Allow pop-up grabs for bottom and background layers

src/handlers/xdg_shell.rs

@@ -289,6 +289,7 @@ impl XdgShellHandler for State {
 
         let popup = PopupKind::Xdg(surface);
         let Ok(root) = find_popup_root_surface(&popup) else {
+            trace!("ignoring popup grab because no root surface");
             return;
         };
 
@@ -297,30 +298,30 @@ impl XdgShellHandler for State {
         // keyboard focus being at the wrong place.
         if self.niri.is_locked() {
             if Some(&root) != self.niri.lock_surface_focus().as_ref() {
+                trace!("ignoring popup grab because the session is locked");
                 let _ = PopupManager::dismiss_popup(&root, &popup);
                 return;
             }
         } else if self.niri.screenshot_ui.is_open() {
+            trace!("ignoring popup grab because the screenshot UI is open");
             let _ = PopupManager::dismiss_popup(&root, &popup);
             return;
         } else if let Some(output) = self.niri.layout.active_output() {
             let layers = layer_map_for_output(output);
 
-            if let Some(layer_surface) =
-                layers.layer_for_surface(&root, WindowSurfaceType::TOPLEVEL)
+            if layers
+                .layer_for_surface(&root, WindowSurfaceType::TOPLEVEL)
+                .is_none()
             {
-                if !matches!(layer_surface.layer(), Layer::Overlay | Layer::Top) {
-                    let _ = PopupManager::dismiss_popup(&root, &popup);
-                    return;
-                }
+                // This is a grab for a regular window; check that there's no layer surface with a
+                // higher input priority.
 
-                // FIXME: popup grabs for on-demand bottom and background layers.
-            } else {
                 if layers.layers_on(Layer::Overlay).any(|l| {
                     l.cached_state().keyboard_interactivity
                         == wlr_layer::KeyboardInteractivity::Exclusive
                         || Some(l) == self.niri.layer_shell_on_demand_focus.as_ref()
                 }) {
+                    trace!("ignoring toplevel popup grab because the overlay layer has focus");
                     let _ = PopupManager::dismiss_popup(&root, &popup);
                     return;
                 }
@@ -333,28 +334,35 @@ impl XdgShellHandler for State {
                             || Some(l) == self.niri.layer_shell_on_demand_focus.as_ref()
                     })
                 {
+                    trace!("ignoring toplevel popup grab because the top layer has focus");
                     let _ = PopupManager::dismiss_popup(&root, &popup);
                     return;
                 }
 
                 let layout_focus = self.niri.layout.focus();
                 if Some(&root) != layout_focus.map(|win| win.toplevel().wl_surface()) {
+                    trace!("ignoring toplevel popup grab because another window has focus");
                     let _ = PopupManager::dismiss_popup(&root, &popup);
                     return;
                 }
             }
         } else {
+            trace!("ignoring popup grab because no output is active");
             let _ = PopupManager::dismiss_popup(&root, &popup);
             return;
         }
 
         let seat = &self.niri.seat;
-        let Ok(mut grab) = self
+        let mut grab = match self
             .niri
             .popups
             .grab_popup(root.clone(), popup, seat, serial)
-        else {
-            return;
+        {
+            Ok(grab) => grab,
+            Err(err) => {
+                trace!("ignoring popup grab: {err:?}");
+                return;
+            }
         };
 
         let keyboard = seat.get_keyboard().unwrap();
@@ -380,6 +388,7 @@ impl XdgShellHandler for State {
             && !(pointer.has_grab(serial)
                 || grab.previous_serial().map_or(true, |s| pointer.has_grab(s)));
         if (can_receive_keyboard_focus && keyboard_grab_mismatches) || pointer_grab_mismatches {
+            trace!("ignoring popup grab because of current grab mismatch");
             grab.ungrab(PopupUngrabStrategy::All);
             return;
         }

src/niri.rs

@@ -920,6 +920,8 @@ impl State {
             // fullscreen layout window. This will need tracking in grab() to avoid handing it out
             // in the first place. Or a better way to structure this code.
             surface = surface.or_else(|| grab_on_layer(Layer::Top));
+            surface = surface.or_else(|| grab_on_layer(Layer::Bottom));
+            surface = surface.or_else(|| grab_on_layer(Layer::Background));
 
             surface = surface.or_else(|| focus_on_layer(Layer::Overlay));