diff --git a/include/desktop/desktop.h b/include/desktop/desktop.h
index 17f7bdd..c0dafc9 100644
--- a/include/desktop/desktop.h
+++ b/include/desktop/desktop.h
@@ -29,10 +29,14 @@ struct kiwmi_desktop {
     struct {
         struct wl_signal new_output;
         struct wl_signal view_map;
+        struct wl_signal request_active_output;
     } events;
 };
 
 bool desktop_init(struct kiwmi_desktop *desktop, struct wlr_renderer *renderer);
 void desktop_fini(struct kiwmi_desktop *desktop);
 
+struct kiwmi_server;
+struct kiwmi_output *desktop_active_output(struct kiwmi_server *server);
+
 #endif /* KIWMI_DESKTOP_DESKTOP_H */
diff --git a/include/luak/luak.h b/include/luak/luak.h
index a35ad55..e1322a2 100644
--- a/include/luak/luak.h
+++ b/include/luak/luak.h
@@ -37,6 +37,7 @@ struct kiwmi_object {
     } events;
 };
 
+void *luaK_toudata(lua_State *L, int ud, const char *tname);
 int luaK_kiwmi_object_gc(lua_State *L);
 struct kiwmi_object *luaK_get_kiwmi_object(
     struct kiwmi_lua *lua,
diff --git a/kiwmi/desktop/desktop.c b/kiwmi/desktop/desktop.c
index 81d93b4..37c5e95 100644
--- a/kiwmi/desktop/desktop.c
+++ b/kiwmi/desktop/desktop.c
@@ -12,6 +12,7 @@
 #include <wayland-server.h>
 #include <wlr/backend.h>
 #include <wlr/types/wlr_compositor.h>
+#include <wlr/types/wlr_cursor.h>
 #include <wlr/types/wlr_data_device.h>
 #include <wlr/types/wlr_export_dmabuf_v1.h>
 #include <wlr/types/wlr_layer_shell_v1.h>
@@ -22,7 +23,10 @@
 
 #include "desktop/layer_shell.h"
 #include "desktop/output.h"
+#include "desktop/view.h"
 #include "desktop/xdg_shell.h"
+#include "input/cursor.h"
+#include "input/input.h"
 #include "server.h"
 
 bool
@@ -67,6 +71,7 @@ desktop_init(struct kiwmi_desktop *desktop, struct wlr_renderer *renderer)
 
     wl_signal_init(&desktop->events.new_output);
     wl_signal_init(&desktop->events.view_map);
+    wl_signal_init(&desktop->events.request_active_output);
 
     return true;
 }
@@ -76,3 +81,37 @@ desktop_fini(struct kiwmi_desktop *desktop)
 {
     wlr_output_layout_destroy(desktop->output_layout);
 }
+
+struct kiwmi_output *
+desktop_active_output(struct kiwmi_server *server)
+{
+    // 1. callback (request_active_output)
+    struct kiwmi_output *output = NULL;
+    wl_signal_emit(&server->desktop.events.request_active_output, &output);
+
+    if (output) {
+        return output;
+    }
+
+
+    // 2. focused view center
+    if (!wl_list_empty(&server->desktop.views)) {
+        struct kiwmi_view *view;
+        wl_list_for_each (view, &server->desktop.views, link) {
+            break; // get first element of list
+        }
+
+        double lx = view->geom.x + view->geom.width / 2;
+        double ly = view->geom.y + view->geom.height / 2;
+
+        struct wlr_output *wlr_output = wlr_output_layout_output_at(server->desktop.output_layout, lx, ly);
+        return wlr_output->data;
+    }
+
+    // 3. cursor
+    double lx = server->input.cursor->cursor->x;
+    double ly = server->input.cursor->cursor->y;
+
+    struct wlr_output *wlr_output = wlr_output_layout_output_at(server->desktop.output_layout, lx, ly);
+    return wlr_output->data;
+}
diff --git a/kiwmi/desktop/layer_shell.c b/kiwmi/desktop/layer_shell.c
index 4965818..acef7d2 100644
--- a/kiwmi/desktop/layer_shell.c
+++ b/kiwmi/desktop/layer_shell.c
@@ -351,13 +351,9 @@ layer_shell_new_surface_notify(struct wl_listener *listener, void *data)
         layer_surface->namespace);
 
     if (!layer_surface->output) {
-        // TODO: assign active output
-        wlr_log(WLR_ERROR, "TODO: assign active output");
-        struct kiwmi_output *output;
-        wl_list_for_each (output, &desktop->outputs, link) {
-            layer_surface->output = output->wlr_output;
-            break;
-        }
+        struct kiwmi_server *server =
+            wl_container_of(desktop, server, desktop);
+        layer_surface->output = desktop_active_output(server)->wlr_output;
     }
 
     struct kiwmi_layer *layer = malloc(sizeof(*layer));
diff --git a/kiwmi/luak/kiwmi_server.c b/kiwmi/luak/kiwmi_server.c
index 71a0b6c..ef05394 100644
--- a/kiwmi/luak/kiwmi_server.c
+++ b/kiwmi/luak/kiwmi_server.c
@@ -305,6 +305,39 @@ kiwmi_server_on_output_notify(struct wl_listener *listener, void *data)
     }
 }
 
+static void
+kiwmi_server_on_request_active_output_notify(struct wl_listener *listener, void *data)
+{
+    struct kiwmi_lua_callback *lc = wl_container_of(listener, lc, listener);
+    struct kiwmi_server *server   = lc->server;
+    lua_State *L                  = server->lua->L;
+    struct kiwmi_output **output  = data;
+
+    lua_rawgeti(L, LUA_REGISTRYINDEX, lc->callback_ref);
+    if (lua_pcall(L, 0, 1, 0)) {
+        wlr_log(WLR_ERROR, "%s", lua_tostring(L, -1));
+        return;
+    }
+
+    if (!lua_isnil(L, -1)) {
+        struct kiwmi_object *obj;
+        struct kiwmi_object **objp;
+        if (!(objp = luaK_toudata(L, -1, "kiwmi_output"))) {
+            wlr_log(WLR_ERROR, "kiwmi_output expected, got %s", luaL_typename(L, -1));
+            return;
+        }
+
+        obj = *objp;
+
+        if (!obj->valid) {
+            wlr_log(WLR_ERROR, "kiwmi_output no longer valid");
+            return;
+        }
+
+        *output = obj->object;
+    }
+}
+
 static void
 kiwmi_server_on_view_notify(struct wl_listener *listener, void *data)
 {
@@ -378,6 +411,30 @@ l_kiwmi_server_on_output(lua_State *L)
     return 0;
 }
 
+static int
+l_kiwmi_server_on_request_active_output(lua_State *L)
+{
+    struct kiwmi_object *obj =
+        *(struct kiwmi_object **)luaL_checkudata(L, 1, "kiwmi_server");
+    luaL_checktype(L, 2, LUA_TFUNCTION);
+
+    struct kiwmi_server *server = obj->object;
+
+    lua_pushcfunction(L, luaK_kiwmi_lua_callback_new);
+    lua_pushlightuserdata(L, server);
+    lua_pushvalue(L, 2);
+    lua_pushlightuserdata(L, kiwmi_server_on_request_active_output_notify);
+    lua_pushlightuserdata(L, &server->desktop.events.request_active_output);
+    lua_pushlightuserdata(L, obj);
+
+    if (lua_pcall(L, 5, 0, 0)) {
+        wlr_log(WLR_ERROR, "%s", lua_tostring(L, -1));
+        return 0;
+    }
+
+    return 0;
+}
+
 static int
 l_kiwmi_server_on_view(lua_State *L)
 {
@@ -405,6 +462,7 @@ l_kiwmi_server_on_view(lua_State *L)
 static const luaL_Reg kiwmi_server_events[] = {
     {"keyboard", l_kiwmi_server_on_keyboard},
     {"output", l_kiwmi_server_on_output},
+    {"request_active_output", l_kiwmi_server_on_request_active_output},
     {"view", l_kiwmi_server_on_view},
     {NULL, NULL},
 };
diff --git a/kiwmi/luak/luak.c b/kiwmi/luak/luak.c
index 8d7748d..2a7e7b6 100644
--- a/kiwmi/luak/luak.c
+++ b/kiwmi/luak/luak.c
@@ -22,6 +22,22 @@
 #include "luak/kiwmi_server.h"
 #include "luak/kiwmi_view.h"
 
+void *
+luaK_toudata(lua_State *L, int ud, const char *tname)
+{
+    void *p = lua_touserdata(L, ud);
+    if (p != NULL) {  /* value is a userdata? */
+        if (lua_getmetatable(L, ud)) {  /* does it have a metatable? */
+            lua_getfield(L, LUA_REGISTRYINDEX, tname);  /* get correct metatable */
+            if (lua_rawequal(L, -1, -2)) {  /* does it have the correct mt? */
+                lua_pop(L, 2);  /* remove both metatables */
+                return p;
+            }
+        }
+    }
+    return NULL;
+}
+
 int
 luaK_kiwmi_object_gc(lua_State *L)
 {
diff --git a/lua_docs.md b/lua_docs.md
index 8434097..1ec953b 100644
--- a/lua_docs.md
+++ b/lua_docs.md
@@ -58,6 +58,13 @@ Get the view at a specified position.
 A new keyboard got attached.
 Callback receives a reference to the keyboard.
 
+#### request_active_output
+
+Called when the active output needs to be requested (for example because a layer-shell surface needs to be positioned).
+Callback receives nothing and optionally returns a kiwmi_output.
+
+If this isn't set or returns `nil`, the compositor defaults to the output the focused view is on, and if there is no view, the output the mouse is on.
+
 #### output
 
 A new output got attached.