Implement output auto-selection in rootston

include/rootston/input.h

@@ -30,4 +30,6 @@ bool input_view_has_focus(struct roots_input *input, struct roots_view *view);
 
 struct roots_seat *input_get_seat(struct roots_input *input, char *name);
 
+struct roots_seat *input_last_active_seat(struct roots_input *input);
+
 #endif

rootston/desktop.c

@@ -326,13 +326,7 @@ bool view_center(struct roots_view *view) {
 
 	struct roots_desktop *desktop = view->desktop;
 	struct roots_input *input = desktop->server->input;
-	struct roots_seat *seat = NULL, *_seat;
-	wl_list_for_each(_seat, &input->seats, link) {
-		if (!seat || (seat->seat->last_event.tv_sec > _seat->seat->last_event.tv_sec &&
-				seat->seat->last_event.tv_nsec > _seat->seat->last_event.tv_nsec)) {
-			seat = _seat;
-		}
-	}
+	struct roots_seat *seat = input_last_active_seat(input);
 	if (!seat) {
 		return false;
 	}

rootston/layer_shell.c

@@ -312,6 +312,18 @@ void handle_layer_shell_surface(struct wl_listener *listener, void *data) {
 		return;
 	}
 
+	if (!layer_surface->output) {
+		struct roots_input *input = desktop->server->input;
+		struct roots_seat *seat = input_last_active_seat(input);
+		assert(seat); // Technically speaking we should handle this case
+		struct wlr_output *output =
+			wlr_output_layout_output_at(desktop->layout,
+					seat->cursor->cursor->x,
+					seat->cursor->cursor->y);
+		assert(output); // And this one
+		layer_surface->output = output;
+	}
+
 	roots_surface->surface_commit.notify = handle_surface_commit;
 	wl_signal_add(&layer_surface->surface->events.commit,
 		&roots_surface->surface_commit);

rootston/seat.c

@@ -999,3 +999,14 @@ void roots_seat_end_compositor_grab(struct roots_seat *seat) {
 
 	cursor->mode = ROOTS_CURSOR_PASSTHROUGH;
 }
+
+struct roots_seat *input_last_active_seat(struct roots_input *input) {
+	struct roots_seat *seat = NULL, *_seat;
+	wl_list_for_each(_seat, &input->seats, link) {
+		if (!seat || (seat->seat->last_event.tv_sec > _seat->seat->last_event.tv_sec &&
+				seat->seat->last_event.tv_nsec > _seat->seat->last_event.tv_nsec)) {
+			seat = _seat;
+		}
+	}
+	return seat;
+}