Introduce Monitor Layout Manager

data/display.gschema.xml

@@ -0,0 +1,19 @@
+<schemalist>
+  <schema id="io.elementary.settings.display" path="/io/elementary/settings/display/">
+
+    <key name="preferred-display-layouts" type="a{sv}">
+      <default>{}</default>
+      <summary>Preferred display layouts</summary>
+      <description>
+        Each profile contains a unique identifier and a list of monitors, with their respective position (x, y) and other properties such as transformation (e.g., rotation).
+        This allows the system to restore or suggest preferred monitor arrangements and settings when displays are connected or configurations change.
+        The expanded variant type is "a{sa{sa{sv}}}"
+        Setting: Dictionary of layouts - key is based on a combination of monitor ids
+        Layout: Dictionary of monitors - key is monitor identifier
+        Monitor: Dictionary of property values - key is property name
+        Property keys: "x", "y", "transform", "primary", "is-active"
+      </description>
+    </key>
+
+  </schema>
+</schemalist>

data/meson.build

@@ -11,3 +11,9 @@ gresource = gnome.compile_resources(
     'gresource',
     'display.gresource.xml'
 )
+
+install_data(
+    'display.gschema.xml',
+    install_dir: datadir / 'glib-2.0' / 'schemas',
+    rename: 'io.elementary.settings.display.gschema.xml'
+)

meson.build

@@ -31,3 +31,5 @@ config_file = configure_file(
 subdir('data')
 subdir('src')
 subdir('po')
+
+gnome.post_install(glib_compile_schemas: true)

src/Objects/MonitorLayoutManager.vala

@@ -0,0 +1,107 @@
+/*
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ * SPDX-FileCopyrightText: 2025 elementary, Inc. <https://elementary.io>
+ *
+ * Authored by: Leonardo Lemos <leonardolemos@live.com>
+ */
+
+public class Display.MonitorLayoutManager : GLib.Object {
+    private Settings settings;
+
+    private const string PREFERRED_MONITOR_LAYOUTS_KEY = "preferred-display-layouts";
+
+    public MonitorLayoutManager () {
+        Object ();
+    }
+
+    construct {
+        settings = new Settings ("io.elementary.settings.display");
+    }
+
+    public void arrange_monitors (Gee.LinkedList<VirtualMonitor> virtual_monitors) {
+        if (virtual_monitors.size == 1) {
+            // If there's only one monitor, no need to arrange
+            // Cloned monitors only have one virtual monitor so will return here
+            return;
+        }
+
+        var layout_key = get_layout_key (virtual_monitors);
+        // Layouts format are 'a{sa{sa{sv}}}'
+        var layouts = settings.get_value (PREFERRED_MONITOR_LAYOUTS_KEY);
+        Variant? monitors = null;
+        if (layouts != null) {
+            monitors = layouts.lookup_value (layout_key, VariantType.VARDICT);
+            foreach (var virtual_monitor in virtual_monitors) {
+                Variant? props = monitors.lookup_value (virtual_monitor.id, VariantType.VARDICT);
+                if (props != null) {
+                    int32 x = 0, y = 0;
+                    uint32 t = 0;
+                    bool p = false, e = false;
+                    if (props.lookup ("x", "i", out x) &&
+                        props.lookup ("y", "i", out y) &&
+                        props.lookup ("transform", "u", out t) &&
+                        props.lookup ("primary", "b", out p) &&
+                        props.lookup ("enabled", "b", out e)) {
+
+                        virtual_monitor.x = x;
+                        virtual_monitor.y = y;
+                        virtual_monitor.transform = t;
+                        virtual_monitor.primary = p;
+                        virtual_monitor.is_active = e;
+                     } else {
+                         warning ("property setting missing for monitor %s", virtual_monitor.get_display_name ());
+                     }
+                } else {
+                    warning ("no property dictionary found for monitor.id %s", virtual_monitor.get_display_name ());
+                }
+            }
+
+            return;
+        } else {
+            warning ("layout key %s not found", layout_key);
+        }
+
+        // If no layout found, we save the current layout to use later
+        save_layout (virtual_monitors);
+    }
+
+    public void save_layout (Gee.LinkedList<VirtualMonitor> virtual_monitors) {
+        var save_key = get_layout_key (virtual_monitors);
+
+        var monitor_dict = new VariantDict ();
+        foreach (var monitor in virtual_monitors) {
+            var props_dict = new VariantDict ();
+            props_dict.insert_value ("x", new Variant.int32 (monitor.x));
+            props_dict.insert_value ("y", new Variant.int32 (monitor.y));
+            props_dict.insert_value ("transform", new Variant.uint32 (monitor.transform));
+            props_dict.insert_value ("primary", new Variant.boolean (monitor.primary));
+            props_dict.insert_value ("enabled", new Variant.boolean (monitor.is_active));
+            monitor_dict.insert_value (monitor.id, props_dict.end ());
+        }
+
+        // Add or update the layouts setting
+        var layouts = settings.get_value (PREFERRED_MONITOR_LAYOUTS_KEY);
+        var layouts_dict = new VariantDict (layouts);
+        layouts_dict.insert_value (save_key, monitor_dict.end ());
+
+        // Save to settings
+        //NOTE The variant yielded by VariantDict.end () always has type "a{sv}"
+        settings.set_value (PREFERRED_MONITOR_LAYOUTS_KEY, layouts_dict.end ());
+    }
+
+    private string get_layout_key (Gee.LinkedList<VirtualMonitor> virtual_monitors) {
+        // Generate a unique key based on the virtual monitors' monitors hashes
+        //NOTE The key depends on the order of the list which will change depending on whether monitors are
+        // active or not (and possibly on the order they were connected).
+        //TODO Consider whether a more controlled key is needed
+        var key = new StringBuilder ();
+
+        foreach (var virtual_monitor in virtual_monitors) {
+            foreach (var monitor in virtual_monitor.monitors) {
+                key.append (virtual_monitor.id);
+            }
+        }
+
+        return key.str;
+    }
+}

src/Objects/MonitorManager.vala

@@ -46,8 +46,11 @@ public class Display.MonitorManager : GLib.Object {
         }
     }
 
+    public signal void monitors_changed ();
+
     private MutterDisplayConfigInterface iface;
     private uint current_serial;
+    private MonitorLayoutManager layout_manager;
 
     private static MonitorManager monitor_manager;
     public static unowned MonitorManager get_default () {
@@ -65,9 +68,16 @@ public class Display.MonitorManager : GLib.Object {
     construct {
         monitors = new Gee.LinkedList<Display.Monitor> ();
         virtual_monitors = new Gee.LinkedList<Display.VirtualMonitor> ();
+        layout_manager = new MonitorLayoutManager ();
         try {
-            iface = Bus.get_proxy_sync (BusType.SESSION, "org.gnome.Mutter.DisplayConfig", "/org/gnome/Mutter/DisplayConfig");
-            iface.monitors_changed.connect (get_monitor_config);
+            iface = Bus.get_proxy_sync (
+                BusType.SESSION,
+                "org.gnome.Mutter.DisplayConfig",
+                "/org/gnome/Mutter/DisplayConfig");
+            iface.monitors_changed.connect (() => {
+                get_monitor_config ();
+                monitors_changed ();
+            });
         } catch (Error e) {
             critical (e.message);
         }
@@ -78,7 +88,10 @@ public class Display.MonitorManager : GLib.Object {
         MutterReadLogicalMonitor[] mutter_logical_monitors;
         GLib.HashTable<string, GLib.Variant> properties;
         try {
-            iface.get_current_state (out current_serial, out mutter_monitors, out mutter_logical_monitors, out properties);
+            iface.get_current_state (out current_serial,
+                out mutter_monitors,
+                out mutter_logical_monitors,
+                out properties);
         } catch (Error e) {
             critical (e.message);
         }
@@ -217,7 +230,7 @@ public class Display.MonitorManager : GLib.Object {
             virtual_monitor.scale = mutter_logical_monitor.scale;
             virtual_monitor.transform = mutter_logical_monitor.transform;
             virtual_monitor.primary = mutter_logical_monitor.primary;
-            add_virtual_monitor (virtual_monitor);
+            virtual_monitors.add (virtual_monitor);
         }
 
         // Look for any monitors that aren't part of a virtual monitor (hence disabled)
@@ -237,9 +250,15 @@ public class Display.MonitorManager : GLib.Object {
                 virtual_monitor.primary = false;
                 virtual_monitor.monitors.add (monitor);
                 virtual_monitor.scale = virtual_monitors[0].scale;
-                add_virtual_monitor (virtual_monitor);
+                virtual_monitors.add (virtual_monitor);
             }
         }
+
+        if (!is_mirrored) {
+            layout_manager.save_layout (virtual_monitors);
+        }
+
+        layout_manager.arrange_monitors (virtual_monitors);
     }
 
     public void set_monitor_config () throws Error {
@@ -402,13 +421,10 @@ public class Display.MonitorManager : GLib.Object {
         virtual_monitors.clear ();
         virtual_monitors.add_all (new_virtual_monitors);
 
-        notify_property ("virtual-monitor-number");
-        notify_property ("is-mirrored");
-    }
+        layout_manager.arrange_monitors (virtual_monitors);
 
-    private void add_virtual_monitor (Display.VirtualMonitor virtual_monitor) {
-        virtual_monitors.add (virtual_monitor);
         notify_property ("virtual-monitor-number");
+        notify_property ("is-mirrored");
     }
 
     private VirtualMonitor? get_virtual_monitor_by_id (string id) {

src/Widgets/DisplaysOverlay.vala

@@ -97,6 +97,7 @@ public class Display.DisplaysOverlay : Gtk.Box {
                 gala_dbus = GLib.Bus.get_proxy.end (res);
                 monitor_manager = Display.MonitorManager.get_default ();
                 monitor_manager.notify["virtual-monitor-number"].connect (() => rescan_displays ());
+                monitor_manager.monitors_changed.connect (() => rescan_displays ());
                 rescan_displays ();
             } catch (GLib.Error e) {
                 critical (e.message);
@@ -185,7 +186,6 @@ public class Display.DisplaysOverlay : Gtk.Box {
 
     public void rescan_displays () {
         scanning = true;
-
         display_widgets.@foreach ((display_widget) => {
             overlay.remove_overlay (display_widget);
             display_widget.destroy ();
@@ -198,6 +198,7 @@ public class Display.DisplaysOverlay : Gtk.Box {
             add_output (virtual_monitor);
         }
 
+        show_windows ();
         change_active_displays_sensitivity ();
         calculate_ratio ();
         scanning = false;
@@ -350,10 +351,6 @@ public class Display.DisplaysOverlay : Gtk.Box {
             check_configuration_change ();
             calculate_ratio ();
         });
-
-        if (!monitor_manager.is_mirrored && virtual_monitor.is_active) {
-            show_windows ();
-        }
     }
 
     private void set_as_primary (Display.VirtualMonitor new_primary) {

src/meson.build

@@ -10,6 +10,7 @@ plug_files = files(
     'Objects/MonitorMode.vala',
     'Objects/MonitorManager.vala',
     'Objects/Monitor.vala',
+    'Objects/MonitorLayoutManager.vala',
     'Views/NightLightView.vala',
     'Views/DisplaysView.vala',
     'Views' / 'FiltersView.vala',