up into */
-	int const divisions = 512;
-
-	/* find the start and end positions of the regions on this playlist */
-	framepos_t start = INT64_MAX;
-	framepos_t end = 0;
-	for (RegionList::const_iterator i = regions.begin(); i != regions.end(); ++i) {
-		start = min (start, (*i)->position());
-		end = max (end, (*i)->position() + (*i)->length());
-	}
-
-	/* hence the size of each time division */
-	double const division_size = (end - start) / double (divisions);
-
-	vector<vector<RegionList> > layers;
-	layers.push_back (vector<RegionList> (divisions));
-
-	/* we want to go through regions from desired lowest to desired highest layer,
-	   which depends on the layer model
-	*/
-
-	RegionList copy = regions.rlist();
-
-	/* sort according to the model and the layering mode that we're in */
-
-	if (_explicit_relayering) {
+Playlist::TemporaryLayers
+Playlist::compute_temporary_layers (RegionList const & relayer_regions)
+{
+	TemporaryLayers temporary_layers;
+	OverlapCache cache (this);
 
-		copy.sort (RegionSortByLayerWithPending ());
+	for (RegionList::const_iterator i = relayer_regions.begin(); i != relayer_regions.end(); ++i) {
 
-	} else if (_session.config.get_layer_model() == MoveAddHigher || _session.config.get_layer_model() == AddHigher) {
+		/* current_overlaps: regions that overlap *i now */
+		RegionList current_overlaps = cache.get ((*i)->bounds ());
+		current_overlaps.remove (*i);
+		
+		/* overlaps_to_preserve: regions that overlap *i now, but which aren't being
+		   worked on during this relayer: these will have their relationship with
+		   *i preserved.
+		*/
+		RegionList overlaps_to_preserve;
 
-		copy.sort (RegionSortByLastLayerOp ());
+		/* overlaps_to_check: regions that overlap *i now, and must be checked to
+		   see if *i is still on the correct layer with respect to them (according
+		   to current layering rules).
+		*/
+		RegionList overlaps_to_check;
 
-	}
+		if (_session.config.get_relayer_on_all_edits () || (*i)->last_layer_op (LayerOpAdd) > (*i)->last_layer_op (LayerOpBoundsChange)) {
+			/* We're configured to relayer on all edits, or this region has had
+			   no edit since it was added to the playlist, so we're relayering
+			   the whole lot; in this case there are no `overlaps_to_preserve'.
+			*/
+			overlaps_to_check = current_overlaps;
+		} else {
+			/* We're only relayering new overlaps; find them */
+			RegionList last_overlaps = cache.get ((*i)->last_relayer_bounds ());
+			last_overlaps.remove (*i);
+			for (RegionList::const_iterator j = current_overlaps.begin(); j != current_overlaps.end(); ++j) {
+				if (find (last_overlaps.begin(), last_overlaps.end(), *j) == last_overlaps.end()) {
+					/* This is a new overlap, which must be checked */
+					overlaps_to_check.push_back (*j);
+				} else {
+					/* This is an existing overlap, which must be preserved */
+					overlaps_to_preserve.push_back (*j);
+				}
+			}
+		}
 
+		if (overlaps_to_check.empty ()) {
+			/* There are no overlaps to check, so just leave everything as it is */
+			continue;
+		}
 
-	for (RegionList::iterator i = copy.begin(); i != copy.end(); ++i) {
+		/* Put *i on our overlaps_to_check_list */
+		overlaps_to_check.push_back (*i);
 
-		/* reset the pending explicit relayer flag for every region, now that we're relayering */
-		(*i)->set_pending_explicit_relayer (false);
+		/* And sort it according to the current layer model */
+		switch (_session.config.get_layer_model()) {
+		case LaterHigher:
+			overlaps_to_check.sort (RegionSortByPosition ());
+			break;
+		case AddOrBoundsChangeHigher:
+			overlaps_to_check.sort (RegionSortByAddOrBounds ());
+			break;
+		case AddHigher:
+			overlaps_to_check.sort (RegionSortByAdd ());
+			break;
+		}
 
-		/* find the time divisions that this region covers; if there are no regions on the list,
-		   division_size will equal 0 and in this case we'll just say that
-		   start_division = end_division = 0.
+		/* Now find *i in our overlaps_to_check list; within this list it will be in the
+		   right place wrt the current layering rules, so we can work out the layers of the
+		   nearest regions below and above.
 		*/
-		int start_division = 0;
-		int end_division = 0;
-
-		if (division_size > 0) {
-			start_division = floor ( ((*i)->position() - start) / division_size);
-			end_division = floor ( ((*i)->position() + (*i)->length() - start) / division_size );
-			if (end_division == divisions) {
-				end_division--;
-			}
+		double previous_layer = -DBL_MAX;
+		double next_layer = DBL_MAX;
+		RegionList::const_iterator j = overlaps_to_check.begin();
+		while (*j != *i) {
+			previous_layer = temporary_layers.get (*j);
+			++j;
 		}
 
-		assert (divisions == 0 || end_division < divisions);
+		/* we must have found *i */
+		assert (j != overlaps_to_check.end ());
 
-		/* find the lowest layer that this region can go on */
-		size_t j = layers.size();
-		while (j > 0) {
-			/* try layer j - 1; it can go on if it overlaps no other region
-			   that is already on that layer
-			*/
+		++j;
+		if (j != overlaps_to_check.end ()) {
+			next_layer = temporary_layers.get (*j);
+		}
 
-			bool overlap = false;
-			for (int k = start_division; k <= end_division; ++k) {
-				RegionList::iterator l = layers[j-1][k].begin ();
-				while (l != layers[j-1][k].end()) {
-					if ((*l)->overlap_equivalent (*i)) {
-						overlap = true;
-						break;
-					}
-					l++;
-				}
+		/* Now we know where *i and overlaps_to_preserve should go: between previous_layer and
+		   next_layer.
+		*/
 
-				if (overlap) {
-					break;
+		/* Recurse into overlaps_to_preserve to find dependents */
+		RegionList recursed_overlaps_to_preserve;
+		
+		for (RegionList::const_iterator k = overlaps_to_preserve.begin(); k != overlaps_to_preserve.end(); ++k) {
+			recursed_overlaps_to_preserve.push_back (*k);
+			RegionList touched = recursive_regions_touched (*k, cache, *i);
+			for (RegionList::iterator m = touched.begin(); m != touched.end(); ++m) {
+				if (find (recursed_overlaps_to_preserve.begin(), recursed_overlaps_to_preserve.end(), *m) == recursed_overlaps_to_preserve.end()) {
+					recursed_overlaps_to_preserve.push_back (*m);
 				}
 			}
-
-			if (overlap) {
-				/* overlap, so we must use layer j */
-				break;
-			}
-
-			--j;
 		}
 
-		if (j == layers.size()) {
-			/* we need a new layer for this region */
-			layers.push_back (vector<RegionList> (divisions));
-		}
+		/* Put *i into the overlaps_to_preserve list */
+		recursed_overlaps_to_preserve.push_back (*i);
 
-		/* put a reference to this region in each of the divisions that it exists in */
-		for (int k = start_division; k <= end_division; ++k) {
-			layers[j][k].push_back (*i);
-		}
+		/* Sort it by layer, so that we preserve layering */
+		recursed_overlaps_to_preserve.sort (SortByTemporaryLayer (temporary_layers));
 
-		if ((*i)->layer() != j) {
-			changed = true;
-		}
+		/* Divide available space up into chunks so that we can relayer everything in that space */
+		double const space = (next_layer - previous_layer) / (recursed_overlaps_to_preserve.size() + 1);
 
-		(*i)->set_layer (j);
+		/* And relayer */
+		int m = 1;
+		for (RegionList::const_iterator k = recursed_overlaps_to_preserve.begin(); k != recursed_overlaps_to_preserve.end(); ++k) {
+			temporary_layers.set (*k, previous_layer + space * m);
+			++m;
+		}
 	}
 
-	if (changed) {
-		notify_layering_changed ();
-	}
+	return temporary_layers;
 }
 
-/* XXX these layer functions are all deprecated */
-
+/** Take a list of temporary layer indices and set up the layers of all regions
+ *  based on them.
+ */
 void
-Playlist::raise_region (boost::shared_ptr<Region> region)
+Playlist::commit_temporary_layers (TemporaryLayers const & temporary_layers)
 {
-	uint32_t top = regions.size() - 1;
-	layer_t target = region->layer() + 1U;
+	/* Sort all the playlist's regions by layer, ascending */
+	RegionList all_regions = regions.rlist ();
+	all_regions.sort (SortByTemporaryLayer (temporary_layers));
 
-	if (target >= top) {
-		/* its already at the effective top */
-		return;
-	}
+	for (RegionList::iterator i = all_regions.begin(); i != all_regions.end(); ++i) {
 
-	move_region_to_layer (target, region, 1);
-}
+		/* Go through the regions that we have already layered and hence work
+		   out the maximum layer index that is in used at some point during
+		   region *i.
+		*/
+		
+		layer_t max_layer_here = 0;
+		bool have_overlap = false;
+		for (RegionList::iterator j = all_regions.begin(); j != i; ++j) {
+			if ((*j)->overlap_equivalent (*i)) {
+				max_layer_here = max ((*j)->layer (), max_layer_here);
+				have_overlap = true;
+			}
+		}
 
-void
-Playlist::lower_region (boost::shared_ptr<Region> region)
-{
-	if (region->layer() == 0) {
-		/* its already at the bottom */
-		return;
+		if (have_overlap) {
+			/* *i overlaps something, so put it on the next available layer */
+			(*i)->set_layer (max_layer_here + 1);
+		} else {
+			/* no overlap, so put on the bottom layer */
+			(*i)->set_layer (0);
+		}
 	}
 
-	layer_t target = region->layer() - 1U;
-
-	move_region_to_layer (target, region, -1);
+	notify_layering_changed ();
 }
 
+/** Relayer a list of regions.
+ *
+ *  Taking each region R in turn, this method examines the regions O that overlap R in time.
+ *  If the session configuration option "relayer-on-all-moves" is false, we reduce O so that
+ *  it contains only those regions with which new overlaps have been formed since the last
+ *  relayer.
+ *
+ *  We then change the layer of R and its indirect overlaps so that R meets the current
+ *  Session layer model with respect to O.  See doc/layering.
+ */
+
 void
-Playlist::raise_region_to_top (boost::shared_ptr<Region> region)
+Playlist::relayer (RegionList const & relayer_regions)
 {
-	/* does nothing useful if layering mode is later=higher */
-	switch (_session.config.get_layer_model()) {
-	case LaterHigher:
+	if (_relayer_suspended) {
 		return;
-	default:
-		break;
 	}
 
-	layer_t top = regions.size() - 1;
+	/* We do this in two parts: first; compute `temporary layer' indices for
+	   regions on the playlist.  These are (possibly) fractional indices, which
+	   are a convenient means of working with things when you want to insert layers
+	   between others.
+	*/
 
-	if (region->layer() >= top) {
-		/* already on the top */
-		return;
-	}
+	TemporaryLayers temporary_layers = compute_temporary_layers (relayer_regions);
 
-	move_region_to_layer (top, region, 1);
-	/* mark the region's last_layer_op as now, so that it remains on top when
-	   doing future relayers (until something else takes over)
-	 */
-	timestamp_layer_op (region);
+	/* Second, we fix up these temporary layers and `commit' them by writing
+	   them to the regions involved.
+	*/
+	
+	commit_temporary_layers (temporary_layers);
 }
 
+/** Put a region on some fractional layer and sort everything else out around it.
+ *  This can be used to force a region into some layering; for example, calling
+ *  this method with temporary_layer == -0.5 will put the region at the bottom of
+ *  the stack.
+ */
+
 void
-Playlist::lower_region_to_bottom (boost::shared_ptr<Region> region)
+Playlist::relayer (boost::shared_ptr<Region> region, double temporary_layer)
 {
-	/* does nothing useful if layering mode is later=higher */
-	switch (_session.config.get_layer_model()) {
-	case LaterHigher:
-		return;
-	default:
-		break;
-	}
-
-	if (region->layer() == 0) {
-		/* already on the bottom */
+	if (_relayer_suspended) {
 		return;
 	}
 
-	move_region_to_layer (0, region, -1);
-	/* force region's last layer op to zero so that it stays at the bottom
-	   when doing future relayers
-	*/
-	region->set_last_layer_op (0);
+	TemporaryLayers t;
+	t.set (region, temporary_layer);
+	commit_temporary_layers (t);
 }
 
-int
-Playlist::move_region_to_layer (layer_t target_layer, boost::shared_ptr<Region> region, int dir)
+void
+Playlist::raise_region (boost::shared_ptr<Region> region)
 {
-	RegionList::iterator i;
-	typedef pair<boost::shared_ptr<Region>,layer_t> LayerInfo;
-	list<LayerInfo> layerinfo;
-
-	{
-		RegionLock rlock (const_cast<Playlist *> (this));
-
-		for (i = regions.begin(); i != regions.end(); ++i) {
-
-			if (region == *i) {
-				continue;
-			}
-
-			layer_t dest;
-
-			if (dir > 0) {
-
-				/* region is moving up, move all regions on intermediate layers
-				   down 1
-				*/
-
-				if ((*i)->layer() > region->layer() && (*i)->layer() <= target_layer) {
-					dest = (*i)->layer() - 1;
-				} else {
-					/* not affected */
-					continue;
-				}
-			} else {
-
-				/* region is moving down, move all regions on intermediate layers
-				   up 1
-				*/
-
-				if ((*i)->layer() < region->layer() && (*i)->layer() >= target_layer) {
-					dest = (*i)->layer() + 1;
-				} else {
-					/* not affected */
-					continue;
-				}
-			}
-
-			LayerInfo newpair;
-
-			newpair.first = *i;
-			newpair.second = dest;
-
-			layerinfo.push_back (newpair);
-		}
-	}
-
-	freeze ();
-
-	/* now reset the layers without holding the region lock */
-
-	for (list<LayerInfo>::iterator x = layerinfo.begin(); x != layerinfo.end(); ++x) {
-		x->first->set_layer (x->second);
-	}
-
-	region->set_layer (target_layer);
-
-	/* now check all dependents, since we changed the layering */
-
-	for (list<LayerInfo>::iterator x = layerinfo.begin(); x != layerinfo.end(); ++x) {
-		check_dependents (x->first, false);
-	}
+	relayer (region, region->layer() + 0.5);
+}
 
-	check_dependents (region, false);
-	notify_layering_changed ();
+void
+Playlist::lower_region (boost::shared_ptr<Region> region)
+{
+	relayer (region, region->layer() - 0.5);
+}
 
-	thaw ();
+void
+Playlist::raise_region_to_top (boost::shared_ptr<Region> region)
+{
+	relayer (region, max_layer);
+}
 
-	return 0;
+void
+Playlist::lower_region_to_bottom (boost::shared_ptr<Region> region)
+{
+	relayer (region, -0.5);
 }
 
 void
@@ -2763,15 +2722,23 @@ Playlist::set_frozen (bool yn)
 }
 
 void
-Playlist::timestamp_layer_op (boost::shared_ptr<Region> region)
+Playlist::timestamp_layer_op (LayerOp op, boost::shared_ptr<Region> region)
 {
-	region->set_last_layer_op (++layer_op_counter);
+	region->set_last_layer_op (op, ++layer_op_counter);
 }
 
 
+/** Find the next or previous region after `region' (next if dir > 0, previous otherwise)
+ *  and swap its position with `region'.
+ */
 void
 Playlist::shuffle (boost::shared_ptr<Region> region, int dir)
 {
+	/* As regards layering, the calls we make to set_position() will
+	   perform layering as if the regions had been moved, which I think
+	   is about right.
+	*/
+	
 	bool moved = false;
 
 	if (region->locked()) {
@@ -2876,13 +2843,9 @@ Playlist::shuffle (boost::shared_ptr<Region> region, int dir)
 	_shuffling = false;
 
 	if (moved) {
-
-		relayer ();
 		check_dependents (region, false);
-
 		notify_contents_changed();
 	}
-
 }
 
 bool
@@ -2921,29 +2884,6 @@ Playlist::foreach_region (boost::function<void(boost::shared_ptr<Region>)> s)
 	}
 }
 
-void
-Playlist::set_explicit_relayering (bool e)
-{
-	if (e == false && _explicit_relayering == true) {
-
-		/* We are changing from explicit to implicit relayering; layering may have been changed whilst
-		   we were in explicit mode, and we don't want that to be undone next time an implicit relayer
-		   occurs.  Hence now we'll set up region last_layer_op values so that an implicit relayer
-		   at this point would keep regions on the same layers.
-
-		   From then on in, it's just you and your towel.
-		*/
-
-		RegionLock rl (this);
-		for (RegionList::iterator i = regions.begin(); i != regions.end(); ++i) {
-			(*i)->set_last_layer_op ((*i)->layer ());
-		}
-	}
-
-	_explicit_relayering = e;
-}
-
-
 bool
 Playlist::has_region_at (framepos_t const p) const
 {
@@ -3323,3 +3263,146 @@ Playlist::set_orig_track_id (const PBD::ID& id)
 {
 	_orig_track_id = id;
 }
+
+/** Set the temporary layer for a region */
+void
+Playlist::TemporaryLayers::set (boost::shared_ptr<Region> r, double l)
+{
+	_map[r] = l;
+}
+
+/** Return the temporary layer for a region, if one has been specified
+ *  to this TemporaryLayers object; if not return the region's current
+ *  layer.
+ */
+double
+Playlist::TemporaryLayers::get (boost::shared_ptr<Region> r) const
+{
+	Map::const_iterator i = _map.find (r);
+	if (i != _map.end ()) {
+		return i->second;
+	}
+
+	return double (r->layer ());
+}
+
+int const Playlist::OverlapCache::_divisions = 512;
+
+/** Set up an OverlapCache for a playlist; the cache will only be valid until
+ *  the Playlist is changed.
+ */
+Playlist::OverlapCache::OverlapCache (Playlist* playlist)
+	: _range (0, 0)
+{
+	/* Find the start and end positions of the regions on this playlist */
+	_range = Evoral::Range<framepos_t> (max_framepos, 0);
+	RegionList const & rl = playlist->region_list().rlist ();
+	for (RegionList::const_iterator i = rl.begin(); i != rl.end(); ++i) {
+		Evoral::Range<framepos_t> const b = (*i)->bounds ();
+		_range.from = min (_range.from, b.from);
+		_range.to = max (_range.to, b.to);
+	}
+
+	/* Hence the size of each time divison */
+	_division_size = (_range.to - _range.from) / double (_divisions);
+
+	_cache.resize (_divisions);
+
+	/* Build the cache */
+	for (RegionList::const_iterator i = rl.begin(); i != rl.end(); ++i) {
+		pair<int, int> ind = cache_indices ((*i)->bounds ());
+		for (int j = ind.first; j < ind.second; ++j) {
+			_cache[j].push_back (*i);
+		}
+	}
+}
+
+/** @param range Range, in frames.
+ *  @return From and to cache indices for  (to is exclusive).
+ */
+pair<int, int>
+Playlist::OverlapCache::cache_indices (Evoral::Range<framepos_t> range) const
+{
+	range.from = max (range.from, _range.from);
+	range.to = min (range.to, _range.to);
+	
+	pair<int, int> const p = make_pair (
+		floor ((range.from - _range.from) / _division_size),
+		ceil ((range.to - _range.from) / _division_size)
+		);
+
+	assert (p.first >= 0);
+	assert (p.second <= _divisions);
+
+	return p;
+}
+
+/** Return the regions that overlap a given range.  The returned list
+ *  is not guaranteed to be in the same order as the Playlist that it was
+ *  generated from.
+ */
+Playlist::RegionList
+Playlist::OverlapCache::get (Evoral::Range<framepos_t> range) const
+{
+	if (_range.from == max_framepos) {
+		return RegionList ();
+	}
+	
+	RegionList r;
+
+	pair<int, int> ind = cache_indices (range);
+	for (int i = ind.first; i < ind.second; ++i) {
+		for (RegionList::const_iterator j = _cache[i].begin(); j != _cache[i].end(); ++j) {
+			if ((*j)->coverage (range.from, range.to) != OverlapNone) {
+				r.push_back (*j);
+			}
+		}
+	}
+
+	r.sort ();
+	r.unique ();
+
+	return r;
+}
+
+void
+Playlist::suspend_relayer ()
+{
+	_relayer_suspended = true;
+}
+
+void
+Playlist::resume_relayer ()
+{
+	_relayer_suspended = false;
+}
+
+/** Examine a region and return regions which overlap it, and also those which overlap those which overlap etc.
+ *  @param ignore Optional region which should be treated as if it doesn't exist (ie not returned in the list,
+ *  and not recursed into).
+ */
+Playlist::RegionList
+Playlist::recursive_regions_touched (boost::shared_ptr<Region> region, OverlapCache const & cache, boost::shared_ptr<Region> ignore) const
+{
+	RegionList touched;
+	recursive_regions_touched_sub (region, cache, ignore, touched);
+
+	touched.remove (region);
+	return touched;
+}
+
+/** Recursive sub-routine of recursive_regions_touched */
+void
+Playlist::recursive_regions_touched_sub (
+	boost::shared_ptr<Region> region, OverlapCache const & cache, boost::shared_ptr<Region> ignore, RegionList & touched
+	) const
+{
+	RegionList r = cache.get (region->bounds ());
+	for (RegionList::iterator i = r.begin(); i != r.end(); ++i) {
+		if (find (touched.begin(), touched.end(), *i) == touched.end() && *i != ignore) {
+			touched.push_back (*i);
+			recursive_regions_touched_sub (*i, cache, ignore, touched);
+		}
+	}
+}
+