Add prefer-no-csd option

resources/default-config.kdl

@@ -56,6 +56,10 @@ focus-ring {
     inactive-color 0.3 0.3 0.3 1.0
 }
 
+// Uncomment this line to ask the clients to omit their client-side decorations if possible.
+// If the client will specifically ask for CSD, the request will be honored.
+// prefer-no-csd
+
 binds {
     // Keys consist of modifiers separated by + signs, followed by an XKB key name
     // in the end. To find an XKB name for a particular key, you may use a program

src/config.rs

@@ -19,6 +19,8 @@ pub struct Config {
     #[knuffel(child, default)]
     pub focus_ring: FocusRing,
     #[knuffel(child, default)]
+    pub prefer_no_csd: bool,
+    #[knuffel(child, default)]
     pub binds: Binds,
     #[knuffel(child, default)]
     pub debug: DebugConfig,
@@ -350,6 +352,8 @@ mod tests {
                 inactive-color 1.0 0.5 0.25 0.0
             }
 
+            prefer-no-csd
+
             binds {
                 Mod+T { spawn "alacritty"; }
                 Mod+Q { close-window; }
@@ -403,6 +407,7 @@ mod tests {
                         a: 0.,
                     },
                 },
+                prefer_no_csd: true,
                 binds: Binds(vec![
                     Bind {
                         key: Key {

src/handlers/xdg_shell.rs

@@ -1,16 +1,18 @@
-use smithay::delegate_xdg_shell;
 use smithay::desktop::{find_popup_root_surface, PopupKind, Window};
 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_toplevel::{self, ResizeEdge};
 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::utils::Serial;
 use smithay::wayland::compositor::with_states;
+use smithay::wayland::shell::xdg::decoration::XdgDecorationHandler;
 use smithay::wayland::shell::xdg::{
     PopupSurface, PositionerState, ToplevelSurface, XdgPopupSurfaceData, XdgShellHandler,
     XdgShellState, XdgToplevelSurfaceData,
 };
+use smithay::{delegate_xdg_decoration, delegate_xdg_shell};
 
 use crate::layout::{configure_new_window, output_size};
 use crate::niri::State;
@@ -164,6 +166,40 @@ impl XdgShellHandler for State {
 
 delegate_xdg_shell!(State);
 
+impl XdgDecorationHandler for State {
+    fn new_decoration(&mut self, toplevel: ToplevelSurface) {
+        let mode = if self.niri.config.borrow().prefer_no_csd {
+            Some(zxdg_toplevel_decoration_v1::Mode::ServerSide)
+        } else {
+            None
+        };
+        toplevel.with_pending_state(|state| {
+            state.decoration_mode = mode;
+        });
+        toplevel.send_configure();
+    }
+
+    fn request_mode(&mut self, toplevel: ToplevelSurface, mode: zxdg_toplevel_decoration_v1::Mode) {
+        toplevel.with_pending_state(|state| {
+            state.decoration_mode = Some(mode);
+        });
+        toplevel.send_configure();
+    }
+
+    fn unset_mode(&mut self, toplevel: ToplevelSurface) {
+        let mode = if self.niri.config.borrow().prefer_no_csd {
+            Some(zxdg_toplevel_decoration_v1::Mode::ServerSide)
+        } else {
+            None
+        };
+        toplevel.with_pending_state(|state| {
+            state.decoration_mode = mode;
+        });
+        toplevel.send_configure();
+    }
+}
+delegate_xdg_decoration!(State);
+
 pub fn send_initial_configure_if_needed(window: &Window) {
     let initial_configure_sent = with_states(window.toplevel().wl_surface(), |states| {
         states

src/niri.rs

@@ -54,6 +54,7 @@ use smithay::wayland::output::OutputManagerState;
 use smithay::wayland::pointer_gestures::PointerGesturesState;
 use smithay::wayland::presentation::PresentationState;
 use smithay::wayland::shell::wlr_layer::{Layer, WlrLayerShellState};
+use smithay::wayland::shell::xdg::decoration::XdgDecorationState;
 use smithay::wayland::shell::xdg::XdgShellState;
 use smithay::wayland::shm::ShmState;
 use smithay::wayland::socket::ListeningSocketSource;
@@ -94,6 +95,7 @@ pub struct Niri {
     // Smithay state.
     pub compositor_state: CompositorState,
     pub xdg_shell_state: XdgShellState,
+    pub xdg_decoration_state: XdgDecorationState,
     pub layer_shell_state: WlrLayerShellState,
     pub shm_state: ShmState,
     pub output_manager_state: OutputManagerState,
@@ -213,6 +215,7 @@ impl Niri {
             &display_handle,
             [WmCapabilities::Fullscreen],
         );
+        let xdg_decoration_state = XdgDecorationState::new::<State>(&display_handle);
         let layer_shell_state = WlrLayerShellState::new::<State>(&display_handle);
         let shm_state = ShmState::new::<State>(&display_handle, vec![]);
         let output_manager_state =
@@ -563,6 +566,7 @@ impl Niri {
 
             compositor_state,
             xdg_shell_state,
+            xdg_decoration_state,
             layer_shell_state,
             shm_state,
             output_manager_state,