Use pan backend for desktop workspace switch

Author: leolost2605

lib/Utils.vala

@@ -40,6 +40,22 @@ namespace Gala {
                 width = actor.width;
                 height = actor.height;
             }
+
+            private Meta.Display? display;
+
+            public Size.primary_monitor_tracking (Meta.Display _display) {
+                display = _display;
+
+                set_size_from_monitor (display, display.get_primary_monitor ());
+                display.get_context ().get_backend ().get_monitor_manager ().monitors_changed.connect (() =>
+                    set_size_from_monitor (display, display.get_primary_monitor ()));
+            }
+
+            public void set_size_from_monitor (Meta.Display display, int monitor_index) {
+                var rect = display.get_monitor_geometry (monitor_index);
+                width = rect.width;
+                height = rect.height;
+            }
         }
 
         private struct CachedIcon {

src/WindowManager.vala

@@ -184,6 +184,9 @@ namespace Gala {
             screensaver.active_changed.connect (update_input_area);
 
             stage = display.get_stage () as Clutter.Stage;
+
+            gesture_tracker.enable_pan (stage, new Utils.Size.primary_monitor_tracking (display));
+
             var background_settings = new GLib.Settings ("org.gnome.desktop.background");
             var color = background_settings.get_string ("primary-color");
             stage.background_color = Clutter.Color.from_string (color);