window-switcher: add order parameter to allow stable window list ordering

Add a new configuration option to control the window switcher traversal order.

`order="focus"` cycling is convenient for quick toggling, but some users - me as well -
prefer a stable taskbar-like order which can now be achieved with `order="age"`.

docs/labwc-config.5.scd

@@ -349,7 +349,7 @@ this is for compatibility with Openbox.
 </windowSwitcher>
 ```
 
-*<windowSwitcher preview="" outlines="" allWorkspaces="" unshade="">*
+*<windowSwitcher preview="" outlines="" allWorkspaces="" unshade="" order="">*
 	*preview* [yes|no] Preview the contents of the selected window when
 	switching between windows. Default is yes.
 
@@ -363,6 +363,11 @@ this is for compatibility with Openbox.
 	*unshade* [yes|no] Temporarily unshade windows when switching between
 	them and permanently unshade on the final selection. Default is yes.
 
+	*order* [focus|age] The order in which windows are cycled. *focus* cycles by
+	recent focus history, starting with the previously focused window. *age* cycles
+	by creation/open order, a stable taskbar-style ordering that doesn’t change on
+	focus. Default is *focus*.
+
 *<windowSwitcher><osd show="" style="" output="" thumbnailLabelFormat="" />*
 	*show* [yes|no] Draw the OnScreenDisplay when switching between
 	windows. Default is yes.

include/config/rcxml.h

@@ -186,6 +186,7 @@ struct rcxml {
 		enum cycle_osd_style style;
 		enum cycle_osd_output_criteria output_criteria;
 		char *thumbnail_label_format;
+		enum window_switcher_order order;
 	} window_switcher;
 
 	struct wl_list window_rules; /* struct window_rule.link */

include/config/types.h

@@ -107,6 +107,11 @@ enum lab_window_type {
 	LAB_WINDOW_TYPE_LEN
 };
 
+enum window_switcher_order {
+	WINDOW_SWITCHER_ORDER_FOCUS,
+	WINDOW_SWITCHER_ORDER_AGE,
+};
+
 enum cycle_osd_style {
 	CYCLE_OSD_STYLE_CLASSIC,
 	CYCLE_OSD_STYLE_THUMBNAIL,

include/labwc.h

@@ -188,6 +188,7 @@ struct server {
 	struct wl_listener xdg_toplevel_icon_set_icon;
 
 	struct wl_list views;
+	uint64_t next_view_creation_id;
 	struct wl_list unmanaged_surfaces;
 
 	struct seat seat;

include/view.h

@@ -174,6 +174,7 @@ struct view {
 
 	bool mapped;
 	bool been_mapped;
+	uint64_t creation_id;
 	enum lab_ssd_mode ssd_mode;
 	enum ssd_preference ssd_preference;
 	bool shaded;

src/config/rcxml.c

@@ -1240,6 +1240,15 @@ entry(xmlNode *node, char *nodename, char *content)
 			wlr_log(WLR_ERROR, "Invalid windowSwitcher output %s: "
 				"should be one of all|focused|cursor", content);
 		}
+	} else if (!strcasecmp(nodename, "order.windowSwitcher")) {
+		if (!strcasecmp(content, "focus")) {
+			rc.window_switcher.order = WINDOW_SWITCHER_ORDER_FOCUS;
+		} else if (!strcasecmp(content, "age")) {
+			rc.window_switcher.order = WINDOW_SWITCHER_ORDER_AGE;
+		} else {
+			wlr_log(WLR_ERROR, "Invalid windowSwitcher order %s: "
+				"should be one of focus|age", content);
+		}
 
 	/* The following two are for backward compatibility only. */
 	} else if (!strcasecmp(nodename, "show.windowSwitcher")) {
@@ -1485,6 +1494,7 @@ rcxml_init(void)
 	rc.window_switcher.criteria = LAB_VIEW_CRITERIA_CURRENT_WORKSPACE
 		| LAB_VIEW_CRITERIA_ROOT_TOPLEVEL
 		| LAB_VIEW_CRITERIA_NO_SKIP_WINDOW_SWITCHER;
+	rc.window_switcher.order = WINDOW_SWITCHER_ORDER_FOCUS;
 
 	rc.resize_indicator = LAB_RESIZE_INDICATOR_NEVER;
 	rc.resize_draw_contents = true;

src/cycle/cycle.c

@@ -276,13 +276,31 @@ create_osd_on_output(struct output *output)
 	assert(output->cycle_osd.tree);
 }
 
+static void
+insert_view_ordered_by_age(struct wl_list *views, struct view *new_view)
+{
+	struct wl_list *link = views;
+	struct view *view;
+	wl_list_for_each(view, views, cycle_link) {
+		if (view->creation_id >= new_view->creation_id) {
+			break;
+		}
+		link = &view->cycle_link;
+	}
+	wl_list_insert(link, &new_view->cycle_link);
+}
+
 /* Return false on failure */
 static bool
 init_cycle(struct server *server)
 {
 	struct view *view;
 	for_each_view(view, &server->views, rc.window_switcher.criteria) {
-		wl_list_append(&server->cycle.views, &view->cycle_link);
+		if (rc.window_switcher.order == WINDOW_SWITCHER_ORDER_AGE) {
+			insert_view_ordered_by_age(&server->cycle.views, view);
+		} else {
+			wl_list_append(&server->cycle.views, &view->cycle_link);
+		}
 	}
 	if (wl_list_empty(&server->cycle.views)) {
 		wlr_log(WLR_DEBUG, "no views to switch between");

src/xdg.c

@@ -1085,6 +1085,7 @@ handle_new_xdg_toplevel(struct wl_listener *listener, void *data)
 	CONNECT_SIGNAL(xdg_surface, xdg_toplevel_view, new_popup);
 
 	wl_list_insert(&server->views, &view->link);
+	view->creation_id = server->next_view_creation_id++;
 }
 
 static void

src/xwayland.c

@@ -1036,6 +1036,7 @@ xwayland_view_create(struct server *server,
 	CONNECT_SIGNAL(xsurface, xwayland_view, map_request);
 
 	wl_list_insert(&view->server->views, &view->link);
+	view->creation_id = view->server->next_view_creation_id++;
 
 	if (xsurface->surface) {
 		handle_associate(&xwayland_view->associate, NULL);