since the root and event window are the same in the case of a button

event on the screen's root window, there's no need to pass down the
entire XButtonEvent event, at least to group_menu(), the only callback
which takes an argument at this point; instead use the already populated
screen.

group.c

@@ -309,16 +309,13 @@ group_cycle(struct screen_ctx *sc, int flags)
 }
 
 void
-group_menu(XButtonEvent *e)
+group_menu(struct screen_ctx *sc)
 {
-	struct screen_ctx	*sc;
 	struct group_ctx	*gc;
 	struct menu		*mi;
 	struct menu_q		 menuq;
 	int			 i;
 
-	sc = screen_fromroot(e->root);
-
 	TAILQ_INIT(&menuq);
 
 	for (i = 0; i < CALMWM_NGROUPS; i++) {