add xdg decoration, scene/tree factories, geometry + seat focus

more wrapper soup. xdg decoration manager, scene/tree node factories so
callers stop touching raw wlr_scene_*_create, a box geometry helper, and
seat pointer/keyboard focus clearing. dragging myself through it.

include/wlr/xdg_decoration.hpp

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: AGPL-3.0-only
+#pragma once
+
+#include <functional>
+
+#include "wlr/wlr.hpp"
+#include "wlr/display.hpp"
+#include "wlr/signals.hpp"
+#include "wlr/xdg_shell.hpp"
+
+namespace wlr {
+
+class XdgToplevelDecoration {
+public:
+	enum Mode { None = 0, ClientSide = 1, ServerSide = 2 };
+
+	XdgToplevelDecoration(struct wlr_xdg_toplevel_decoration_v1* d) : m_dec(d) {}
+	struct wlr_xdg_toplevel_decoration_v1* raw() const { return m_dec; }
+	explicit operator bool() const { return m_dec != nullptr; }
+
+	Mode current_mode() const { return static_cast<Mode>(m_dec->current.mode); }
+	Mode requested_mode() const { return static_cast<Mode>(m_dec->requested_mode); }
+	void set_mode(Mode m) {
+		wlr_xdg_toplevel_decoration_v1_set_mode(m_dec,
+			static_cast<enum wlr_xdg_toplevel_decoration_v1_mode>(m));
+	}
+
+	Toplevel toplevel() const { return Toplevel{m_dec->toplevel}; }
+
+	void on_request_mode(std::function<void(void*)> cb) {
+		m_request.connect(&m_dec->events.request_mode, std::move(cb));
+	}
+	void on_destroy(std::function<void(void*)> cb) {
+		m_destroy.connect(&m_dec->events.destroy, std::move(cb));
+	}
+
+private:
+	struct wlr_xdg_toplevel_decoration_v1* m_dec;
+	SignalSink m_request;
+	SignalSink m_destroy;
+};
+
+class XdgDecorationManager {
+public:
+	XdgDecorationManager(Display& d)
+		: m_mgr(wlr_xdg_decoration_manager_v1_create(d.raw())) {}
+	struct wlr_xdg_decoration_manager_v1* raw() const { return m_mgr; }
+	explicit operator bool() const { return m_mgr != nullptr; }
+
+	void on_new_toplevel_decoration(std::function<void(void*)> cb) {
+		m_new.connect(&m_mgr->events.new_toplevel_decoration, std::move(cb));
+	}
+
+private:
+	struct wlr_xdg_decoration_manager_v1* m_mgr;
+	SignalSink m_new;
+};
+
+}