Handle KDE decorations in Mapped::has_ssd

This fixes an issue with default CSD border being drawn for SSD
rendering firefox, because only xdg decorations were checked.

src/handlers/mod.rs

@@ -62,6 +62,7 @@ use smithay::{
     delegate_virtual_keyboard_manager, delegate_xdg_activation,
 };
 
+pub use crate::handlers::xdg_shell::KdeDecorationsModeState;
 use crate::niri::{ClientState, State};
 use crate::protocols::foreign_toplevel::{
     self, ForeignToplevelHandler, ForeignToplevelManagerState,

src/handlers/xdg_shell.rs

@@ -1,3 +1,5 @@
+use std::cell::Cell;
+
 use smithay::desktop::{
     find_popup_root_surface, get_popup_toplevel_coords, layer_map_for_output, utils, LayerSurface,
     PopupKeyboardGrab, PopupKind, PopupManager, PopupPointerGrab, PopupUngrabStrategy, Window,
@@ -8,10 +10,11 @@ use smithay::output::Output;
 use smithay::reexports::wayland_protocols::xdg::decoration::zv1::server::zxdg_toplevel_decoration_v1;
 use smithay::reexports::wayland_protocols::xdg::shell::server::xdg_positioner::ConstraintAdjustment;
 use smithay::reexports::wayland_protocols::xdg::shell::server::xdg_toplevel::{self};
+use smithay::reexports::wayland_protocols_misc::server_decoration::server::org_kde_kwin_server_decoration;
 use smithay::reexports::wayland_server::protocol::wl_output;
 use smithay::reexports::wayland_server::protocol::wl_seat::WlSeat;
 use smithay::reexports::wayland_server::protocol::wl_surface::WlSurface;
-use smithay::reexports::wayland_server::Resource;
+use smithay::reexports::wayland_server::{self, Resource, WEnum};
 use smithay::utils::{Logical, Rectangle, Serial};
 use smithay::wayland::compositor::{
     add_pre_commit_hook, with_states, BufferAssignment, HookId, SurfaceAttributes,
@@ -544,10 +547,44 @@ impl XdgDecorationHandler for State {
 }
 delegate_xdg_decoration!(State);
 
+/// Whether KDE server decorations are in use.
+#[derive(Default)]
+pub struct KdeDecorationsModeState {
+    server: Cell<bool>,
+}
+
+impl KdeDecorationsModeState {
+    pub fn is_server(&self) -> bool {
+        self.server.get()
+    }
+}
+
 impl KdeDecorationHandler for State {
     fn kde_decoration_state(&self) -> &KdeDecorationState {
         &self.niri.kde_decoration_state
     }
+
+    fn request_mode(
+        &mut self,
+        surface: &WlSurface,
+        decoration: &org_kde_kwin_server_decoration::OrgKdeKwinServerDecoration,
+        mode: wayland_server::WEnum<org_kde_kwin_server_decoration::Mode>,
+    ) {
+        let WEnum::Value(mode) = mode else {
+            return;
+        };
+
+        decoration.mode(mode);
+
+        with_states(surface, |states| {
+            let state = states
+                .data_map
+                .get_or_insert(KdeDecorationsModeState::default);
+            state
+                .server
+                .set(mode == org_kde_kwin_server_decoration::Mode::Server);
+        });
+    }
 }
 delegate_kde_decoration!(State);
 

src/window/mapped.rs

@@ -17,6 +17,7 @@ use smithay::wayland::compositor::{remove_pre_commit_hook, with_states, HookId};
 use smithay::wayland::shell::xdg::{SurfaceCachedState, ToplevelSurface};
 
 use super::{ResolvedWindowRules, WindowRef};
+use crate::handlers::KdeDecorationsModeState;
 use crate::layout::{
     InteractiveResizeData, LayoutElement, LayoutElementRenderElement, LayoutElementRenderSnapshot,
 };
@@ -422,8 +423,21 @@ impl LayoutElement for Mapped {
     }
 
     fn has_ssd(&self) -> bool {
-        self.toplevel().current_state().decoration_mode
-            == Some(zxdg_toplevel_decoration_v1::Mode::ServerSide)
+        let toplevel = self.toplevel();
+        let mode = toplevel.current_state().decoration_mode;
+
+        match mode {
+            Some(zxdg_toplevel_decoration_v1::Mode::ServerSide) => true,
+            // Check KDE decorations when XDG are not in use.
+            None => with_states(toplevel.wl_surface(), |states| {
+                states
+                    .data_map
+                    .get::<KdeDecorationsModeState>()
+                    .map(KdeDecorationsModeState::is_server)
+                    == Some(true)
+            }),
+            _ => false,
+        }
     }
 
     fn output_enter(&self, output: &Output) {