Arrange backgrounds only when required

include/layout.h

@@ -59,6 +59,7 @@ void move_workspace_to(swayc_t* workspace, swayc_t* destination);
 void update_layout_geometry(swayc_t *parent, enum swayc_layouts prev_layout);
 void update_geometry(swayc_t *view);
 void arrange_windows(swayc_t *container, double width, double height);
+void arrange_backgrounds(void);
 
 swayc_t *get_focused_container(swayc_t *parent);
 swayc_t *get_swayc_in_direction(swayc_t *container, enum movement_direction dir);

sway/focus.c

@@ -158,6 +158,7 @@ bool set_focused_container(swayc_t *c) {
 		// rearrange if parent container is tabbed/stacked
 		swayc_t *parent = swayc_tabbed_stacked_ancestor(p);
 		if (parent != NULL) {
+			arrange_backgrounds();
 			arrange_windows(parent, -1, -1);
 		}
 	} else if (p->type == C_WORKSPACE) {

sway/layout.c

@@ -961,9 +961,12 @@ void arrange_windows(swayc_t *container, double width, double height) {
 	update_visibility(container);
 	arrange_windows_r(container, width, height);
 	layout_log(&root_container, 0);
+}
 
+void arrange_backgrounds(void) {
+	struct background_config *bg;
 	for (int i = 0; i < desktop_shell.backgrounds->length; ++i) {
-		struct background_config *bg = desktop_shell.backgrounds->items[i];
+		bg = desktop_shell.backgrounds->items[i];
 		wlc_view_send_to_back(bg->handle);
 	}
 }

sway/workspace.c

@@ -308,6 +308,7 @@ bool workspace_switch(swayc_t *workspace) {
 		return false;
 	}
 	swayc_t *output = swayc_parent_by_type(workspace, C_OUTPUT);
+	arrange_backgrounds();
 	arrange_windows(output, -1, -1);
 	return true;
 }