Improve window dragging between workspaces (#1874)

src/WindowGrabTracker.vala

@@ -0,0 +1,30 @@
+/*
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ * SPDX-FileCopyrightText: 2024 elementary, Inc. (https://elementary.io)
+ */
+
+public class Gala.WindowGrabTracker : GLib.Object {
+    public Meta.Display display { get; construct; }
+    public Meta.Window? current_window { get; private set; }
+
+    public WindowGrabTracker (Meta.Display display) {
+        Object (display: display);
+    }
+
+    construct {
+        display.grab_op_begin.connect (on_grab_op_begin);
+        display.grab_op_end.connect (on_grab_op_end);
+    }
+
+    private void on_grab_op_begin (Meta.Window window, Meta.GrabOp op) {
+        if (op != MOVING) {
+            return;
+        }
+
+        current_window = window;
+    }
+
+    private void on_grab_op_end (Meta.Window window, Meta.GrabOp op) {
+        current_window = null;
+    }
+}

src/WindowManager.vala

@@ -83,6 +83,8 @@ namespace Gala {
 
         private DaemonManager daemon_manager;
 
+        private WindowGrabTracker window_grab_tracker;
+
         private NotificationStack notification_stack;
 
         private Gee.LinkedList<ModalProxy> modal_stack = new Gee.LinkedList<ModalProxy> ();
@@ -139,6 +141,7 @@ namespace Gala {
 
         public override void start () {
             daemon_manager = new DaemonManager (get_display ());
+            window_grab_tracker = new WindowGrabTracker (get_display ());
 
             show_stage ();
 
@@ -1915,21 +1918,37 @@ namespace Gala {
                 clutter_actor_reparent (moving_actor, static_windows);
             }
 
+            unowned var grabbed_window = window_grab_tracker.current_window;
+
+            if (grabbed_window != null) {
+                unowned var moving_actor = (Meta.WindowActor) grabbed_window.get_compositor_private ();
+
+                windows.prepend (moving_actor);
+                parents.prepend (moving_actor.get_parent ());
+
+                moving_actor.set_translation (-clone_offset_x, -clone_offset_y, 0);
+                clutter_actor_reparent (moving_actor, static_windows);
+            }
+
             var to_has_fullscreened = false;
             var from_has_fullscreened = false;
             var docks = new List<Meta.WindowActor> ();
 
             // collect all windows and put them in the appropriate containers
             foreach (unowned Meta.WindowActor actor in display.get_window_actors ()) {
-                if (actor.is_destroyed ())
+                if (actor.is_destroyed ()) {
                     continue;
+                }
 
-                unowned Meta.Window window = actor.get_meta_window ();
+                unowned var window = actor.get_meta_window ();
 
                 if (!window.showing_on_its_workspace () ||
-                    (move_primary_only && !window.is_on_primary_monitor ()) ||
-                    (moving != null && window == moving))
+                    move_primary_only && !window.is_on_primary_monitor () ||
+                    window == moving ||
+                    window == grabbed_window) {
+
                     continue;
+                }
 
                 if (window.on_all_workspaces) {
                     // only collect docks here that need to be displayed on both workspaces

src/meson.build

@@ -13,6 +13,7 @@ gala_bin_sources = files(
     'ScreenSaverManager.vala',
     'ScreenshotManager.vala',
     'SessionManager.vala',
+    'WindowGrabTracker.vala',
     'WindowListener.vala',
     'WindowManager.vala',
     'WindowStateSaver.vala',