Put Greeter below all windows

protocol/pantheon-desktop-shell-v1.xml

@@ -35,6 +35,14 @@
       <arg name="output" type="new_id" interface="io_elementary_pantheon_extended_behavior_v1"/>
       <arg name="surface" type="object" interface="wl_surface"/>
     </request>
+
+    <request name="get_greeter">
+      <description summary="create a greeter surface from a surface">
+        Create a greeter surface from an existing surface.
+      </description>
+      <arg name="output" type="new_id" interface="io_elementary_pantheon_greeter_v1"/>
+      <arg name="surface" type="object" interface="wl_surface"/>
+    </request>
   </interface>
 
   <interface name="io_elementary_pantheon_panel_v1" version="1">
@@ -169,4 +177,15 @@
       <arg name="monitor_index" type="int" summary="the index of the monitor this surface should label"/>
     </request>
   </interface>
+
+  <interface name="io_elementary_pantheon_greeter_v1" version="1">
+    <request name="destroy" type="destructor"/>
+
+    <request name="make_greeter">
+      <description summary="make greeter">
+        Request to make the surface a Greeter window, which will be displayed bellow other windows
+        when running in greeter compositor mode.
+      </description>
+    </request>
+  </interface>
 </protocol>

protocol/pantheon-desktop-shell.vapi

@@ -1,5 +1,5 @@
 /*
- * Copyright 2023 elementary, Inc. <https://elementary.io>
+ * Copyright 2023-2026 elementary, Inc. <https://elementary.io>
  * Copyright 2023 Corentin Noël <tintou@noel.tf>
  * SPDX-License-Identifier: GPL-3.0-or-later
  */
@@ -12,7 +12,7 @@ namespace Pantheon.Desktop {
         public Pantheon.Desktop.GetPanel get_panel;
         public Pantheon.Desktop.GetWidget get_widget;
         public Pantheon.Desktop.GetExtendedBehavior get_extended_behavior;
-
+        public Pantheon.Desktop.GetGreeter get_greeter;
     }
 
     [CCode (cheader_filename = "pantheon-desktop-shell-server-protocol.h", cname = "enum io_elementary_pantheon_panel_v1_anchor", cprefix="IO_ELEMENTARY_PANTHEON_PANEL_V1_ANCHOR_", has_type_id = false)]
@@ -65,13 +65,23 @@ namespace Pantheon.Desktop {
         public MakeMonitorLabel make_monitor_label;
     }
 
+    [CCode (cheader_filename = "pantheon-desktop-shell-server-protocol.h", cname = "struct io_elementary_pantheon_greeter_v1_interface")]
+    public struct GreeterInterface {
+        [CCode (cheader_filename = "pantheon-desktop-shell-server-protocol.h", cname = "io_elementary_pantheon_greeter_v1_interface")]
+        public static Wl.Interface iface;
+        public Destroy destroy;
+        public MakeGreeter make_greeter;
+    }
+
     [CCode (has_target = false, has_typedef = false)]
     public delegate void GetPanel (Wl.Client client, Wl.Resource resource, uint32 output, Wl.Resource surface);
     [CCode (has_target = false, has_typedef = false)]
     public delegate void GetWidget (Wl.Client client, Wl.Resource resource, uint32 output, Wl.Resource surface);
     [CCode (has_target = false, has_typedef = false)]
     public delegate void GetExtendedBehavior (Wl.Client client, Wl.Resource resource, uint32 output, Wl.Resource surface);
     [CCode (has_target = false, has_typedef = false)]
+    public delegate void GetGreeter (Wl.Client client, Wl.Resource resource, uint32 output, Wl.Resource surface);
+    [CCode (has_target = false, has_typedef = false)]
     public delegate void SetAnchor (Wl.Client client, Wl.Resource resource, [CCode (type = "uint32_t")] Anchor anchor);
     [CCode (has_target = false, has_typedef = false)]
     public delegate void Focus (Wl.Client client, Wl.Resource resource);
@@ -94,5 +104,7 @@ namespace Pantheon.Desktop {
     [CCode (has_target = false, has_typedef = false)]
     public delegate void MakeMonitorLabel (Wl.Client client, Wl.Resource resource, int monitor_index);
     [CCode (has_target = false, has_typedef = false)]
+    public delegate void MakeGreeter (Wl.Client client, Wl.Resource resource);
+    [CCode (has_target = false, has_typedef = false)]
     public delegate void Destroy (Wl.Client client, Wl.Resource resource);
 }

src/PantheonShell.vala

@@ -18,6 +18,7 @@ namespace Gala {
     private static Pantheon.Desktop.PanelInterface wayland_pantheon_panel_interface;
     private static Pantheon.Desktop.WidgetInterface wayland_pantheon_widget_interface;
     private static Pantheon.Desktop.ExtendedBehaviorInterface wayland_pantheon_extended_behavior_interface;
+    private static Pantheon.Desktop.GreeterInterface wayland_pantheon_greeter_interface;
     private static Wl.Global shell_global;
 
     public void init_pantheon_shell (Meta.Context context) {
@@ -31,6 +32,7 @@ namespace Gala {
             get_panel,
             get_widget,
             get_extended_behavior,
+            get_greeter,
         };
 
         wayland_pantheon_panel_interface = {
@@ -57,9 +59,15 @@ namespace Gala {
             make_monitor_label,
         };
 
+        wayland_pantheon_greeter_interface = {
+            destroy_greeter_surface,
+            make_greeter,
+        };
+
         PanelSurface.quark = GLib.Quark.from_string ("-gala-wayland-panel-surface-data");
         WidgetSurface.quark = GLib.Quark.from_string ("-gala-wayland-widget-surface-data");
         ExtendedBehaviorSurface.quark = GLib.Quark.from_string ("-gala-wayland-extended-behavior-surface-data");
+        GreeterSurface.quark = GLib.Quark.from_string ("-gala-wayland-greeter-surface-data");
 
         shell_global = Wl.Global.create (wl_disp, ref Pantheon.Desktop.ShellInterface.iface, 1, (client, version, id) => {
             unowned var resource = client.create_resource (ref Pantheon.Desktop.ShellInterface.iface, (int) version, id);
@@ -124,6 +132,25 @@ namespace Gala {
         }
     }
 
+    public class GreeterSurface : GLib.Object {
+        public static GLib.Quark quark = 0;
+        public unowned GLib.Object? wayland_surface;
+
+        public GreeterSurface (GLib.Object wayland_surface) {
+            this.wayland_surface = wayland_surface;
+        }
+
+        ~GreeterSurface () {
+            if (wayland_surface != null) {
+                wayland_surface.steal_qdata<unowned GLib.Object> (quark);
+            }
+        }
+
+        public void on_wayland_surface_disposed () {
+            wayland_surface = null;
+        }
+    }
+
     static void unref_obj_on_destroy (Wl.Resource resource) {
         resource.get_user_data<GLib.Object> ().unref ();
     }
@@ -215,6 +242,35 @@ namespace Gala {
         );
     }
 
+    internal static void get_greeter (Wl.Client client, Wl.Resource resource, uint32 output, Wl.Resource surface_resource) {
+        unowned GLib.Object? wayland_surface = surface_resource.get_user_data<GLib.Object> ();
+        GreeterSurface? greeter_surface = wayland_surface.get_qdata (GreeterSurface.quark);
+        if (greeter_surface != null) {
+            surface_resource.post_error (
+                Wl.DisplayError.INVALID_OBJECT,
+                "io_elementary_pantheon_shell_v1_interface::get_greeter already requested"
+            );
+            return;
+        }
+
+        greeter_surface = new GreeterSurface (wayland_surface);
+        unowned var greeter_resource = client.create_resource (
+            ref Pantheon.Desktop.GreeterInterface.iface,
+            resource.get_version (),
+            output
+        );
+        greeter_resource.set_implementation (
+            &wayland_pantheon_greeter_interface,
+            greeter_surface.ref (),
+            unref_obj_on_destroy
+        );
+        wayland_surface.set_qdata_full (
+            GreeterSurface.quark,
+            greeter_surface,
+            (GLib.DestroyNotify) GreeterSurface.on_wayland_surface_disposed
+        );
+    }
+
     internal static void set_anchor (Wl.Client client, Wl.Resource resource, [CCode (type = "uint32_t")] Pantheon.Desktop.Anchor anchor) {
         unowned PanelSurface? panel_surface = resource.get_user_data<PanelSurface> ();
         if (panel_surface.wayland_surface == null) {
@@ -408,6 +464,23 @@ namespace Gala {
         ShellClientsManager.get_instance ().make_monitor_label (window, monitor_index);
     }
 
+    internal static void make_greeter (Wl.Client client, Wl.Resource resource) {
+        unowned GreeterSurface? greeter_surface = resource.get_user_data<GreeterSurface> ();
+        if (greeter_surface.wayland_surface == null) {
+            warning ("Window tried to make greeter but wayland surface is null.");
+            return;
+        }
+
+        Meta.Window? window;
+        greeter_surface.wayland_surface.get ("window", out window, null);
+        if (window == null) {
+            warning ("Window tried to make greeter but wayland surface had no associated window.");
+            return;
+        }
+
+        ShellClientsManager.get_instance ().make_greeter (window);
+    }
+
     internal static void destroy_panel_surface (Wl.Client client, Wl.Resource resource) {
         resource.destroy ();
     }
@@ -419,4 +492,8 @@ namespace Gala {
     internal static void destroy_extended_behavior_surface (Wl.Client client, Wl.Resource resource) {
         resource.destroy ();
     }
+
+    internal static void destroy_greeter_surface (Wl.Client client, Wl.Resource resource) {
+        resource.destroy ();
+    }
 }

src/ShellClients/ShellClientsManager.vala

@@ -138,7 +138,7 @@ public class Gala.ShellClientsManager : Object, GestureTarget {
         }
     }
 
-    public void make_dock (Meta.Window window) {
+    private void make_dock (Meta.Window window) {
 #if HAS_MUTTER49
         window.set_type (Meta.WindowType.DOCK);
 #else
@@ -182,6 +182,31 @@ public class Gala.ShellClientsManager : Object, GestureTarget {
     }
 #endif
 
+    private void make_desktop (Meta.Window window) {
+#if HAS_MUTTER49
+        window.set_type (Meta.WindowType.DESKTOP);
+#else
+        if (Meta.Util.is_wayland_compositor ()) {
+            make_desktop_wayland (window);
+        } else {
+            critical ("Making desktop window on X11 is not supported.");
+        }
+#endif
+    }
+
+#if !HAS_MUTTER49
+    private void make_desktop_wayland (Meta.Window window) requires (Meta.Util.is_wayland_compositor ()) {
+        foreach (var client in protocol_clients) {
+            if (client.wayland_client.owns_window (window)) {
+#if HAS_MUTTER46
+                client.wayland_client.make_desktop (window);
+#endif
+                break;
+            }
+        }
+    }
+#endif
+
     public void set_anchor (Meta.Window window, Pantheon.Desktop.Anchor anchor) {
         if (window in panel_windows) {
             panel_windows[window].anchor = anchor;
@@ -290,6 +315,12 @@ public class Gala.ShellClientsManager : Object, GestureTarget {
         window.unmanaged.connect_after (() => ibus_candidate_window = null);
     }
 
+    public void make_greeter (Meta.Window window) {
+        make_desktop (window);
+
+        wm.override_window_group (window, LOCK_SCREEN);
+    }
+
     public void propagate (UpdateType update_type, GestureAction action, double progress) {
         foreach (var window in positioned_windows.get_values ()) {
             window.propagate (update_type, action, progress);