different approach to independent scrolling, involving ArdourCanvas::ScrollGroup

The idea now is that a scroll group item can be added to the canvas which will causes its children to scroll in either or both
directions (horizontal or vertical). There are few complications: the position() of the ScrollGroup is ambiguous depending
on whether you want it with scroll taken into account or not, so Item::canvas_position() was added, which defaults to
the same value as Item::position() but is overridden by ScrollGroup to return the position independent of scrolling. This
method is used when translating between item/canvas/window coordinate systems.

Note that the basic idea is that we MOVE the scroll group when a scroll happens. This mirrors what happens in the GnomeCanvas,
where Nick Mainsbridge came up with a great idea that allowed unification of the time bar and track canvases.

9 files changed, 152 insertions, 92 deletions

diff --git a/libs/canvas/canvas.cc b/libs/canvas/canvas.cc
index 8d4c1b8858..aad614d906 100644
--- a/libs/canvas/canvas.cc
+++ b/libs/canvas/canvas.cc
@@ -50,11 +50,9 @@ Canvas::scroll_to (Coord x, Coord y)
 {
 	Duple d (x, y);
 	
-	if (_global_scroll) {
-		_scroll_offset = d;
-	}
-	
-	//_root.scroll_to (d);
+	_scroll_offset = d;
+
+	_root.scroll_to (d);
 
 	pick_current_item (0); // no current mouse position 
 }
@@ -81,9 +79,9 @@ Canvas::render (Rect const & area, Cairo::RefPtr<Cairo::Context> const & context
 #ifdef CANVAS_DEBUG
 	if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
 		cerr << this << " RENDER: " << area << endl;
-		cerr << "CANVAS @ " << this << endl;
-		dump (cerr);
-		cerr << "-------------------------\n";
+		//cerr << "CANVAS @ " << this << endl;
+		//dump (cerr);
+		//cerr << "-------------------------\n";
 	}
 #endif
 
@@ -208,13 +206,14 @@ Canvas::canvas_to_window (Duple const & d, bool rounded) const
 	Duple wd = d.translate (Duple (-_scroll_offset.x, -_scroll_offset.y));
 
 	/* Note that this intentionally almost always returns integer coordinates */
+
 	if (rounded) {
 		wd.x = round (wd.x);
 		wd.y = round (wd.y);
 	}
 
 	return wd;
-}	
+}
 
 Rect
 Canvas::window_to_canvas (Rect const & r) const
diff --git a/libs/canvas/canvas/item.h b/libs/canvas/canvas/item.h
index 429df33894..487efae4d0 100644
--- a/libs/canvas/canvas/item.h
+++ b/libs/canvas/canvas/item.h
@@ -112,22 +112,17 @@ public:
 	void set_y_position (Coord);
 	void move (Duple);
 
-	enum ScrollSensitivity {
-		ScrollsVertically = 0x1,
-		ScrollsHorizontally = 0x2
-	};
-	
-	void set_scroll_sensitivity (ScrollSensitivity s);
-	ScrollSensitivity scroll_sensitivity () const { return _scroll_sensitivity; }
-
-	virtual void scroll_to (Duple const& d);
-	Duple scroll_offset() const { return _scroll_offset; }
+	virtual void scroll_to (Duple const&) {}
 
 	/** @return Position of this item in the parent's coordinates */
 	Duple position () const {
 		return _position;
 	}
 
+	virtual Duple canvas_position () const {
+		return _position;
+	}
+
 	boost::optional<Rect> bounding_box () const;
         Coord height() const;
         Coord width() const;
@@ -248,8 +243,6 @@ private:
 	void init ();
 
 	bool _ignore_events;
-	ScrollSensitivity _scroll_sensitivity;
-	Duple _scroll_offset;
 };
 
 extern LIBCANVAS_API std::ostream& operator<< (std::ostream&, const ArdourCanvas::Item&);
diff --git a/libs/canvas/canvas/scroll_group.h b/libs/canvas/canvas/scroll_group.h
new file mode 100644
index 0000000000..c2b26bf9d9
--- /dev/null
+++ b/libs/canvas/canvas/scroll_group.h
@@ -0,0 +1,47 @@
+/*
+    Copyright (C) 2014 Paul Davis
+
+    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_SCROLL_GROUP_H__
+#define __CANVAS_SCROLL_GROUP_H__
+
+#include "canvas/group.h"
+
+namespace ArdourCanvas {
+
+class LIBCANVAS_API ScrollGroup : public Group
+{
+  public:
+	enum ScrollSensitivity {
+		ScrollsVertically = 0x1,
+		ScrollsHorizontally = 0x2
+	};
+	
+	explicit ScrollGroup (Group *, ScrollSensitivity);
+	explicit ScrollGroup (Group *, Duple, ScrollSensitivity);
+
+	void scroll_to (Duple const& d);
+	Duple canvas_position() const;
+
+  private:
+	ScrollSensitivity _scroll_sensitivity;
+	Duple             _scroll_offset;
+};
+
+}
+
+#endif
diff --git a/libs/canvas/canvas/wave_view.h b/libs/canvas/canvas/wave_view.h
index 307528c685..0ddffca180 100644
--- a/libs/canvas/canvas/wave_view.h
+++ b/libs/canvas/canvas/wave_view.h
@@ -173,7 +173,7 @@ private:
         void handle_clip_level_change ();
 
         void ensure_cache (ARDOUR::framepos_t sample_start, ARDOUR::framepos_t sample_end) const;
-        ArdourCanvas::Coord position (double) const;
+        ArdourCanvas::Coord y_extent (double) const;
         void draw_image (ARDOUR::PeakData*, int npeaks) const;
 };
 
diff --git a/libs/canvas/group.cc b/libs/canvas/group.cc
index b6df3dfee6..509be0b51a 100644
--- a/libs/canvas/group.cc
+++ b/libs/canvas/group.cc
@@ -117,7 +117,9 @@ Group::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
 						     << (*i)->whatami()
 						     << ' '
 						     << (*i)->name
-						     << " item = " 
+						     << " item "
+						     << item_bbox.get()
+						     << " window = " 
 						     << item
 						     << " intersect = "
 						     << draw
@@ -136,8 +138,8 @@ Group::render (Rect const & area, Cairo::RefPtr<Cairo::Context> context) const
 
 #ifdef CANVAS_DEBUG
 			if (DEBUG_ENABLED(PBD::DEBUG::CanvasRender)) {
-				cerr << string_compose ("%1skip render of %2 %3, no intersection\n", _canvas->render_indent(), (*i)->whatami(),
-							(*i)->name);
+				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
 
@@ -152,7 +154,7 @@ Group::scroll_to (Duple const& d)
 {
 	Item::scroll_to (d);
 	
-	for (list<Item*>::iterator i = _items.begin(); i != _items.end(); ) {
+	for (list<Item*>::iterator i = _items.begin(); i != _items.end(); ++i) {
 		(*i)->scroll_to (d);
 	}
 }
diff --git a/libs/canvas/item.cc b/libs/canvas/item.cc
index 7a55e9604f..c6652f9d3a 100644
--- a/libs/canvas/item.cc
+++ b/libs/canvas/item.cc
@@ -35,7 +35,6 @@ using namespace ArdourCanvas;
 Item::Item (Canvas* canvas)
 	: _canvas (canvas)
 	, _parent (0)
-	, _scroll_sensitivity (ScrollSensitivity (0))
 {
 	init ();
 }
@@ -43,7 +42,6 @@ Item::Item (Canvas* canvas)
 Item::Item (Group* parent)
 	: _canvas (parent->canvas ())
 	, _parent (parent)
-	, _scroll_sensitivity (ScrollSensitivity (0))
 {
 	init ();
 }
@@ -52,7 +50,6 @@ Item::Item (Group* parent, Duple position)
 	: _canvas (parent->canvas())
 	, _parent (parent)
 	, _position (position)
-	, _scroll_sensitivity (ScrollSensitivity (0))	
 {
 	init ();
 }
@@ -82,24 +79,6 @@ Item::~Item ()
 	}
 }
 
-void
-Item::scroll_to (Duple const& d)
-{
-	if (_scroll_sensitivity & ScrollsVertically) {
-		_scroll_offset.y = d.y;
-	}
-
-	if (_scroll_sensitivity & ScrollsHorizontally) {
-		_scroll_offset.x = d.x;
-	}
-}
-
-void
-Item::set_scroll_sensitivity (ScrollSensitivity s)
-{
-	_scroll_sensitivity = s;
-}
-
 ArdourCanvas::Rect
 Item::item_to_parent (ArdourCanvas::Rect const & r) const
 {
@@ -113,7 +92,7 @@ Item::item_to_canvas (ArdourCanvas::Rect const & r) const
 	Duple offset;
 
 	while (i) {
-		offset = offset.translate (i->position());
+		offset = offset.translate (i->canvas_position());
 		i = i->parent();
 	}
 
@@ -127,7 +106,7 @@ Item::item_to_canvas (ArdourCanvas::Duple const & d) const
 	Duple offset;
 
 	while (i) {
-		offset = offset.translate (i->position());
+		offset = offset.translate (i->canvas_position());
 		i = i->parent();
 	}
 
@@ -141,7 +120,7 @@ Item::canvas_to_item (ArdourCanvas::Duple const & d) const
 	Duple offset;
 
 	while (i) {
-		offset = offset.translate (-(i->position()));
+		offset = offset.translate (-(i->canvas_position()));
 		i = i->parent();
 	}
 
@@ -155,7 +134,7 @@ Item::canvas_to_item (ArdourCanvas::Rect const & d) const
 	Duple offset;
 
 	while (i) {
-		offset = offset.translate (-(i->position()));
+		offset = offset.translate (-(i->canvas_position()));
 		i = i->parent();
 	}
 
@@ -197,43 +176,19 @@ Item::item_to_window (ArdourCanvas::Duple const & d, bool rounded) const
 Duple
 Item::window_to_item (ArdourCanvas::Duple const & d) const
 {
-	Item const * i = this;
-	Duple offset;
-
-	while (i) {
-		offset = offset.translate (-i->scroll_offset());
-		i = i->parent();
-	}
-	
-	return _canvas->window_to_canvas (d.translate (offset));
+	return canvas_to_item (_canvas->window_to_canvas (d));
 }
 
 ArdourCanvas::Rect
 Item::item_to_window (ArdourCanvas::Rect const & r) const
 {
-	Item const * i = this;
-	Duple offset;
-
-	while (i) {
-		offset = offset.translate (i->scroll_offset());
-		i = i->parent();
-	}
-
-	return _canvas->canvas_to_window (item_to_canvas (r.translate (offset)));
+	return _canvas->canvas_to_window (item_to_canvas (r));
 }
 
 ArdourCanvas::Rect
 Item::window_to_item (ArdourCanvas::Rect const & r) const
 {
-	Item const * i = this;
-	Duple offset;
-
-	while (i) {
-		offset = offset.translate (-i->scroll_offset());
-		i = i->parent();
-	}
-
-	return canvas_to_item (_canvas->window_to_canvas (r).translate (offset));
+	return canvas_to_item (_canvas->window_to_canvas (r));
 }
 
 /** Set the position of this item in the parent's coordinates */
@@ -576,7 +531,7 @@ Item::dump (ostream& o) const
 	boost::optional<ArdourCanvas::Rect> bb = bounding_box();
 
 	o << _canvas->indent() << whatami() << ' ' << this << " Visible ? " << _visible;
-	o << " @ " << position() << " scrolled-to " << _scroll_offset;
+	o << " @ " << position();
 	
 #ifdef CANVAS_DEBUG
 	if (!name.empty()) {
diff --git a/libs/canvas/scroll_group.cc b/libs/canvas/scroll_group.cc
new file mode 100644
index 0000000000..bda6911ca7
--- /dev/null
+++ b/libs/canvas/scroll_group.cc
@@ -0,0 +1,63 @@
+/*
+    Copyright (C) 2014 Paul Davis
+
+    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 "canvas/scroll_group.h"
+
+using namespace std;
+using namespace ArdourCanvas;
+
+ScrollGroup::ScrollGroup (Group* parent, ScrollSensitivity s)
+	: Group (parent)
+	, _scroll_sensitivity (s)	
+{
+}
+
+ScrollGroup::ScrollGroup (Group* parent, Duple position, ScrollSensitivity s)
+	: Group (parent, position)
+	, _scroll_sensitivity (s)
+{
+}
+
+void
+ScrollGroup::scroll_to (Duple const& d)
+{
+	Duple base_pos (position().translate (_scroll_offset));
+
+	if (_scroll_sensitivity & ScrollsHorizontally) {
+		base_pos.x -= d.x;
+		_scroll_offset.x = d.x;
+	} 
+
+	if (_scroll_sensitivity & ScrollsVertically) {
+		base_pos.y -= d.y;
+		_scroll_offset.y = d.y;
+	}
+
+	set_position (base_pos);
+}
+
+Duple
+ScrollGroup::canvas_position() const
+{
+	/* return the normal "base" position of this item
+	   rather its position as affected by any scroll
+	   offset.
+	*/
+	return _position.translate (_scroll_offset);
+}
diff --git a/libs/canvas/wave_view.cc b/libs/canvas/wave_view.cc
index fa2c617d7b..3de5af1c51 100644
--- a/libs/canvas/wave_view.cc
+++ b/libs/canvas/wave_view.cc
@@ -219,7 +219,7 @@ WaveView::draw_image (PeakData* _peaks, int n_peaks) const
 		if (_logscaled) {
 			for (int i = 0; i < n_peaks; ++i) {
 				tips[i].bot = height();
-				tips[i].top = position (alt_log_meter (fast_coefficient_to_dB (max (fabs (_peaks[i].max), fabs (_peaks[i].min)))));
+				tips[i].top = y_extent (alt_log_meter (fast_coefficient_to_dB (max (fabs (_peaks[i].max), fabs (_peaks[i].min)))));
 
 				if (fabs (_peaks[i].max) >= clip_level) {
 					tips[i].clip_max = true;
@@ -231,7 +231,7 @@ WaveView::draw_image (PeakData* _peaks, int n_peaks) const
 			}
 		} else {for (int i = 0; i < n_peaks; ++i) {
 				tips[i].bot = height();
-				tips[i].top = position (max (fabs (_peaks[i].max), fabs (_peaks[i].min)));
+				tips[i].top = y_extent (max (fabs (_peaks[i].max), fabs (_peaks[i].min)));
 
 				if (fabs (_peaks[i].max) >= clip_level) {
 					tips[i].clip_max = true;
@@ -259,19 +259,19 @@ WaveView::draw_image (PeakData* _peaks, int n_peaks) const
 				}
 
 				if (top > 0.0) {
-					top = position (alt_log_meter (fast_coefficient_to_dB (top)));
+					top = y_extent (alt_log_meter (fast_coefficient_to_dB (top)));
 				} else if (top < 0.0) {
-					top = position (-alt_log_meter (fast_coefficient_to_dB (-top)));
+					top = y_extent (-alt_log_meter (fast_coefficient_to_dB (-top)));
 				} else {
-					top = position (0.0);
+					top = y_extent (0.0);
 				}
 
 				if (bot > 0.0) {
-					bot = position (alt_log_meter (fast_coefficient_to_dB (bot)));
+					bot = y_extent (alt_log_meter (fast_coefficient_to_dB (bot)));
 				} else if (bot < 0.0) {
-					bot = position (-alt_log_meter (fast_coefficient_to_dB (-bot)));
+					bot = y_extent (-alt_log_meter (fast_coefficient_to_dB (-bot)));
 				} else {
-					bot = position (0.0);
+					bot = y_extent (0.0);
 				}
 
 				tips[i].top = top;
@@ -289,8 +289,8 @@ WaveView::draw_image (PeakData* _peaks, int n_peaks) const
 					tips[i].clip_min = true;
 				}
 
-				tips[i].top = position (_peaks[i].min);
-				tips[i].bot = position (_peaks[i].max);
+				tips[i].top = y_extent (_peaks[i].min);
+				tips[i].bot = y_extent (_peaks[i].max);
 
 
 			}
@@ -402,8 +402,8 @@ WaveView::draw_image (PeakData* _peaks, int n_peaks) const
 
 		set_source_rgba (context, _zero_color);
 		context->set_line_width (1.0);
-		context->move_to (0, position (0.0) + 0.5);
-		context->line_to (n_peaks, position (0.0) + 0.5);
+		context->move_to (0, y_extent (0.0) + 0.5);
+		context->line_to (n_peaks, y_extent (0.0) + 0.5);
 		context->stroke ();
 	}
 }
@@ -668,7 +668,7 @@ WaveView::region_resized ()
 }
 
 Coord
-WaveView::position (double s) const
+WaveView::y_extent (double s) const
 {
 	/* it is important that this returns an integral value, so that we 
 	   can ensure correct single pixel behaviour.
diff --git a/libs/canvas/wscript b/libs/canvas/wscript
index 913f8298fa..d0cbfc882f 100644
--- a/libs/canvas/wscript
+++ b/libs/canvas/wscript
@@ -50,6 +50,7 @@ canvas_sources = [
         'polygon.cc',
         'rectangle.cc',
         'root_group.cc',
+        'scroll_group.cc',
         'stateful_image.cc',
         'text.cc',
         'types.cc',