long enough to know

code/__DEFINES/dcs/signals/atom/signals_atom.dm

@@ -54,3 +54,11 @@
 
 /// Called when an atom has emp_act called on it, from /atom/emp_act: (severity)
 #define COMSIG_ATOM_EMP_ACT "atom_emp_act"
+
+//from base of atom/update_icon(): ()
+#define COMSIG_ATOM_UPDATE_ICON "atom_update_icon"
+	#define COMSIG_ATOM_NO_UPDATE_ICON_STATE (1<<0)
+	#define COMSIG_ATOM_NO_UPDATE_OVERLAYS (1<<1)
+
+//from base of atom/update_overlays(): (list/new_overlays)
+#define COMSIG_ATOM_UPDATE_OVERLAYS "atom_update_overlays"

code/_onclick/hud/map_popups.dm

@@ -68,7 +68,7 @@
 	plane = GAME_PLANE
 
 ///le awesome parent type
-/atom/movable/screen/proc/update_icon()
+/atom/movable/screen/update_icon()
 	return
 
 /**

code/game/atoms.dm

@@ -95,6 +95,9 @@
 	///The color this atom will be if we choose to draw it on the minimap
 	var/minimap_color = MINIMAP_SOLID
 
+	///overlays managed by update_overlays() to prevent removing overlays that weren't added by the same proc
+	var/list/managed_overlays
+
 /atom/New(loc, ...)
 	var/do_initialize = SSatoms.initialized
 	if(do_initialize != INITIALIZATION_INSSATOMS)
@@ -660,6 +663,29 @@ Parameters are passed from New.
 /atom/proc/reset_light()
 	turn_light(null, TRUE, 1 SECONDS, FALSE, TRUE)
 
+/atom/proc/update_icon()
+	var/signalOut = SEND_SIGNAL(src, COMSIG_ATOM_UPDATE_ICON)
+
+	if(!(signalOut & COMSIG_ATOM_NO_UPDATE_ICON_STATE))
+		update_icon_state()
+
+	if(!(signalOut & COMSIG_ATOM_NO_UPDATE_OVERLAYS))
+		var/list/new_overlays = update_overlays()
+		if(managed_overlays)
+			overlays -= managed_overlays
+			managed_overlays = null
+		if(length(new_overlays))
+			managed_overlays = new_overlays
+			overlays += new_overlays
+
+/// Updates the icon state of the atom
+/atom/proc/update_icon_state()
+
+/atom/proc/update_overlays()
+	SHOULD_CALL_PARENT(TRUE)
+	. = list()
+	SEND_SIGNAL(src, COMSIG_ATOM_UPDATE_OVERLAYS, .)
+
 /**
  * Return the markup to for the dropdown list for the VV panel for this atom
  *

code/game/atoms_movable.dm

@@ -94,8 +94,6 @@
 	if(light_system == DIRECTIONAL_LIGHT)
 		AddComponent(/datum/component/overlay_lighting, is_directional = TRUE)
 
-/*
-
 ///Updates this movables emissive overlay
 /atom/movable/proc/update_emissive_block()
 	if(!blocks_emissive)
@@ -114,8 +112,6 @@
 
 	. += update_emissive_block()
 
-*/
-
 /atom/movable/vv_get_dropdown()
 	. = ..()
 	VV_DROPDOWN_OPTION(VV_HK_EDIT_PARTICLES, "Edit Particles")

code/game/machinery/doors/windowdoor.dm

@@ -14,7 +14,7 @@
 
 /obj/structure/machinery/door/window/Initialize()
 	. = ..()
-	addtimer(CALLBACK(src, PROC_REF(update_icon)), 1)
+	addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), 1)
 	if (src.req_access && src.req_access.len)
 		src.icon_state = "[src.icon_state]"
 		src.base_state = src.icon_state

code/game/machinery/fire_alarm.dm

@@ -128,7 +128,7 @@ FIRE ALARM
 
 /obj/structure/machinery/firealarm/power_change()
 	..()
-	addtimer(CALLBACK(src, PROC_REF(update_icon)), rand(0,15))
+	addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), rand(0,15))
 
 /obj/structure/machinery/firealarm/attack_hand(mob/user as mob)
 	if(user.stat || inoperable())

code/game/machinery/lightswitch.dm

@@ -22,11 +22,11 @@
 		name = "light switch ([area.name])"
 
 	src.on = src.area.lightswitch
-	updateicon()
+	update_icon()
 
 
 
-/obj/structure/machinery/light_switch/proc/updateicon()
+/obj/structure/machinery/light_switch/update_icon_state()
 	if(stat & NOPOWER)
 		icon_state = "light-p"
 	else
@@ -35,6 +35,12 @@
 		else
 			icon_state = "light0"
 
+/obj/structure/machinery/light_switch/update_overlays()
+	. = ..()
+	if(stat & NOPOWER)
+		return
+	. += emissive_appearance(icon, "light[on]_emissive")
+
 /obj/structure/machinery/light_switch/get_examine_text(mob/user)
 	. = ..()
 	. += "It is [on? "on" : "off"]."
@@ -47,7 +53,7 @@
 
 	for(var/obj/structure/machinery/light_switch/L in area)
 		L.on = on
-		L.updateicon()
+		L.update_icon()
 
 	area.power_change()
 
@@ -59,7 +65,7 @@
 		else
 			stat |= NOPOWER
 
-		updateicon()
+		update_icon()
 
 /obj/structure/machinery/light_switch/emp_act(severity)
 	. = ..()

code/game/machinery/vending/vending.dm

@@ -922,7 +922,7 @@ GLOBAL_LIST_EMPTY_TYPED(total_vending_machines, /obj/structure/machinery/vending
 /obj/structure/machinery/vending/power_change()
 	..()
 	if(stat & NOPOWER)
-		addtimer(CALLBACK(src, PROC_REF(update_icon)), rand(1, 15))
+		addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), rand(1, 15))
 		return
 	update_icon()
 

code/game/objects/items.dm

@@ -4,6 +4,7 @@
 	mouse_drag_pointer = MOUSE_ACTIVE_POINTER
 	layer = ITEM_LAYER
 	light_system = MOVABLE_LIGHT
+	blocks_emissive = EMISSIVE_BLOCK_GENERIC
 	/// this saves our blood splatter overlay, which will be processed not to go over the edges of the sprite
 	var/image/blood_overlay = null
 	var/randpixel = 6

code/game/objects/items/devices/portable_vendor.dm

@@ -198,14 +198,15 @@
 	fabricating = FALSE
 	update_overlays()
 
-/obj/item/device/portable_vendor/proc/update_overlays()
-	if(overlays) overlays.Cut()
+/obj/item/device/portable_vendor/update_overlays()
+	. = ..()
+
 	if (broken)
-		overlays += image(icon, "securespark")
+		. += image(icon, "securespark")
 	else if (fabricating)
-		overlays += image(icon, "secureb")
+		. += image(icon, "secureb")
 	else
-		overlays += image(icon, "secure0")
+		. += image(icon, "secure0")
 
 
 /obj/item/device/portable_vendor/process()

code/game/objects/items/devices/scanners.dm

@@ -439,7 +439,7 @@ FORENSIC SCANNER
 				overlays += image('icons/obj/items/devices.dmi', "+mendoza_scanner_value_cyan")
 			else
 				overlays += image('icons/obj/items/devices.dmi', "+mendoza_scanner_value_white")
-		addtimer(CALLBACK(src, PROC_REF(update_icon)), 1 SECONDS)
+		addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), 1 SECONDS)
 	else
 		overlays += image('icons/obj/items/devices.dmi', "+mendoza_scanner_clamp_off")
 

code/game/objects/items/tools/experimental_tools.dm

@@ -219,7 +219,7 @@
 
 	if(detaching)
 		overlays += "+draining"
-		addtimer(CALLBACK(src, PROC_REF(update_icon)), attach_time)
+		addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), attach_time)
 
 	else if(attaching)
 		overlays += "+filling"

code/game/objects/objs.dm

@@ -174,13 +174,12 @@
 /obj/proc/interact(mob/user)
 	return
 
-/obj/proc/update_icon()
+/obj/update_overlays()
+	. = ..()
+
 	for(var/datum/effects/E in effects_list)
 		if(E.icon_path && E.obj_icon_state_path)
-			overlays += image(E.icon_path, icon_state = E.obj_icon_state_path)
-	return
-
-
+			. += image(E.icon_path, icon_state = E.obj_icon_state_path)
 
 /obj/item/proc/updateSelfDialog()
 	var/mob/M = loc

code/game/objects/structures/barricade/barricade.dm

@@ -42,7 +42,7 @@
 		update_health(0, TRUE)
 	if(user)
 		user.count_niche_stat(STATISTICS_NICHE_CADES)
-	addtimer(CALLBACK(src, PROC_REF(update_icon)), 0)
+	addtimer(CALLBACK(src, TYPE_PROC_REF(/atom, update_icon)), 0)
 	starting_maxhealth = maxhealth
 
 /obj/structure/barricade/initialize_pass_flags(datum/pass_flags_container/pass_flags)

code/game/objects/structures/crates_lockers/closets.dm

@@ -5,6 +5,7 @@
 	icon_state = "closed"
 	density = TRUE
 	layer = BELOW_OBJ_LAYER
+	blocks_emissive = EMISSIVE_BLOCK_GENERIC
 	var/icon_closed = "closed"
 	var/icon_opened = "open"
 	var/opened = 0

code/game/objects/structures/noticeboard.dm

@@ -96,10 +96,11 @@
 			remove_item(item, user)
 			return TRUE
 
-/obj/structure/noticeboard/proc/update_overlays()
-	if(overlays) overlays.Cut()
+/obj/structure/noticeboard/update_overlays()
+	. = ..()
+
 	if(notices)
-		overlays += image(icon, "notices_[notices]")
+		. += image(icon, "notices_[notices]")
 
 /obj/structure/noticeboard/proc/remove_item(obj/item/item, mob/user)
 	item.forceMove(loc)

code/game/objects/structures/stool_bed_chair_nest/chairs.dm

@@ -162,8 +162,9 @@
 	I.throw_atom(starting_turf, rand(2, 5), SPEED_FAST, null, TRUE)
 	qdel(src)
 
-/obj/structure/bed/chair/proc/update_overlays()
-	overlays.Cut()
+/obj/structure/bed/chair/update_overlays()
+	. = ..()
+
 	if(!stacked_size)
 		name = initial(name)
 		desc = initial(desc)
@@ -201,7 +202,7 @@
 					I.pixel_y = previous_chair_overlay.pixel_y + 3
 		if(stacked_size > 8)
 			I.pixel_x = I.pixel_x + pick(list(-1, 1))
-		overlays += I
+		. += I
 
 /obj/structure/bed/chair/verb/rotate()
 	set name = "Rotate Chair"

code/game/turfs/open.dm

@@ -19,7 +19,7 @@
 	update_icon()
 
 /turf/open/update_icon()
-	overlays.Cut()
+	. = ..()
 
 	add_cleanable_overlays()
 
@@ -473,16 +473,17 @@
 	..()
 	update_overlays()
 
-/turf/open/gm/river/proc/update_overlays()
-	overlays.Cut()
+/turf/open/gm/river/update_overlays()
+	. = ..()
+
 	if(no_overlay)
 		return
 	if(covered)
 		name = covered_name
-		overlays += image("icon"=src.cover_icon,"icon_state"=cover_icon_state,"layer"=CATWALK_LAYER,"dir" = dir)
+		. += image("icon"=src.cover_icon,"icon_state"=cover_icon_state,"layer"=CATWALK_LAYER,"dir" = dir)
 	else
 		name = default_name
-		overlays += image("icon"=src.icon,"icon_state"=icon_overlay,"layer"=ABOVE_MOB_LAYER,"dir" = dir)
+		. += image("icon"=src.icon,"icon_state"=icon_overlay,"layer"=ABOVE_MOB_LAYER,"dir" = dir)
 
 /turf/open/gm/river/ex_act(severity)
 	if(covered & severity >= EXPLOSION_THRESHOLD_LOW)

code/game/turfs/turf.dm

@@ -145,9 +145,6 @@
 /turf/ex_act(severity)
 	return 0
 
-/turf/proc/update_icon() //Base parent. - Abby
-	return
-
 /turf/proc/add_cleanable_overlays()
 	for(var/cleanable_type in cleanables)
 		var/obj/effect/decal/cleanable/C = cleanables[cleanable_type]

code/modules/mob/living/carbon/human/human_defines.dm

@@ -1,6 +1,7 @@
 /mob/living/carbon/human
 	light_system = MOVABLE_LIGHT
 	rotate_on_lying = TRUE
+	blocks_emissive = EMISSIVE_BLOCK_UNIQUE
 	//Hair color and style
 	var/r_hair = 0
 	var/g_hair = 0

code/modules/mob/living/simple_animal/friendly/spiderbot.dm

@@ -149,7 +149,7 @@
 	eject_brain()
 	death(cause)
 
-/mob/living/simple_animal/spiderbot/proc/update_icon()
+/mob/living/simple_animal/spiderbot/update_icon_state()
 	if(mmi)
 		if(istype(mmi,/obj/item/device/mmi))
 			icon_state = "spiderbot-chassis-mmi"

code/modules/mob/mob_defines.dm

@@ -3,6 +3,7 @@
 	layer = MOB_LAYER
 	animate_movement = 2
 	rebounds = TRUE
+	blocks_emissive = EMISSIVE_BLOCK_GENERIC
 	var/mob_flags = NO_FLAGS
 	var/datum/mind/mind
 

code/modules/projectiles/gun_helpers.dm

@@ -410,7 +410,9 @@ DEFINES in setup.dm, referenced here.
 	if(attachable_offset && attachments[attachable])
 		update_overlays(attachments[attachable], attachable)
 
-/obj/item/weapon/gun/proc/update_overlays(obj/item/attachable/attachment, slot)
+/obj/item/weapon/gun/update_overlays(obj/item/attachable/attachment, slot)
+	. = ..()
+
 	var/image/gun_image = attachable_overlays[slot]
 	overlays -= gun_image
 	attachable_overlays[slot] = null
@@ -422,7 +424,7 @@ DEFINES in setup.dm, referenced here.
 		gun_image.pixel_x = attachable_offset["[slot]_x"] - attachment.pixel_shift_x + x_offset_by_attachment_type(attachment.type)
 		gun_image.pixel_y = attachable_offset["[slot]_y"] - attachment.pixel_shift_y + y_offset_by_attachment_type(attachment.type)
 		attachable_overlays[slot] = gun_image
-		overlays += gun_image
+		. += gun_image
 	else attachable_overlays[slot] = null
 
 /obj/item/weapon/gun/proc/x_offset_by_attachment_type(attachment_type)

code/modules/vehicles/vehicle.dm

@@ -6,6 +6,7 @@
 	anchored = TRUE
 	animate_movement = 1
 	can_buckle = TRUE
+	blocks_emissive = EMISSIVE_BLOCK_GENERIC
 
 	// The mobs that are in each position/seat of the vehicle
 	var/list/mob/seats = list(