1 files changed, 74 insertions, 0 deletions
diff --git a/crates/wayland/src/protocols/kde_decoration.rs b/crates/wayland/src/protocols/kde_decoration.rs
new file mode 100644
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--- /dev/null
+++ b/crates/wayland/src/protocols/kde_decoration.rs
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+//! `org_kde_kwin_server_decoration`: KDE's older decoration protocol, and
+//! the only decoration protocol GTK actually speaks.
+//!
+//! GTK has never implemented `xdg-decoration`. It does implement this one:
+//! `org_kde_kwin_server_decoration_manager` is present in libgtk-4 on this
+//! machine (confirmed by reading the library's own symbol strings), and it
+//! is how a KDE session gets GTK applications to stop drawing their own
+//! frame. A compositor that advertises only `xdg-decoration` is invisible
+//! to those clients, which is why "set the decoration once and every
+//! application follows" stopped at srdwm's own titlebars.
+//!
+//! Both protocols are advertised, and both answer with the same policy
+//! (`theme.default_decorated`, `theme.force_server_side`), so a client is
+//! told the same thing whichever one it asks through.
+//!
+//! The protocol's own warning applies here: a client may ignore the mode
+//! the compositor suggests and ask for its own. That is honoured the same
+//! way `xdg_decoration.rs` honours it, and for the same reason - a client
+//! that draws its own titlebar regardless (Firefox with its system-titlebar
+//! setting off) would otherwise get srdwm's row on top of its own.
+
+use smithay::reexports::wayland_protocols_misc::server_decoration::server::org_kde_kwin_server_decoration::{
+    Mode, OrgKdeKwinServerDecoration,
+};
+use smithay::reexports::wayland_server::protocol::wl_surface::WlSurface;
+use smithay::reexports::wayland_server::WEnum;
+use smithay::wayland::shell::kde::decoration::{KdeDecorationHandler, KdeDecorationState};
+
+use crate::state::CompState;
+
+impl KdeDecorationHandler for CompState {
+    fn kde_decoration_state(&self) -> &KdeDecorationState {
+        &self.kde_decoration_state
+    }
+
+    /// Tells a client, the moment it asks, which mode this compositor
+    /// wants - the same answer `XdgDecorationHandler::new_decoration`
+    /// gives through the other protocol.
+    ///
+    /// The manager's own default mode (set once, at startup) is what a
+    /// client sees before it creates a decoration object at all; this is
+    /// what it sees afterward, and it has to agree, or a client that reads
+    /// both ends up with two different answers.
+    fn new_decoration(&mut self, surface: &WlSurface, decoration: &OrgKdeKwinServerDecoration) {
+        let server = self.wm.borrow().theme.default_decorated;
+        decoration.mode(if server { Mode::Server } else { Mode::Client });
+        self.set_decorated_from_mode(surface, server);
+    }
+
+    /// Honours what the client asked for, unless `force_server_side` says
+    /// otherwise - identical policy to the xdg-decoration path, and the
+    /// mode is echoed back either way because the protocol requires the
+    /// compositor to confirm what it decided.
+    fn request_mode(&mut self, surface: &WlSurface, decoration: &OrgKdeKwinServerDecoration, mode: WEnum<Mode>) {
+        let WEnum::Value(requested) = mode else { return };
+        let forced = self.wm.borrow().theme.force_server_side;
+        // `Mode::None` means no decoration at all, which for srdwm's
+        // purposes is a client saying it wants nothing drawn around it --
+        // treated as client-side, the same as `Mode::Client`, rather than
+        // as a request for a titlebar.
+        let server = forced || requested == Mode::Server;
+        let granted = if server { Mode::Server } else { requested };
+        decoration.mode(granted);
+        self.set_decorated_from_mode(surface, server);
+    }
+
+    /// The client is going away, or has dropped its decoration object.
+    /// Nothing to undo: `remove_window` already clears everything keyed on
+    /// this surface, and a surface with no decoration object keeps
+    /// whatever mode it last negotiated, exactly as before.
+    fn release(&mut self, _decoration: &OrgKdeKwinServerDecoration, _surface: &WlSurface) {}
+}
+
+smithay::delegate_kde_decoration!(CompState);