refactor Canvas so that all Items have children; add Container abstract base class; rename Group as "Layout" and retain only drawing semantics

51 files changed, 442 insertions, 637 deletions

diff --git a/libs/canvas/arc.cc b/libs/canvas/arc.cc
index 80141d4c66..baec2fafb1 100644
--- a/libs/canvas/arc.cc
+++ b/libs/canvas/arc.cc
@@ -39,8 +39,8 @@ Arc::Arc (Canvas* c)
 {
 }
 
-Arc::Arc (Group* g)
-	: Item (g)
+Arc::Arc (Item* parent)
+	: Item (parent)
 	, _radius (0.0)
 	, _arc_degrees (0.0)
 	, _start_degrees (0.0)
diff --git a/libs/canvas/arrow.cc b/libs/canvas/arrow.cc
index 86d4e33ca9..5cac31300e 100644
--- a/libs/canvas/arrow.cc
+++ b/libs/canvas/arrow.cc
@@ -35,13 +35,13 @@ using namespace ArdourCanvas;
  *  @param parent Parent canvas group.
  */
 Arrow::Arrow (Canvas* c)
-	: Group (c)
+	: Layout (c)
 {
 	setup ();
 }
 
-Arrow::Arrow (Group* g)
-	: Group (g)
+Arrow::Arrow (Item* parent)
+	: Layout (parent)
 {
 	setup ();
 }
diff --git a/libs/canvas/canvas.cc b/libs/canvas/canvas.cc
index 4ccf46b019..8c7960a217 100644
--- a/libs/canvas/canvas.cc
+++ b/libs/canvas/canvas.cc
@@ -396,7 +396,7 @@ GtkCanvas::pick_current_item (Duple const & point, int state)
 
 		/* We ignore invisible items, groups and items that ignore events */
 
-		if (!new_item->visible() || new_item->ignore_events() || dynamic_cast<Group const *>(new_item) != 0) {
+		if (!new_item->visible() || new_item->ignore_events() || dynamic_cast<Container const *>(new_item) != 0) {
 			continue;
 		}
 		
diff --git a/libs/canvas/canvas/arc.h b/libs/canvas/canvas/arc.h
index 5eaa4a0ab9..c2b32d9e10 100644
--- a/libs/canvas/canvas/arc.h
+++ b/libs/canvas/canvas/arc.h
@@ -32,7 +32,7 @@ class LIBCANVAS_API Arc : public Item
 {
 public:
 	Arc (Canvas*);
-	Arc (Group*);
+	Arc (Item*);
 
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
 	void compute_bounding_box () const;
diff --git a/libs/canvas/canvas/arrow.h b/libs/canvas/canvas/arrow.h
index 75c21da07c..7db225553e 100644
--- a/libs/canvas/canvas/arrow.h
+++ b/libs/canvas/canvas/arrow.h
@@ -26,8 +26,7 @@
 #define __CANVAS_ARROW_H__
 
 #include "canvas/visibility.h"
-
-#include "canvas/group.h"
+#include "canvas/layout.h"
 
 namespace ArdourCanvas {
 
@@ -46,11 +45,11 @@ class Polygon;
  *  to draw lines at any angle.
  */
 	
-class LIBCANVAS_API Arrow : public Group
+class LIBCANVAS_API Arrow : public Layout
 {
 public:
 	Arrow (Canvas*);
-	Arrow (Group*);
+	Arrow (Item*);
 
 	void set_show_head (int, bool);
 	void set_head_outward (int, bool);
diff --git a/libs/canvas/canvas/canvas.h b/libs/canvas/canvas/canvas.h
index fac9367985..94005f4cc7 100644
--- a/libs/canvas/canvas/canvas.h
+++ b/libs/canvas/canvas/canvas.h
@@ -42,7 +42,7 @@ namespace ArdourCanvas
 {
 
 class Rect;
-class Group;	
+class Item;
 class ScrollGroup;
 
 /** The base class for our different types of canvas.
@@ -78,7 +78,7 @@ public:
 	void render (Rect const &, Cairo::RefPtr<Cairo::Context> const &) const;
 
 	/** @return root group */
-	Group* root () {
+	Item* root () {
 		return &_root;
 	}
 
@@ -122,8 +122,8 @@ public:
 protected:
 	void queue_draw_item_area (Item *, Rect);
 	
-	/** our root group */
-	RootGroup _root;
+	/** our root item */
+	Root _root;
 
         virtual void pick_current_item (int state) = 0;
         virtual void pick_current_item (Duple const &, int state) = 0;
diff --git a/libs/canvas/canvas/circle.h b/libs/canvas/canvas/circle.h
index 1ca376a7a2..c84e3aceec 100644
--- a/libs/canvas/canvas/circle.h
+++ b/libs/canvas/canvas/circle.h
@@ -29,7 +29,7 @@ class LIBCANVAS_API Circle : public Arc
 {
   public:
 	Circle (Canvas*);
-	Circle (Group*);
+	Circle (Item*);
 };
 	
 }
diff --git a/libs/canvas/canvas/curve.h b/libs/canvas/canvas/curve.h
index 1bcab58e32..d27291e353 100644
--- a/libs/canvas/canvas/curve.h
+++ b/libs/canvas/canvas/curve.h
@@ -33,7 +33,7 @@ class LIBCANVAS_API Curve : public PolyItem, public InterpolatedCurve
 {
   public:
     Curve (Canvas*);
-    Curve (Group*);
+    Curve (Item*);
 
     enum CurveFill {
 	    None,
diff --git a/libs/canvas/canvas/flag.h b/libs/canvas/canvas/flag.h
index 2429e1775e..05c0e2777d 100644
--- a/libs/canvas/canvas/flag.h
+++ b/libs/canvas/canvas/flag.h
@@ -18,8 +18,8 @@
 */
 
 #include "canvas/visibility.h"
-#include "canvas/group.h"
 #include "canvas/types.h"
+#include "canvas/layout.h"
 
 namespace ArdourCanvas {
 
@@ -27,11 +27,11 @@ class Text;
 class Line;
 class Rectangle;
 
-class LIBCANVAS_API Flag : public Group
+class LIBCANVAS_API Flag : public Layout
 {
 public:
 	Flag (Canvas *, Distance, Color, Color, Duple);
-	Flag (Group*, Distance, Color, Color, Duple);
+	Flag (Item*, Distance, Color, Color, Duple);
 
 	void set_text (std::string const &);
 	void set_height (Distance);
diff --git a/libs/canvas/canvas/fwd.h b/libs/canvas/canvas/fwd.h
index 728e6988d4..61cab3c9d2 100644
--- a/libs/canvas/canvas/fwd.h
+++ b/libs/canvas/canvas/fwd.h
@@ -33,6 +33,7 @@ namespace ArdourCanvas {
 	class GtkCanvasViewport;
 	class Text;
 	class Curve;
+        class ScrollGroup;
 }
 
 #endif /* __canvas_canvas_fwd_h__ */
diff --git a/libs/canvas/canvas/group.h b/libs/canvas/canvas/group.h
deleted file mode 100644
index 6bfc40ba28..0000000000
--- a/libs/canvas/canvas/group.h
+++ /dev/null
@@ -1,79 +0,0 @@
-/*
-    Copyright (C) 2011-2013 Paul Davis
-    Author: Carl Hetherington <cth@carlh.net>
-
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
-*/
-
-#ifndef __CANVAS_GROUP_H__
-#define __CANVAS_GROUP_H__
-
-#include <list>
-#include <vector>
-
-#include "canvas/visibility.h"
-#include "canvas/item.h"
-#include "canvas/types.h"
-#include "canvas/lookup_table.h"
-
-namespace ArdourCanvas {
-
-class LIBCANVAS_API Group : public Item
-{
-public:
-	Group (Canvas*);
-	Group (Group*);
-	Group (Group*, Duple const& positon);
-	virtual ~Group ();
-
-	void render (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
-	virtual void compute_bounding_box () const;
-
-	void add (Item *);
-	void remove (Item *);
-         void clear (bool with_delete = false);
-	std::list<Item*> const & items () const {
-		return _items;
-	}
-
-	void raise_child_to_top (Item *);
-	void raise_child (Item *, int);
-	void lower_child_to_bottom (Item *);
-	void child_changed ();
-	
-	void scroll_to (Duple const& d);
-	
-	void add_items_at_point (Duple, std::vector<Item const *> &) const;
-
-        void dump (std::ostream&) const;
-
-	static int default_items_per_cell;
-
-private:
-	friend class ::OptimizingLookupTableTest;
-	
-	void ensure_lut () const;
-	void invalidate_lut () const;
-	void clear_items (bool with_delete);
-
-	/* our items, from lowest to highest in the stack */
-	std::list<Item*> _items;
-
-	mutable LookupTable* _lut;
-};
-
-}
-
-#endif
diff --git a/libs/canvas/canvas/image.h b/libs/canvas/canvas/image.h
index fd86818c21..64d70a5751 100644
--- a/libs/canvas/canvas/image.h
+++ b/libs/canvas/canvas/image.h
@@ -35,7 +35,7 @@ class LIBCANVAS_API Image : public Item
 {
 public:
     Image (Canvas *, Cairo::Format, int width, int height);
-    Image (Group*, Cairo::Format, int width, int height);
+    Image (Item*, Cairo::Format, int width, int height);
     
     struct Data {
 	Data (uint8_t *d, int w, int h, int s, Cairo::Format fmt)
diff --git a/libs/canvas/canvas/item.h b/libs/canvas/canvas/item.h
index bf752f66db..ced94e1e3b 100644
--- a/libs/canvas/canvas/item.h
+++ b/libs/canvas/canvas/item.h
@@ -32,12 +32,12 @@
 #include "canvas/types.h"
 #include "canvas/fill.h"
 #include "canvas/outline.h"
+#include "canvas/lookup_table.h"
 
 namespace ArdourCanvas
 {
 
 class Canvas;
-class Group;
 class Rect;	
 class ScrollGroup;
 
@@ -56,8 +56,8 @@ class LIBCANVAS_API Item : public Fill, public Outline
 {
 public:
 	Item (Canvas *);
-	Item (Group *);
-	Item (Group *, Duple const& p);
+	Item (Item *);
+	Item (Item *, Duple const& p);
 	virtual ~Item ();
 
         void redraw () const;
@@ -80,13 +80,11 @@ public:
 	 *
 	 * Note that Item::add_items_at_window_point() is only intended to be 
 	 * called on items already looked up in a LookupTable (i.e. by a
-	 * parent group) and thus known to cover @param point already.
+	 * parent) and thus known to cover @param point already.
 	 *
-	 * Derived classes may add more items than themselves (e.g. Group).
+	 * Derived classes may add more items than themselves (e.g. containers).
 	 */
-	virtual void add_items_at_point (Duple /*point*/, std::vector<Item const *>& items) const {
-		items.push_back (this);
-	}
+	virtual void add_items_at_point (Duple /*point*/, std::vector<Item const *>& items) const;
 
         virtual bool covers (Duple const &) const;
 
@@ -97,10 +95,10 @@ public:
 	void ungrab ();
 	
 	void unparent ();
-	void reparent (Group *);
+	void reparent (Item *);
 
 	/** @return Parent group, or 0 if this is the root group */
-	Group* parent () const {
+	Item* parent () const {
 		return _parent;
 	}
     
@@ -124,8 +122,6 @@ public:
 	void set_y_position (Coord);
 	void move (Duple);
 
-	virtual void scroll_to (Duple const&) {}
-
 	/** @return Position of this item in the parent's coordinates */
 	Duple position () const {
 		return _position;
@@ -187,6 +183,21 @@ public:
 
 	void set_data (std::string const &, void *);
 	void* get_data (std::string const &) const;
+
+	/* nested item ("grouping") API */
+	void add (Item *);
+	void remove (Item *);
+        void clear (bool with_delete = false);
+	std::list<Item*> const & items () const {
+		return _items;
+	}
+	void raise_child_to_top (Item *);
+	void raise_child (Item *, int);
+	void lower_child_to_bottom (Item *);
+	void child_changed ();
+
+	static int default_items_per_cell;
+
 	
 	/* This is a sigc++ signal because it is solely
 	   concerned with GUI stuff and is thus single-threaded
@@ -243,7 +254,7 @@ protected:
 
 	Canvas* _canvas;
 	/** parent group; may be 0 if we are the root group or if we have been unparent()ed */
-	Group* _parent;
+	Item* _parent;
 	/** scroll parent group; may be 0 if we are the root group or if we have been unparent()ed */
 	ScrollGroup* _scroll_parent;
 	/** position of this item in parent coordinates */
@@ -261,6 +272,18 @@ protected:
 	/* XXX: this is a bit grubby */
 	std::map<std::string, void *> _data;
 
+	/* nesting ("grouping") API */
+
+	void invalidate_lut () const;
+	void clear_items (bool with_delete);
+
+	void ensure_lut () const;
+	mutable LookupTable* _lut;
+	/* our items, from lowest to highest in the stack */
+	std::list<Item*> _items;
+
+	void add_child_bounding_boxes() const;
+
 private:
 	void init ();
 
diff --git a/libs/canvas/canvas/line.h b/libs/canvas/canvas/line.h
index e8f57a00ba..b178554c84 100644
--- a/libs/canvas/canvas/line.h
+++ b/libs/canvas/canvas/line.h
@@ -31,7 +31,7 @@ class LIBCANVAS_API Line : public Item
 {
   public:
 	Line (Canvas*);
-	Line (Group*);
+	Line (Item*);
 
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
 	void compute_bounding_box () const;
diff --git a/libs/canvas/canvas/line_set.h b/libs/canvas/canvas/line_set.h
index 38f97250ce..fad100fdf9 100644
--- a/libs/canvas/canvas/line_set.h
+++ b/libs/canvas/canvas/line_set.h
@@ -36,7 +36,7 @@ public:
 	};
 
 	LineSet (Canvas*, Orientation o = Vertical);
-	LineSet (Group*, Orientation o = Vertical);
+	LineSet (Item*, Orientation o = Vertical);
 
 	void compute_bounding_box () const;
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
diff --git a/libs/canvas/canvas/lookup_table.h b/libs/canvas/canvas/lookup_table.h
index 5be33c1bca..29452365cd 100644
--- a/libs/canvas/canvas/lookup_table.h
+++ b/libs/canvas/canvas/lookup_table.h
@@ -31,12 +31,11 @@ class OptimizingLookupTableTest;
 namespace ArdourCanvas {
 
 class Item;
-class Group;
 
 class LIBCANVAS_API LookupTable
 {
 public:
-    LookupTable (Group const &);
+    LookupTable (Item const &);
     virtual ~LookupTable ();
     
     virtual std::vector<Item*> get (Rect const &) = 0;
@@ -45,13 +44,13 @@ public:
 
 protected:
 	
-    Group const & _group;
+    Item const & _item;
 };
 
 class LIBCANVAS_API DumbLookupTable : public LookupTable
 {
 public:
-    DumbLookupTable (Group const &);
+	DumbLookupTable (Item const &);
     
     std::vector<Item*> get (Rect const &);
     std::vector<Item*> items_at_point (Duple const &) const;
@@ -61,7 +60,7 @@ public:
 class LIBCANVAS_API OptimizingLookupTable : public LookupTable
 {
 public:
-    OptimizingLookupTable (Group const &, int);
+    OptimizingLookupTable (Item const &, int);
     ~OptimizingLookupTable ();
     std::vector<Item*> get (Rect const &);
     std::vector<Item*> items_at_point (Duple const &) const;
diff --git a/libs/canvas/canvas/pixbuf.h b/libs/canvas/canvas/pixbuf.h
index eba73e57bf..2749b96668 100644
--- a/libs/canvas/canvas/pixbuf.h
+++ b/libs/canvas/canvas/pixbuf.h
@@ -35,7 +35,7 @@ class LIBCANVAS_API Pixbuf : public Item
 {
 public:
 	Pixbuf (Canvas*);
-	Pixbuf (Group*);
+	Pixbuf (Item*);
 
 	void render (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
 	void compute_bounding_box () const;
diff --git a/libs/canvas/canvas/poly_item.h b/libs/canvas/canvas/poly_item.h
index ab68204ff0..732adb14b3 100644
--- a/libs/canvas/canvas/poly_item.h
+++ b/libs/canvas/canvas/poly_item.h
@@ -30,7 +30,7 @@ class LIBCANVAS_API PolyItem : public Item
 {
 public:
 	PolyItem (Canvas*);
-	PolyItem (Group*);
+	PolyItem (Item*);
 
 	void compute_bounding_box () const;
 
diff --git a/libs/canvas/canvas/poly_line.h b/libs/canvas/canvas/poly_line.h
index 5476711e97..16db9a69e2 100644
--- a/libs/canvas/canvas/poly_line.h
+++ b/libs/canvas/canvas/poly_line.h
@@ -30,7 +30,7 @@ class LIBCANVAS_API PolyLine : public PolyItem
 {
   public:
 	PolyLine (Canvas*);
-	PolyLine (Group*);
+	PolyLine (Item*);
 	
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
 	
diff --git a/libs/canvas/canvas/polygon.h b/libs/canvas/canvas/polygon.h
index a3eed37cdc..9703eb46e9 100644
--- a/libs/canvas/canvas/polygon.h
+++ b/libs/canvas/canvas/polygon.h
@@ -31,7 +31,7 @@ class LIBCANVAS_API Polygon : public PolyItem
 {
 public:
 	Polygon (Canvas*);
-	Polygon (Group*);
+	Polygon (Item*);
         virtual ~Polygon();
 
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
diff --git a/libs/canvas/canvas/rectangle.h b/libs/canvas/canvas/rectangle.h
index ff6eca3cd9..2983d33ed2 100644
--- a/libs/canvas/canvas/rectangle.h
+++ b/libs/canvas/canvas/rectangle.h
@@ -34,8 +34,8 @@ class LIBCANVAS_API Rectangle : public Item
 public:
 	Rectangle (Canvas*);
 	Rectangle (Canvas*, Rect const &);
-	Rectangle (Group*);
-	Rectangle (Group*, Rect const &);
+	Rectangle (Item*);
+	Rectangle (Item*, Rect const &);
 	
 	void render (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
 	void compute_bounding_box () const;
diff --git a/libs/canvas/canvas/root_group.h b/libs/canvas/canvas/root_group.h
index 70c3e5b90b..5db8024f51 100644
--- a/libs/canvas/canvas/root_group.h
+++ b/libs/canvas/canvas/root_group.h
@@ -21,19 +21,18 @@
 #define __CANVAS_ROOT_GROUP_H__
 
 #include "canvas/visibility.h"
-#include "canvas/group.h"
+#include "canvas/layout.h"
 
 namespace ArdourCanvas {
 
-class LIBCANVAS_API RootGroup : public Group
+class LIBCANVAS_API Root : public Layout
 {
 private:
 	friend class Canvas;
 	
-	RootGroup (Canvas *);
+	Root (Canvas *);
 
 	void compute_bounding_box () const;
-	void child_changed ();
 };
 
 }
diff --git a/libs/canvas/canvas/ruler.h b/libs/canvas/canvas/ruler.h
index 633a1d569e..25040247c9 100644
--- a/libs/canvas/canvas/ruler.h
+++ b/libs/canvas/canvas/ruler.h
@@ -57,8 +57,8 @@ public:
 	
 	Ruler (Canvas*, const Metric& m);
 	Ruler (Canvas*, const Metric& m, Rect const&);
-	Ruler (Group*, const Metric& m);
-	Ruler (Group*, const Metric& m, Rect const&);
+	Ruler (Item*, const Metric& m);
+	Ruler (Item*, const Metric& m, Rect const&);
 	
 	void set_range (double lower, double upper);
 	void set_font_description (Pango::FontDescription);
diff --git a/libs/canvas/canvas/scroll_group.h b/libs/canvas/canvas/scroll_group.h
index 552538eb21..013d769c2f 100644
--- a/libs/canvas/canvas/scroll_group.h
+++ b/libs/canvas/canvas/scroll_group.h
@@ -19,11 +19,15 @@
 #ifndef __CANVAS_SCROLL_GROUP_H__
 #define __CANVAS_SCROLL_GROUP_H__
 
-#include "canvas/group.h"
+#include "canvas/layout.h"
 
 namespace ArdourCanvas {
 
-class LIBCANVAS_API ScrollGroup : public Group
+/** A ScrollGroup has no contents of its own, but renders
+ *  its children in a way that reflects the most recent
+ *  call to its scroll_to() method.
+ */
+class LIBCANVAS_API ScrollGroup : public Layout
 {
   public:
 	enum ScrollSensitivity {
@@ -32,7 +36,7 @@ class LIBCANVAS_API ScrollGroup : public Group
 	};
 	
 	ScrollGroup (Canvas*, ScrollSensitivity);
-	ScrollGroup (Group*, ScrollSensitivity);
+	ScrollGroup (Item*, ScrollSensitivity);
 
 	void scroll_to (Duple const& d);
 	Duple scroll_offset() const { return _scroll_offset; }
diff --git a/libs/canvas/canvas/stateful_image.h b/libs/canvas/canvas/stateful_image.h
index 5952752e71..7c00b0c5a4 100644
--- a/libs/canvas/canvas/stateful_image.h
+++ b/libs/canvas/canvas/stateful_image.h
@@ -50,7 +50,7 @@ class StatefulImage : public Item
   public:
 
     StatefulImage (Canvas*, const XMLNode&);
-    StatefulImage (Group*, const XMLNode&);
+    StatefulImage (Item*, const XMLNode&);
     ~StatefulImage ();
 
     bool set_state (States::size_type);
diff --git a/libs/canvas/canvas/text.h b/libs/canvas/canvas/text.h
index cc6d5c815d..85262ee984 100644
--- a/libs/canvas/canvas/text.h
+++ b/libs/canvas/canvas/text.h
@@ -32,7 +32,7 @@ class LIBCANVAS_API Text : public Item
 {
 public:
 	Text (Canvas*);
-	Text (Group*);
+	Text (Item*);
        ~Text();
 
 	void render (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
diff --git a/libs/canvas/canvas/wave_view.h b/libs/canvas/canvas/wave_view.h
index c98c62c7a3..042414e1e2 100644
--- a/libs/canvas/canvas/wave_view.h
+++ b/libs/canvas/canvas/wave_view.h
@@ -92,7 +92,7 @@ public:
 
 
 	WaveView (Canvas *, boost::shared_ptr<ARDOUR::AudioRegion>);
-	WaveView (Group*, boost::shared_ptr<ARDOUR::AudioRegion>);
+	WaveView (Item*, boost::shared_ptr<ARDOUR::AudioRegion>);
        ~WaveView ();
 
 	void render (Rect const & area, Cairo::RefPtr<Cairo::Context>) const;
diff --git a/libs/canvas/canvas/widget.h b/libs/canvas/canvas/widget.h
index 842f336a51..590bb3af7d 100644
--- a/libs/canvas/canvas/widget.h
+++ b/libs/canvas/canvas/widget.h
@@ -32,7 +32,7 @@ class LIBCANVAS_API Widget : public Item
 {
 public:
 	Widget (Canvas*, CairoWidget&);
-	Widget (Group*, CairoWidget&);
+	Widget (Item*, CairoWidget&);
 	
 	void render (Rect const &, Cairo::RefPtr<Cairo::Context>) const;
 	void compute_bounding_box () const;
diff --git a/libs/canvas/canvas/xfade_curve.h b/libs/canvas/canvas/xfade_curve.h
index d6a10d1f86..c63e47c583 100644
--- a/libs/canvas/canvas/xfade_curve.h
+++ b/libs/canvas/canvas/xfade_curve.h
@@ -36,8 +36,8 @@ public:
 
 	XFadeCurve (Canvas *);
 	XFadeCurve (Canvas *, XFadePosition);
-	XFadeCurve (Group*);
-	XFadeCurve (Group*, XFadePosition);
+	XFadeCurve (Item*);
+	XFadeCurve (Item*, XFadePosition);
 
 	void set_fade_position (XFadePosition xfp) { _xfadeposition = xfp; }
 	
diff --git a/libs/canvas/circle.cc b/libs/canvas/circle.cc
index 3799bf60ac..1859434123 100644
--- a/libs/canvas/circle.cc
+++ b/libs/canvas/circle.cc
@@ -26,8 +26,8 @@ Circle::Circle (Canvas* c)
 	set_arc (360.0);
 }
 
-Circle::Circle (Group* g)
-	: Arc (g)
+Circle::Circle (Item * parent)
+	: Arc (parent)
 {
 	set_arc (360.0);
 }
diff --git a/libs/canvas/curve.cc b/libs/canvas/curve.cc
index 547783ae08..ba6ac68df6 100644
--- a/libs/canvas/curve.cc
+++ b/libs/canvas/curve.cc
@@ -36,8 +36,8 @@ Curve::Curve (Canvas* c)
 {
 }
 
-Curve::Curve (Group* g)
-	: PolyItem (g)
+Curve::Curve (Item* parent)
+	: PolyItem (parent)
 	, n_samples (0)
 	, points_per_segment (16)
 	, curve_type (CatmullRomCentripetal)
diff --git a/libs/canvas/flag.cc b/libs/canvas/flag.cc
index f5379791df..b6532d7fd2 100644
--- a/libs/canvas/flag.cc
+++ b/libs/canvas/flag.cc
@@ -26,15 +26,15 @@ using namespace std;
 using namespace ArdourCanvas;
 
 Flag::Flag (Canvas* canvas, Distance height, Color outline_color, Color fill_color, Duple position)
-	: Group (canvas)
+	: Layout (canvas)
 	, _outline_color (outline_color)
 	, _fill_color (fill_color)
 {
 	setup (height, position);
 }
 
-Flag::Flag (Group* group, Distance height, Color outline_color, Color fill_color, Duple position)
-	: Group (group)
+Flag::Flag (Item* parent, Distance height, Color outline_color, Color fill_color, Duple position)
+	: Layout (parent)
 	, _outline_color (outline_color)
 	, _fill_color (fill_color)
 {
diff --git a/libs/canvas/group.cc b/libs/canvas/group.cc
deleted file mode 100644
index d63b217396..0000000000
--- a/libs/canvas/group.cc
+++ /dev/null
@@ -1,395 +0,0 @@
-/*
-    Copyright (C) 2011-2013 Paul Davis
-    Author: Carl Hetherington <cth@carlh.net>
-
-    This program is free software; you can redistribute it and/or modify
-    it under the terms of the GNU General Public License as published by
-    the Free Software Foundation; either version 2 of the License, or
-    (at your option) any later version.
-
-    This program is distributed in the hope that it will be useful,
-    but WITHOUT ANY WARRANTY; without even the implied warranty of
-    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-    GNU General Public License for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with this program; if not, write to the Free Software
-    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
-*/
-
-#include <iostream>
-#include <cairomm/context.h>
-
-#include "pbd/stacktrace.h"
-#include "pbd/compose.h"
-
-#include "canvas/group.h"
-#include "canvas/types.h"
-#include "canvas/debug.h"
-#include "canvas/item.h"
-#include "canvas/canvas.h"
-
-using namespace std;
-using namespace ArdourCanvas;
-
-int Group::default_items_per_cell = 64;
-
-
-Group::Group (Canvas* canvas)
-	: Item (canvas)
-	, _lut (0)
-{
-}
-
-Group::Group (Group* group)
-	: Item (group)
-	, _lut (0)
-{
-}
-
-Group::Group (Group* group, Duple const& p)
-	: Item (group, p)
-	, _lut (0)
-{
-}
-
-Group::~Group ()
-{
-	clear_items (true);
-}
-
-/** @param area Area to draw in window coordinates.
- *  @param context Context, set up with its origin at this group's position.
- */
-void
-Group::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
-{
-	ensure_lut ();
-	vector<Item*> items = _lut->get (area);
-
-#ifdef CANVAS_DEBUG
-	if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-		cerr << string_compose ("%1GROUP %2 @ %7 render %5 @ %6 %3 items out of %4\n", 
-					_canvas->render_indent(), (name.empty() ? string ("[unnamed]") : name), items.size(), _items.size(), area, _position, this);
-	}
-#endif
-
-	++render_depth;
-		
-	for (vector<Item*>::const_iterator i = items.begin(); i != items.end(); ++i) {
-
-		if (!(*i)->visible ()) {
-#ifdef CANVAS_DEBUG
-			if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-				cerr << _canvas->render_indent() << "Item " << (*i)->whatami() << " [" << (*i)->name << "] invisible - skipped\n";
-			}
-#endif
-			continue;
-		}
-		
-		boost::optional<Rect> item_bbox = (*i)->bounding_box ();
-
-		if (!item_bbox) {
-#ifdef CANVAS_DEBUG
-			if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-				cerr << _canvas->render_indent() << "Item " << (*i)->whatami() << " [" << (*i)->name << "] empty - skipped\n";
-			}
-#endif
-			continue;
-		}
-		
-		Rect item = (*i)->item_to_window (item_bbox.get());
-		boost::optional<Rect> d = item.intersection (area);
-		
-		if (d) {
-			Rect draw = d.get();
-			if (draw.width() && draw.height()) {
-#ifdef CANVAS_DEBUG
-				if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-					if (dynamic_cast<Group*>(*i) == 0) {
-						cerr << _canvas->render_indent() << "render "
-						     << ' ' 
-						     << (*i)
-						     << ' '
-						     << (*i)->whatami()
-						     << ' '
-						     << (*i)->name
-						     << " item "
-						     << item_bbox.get()
-						     << " window = " 
-						     << item
-						     << " intersect = "
-						     << draw
-						     << " @ " 
-						     << _position
-						     << endl;
-					}
-				}
-#endif
-
-				(*i)->render (area, context);
-				++render_count;
-			}
-
-		} else {
-
-#ifdef CANVAS_DEBUG
-			if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-				cerr << string_compose ("%1skip render of %2 %3, no intersection between %4 and %5\n", _canvas->render_indent(), (*i)->whatami(),
-							(*i)->name, item, area);
-			}
-#endif
-
-		}
-	}
-
-	--render_depth;
-}
-
-void
-Group::scroll_to (Duple const& d)
-{
-	Item::scroll_to (d);
-	
-	for (list<Item*>::iterator i = _items.begin(); i != _items.end(); ++i) {
-		(*i)->scroll_to (d);
-	}
-}
-
-void
-Group::compute_bounding_box () const
-{
-	Rect bbox;
-	bool have_one = false;
-
-	for (list<Item*>::const_iterator i = _items.begin(); i != _items.end(); ++i) {
-
-		boost::optional<Rect> item_bbox = (*i)->bounding_box ();
-
-		if (!item_bbox) {
-			continue;
-		}
-
-		Rect group_bbox = (*i)->item_to_parent (item_bbox.get ());
-		if (have_one) {
-			bbox = bbox.extend (group_bbox);
-		} else {
-			bbox = group_bbox;
-			have_one = true;
-		}
-	}
-
-	if (!have_one) {
-		_bounding_box = boost::optional<Rect> ();
-	} else {
-		_bounding_box = bbox;
-	}
-
-	_bounding_box_dirty = false;
-}
-
-void
-Group::add (Item* i)
-{
-	/* XXX should really notify canvas about this */
-
-	_items.push_back (i);
-	i->reparent (this);
-	invalidate_lut ();
-	_bounding_box_dirty = true;
-}
-
-void
-Group::remove (Item* i)
-{
-
-	if (i->parent() != this) {
-		return;
-	}
-
-	/* we cannot call bounding_box() here because that will iterate over
-	   _items, one of which (the argument, i) may be in the middle of
-	   deletion, making it impossible to call compute_bounding_box()
-	   on it.
-	*/
-
-	if (_bounding_box) {
-		_pre_change_bounding_box = _bounding_box;
-	} else {
-		_pre_change_bounding_box = Rect();
-	}
-
-	i->unparent ();
-	_items.remove (i);
-	invalidate_lut ();
-	_bounding_box_dirty = true;
-	
-	end_change ();
-}
-
-void
-Group::clear (bool with_delete)
-{
-	begin_change ();
-
-	clear_items (with_delete);
-
-	invalidate_lut ();
-	_bounding_box_dirty = true;
-
-	end_change ();
-}
-
-void
-Group::clear_items (bool with_delete)
-{
-	for (list<Item*>::iterator i = _items.begin(); i != _items.end(); ) {
-
-		list<Item*>::iterator tmp = i;
-		Item *item = *i;
-
-		++tmp;
-
-		/* remove from list before doing anything else, because we
-		 * don't want to find the item in _items during any activity
-		 * driven by unparent-ing or deletion.
-		 */
-
-		_items.erase (i);
-		item->unparent ();
-		
-		if (with_delete) {
-			delete item;
-		}
-
-		i = tmp;
-	}
-}
-
-void
-Group::raise_child_to_top (Item* i)
-{
-	if (!_items.empty()) {
-		if (_items.back() == i) {
-			return;
-		}
-	}
-
-	_items.remove (i);
-	_items.push_back (i);
-	invalidate_lut ();
-}
-
-void
-Group::raise_child (Item* i, int levels)
-{
-	list<Item*>::iterator j = find (_items.begin(), _items.end(), i);
-	assert (j != _items.end ());
-
-	++j;
-	_items.remove (i);
-
-	while (levels > 0 && j != _items.end ()) {
-		++j;
-		--levels;
-	}
-
-	_items.insert (j, i);
-	invalidate_lut ();
-}
-
-void
-Group::lower_child_to_bottom (Item* i)
-{
-	if (!_items.empty()) {
-		if (_items.front() == i) {
-			return;
-		}
-	}
-	_items.remove (i);
-	_items.push_front (i);
-	invalidate_lut ();
-}
-
-void
-Group::ensure_lut () const
-{
-	if (!_lut) {
-		_lut = new DumbLookupTable (*this);
-	}
-}
-
-void
-Group::invalidate_lut () const
-{
-	delete _lut;
-	_lut = 0;
-}
-
-void
-Group::child_changed ()
-{
-	invalidate_lut ();
-	_bounding_box_dirty = true;
-
-	if (_parent) {
-		_parent->child_changed ();
-	}
-}
-
-void
-Group::add_items_at_point (Duple const point, vector<Item const *>& items) const
-{
-	boost::optional<Rect> const bbox = bounding_box ();
-
-	/* Point is in window coordinate system */
-
-	if (!bbox || !item_to_window (bbox.get()).contains (point)) {
-		return;
-	}
-
-	/* now recurse and add any items within our group that contain point */
-
-	ensure_lut ();
-	vector<Item*> our_items = _lut->items_at_point (point);
-
-	if (!our_items.empty()) {
-		/* this adds this group itself to the list of items at point */
-		Item::add_items_at_point (point, items);
-	}
-
-	for (vector<Item*>::iterator i = our_items.begin(); i != our_items.end(); ++i) {
-		(*i)->add_items_at_point (point, items);
-	}
-}
-
-void
-Group::dump (ostream& o) const
-{
-#ifdef CANVAS_DEBUG
-	o << _canvas->indent();
-	o << "Group " << this << " [" << name << ']';
-	o << " @ " << position();
-	o << " Items: " << _items.size();
-	o << " Visible ? " << _visible;
-
-	boost::optional<Rect> bb = bounding_box();
-
-	if (bb) {
-		o << endl << _canvas->indent() << "  bbox: " << bb.get();
-		o << endl << _canvas->indent() << "  CANVAS bbox: " << item_to_canvas (bb.get());
-	} else {
-		o << "  bbox unset";
-	}
-
-	o << endl;
-#endif
-
-	ArdourCanvas::dump_depth++;
-
-	for (list<Item*>::const_iterator i = _items.begin(); i != _items.end(); ++i) {
-		o << **i;
-	}
-
-	ArdourCanvas::dump_depth--;
-}
diff --git a/libs/canvas/image.cc b/libs/canvas/image.cc
index 5ab280cbbc..46cadd0d1c 100644
--- a/libs/canvas/image.cc
+++ b/libs/canvas/image.cc
@@ -32,8 +32,8 @@ Image::Image (Canvas* canvas, Cairo::Format fmt, int width, int height)
 	DataReady.connect (data_connections, MISSING_INVALIDATOR, boost::bind (&Image::accept_data, this), gui_context());
 }
 
-Image::Image (Group* group, Cairo::Format fmt, int width, int height)
-	: Item (group)
+Image::Image (Item* parent, Cairo::Format fmt, int width, int height)
+	: Item (parent)
 	, _format (fmt)
 	, _width (width)
 	, _height (height)
diff --git a/libs/canvas/item.cc b/libs/canvas/item.cc
index ea77008b5f..e58411f17f 100644
--- a/libs/canvas/item.cc
+++ b/libs/canvas/item.cc
@@ -25,7 +25,6 @@
 
 #include "canvas/canvas.h"
 #include "canvas/debug.h"
-#include "canvas/group.h"
 #include "canvas/item.h"
 #include "canvas/scroll_group.h"
 
@@ -33,6 +32,8 @@ using namespace std;
 using namespace PBD;
 using namespace ArdourCanvas;
 
+int Item::default_items_per_cell = 64;
+
 Item::Item (Canvas* canvas)
 	: Fill (*this)
 	, Outline (*this)
@@ -41,12 +42,13 @@ Item::Item (Canvas* canvas)
 	, _scroll_parent (0)
 	, _visible (true)
 	, _bounding_box_dirty (true)
+	, _lut (0)
 	, _ignore_events (false)
 {
 	DEBUG_TRACE (DEBUG::CanvasItems, string_compose ("new canvas item %1\n", this));
 }	
 
-Item::Item (Group* parent)
+Item::Item (Item* parent)
 	: Fill (*this)
 	, Outline (*this)
 	,  _canvas (parent->canvas())
@@ -54,6 +56,7 @@ Item::Item (Group* parent)
 	, _scroll_parent (0)
 	, _visible (true)
 	, _bounding_box_dirty (true)
+	, _lut (0)
 	, _ignore_events (false)
 {
 	DEBUG_TRACE (DEBUG::CanvasItems, string_compose ("new canvas item %1\n", this));
@@ -65,7 +68,7 @@ Item::Item (Group* parent)
 	find_scroll_parent ();
 }	
 
-Item::Item (Group* parent, Duple const& p)
+Item::Item (Item* parent, Duple const& p)
 	: Fill (*this)
 	, Outline (*this)
 	,  _canvas (parent->canvas())
@@ -74,6 +77,7 @@ Item::Item (Group* parent, Duple const& p)
 	, _position (p)
 	, _visible (true)
 	, _bounding_box_dirty (true)
+	, _lut (0)
 	, _ignore_events (false)
 {
 	DEBUG_TRACE (DEBUG::CanvasItems, string_compose ("new canvas item %1\n", this));
@@ -95,6 +99,9 @@ Item::~Item ()
 	if (_canvas) {
 		_canvas->item_going_away (this, _bounding_box);
 	}
+
+	clear_items (true);
+	delete _lut;
 }
 
 Duple
@@ -350,7 +357,7 @@ Item::unparent ()
 }
 
 void
-Item::reparent (Group* new_parent)
+Item::reparent (Item* new_parent)
 {
 	if (new_parent == _parent) {
 		return;
@@ -516,6 +523,7 @@ Item::bounding_box () const
 	if (_bounding_box_dirty) {
 		compute_bounding_box ();
 		assert (!_bounding_box_dirty);
+		add_child_bounding_boxes ();
 	}
 
 	return _bounding_box;
@@ -626,30 +634,6 @@ Item::set_ignore_events (bool ignore)
 	_ignore_events = ignore;
 }
 
-void
-Item::dump (ostream& o) const
-{
-	boost::optional<ArdourCanvas::Rect> bb = bounding_box();
-
-	o << _canvas->indent() << whatami() << ' ' << this << " Visible ? " << _visible;
-	o << " @ " << position();
-	
-#ifdef CANVAS_DEBUG
-	if (!name.empty()) {
-		o << ' ' << name;
-	}
-#endif
-
-	if (bb) {
-		o << endl << _canvas->indent() << "\tbbox: " << bb.get();
-		o << endl << _canvas->indent() << "\tCANVAS bbox: " << item_to_canvas (bb.get());
-	} else {
-		o << " bbox unset";
-	}
-
-	o << endl;
-}
-
 std::string
 Item::whatami () const 
 {
@@ -687,6 +671,276 @@ Item::covers (Duple const & point) const
 	return r.get().contains (p);
 }
 
+/* nesting/grouping API */
+
+void
+Item::add_child_bounding_boxes() const
+{
+	boost::optional<Rect> self;
+	Rect bbox;
+	bool have_one = false;
+
+	if (_bounding_box) {
+		bbox = _bounding_box.get();
+		have_one = true;
+	}
+
+	for (list<Item*>::const_iterator i = _items.begin(); i != _items.end(); ++i) {
+
+		boost::optional<Rect> item_bbox = (*i)->bounding_box ();
+
+		if (!item_bbox) {
+			continue;
+		}
+
+		Rect group_bbox = (*i)->item_to_parent (item_bbox.get ());
+		if (have_one) {
+			bbox = bbox.extend (group_bbox);
+		} else {
+			bbox = group_bbox;
+			have_one = true;
+		}
+	}
+
+	if (!have_one) {
+		_bounding_box = boost::optional<Rect> ();
+	} else {
+		_bounding_box = bbox;
+	}
+}
+
+void
+Item::add (Item* i)
+{
+	/* XXX should really notify canvas about this */
+
+	_items.push_back (i);
+	i->reparent (this);
+	invalidate_lut ();
+	_bounding_box_dirty = true;
+}
+
+void
+Item::remove (Item* i)
+{
+
+	if (i->parent() != this) {
+		return;
+	}
+
+	/* we cannot call bounding_box() here because that will iterate over
+	   _items, one of which (the argument, i) may be in the middle of
+	   deletion, making it impossible to call compute_bounding_box()
+	   on it.
+	*/
+
+	if (_bounding_box) {
+		_pre_change_bounding_box = _bounding_box;
+	} else {
+		_pre_change_bounding_box = Rect();
+	}
+
+	i->unparent ();
+	_items.remove (i);
+	invalidate_lut ();
+	_bounding_box_dirty = true;
+	
+	end_change ();
+}
+
+void
+Item::clear (bool with_delete)
+{
+	begin_change ();
+
+	clear_items (with_delete);
+
+	invalidate_lut ();
+	_bounding_box_dirty = true;
+
+	end_change ();
+}
+
+void
+Item::clear_items (bool with_delete)
+{
+	for (list<Item*>::iterator i = _items.begin(); i != _items.end(); ) {
+
+		list<Item*>::iterator tmp = i;
+		Item *item = *i;
+
+		++tmp;
+
+		/* remove from list before doing anything else, because we
+		 * don't want to find the item in _items during any activity
+		 * driven by unparent-ing or deletion.
+		 */
+
+		_items.erase (i);
+		item->unparent ();
+		
+		if (with_delete) {
+			delete item;
+		}
+
+		i = tmp;
+	}
+}
+
+void
+Item::raise_child_to_top (Item* i)
+{
+	if (!_items.empty()) {
+		if (_items.back() == i) {
+			return;
+		}
+	}
+
+	_items.remove (i);
+	_items.push_back (i);
+	invalidate_lut ();
+}
+
+void
+Item::raise_child (Item* i, int levels)
+{
+	list<Item*>::iterator j = find (_items.begin(), _items.end(), i);
+	assert (j != _items.end ());
+
+	++j;
+	_items.remove (i);
+
+	while (levels > 0 && j != _items.end ()) {
+		++j;
+		--levels;
+	}
+
+	_items.insert (j, i);
+	invalidate_lut ();
+}
+
+void
+Item::lower_child_to_bottom (Item* i)
+{
+	if (!_items.empty()) {
+		if (_items.front() == i) {
+			return;
+		}
+	}
+	_items.remove (i);
+	_items.push_front (i);
+	invalidate_lut ();
+}
+
+void
+Item::ensure_lut () const
+{
+	if (!_lut) {
+		_lut = new DumbLookupTable (*this);
+	}
+}
+
+void
+Item::invalidate_lut () const
+{
+	delete _lut;
+	_lut = 0;
+}
+
+void
+Item::child_changed ()
+{
+	invalidate_lut ();
+	_bounding_box_dirty = true;
+
+	if (_parent) {
+		_parent->child_changed ();
+	}
+}
+
+void
+Item::add_items_at_point (Duple const point, vector<Item const *>& items) const
+{
+	boost::optional<Rect> const bbox = bounding_box ();
+
+	/* Point is in window coordinate system */
+
+	if (!bbox || !item_to_window (bbox.get()).contains (point)) {
+		return;
+	}
+
+	/* recurse and add any items within our group that contain point */
+
+	vector<Item*> our_items;
+
+	if (!_items.empty()) {
+		ensure_lut ();
+		our_items = _lut->items_at_point (point);
+	}
+
+	if (!our_items.empty() || covers (point)) {
+		/* this adds this item itself to the list of items at point */
+		items.push_back (this);
+	}
+
+	for (vector<Item*>::iterator i = our_items.begin(); i != our_items.end(); ++i) {
+		(*i)->add_items_at_point (point, items);
+	}
+}
+
+void
+Item::dump (ostream& o) const
+{
+	boost::optional<ArdourCanvas::Rect> bb = bounding_box();
+
+	o << _canvas->indent() << whatami() << ' ' << this << " Visible ? " << _visible;
+	o << " @ " << position();
+	
+#ifdef CANVAS_DEBUG
+	if (!name.empty()) {
+		o << ' ' << name;
+	}
+#endif
+
+	if (bb) {
+		o << endl << _canvas->indent() << "\tbbox: " << bb.get();
+		o << endl << _canvas->indent() << "\tCANVAS bbox: " << item_to_canvas (bb.get());
+	} else {
+		o << " bbox unset";
+	}
+
+	o << endl;
+
+	if (!_items.empty()) {
+
+#ifdef CANVAS_DEBUG
+		o << _canvas->indent();
+		o << " @ " << position();
+		o << " Items: " << _items.size();
+		o << " Visible ? " << _visible;
+		
+		boost::optional<Rect> bb = bounding_box();
+		
+		if (bb) {
+			o << endl << _canvas->indent() << "  bbox: " << bb.get();
+			o << endl << _canvas->indent() << "  CANVAS bbox: " << item_to_canvas (bb.get());
+		} else {
+			o << "  bbox unset";
+		}
+		
+		o << endl;
+#endif
+		
+		ArdourCanvas::dump_depth++;
+		
+		for (list<Item*>::const_iterator i = _items.begin(); i != _items.end(); ++i) {
+			o << **i;
+		}
+		
+		ArdourCanvas::dump_depth--;
+	}
+}
+
 ostream&
 ArdourCanvas::operator<< (ostream& o, const Item& i)
 {
diff --git a/libs/canvas/line.cc b/libs/canvas/line.cc
index 844f05522d..8bd26b9067 100644
--- a/libs/canvas/line.cc
+++ b/libs/canvas/line.cc
@@ -34,8 +34,8 @@ Line::Line (Canvas* c)
 {
 }
 
-Line::Line (Group* group)
-	: Item (group)
+Line::Line (Item* parent)
+	: Item (parent)
 {
 }
 
diff --git a/libs/canvas/line_set.cc b/libs/canvas/line_set.cc
index 3eacadaba2..54fe980b1c 100644
--- a/libs/canvas/line_set.cc
+++ b/libs/canvas/line_set.cc
@@ -38,8 +38,8 @@ LineSet::LineSet (Canvas* c, Orientation o)
 
 }
 
-LineSet::LineSet (Group* group, Orientation o)
-	: Item (group)
+LineSet::LineSet (Item* parent, Orientation o)
+	: Item (parent)
 	, _extent (0)
 	, _orientation (o)
 {
diff --git a/libs/canvas/lookup_table.cc b/libs/canvas/lookup_table.cc
index 8e744638d8..2396f59635 100644
--- a/libs/canvas/lookup_table.cc
+++ b/libs/canvas/lookup_table.cc
@@ -17,14 +17,14 @@
     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */
 
+#include "canvas/item.h"
 #include "canvas/lookup_table.h"
-#include "canvas/group.h"
 
 using namespace std;
 using namespace ArdourCanvas;
 
-LookupTable::LookupTable (Group const & group)
-	: _group (group)
+LookupTable::LookupTable (Item const & item)
+	: _item (item)
 {
 
 }
@@ -34,8 +34,8 @@ LookupTable::~LookupTable ()
 
 }
 
-DumbLookupTable::DumbLookupTable (Group const & group)
-	: LookupTable (group)
+DumbLookupTable::DumbLookupTable (Item const & item)
+	: LookupTable (item)
 {
 
 }
@@ -43,7 +43,7 @@ DumbLookupTable::DumbLookupTable (Group const & group)
 vector<Item *>
 DumbLookupTable::get (Rect const &)
 {
-	list<Item *> const & items = _group.items ();
+	list<Item *> const & items = _item.items ();
 	vector<Item *> vitems;
 	copy (items.begin(), items.end(), back_inserter (vitems));
 	return vitems;
@@ -54,7 +54,7 @@ DumbLookupTable::items_at_point (Duple const & point) const
 {
 	/* Point is in window coordinate system */
 
-	list<Item *> const & items (_group.items ());
+	list<Item *> const & items (_item.items ());
 	vector<Item *> vitems;
 
 	for (list<Item *>::const_iterator i = items.begin(); i != items.end(); ++i) {
@@ -73,7 +73,7 @@ DumbLookupTable::has_item_at_point (Duple const & point) const
 {
 	/* Point is in window coordinate system */
 
-	list<Item *> const & items (_group.items ());
+	list<Item *> const & items (_item.items ());
 	vector<Item *> vitems;
 
 	for (list<Item *>::const_iterator i = items.begin(); i != items.end(); ++i) {
@@ -92,12 +92,12 @@ DumbLookupTable::has_item_at_point (Duple const & point) const
 	return false;
 }
 
-OptimizingLookupTable::OptimizingLookupTable (Group const & group, int items_per_cell)
-	: LookupTable (group)
+OptimizingLookupTable::OptimizingLookupTable (Item const & item, int items_per_cell)
+	: LookupTable (item)
 	, _items_per_cell (items_per_cell)
 	, _added (false)
 {
-	list<Item*> const & items = _group.items ();
+	list<Item*> const & items = _item.items ();
 
 	/* number of cells */
 	int const cells = items.size() / _items_per_cell;
@@ -109,8 +109,8 @@ OptimizingLookupTable::OptimizingLookupTable (Group const & group, int items_per
 		_cells[i] = new Cell[_dimension];
 	}
 
-	/* our group's bounding box in its coordinates */
-	boost::optional<Rect> bbox = _group.bounding_box ();
+	/* our item's bounding box in its coordinates */
+	boost::optional<Rect> bbox = _item.bounding_box ();
 	if (!bbox) {
 		return;
 	}
@@ -130,11 +130,11 @@ OptimizingLookupTable::OptimizingLookupTable (Group const & group, int items_per
 			continue;
 		}
 
-		/* and in the group's coordinates */
-		Rect const item_bbox_in_group = (*i)->item_to_parent (item_bbox.get ());
+		/* and in the item's coordinates */
+		Rect const item_bbox_in_item = (*i)->item_to_parent (item_bbox.get ());
 
 		int x0, y0, x1, y1;
-		area_to_indices (item_bbox_in_group, x0, y0, x1, y1);
+		area_to_indices (item_bbox_in_item, x0, y0, x1, y1);
 
 		/* XXX */
 		assert (x0 >= 0);
@@ -147,19 +147,19 @@ OptimizingLookupTable::OptimizingLookupTable (Group const & group, int items_per
 		//assert (y1 <= _dimension);
 
 		if (x0 > _dimension) {
-			cout << "WARNING: item outside bbox by " << (item_bbox_in_group.x0 - bbox.get().x0) << "\n";
+			cout << "WARNING: item outside bbox by " << (item_bbox_in_item.x0 - bbox.get().x0) << "\n";
 			x0 = _dimension;
 		}
 		if (x1 > _dimension) {
-			cout << "WARNING: item outside bbox by " << (item_bbox_in_group.x1 - bbox.get().x1) << "\n";
+			cout << "WARNING: item outside bbox by " << (item_bbox_in_item.x1 - bbox.get().x1) << "\n";
 			x1 = _dimension;
 		}
 		if (y0 > _dimension) {
-			cout << "WARNING: item outside bbox by " << (item_bbox_in_group.y0 - bbox.get().y0) << "\n";
+			cout << "WARNING: item outside bbox by " << (item_bbox_in_item.y0 - bbox.get().y0) << "\n";
 			y0 = _dimension;
 		}
 		if (y1 > _dimension) {
-			cout << "WARNING: item outside bbox by " << (item_bbox_in_group.y1 - bbox.get().y1) << "\n";
+			cout << "WARNING: item outside bbox by " << (item_bbox_in_item.y1 - bbox.get().y1) << "\n";
 			y1 = _dimension;
 		}
 
@@ -284,7 +284,7 @@ OptimizingLookupTable::has_item_at_point (Duple const & point) const
 	return false;
 }
 	
-/** @param area Area in our owning group's coordinates */
+/** @param area Area in our owning item's coordinates */
 vector<Item*>
 OptimizingLookupTable::get (Rect const & area)
 {
diff --git a/libs/canvas/pixbuf.cc b/libs/canvas/pixbuf.cc
index 82eb916397..d285c41b10 100644
--- a/libs/canvas/pixbuf.cc
+++ b/libs/canvas/pixbuf.cc
@@ -30,8 +30,8 @@ Pixbuf::Pixbuf (Canvas* c)
 {
 }
 
-Pixbuf::Pixbuf (Group* g)
-	: Item (g)
+Pixbuf::Pixbuf (Item* parent)
+	: Item (parent)
 {
 }
 
diff --git a/libs/canvas/poly_item.cc b/libs/canvas/poly_item.cc
index 618983db97..d50c097e07 100644
--- a/libs/canvas/poly_item.cc
+++ b/libs/canvas/poly_item.cc
@@ -32,8 +32,8 @@ PolyItem::PolyItem (Canvas* c)
 {
 }
 
-PolyItem::PolyItem (Group* g)
-	: Item (g)
+PolyItem::PolyItem (Item* parent)
+	: Item (parent)
 {
 }
 
diff --git a/libs/canvas/poly_line.cc b/libs/canvas/poly_line.cc
index bade7d855e..60bca6bccf 100644
--- a/libs/canvas/poly_line.cc
+++ b/libs/canvas/poly_line.cc
@@ -31,8 +31,8 @@ PolyLine::PolyLine (Canvas* c)
 {
 }
 
-PolyLine::PolyLine (Group* g)
-	: PolyItem (g)
+PolyLine::PolyLine (Item* parent)
+	: PolyItem (parent)
 	, _threshold (1.0)
 {
 }
diff --git a/libs/canvas/polygon.cc b/libs/canvas/polygon.cc
index d84bca4af6..aa16a60178 100644
--- a/libs/canvas/polygon.cc
+++ b/libs/canvas/polygon.cc
@@ -29,8 +29,8 @@ Polygon::Polygon (Canvas* c)
 {
 }
 
-Polygon::Polygon (Group* g)
-	: PolyItem (g)
+Polygon::Polygon (Item* parent)
+	: PolyItem (parent)
 	, multiple (0)
 	, constant (0)
 	, cached_size (0)
diff --git a/libs/canvas/rectangle.cc b/libs/canvas/rectangle.cc
index ac05003693..bc4ad0c960 100644
--- a/libs/canvas/rectangle.cc
+++ b/libs/canvas/rectangle.cc
@@ -43,14 +43,14 @@ Rectangle::Rectangle (Canvas* c, Rect const & rect)
 {
 }
 
-Rectangle::Rectangle (Group* g)
-	: Item (g)
+Rectangle::Rectangle (Item* parent)
+	: Item (parent)
 	, _outline_what ((What) (LEFT | RIGHT | TOP | BOTTOM))
 {
 }
 
-Rectangle::Rectangle (Group* g, Rect const & rect)
-	: Item (g)
+Rectangle::Rectangle (Item* parent, Rect const & rect)
+	: Item (parent)
 	, _rect (rect)
 	, _outline_what ((What) (LEFT | RIGHT | TOP | BOTTOM))
 {
diff --git a/libs/canvas/root_group.cc b/libs/canvas/root_group.cc
index cded570b2c..015f52bb54 100644
--- a/libs/canvas/root_group.cc
+++ b/libs/canvas/root_group.cc
@@ -23,8 +23,8 @@
 using namespace std;
 using namespace ArdourCanvas;
 
-RootGroup::RootGroup (Canvas* canvas)
-	: Group (canvas)
+Root::Root (Canvas* canvas)
+	: Layout (canvas)
 {
 #ifdef CANVAS_DEBUG
 	name = "ROOT";
@@ -32,11 +32,12 @@ RootGroup::RootGroup (Canvas* canvas)
 }
 
 void
-RootGroup::compute_bounding_box () const
+Root::compute_bounding_box () const
 {
-	Group::compute_bounding_box ();
+	Layout::compute_bounding_box ();
 
 	if (_bounding_box) {
-		_canvas->request_size (Duple (_bounding_box.get().width (), _bounding_box.get().height ()));
+		Rect r (_bounding_box.get());
+		_canvas->request_size (Duple (r.width (), r.height ()));
 	}
 }
diff --git a/libs/canvas/ruler.cc b/libs/canvas/ruler.cc
index 1e7a731899..120ba845a5 100644
--- a/libs/canvas/ruler.cc
+++ b/libs/canvas/ruler.cc
@@ -49,8 +49,8 @@ Ruler::Ruler (Canvas* c, const Metric& m, Rect const& r)
 {
 }
 
-Ruler::Ruler (Group* g, const Metric& m)
-	: Rectangle (g)
+Ruler::Ruler (Item* parent, const Metric& m)
+	: Rectangle (parent)
 	, _metric (m)
 	, _lower (0)
 	, _upper (0)
@@ -58,8 +58,8 @@ Ruler::Ruler (Group* g, const Metric& m)
 {
 }
 
-Ruler::Ruler (Group* g, const Metric& m, Rect const& r)
-	: Rectangle (g, r)
+Ruler::Ruler (Item* parent, const Metric& m, Rect const& r)
+	: Rectangle (parent, r)
 	, _metric (m)
 	, _lower (0)
 	, _upper (0)
diff --git a/libs/canvas/scroll_group.cc b/libs/canvas/scroll_group.cc
index d78caf4ed0..15b607a564 100644
--- a/libs/canvas/scroll_group.cc
+++ b/libs/canvas/scroll_group.cc
@@ -28,13 +28,13 @@ using namespace std;
 using namespace ArdourCanvas;
 
 ScrollGroup::ScrollGroup (Canvas* c, ScrollSensitivity s)
-	: Group (c)
+	: Layout (c)
 	, _scroll_sensitivity (s)	
 {
 }
 
-ScrollGroup::ScrollGroup (Group* g, ScrollSensitivity s)
-	: Group (g)
+ScrollGroup::ScrollGroup (Item* parent, ScrollSensitivity s)
+	: Layout (parent)
 	, _scroll_sensitivity (s)	
 {
 }
@@ -60,12 +60,10 @@ ScrollGroup::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) c
 	context->save ();
 	context->rectangle (self.x0, self.y0, self.width(), self.height());
 	context->clip ();
-
-	Group::render (area, context);
+	
+	Layout::render (area, context);
 
 	context->restore ();
-
-
 }
 
 void
diff --git a/libs/canvas/text.cc b/libs/canvas/text.cc
index 4c2077a70b..cfad375814 100644
--- a/libs/canvas/text.cc
+++ b/libs/canvas/text.cc
@@ -43,8 +43,8 @@ Text::Text (Canvas* c)
 {
 }
 
-Text::Text (Group* g)
-	: Item (g)
+Text::Text (Item* parent)
+	: Item (parent)
 	, _color (0x000000ff)
 	, _font_description (0)
 	, _alignment (Pango::ALIGN_LEFT)
diff --git a/libs/canvas/wave_view.cc b/libs/canvas/wave_view.cc
index 631be6254a..3e131487b6 100644
--- a/libs/canvas/wave_view.cc
+++ b/libs/canvas/wave_view.cc
@@ -76,8 +76,8 @@ WaveView::WaveView (Canvas* c, boost::shared_ptr<ARDOUR::AudioRegion> region)
 	ClipLevelChanged.connect_same_thread (invalidation_connection, boost::bind (&WaveView::handle_clip_level_change, this));
 }
 
-WaveView::WaveView (Group* g, boost::shared_ptr<ARDOUR::AudioRegion> region)
-	: Item (g)
+WaveView::WaveView (Item* parent, boost::shared_ptr<ARDOUR::AudioRegion> region)
+	: Item (parent)
 	, _region (region)
 	, _channel (0)
 	, _samples_per_pixel (0)
diff --git a/libs/canvas/widget.cc b/libs/canvas/widget.cc
index 0961382128..17d0d29e59 100644
--- a/libs/canvas/widget.cc
+++ b/libs/canvas/widget.cc
@@ -36,8 +36,8 @@ Widget::Widget (Canvas* c, CairoWidget& w)
 	Event.connect (sigc::mem_fun (*this, &Widget::event_proxy));
 }
 
-Widget::Widget (Group* g, CairoWidget& w)
-	: Item (g)
+Widget::Widget (Item* parent, CairoWidget& w)
+	: Item (parent)
 	, _widget (w)
 {
 	Event.connect (sigc::mem_fun (*this, &Widget::event_proxy));
diff --git a/libs/canvas/wscript b/libs/canvas/wscript
index 483e19d338..c6e31cafd6 100644
--- a/libs/canvas/wscript
+++ b/libs/canvas/wscript
@@ -32,13 +32,14 @@ canvas_sources = [
         'arrow.cc',
         'canvas.cc',
         'circle.cc',
+        'container.cc',
         'curve.cc',
         'debug.cc',
         'item.cc',
         'fill.cc',
         'flag.cc',
-        'group.cc',
         'image.cc',
+        'layout.cc',
         'line.cc',
         'line_set.cc',
         'lookup_table.cc',
diff --git a/libs/canvas/xfade_curve.cc b/libs/canvas/xfade_curve.cc
index 9a854cd54e..f97cd234d2 100644
--- a/libs/canvas/xfade_curve.cc
+++ b/libs/canvas/xfade_curve.cc
@@ -48,8 +48,8 @@ XFadeCurve::XFadeCurve (Canvas* c, XFadePosition pos)
 {
 }
 
-XFadeCurve::XFadeCurve (Group* g)
-	: Item (g)
+XFadeCurve::XFadeCurve (Item* parent)
+	: Item (parent)
 	, points_per_segment (32)
 	, _xfadeposition (Start)
 	, _outline_color (0x000000ff)
@@ -57,8 +57,8 @@ XFadeCurve::XFadeCurve (Group* g)
 {
 }
 
-XFadeCurve::XFadeCurve (Group* g, XFadePosition pos)
-	: Item (g)
+XFadeCurve::XFadeCurve (Item* parent, XFadePosition pos)
+	: Item (parent)
 	, points_per_segment (32)
 	, _xfadeposition (pos)
 	, _outline_color (0x000000ff)