Constrain height of group-tab to the editor's height

Previously the group-tab extended all the way down to the
last track. Potentially with a widget height of > 2^15 px.

This caused issues with gtk widgets (notably on Windows)
```
unhandled exception (type std::exception) in signal handler:
what: invalid value (typically too big) for the size of the input (surface, pattern, etc.)
```

This also prepares for Mixer Tab-Group to use the same
separation between visible and total extent.

gtk2_ardour/editor.cc

@@ -591,11 +591,8 @@ Editor::Editor ()
 	vertical_adjustment.signal_value_changed().connect (sigc::mem_fun(*this, &Editor::tie_vertical_scrolling), true);
 	_track_canvas->signal_map_event().connect (sigc::mem_fun (*this, &Editor::track_canvas_map_handler));
 
-	HBox* h = manage (new HBox);
 	_group_tabs = new EditorGroupTabs (this);
-	h->pack_start (*_group_tabs, PACK_SHRINK);
-	h->pack_start (edit_controls_vbox);
-	controls_layout.add (*h);
+	controls_layout.add (edit_controls_vbox);
 
 	HSeparator* separator = manage (new HSeparator());
 	separator->set_name("TrackSeparator");
@@ -609,6 +606,8 @@ Editor::Editor ()
 	controls_layout.signal_button_release_event().connect (sigc::mem_fun(*this, &Editor::edit_controls_button_event));
 	controls_layout.signal_scroll_event().connect (sigc::mem_fun(*this, &Editor::control_layout_scroll), false);
 
+	_group_tabs->signal_scroll_event().connect (sigc::mem_fun(*this, &Editor::control_layout_scroll), false);
+
 	_cursors = new MouseCursors;
 	_cursors->set_cursor_set (UIConfiguration::instance().get_icon_set());
 
@@ -645,11 +644,12 @@ Editor::Editor ()
 #endif
 
 	/* labels for the time bars */
-	edit_packer.attach (time_bars_event_box,     1, 2, 0, 1,    FILL,        SHRINK, 0, 0);
+	edit_packer.attach (time_bars_event_box,     1, 3, 0, 1,    FILL,        SHRINK,      0, 0);
 	/* track controls */
-	edit_packer.attach (controls_layout,         1, 2, 1, 2,    FILL,        FILL|EXPAND, 0, 0);
+	edit_packer.attach (*_group_tabs,            1, 2, 1, 2,    FILL,        FILL|EXPAND, 0, 0);
+	edit_packer.attach (controls_layout,         2, 3, 1, 2,    FILL,        FILL|EXPAND, 0, 0);
 	/* canvas */
-	edit_packer.attach (*_track_canvas_viewport,  2, 3, 0, 2,    FILL|EXPAND, FILL|EXPAND, 0, 0);
+	edit_packer.attach (*_track_canvas_viewport, 3, 4, 0, 2,    FILL|EXPAND, FILL|EXPAND, 0, 0);
 
 	bottom_hbox.set_border_width (2);
 	bottom_hbox.set_spacing (3);

gtk2_ardour/editor_canvas.cc

@@ -347,11 +347,6 @@ Editor::reset_controls_layout_width ()
 	req = edit_controls_vbox.size_request ();
 	w = req.width;
 
-	if (_group_tabs->get_visible()) {
-		req = _group_tabs->size_request ();
-		w += req.width;
-	}
-
 	/* the controls layout has no horizontal scrolling, its visible
 	   width is always equal to the total width of its contents.
 	*/
@@ -381,6 +376,7 @@ Editor::reset_controls_layout_height (int32_t h)
 
 	controls_layout.property_height() = h;
 
+	_group_tabs->set_extent (h);
 }
 
 bool
@@ -1016,6 +1012,7 @@ Editor::tie_vertical_scrolling ()
 		_region_peak_cursor->hide ();
 		_summary->set_overlays_dirty ();
 	}
+	_group_tabs->set_offset (vertical_adjustment.get_value ());
 }
 
 void

gtk2_ardour/editor_group_tabs.cc

@@ -87,6 +87,13 @@ EditorGroupTabs::compute_tabs () const
 void
 EditorGroupTabs::draw_tab (cairo_t* cr, Tab const & tab)
 {
+	const double from = tab.from - offset ();
+	const double to   = tab.to   - offset ();
+
+	if (from > visible_extent () || to < 0) {
+		return;
+	}
+
 	double const arc_radius = get_width();
 	double r, g, b, a;
 
@@ -99,14 +106,14 @@ EditorGroupTabs::draw_tab (cairo_t* cr, Tab const & tab)
 	a = 1.0;
 
 	cairo_set_source_rgba (cr, r, g, b, a);
-	cairo_move_to (cr, 0, tab.from + arc_radius);
-	cairo_arc (cr, get_width(), tab.from + arc_radius, arc_radius, M_PI, 3 * M_PI / 2);
-	cairo_line_to (cr, get_width(), tab.to);
-	cairo_arc (cr, get_width(), tab.to - arc_radius, arc_radius, M_PI / 2, M_PI);
-	cairo_line_to (cr, 0, tab.from + arc_radius);
+	cairo_move_to (cr, 0, from + arc_radius);
+	cairo_arc (cr, get_width(), from + arc_radius, arc_radius, M_PI, 3 * M_PI / 2);
+	cairo_line_to (cr, get_width(), to);
+	cairo_arc (cr, get_width(), to - arc_radius, arc_radius, M_PI / 2, M_PI);
+	cairo_line_to (cr, 0, from + arc_radius);
 	cairo_fill (cr);
 
-	if (tab.group && (tab.to - tab.from) > arc_radius) {
+	if (tab.group && (to - from) > arc_radius) {
 		int text_width, text_height;
 
 		Glib::RefPtr<Pango::Layout> layout;
@@ -114,10 +121,10 @@ EditorGroupTabs::draw_tab (cairo_t* cr, Tab const & tab)
 		layout->set_ellipsize (Pango::ELLIPSIZE_MIDDLE);
 
 		layout->set_text (tab.group->name ());
-		layout->set_width ((tab.to - tab.from - arc_radius) * PANGO_SCALE);
+		layout->set_width ((to - from - arc_radius) * PANGO_SCALE);
 		layout->get_pixel_size (text_width, text_height);
 
-		cairo_move_to (cr, (get_width() - text_height) * .5, (text_width + tab.to + tab.from) * .5);
+		cairo_move_to (cr, (get_width() - text_height) * .5, (text_width + to + from) * .5);
 
 		Gtkmm2ext::Color c = Gtkmm2ext::contrasting_text_color (Gtkmm2ext::rgba_to_color (r, g, b, a));
 		Gtkmm2ext::color_to_rgba (c, r, g, b, a);
@@ -133,7 +140,7 @@ EditorGroupTabs::draw_tab (cairo_t* cr, Tab const & tab)
 double
 EditorGroupTabs::primary_coordinate (double, double y) const
 {
-	return y;
+	return y + offset ();
 }
 
 RouteList

gtk2_ardour/editor_group_tabs.h

@@ -35,11 +35,12 @@ private:
 	void draw_tab (cairo_t *, Tab const &);
 	double primary_coordinate (double, double) const;
 	ARDOUR::RouteList routes_for_tab (Tab const *) const;
-	double extent () const {
-		return get_height();
-	}
 	void add_menu_items (Gtk::Menu *, ARDOUR::RouteGroup *);
 	ARDOUR::RouteList selected_routes () const;
+
+	double visible_extent () const { 
+		return get_height();
+	}
 };
 
 #endif // __gtk_ardour_editor_group_tabs_h__

gtk2_ardour/group_tabs.cc

@@ -52,6 +52,8 @@ GroupTabs::GroupTabs ()
 	: _menu (0)
 	, _dragging (0)
 	, _dragging_new_tab (0)
+	, _extent (-1)
+	, _offset (0)
 {
 	add_events (Gdk::BUTTON_PRESS_MASK|Gdk::BUTTON_RELEASE_MASK|Gdk::POINTER_MOTION_MASK);
 	UIConfiguration::instance().ColorsChanged.connect (sigc::mem_fun (*this, &GroupTabs::queue_draw));
@@ -82,6 +84,27 @@ GroupTabs::set_session (Session* s)
 	}
 }
 
+void
+GroupTabs::set_extent (double extent)
+{
+	if (_extent == extent) {
+		return;
+	}
+	_extent = extent;
+	set_dirty ();
+	queue_draw ();
+}
+
+void
+GroupTabs::set_offset (double offset)
+{
+	if (_offset == offset) {
+		return;
+	}
+	_offset = offset;
+	set_dirty ();
+	queue_draw ();
+}
 
 /** Handle a size request.
  *  @param req GTK requisition

gtk2_ardour/group_tabs.h

@@ -65,6 +65,9 @@ public:
 
 	void run_new_group_dialog (ARDOUR::RouteList const *, bool with_master);
 
+	void set_extent (double);
+	void set_offset (double);
+
 	static void set_group_color (ARDOUR::RouteGroup *, uint32_t);
 	static std::string group_gui_id (ARDOUR::RouteGroup *);
 	static uint32_t group_color (ARDOUR::RouteGroup *);
@@ -80,6 +83,15 @@ protected:
 		ARDOUR::RouteGroup* group; ///< route group
 	};
 
+	/** @return Size of the widget along the primary axis */
+	virtual double visible_extent () const = 0;
+
+	/** @return Size of all contained strips along the primary axis */
+	double extent () const { return _extent < 0 ? visible_extent () : _extent; }
+
+	/** @return Scroll offset of \ref visible_extent along the primary axis */
+	double offset () const { return _offset; }
+
 private:
 	static void emit_gui_changed_for_members (std::shared_ptr<ARDOUR::RouteList>);
 
@@ -102,10 +114,6 @@ private:
 	virtual double primary_coordinate (double x, double y) const = 0;
 
 	virtual ARDOUR::RouteList routes_for_tab (Tab const * t) const = 0;
-
-	/** @return Size of the widget along the primary axis */
-	virtual double extent () const = 0;
-
 	virtual void add_menu_items (Gtk::Menu *, ARDOUR::RouteGroup *) {}
 	virtual ARDOUR::RouteList selected_routes () const = 0;
 
@@ -162,6 +170,8 @@ private:
 	double _drag_min; ///< minimum position for drag
 	double _drag_max; ///< maximum position for drag
 	double _drag_first; ///< first mouse pointer position during drag
+	double _extent;
+	double _offset;
 
 	/** colors that have been used for new route group tabs */
 	static std::list<Gdk::Color> _used_colors;

gtk2_ardour/mixer_group_tabs.h

@@ -34,7 +34,8 @@ private:
 	void draw_tab (cairo_t *, Tab const &);
 	double primary_coordinate (double, double) const;
 	ARDOUR::RouteList routes_for_tab (Tab const *) const;
-	double extent () const {
+
+	double visible_extent () const {
 		return get_width();
 	}
 

gtk2_ardour/recorder_group_tabs.cc

@@ -39,7 +39,7 @@ RecorderGroupTabs::primary_coordinate (double, double y) const
 }
 
 double
-RecorderGroupTabs::extent () const
+RecorderGroupTabs::visible_extent () const
 {
 	return get_height ();
 }

gtk2_ardour/recorder_group_tabs.h

@@ -34,7 +34,7 @@ private:
 	ARDOUR::RouteList routes_for_tab (Tab const*) const;
 	ARDOUR::RouteList selected_routes () const;
 	double            primary_coordinate (double, double) const;
-	double            extent () const;
+	double            visible_extent () const;
 
 	RecorderUI* _recorder;
 };