output: Add output_update_usable_area/all_usable_areas()

Move the desktop_arrange_all_views() call outside layers_arrange() into
a new function, output_update_usable_area().  The new function currently
does exactly what layers_arrange() used to, but will be expanded in a
later commit.

Add output_update_all_usable_areas(), which is the same as calling
output_update_usable_area() for each output, but only calls
desktop_arrange_all_views() once.

Rebased and slightly modified by @Consolatis

include/labwc.h

@@ -423,6 +423,8 @@ void output_init(struct server *server);
 void output_manager_init(struct server *server);
 struct output *output_from_wlr_output(struct server *server,
 	struct wlr_output *wlr_output);
+void output_update_usable_area(struct output *output);
+void output_update_all_usable_areas(struct server *server, bool enforce_view_arrange);
 struct wlr_box output_usable_area_in_layout_coords(struct output *output);
 struct wlr_box output_usable_area_from_cursor_coords(struct server *server);
 void handle_output_power_manager_set_mode(struct wl_listener *listener,

src/layers.c

@@ -35,6 +35,11 @@ arrange_one_layer(struct output *output, const struct wlr_box *full_area,
 	}
 }
 
+/*
+ * To ensure outputs/views are left in a consistent state, this
+ * function should be called ONLY from output_update_usable_area()
+ * or output_update_all_usable_areas().
+ */
 void
 layers_arrange(struct output *output)
 {
@@ -43,7 +48,6 @@ layers_arrange(struct output *output)
 	wlr_output_effective_resolution(output->wlr_output,
 		&full_area.width, &full_area.height);
 	struct wlr_box usable_area = full_area;
-	struct wlr_box old_usable_area = output->usable_area;
 
 	struct server *server = output->server;
 	struct wlr_scene_output *scene_output =
@@ -103,12 +107,6 @@ layers_arrange(struct output *output)
 			!seat->focused_layer->current.keyboard_interactive) {
 		seat_set_focus_layer(seat, NULL);
 	}
-
-	/* Finally re-arrange all views based on usable_area */
-	if (!wlr_box_equal(&old_usable_area, &usable_area)) {
-		desktop_arrange_all_views(server);
-	}
-	cursor_update_focus(output->server);
 }
 
 static void
@@ -145,7 +143,12 @@ handle_surface_commit(struct wl_listener *listener, void *data)
 
 	if (committed || layer->mapped != layer_surface->mapped) {
 		layer->mapped = layer_surface->mapped;
-		layers_arrange(output);
+		output_update_usable_area(output);
+		/*
+		 * Update cursor focus here to ensure we
+		 * enter a new/moved/resized layer surface.
+		 */
+		cursor_update_focus(layer->server);
 	}
 }
 
@@ -171,7 +174,7 @@ handle_unmap(struct wl_listener *listener, void *data)
 	struct wlr_layer_surface_v1 *layer_surface =
 		layer->scene_layer_surface->layer_surface;
 	if (layer_surface->output) {
-		layers_arrange(layer_surface->output->data);
+		output_update_usable_area(layer_surface->output->data);
 	}
 	struct seat *seat = &layer->server->seat;
 	if (seat->focused_layer == layer_surface) {
@@ -183,7 +186,11 @@ static void
 handle_map(struct wl_listener *listener, void *data)
 {
 	struct lab_layer_surface *layer = wl_container_of(listener, layer, map);
-	layers_arrange(layer->scene_layer_surface->layer_surface->output->data);
+	struct wlr_output *wlr_output =
+		layer->scene_layer_surface->layer_surface->output;
+	if (wlr_output) {
+		output_update_usable_area(wlr_output->data);
+	}
 	/*
 	 * Since moving to the wlroots scene-graph API, there is no need to
 	 * call wlr_surface_send_enter() from here since that will be done
@@ -374,7 +381,7 @@ handle_new_layer_surface(struct wl_listener *listener, void *data)
 	 */
 	struct wlr_layer_surface_v1_state old_state = layer_surface->current;
 	layer_surface->current = layer_surface->pending;
-	layers_arrange(output);
+	output_update_usable_area(output);
 	layer_surface->current = old_state;
 }
 

src/output.c

@@ -240,8 +240,7 @@ output_init(struct server *server)
 static void
 output_update_for_layout_change(struct server *server)
 {
-	/* Adjust window positions/sizes */
+	output_update_all_usable_areas(server, /*enforce_view_arrange*/ true);
-	desktop_arrange_all_views(server);
 
 	/*
 	 * "Move" each wlr_output_cursor (in per-output coordinates) to
@@ -395,11 +394,6 @@ do_output_layout_change(struct server *server)
 			wlr_log(WLR_ERROR,
 				"wlr_output_manager_v1_set_configuration()");
 		}
-		struct output *output;
-
-		wl_list_for_each(output, &server->outputs, link) {
-			layers_arrange(output);
-		}
 		output_update_for_layout_change(server);
 	}
 }
@@ -438,6 +432,38 @@ output_from_wlr_output(struct server *server, struct wlr_output *wlr_output)
 	return NULL;
 }
 
+/* returns true if usable area changed */
+static bool
+update_usable_area(struct output *output)
+{
+	struct wlr_box old = output->usable_area;
+	layers_arrange(output);
+
+	return !wlr_box_equal(&old, &output->usable_area);
+}
+
+void
+output_update_usable_area(struct output *output)
+{
+	if (update_usable_area(output)) {
+		desktop_arrange_all_views(output->server);
+	}
+}
+
+void
+output_update_all_usable_areas(struct server *server, bool enforce_view_arrange)
+{
+	bool usable_area_changed = false;
+	struct output *output;
+
+	wl_list_for_each(output, &server->outputs, link) {
+		usable_area_changed |= update_usable_area(output);
+	}
+	if (usable_area_changed || enforce_view_arrange) {
+		desktop_arrange_all_views(server);
+	}
+}
+
 struct wlr_box
 output_usable_area_in_layout_coords(struct output *output)
 {

src/server.c

@@ -97,10 +97,7 @@ seat_disinhibit_input(struct seat *seat)
 	 * Triggers a refocus of the topmost surface layer if necessary
 	 * TODO: Make layer surface focus per-output based on cursor position
 	 */
-	struct output *output;
+	output_update_all_usable_areas(seat->server, /*enforce_view_arrange*/ false);
-	wl_list_for_each(output, &seat->server->outputs, link) {
-		layers_arrange(output);
-	}
 }
 
 static void