Observers can see through some alternate apperances (#1829)

code/game/alternate_appearance.dm

@@ -10,6 +10,7 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 			var/datum/atom_hud/alternate_appearance/AA = alternate_appearances[K]
 			if(AA.appearance_key == key)
 				AA.remove_from_hud(src)
+				break
 
 /atom/proc/add_alt_appearance(type, key, ...)
 	if(!type || !key)
@@ -59,6 +60,8 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 /datum/atom_hud/alternate_appearance/basic
 	var/atom/target
 	var/image/theImage
+	var/add_ghost_version = FALSE
+	var/ghost_appearance
 
 /datum/atom_hud/alternate_appearance/basic/New(key, image/I, target_sees_appearance = TRUE)
 	..()
@@ -68,6 +71,16 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 	add_to_hud(target, I)
 	if(target_sees_appearance && ismob(target))
 		add_hud_to(target)
+	if(add_ghost_version)
+		var/image/ghost_image = image(icon = I.icon , icon_state = I.icon_state, loc = I.loc)
+		ghost_image.override = FALSE
+		ghost_image.alpha = 128
+		ghost_appearance = new /datum/atom_hud/alternate_appearance/basic/observers(key + "_observer", ghost_image, FALSE)
+
+/datum/atom_hud/alternate_appearance/basic/Destroy()
+	. = ..()
+	if(ghost_appearance)
+		QDEL_NULL(ghost_appearance)
 
 /datum/atom_hud/alternate_appearance/basic/add_to_hud(atom/A)
 	A.hud_list[appearance_key] = theImage
@@ -76,32 +89,42 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 /datum/atom_hud/alternate_appearance/basic/remove_from_hud(atom/A)
 	. = ..()
 	A.hud_list -= appearance_key
-
-/datum/atom_hud/alternate_appearance/basic/remove_from_hud(atom/A)
-	. = ..()
-	if(.)
+	if(. && !QDELETED(src))
 		qdel(src)
 
 /datum/atom_hud/alternate_appearance/basic/everyone
+	add_ghost_version = TRUE
 
 /datum/atom_hud/alternate_appearance/basic/everyone/New()
 	..()
-	for(var/mob in GLOB.player_list)
-		if(mob)
+	for(var/mob in GLOB.mob_list)
+		if(mobShouldSee(mob))
 			add_hud_to(mob)
 
 /datum/atom_hud/alternate_appearance/basic/everyone/mobShouldSee(mob/M)
-	return TRUE
+	return !isobserver(M)
 
 /datum/atom_hud/alternate_appearance/basic/silicons
 
 /datum/atom_hud/alternate_appearance/basic/silicons/New()
 	..()
 	for(var/mob in GLOB.silicon_mobs)
-		if(mob)
+		if(mobShouldSee(mob))
 			add_hud_to(mob)
 
 /datum/atom_hud/alternate_appearance/basic/silicons/mobShouldSee(mob/M)
 	if(issilicon(M))
 		return TRUE
 	return FALSE
+
+/datum/atom_hud/alternate_appearance/basic/observers
+	add_ghost_version = FALSE //just in case, to prevent infinite loops
+
+/datum/atom_hud/alternate_appearance/basic/observers/New()
+	..()
+	for(var/mob in GLOB.dead_mob_list)
+		if(mobShouldSee(mob))
+			add_hud_to(mob)
+
+/datum/atom_hud/alternate_appearance/basic/observers/mobShouldSee(mob/M)
+	return isobserver(M)

code/modules/mob/dead/observer/observer.dm

@@ -120,6 +120,12 @@ GLOBAL_VAR_INIT(observer_default_invisibility, INVISIBILITY_OBSERVER)
 
 	GLOB.dead_mob_list += src
 
+	for(var/v in GLOB.active_alternate_appearances)
+		if(!v)
+			continue
+		var/datum/atom_hud/alternate_appearance/AA = v
+		AA.onNewMob(src)
+
 	. = ..()
 
 	grant_all_languages()