make placement of icon groups more stable, prepare for window insert code

src/Makefile.am

@@ -52,6 +52,7 @@ gala_VALASOURCES = \
 	Widgets/WindowSwitcher.vala \
 	Widgets/WindowThumb.vala \
 	Widgets/MultitaskingView/IconGroup.vala \
+	Widgets/MultitaskingView/IconGroupContainer.vala \
 	Widgets/MultitaskingView/MonitorClone.vala \
 	Widgets/MultitaskingView/MultitaskingView.vala \
 	Widgets/MultitaskingView/TiledWindow.vala \

src/Widgets/MultitaskingView/IconGroupContainer.vala

@@ -0,0 +1,71 @@
+//
+//  Copyright (C) 2014 Tom Beckmann
+//
+//  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 3 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, see <http://www.gnu.org/licenses/>.
+//
+
+using Clutter;
+using Meta;
+
+namespace Gala
+{
+	// TODO: allow DnD to insert new workspaces
+	public class IconGroupContainer : Actor
+	{
+		const int SPACING = 48;
+
+		public Screen screen { get; construct; }
+
+		public IconGroupContainer (Screen screen)
+		{
+			Object (screen: screen);
+		}
+
+		void update_positions ()
+		{
+			unowned List<Workspace> existing_workspaces = screen.get_workspaces ();
+
+			foreach (var child in get_children ()) {
+				var icon_group = child as IconGroup;
+
+				// we don't use meta_workspace_index() here because it crashes
+				// the wm if the workspace has already been removed. This could
+				// happen here if two workspaces are removed very shortly after
+				// each other and a transition is still playing. Also, 
+				// meta_workspace_index() does the exact same thing.
+				var index = existing_workspaces.index (icon_group.workspace);
+
+				if (index < 0)
+					child.visible = false;
+				else
+					child.x = index * (child.width + SPACING);
+			}
+		}
+
+		public void add_group (IconGroup group)
+		{
+			add_child (group);
+
+			update_positions ();
+		}
+
+		public void remove_group (IconGroup group)
+		{
+			remove_child (group);
+
+			update_positions ();
+		}
+	}
+}
+

src/Widgets/MultitaskingView/MultitaskingView.vala

@@ -30,7 +30,7 @@ namespace Gala
 
 		List<MonitorClone> window_containers_monitors;
 
-		Actor icon_groups;
+		IconGroupContainer icon_groups;
 		Actor workspaces;
 
 		public MultitaskingView (WindowManager wm)
@@ -44,9 +44,7 @@ namespace Gala
 			workspaces = new Actor ();
 			workspaces.set_easing_mode (AnimationMode.EASE_OUT_QUAD);
 
-			icon_groups = new Actor ();
-			icon_groups.layout_manager = new BoxLayout ();
-			(icon_groups.layout_manager as BoxLayout).spacing = 48;
+			icon_groups = new IconGroupContainer (screen);
 
 			add_child (icon_groups);
 			add_child (workspaces);
@@ -82,7 +80,9 @@ namespace Gala
 						if (existing_workspaces.index (workspace_clone.workspace) < 0) {
 							workspace_clone.window_selected.disconnect (window_selected);
 							workspace_clone.selected.disconnect (activate_workspace);
-							workspace_clone.icon_group.destroy ();
+
+							icon_groups.remove_group (workspace_clone.icon_group);
+
 							workspace_clone.destroy ();
 						}
 					}
@@ -187,7 +187,7 @@ namespace Gala
 			workspace.selected.connect (activate_workspace);
 
 			workspaces.insert_child_at_index (workspace, num);
-			icon_groups.insert_child_at_index (workspace.icon_group, num);
+			icon_groups.add_group (workspace.icon_group);
 
 			update_positions (opened);
 
@@ -223,10 +223,11 @@ namespace Gala
 			var transition = workspace.icon_group.get_transition ("opacity");
 			if (transition != null)
 				transition.completed.connect (() => {
-					workspace.icon_group.destroy ();
+					icon_groups.remove_group (workspace.icon_group);
 				});
 			else
-				workspace.icon_group.destroy ();
+				icon_groups.remove_group (workspace.icon_group);
+
 			workspace.destroy ();
 
 			update_positions (opened);

src/WorkspaceManager.vala

@@ -106,9 +106,9 @@ namespace Gala
 			}
 		}
 
-		void window_added (Workspace workspace, Window window)
+		void window_added (Workspace? workspace, Window window)
 		{
-			if (!Prefs.get_dynamic_workspaces ())
+			if (workspace == null || !Prefs.get_dynamic_workspaces ())
 				return;
 
 			if ((window.window_type == WindowType.NORMAL
@@ -118,9 +118,9 @@ namespace Gala
 				append_workspace ();
 		}
 
-		void window_removed (Workspace workspace, Window window)
+		void window_removed (Workspace? workspace, Window window)
 		{
-			if (!Prefs.get_dynamic_workspaces ())
+			if (workspace == null || !Prefs.get_dynamic_workspaces ())
 				return;
 
 			if (window.window_type != WindowType.NORMAL