Porting update_icon improvements. Part 1.

code/game/machinery/computer/_computer.dm

@@ -48,13 +48,13 @@
 		icon_state = initial(icon_state)
 		update_icon()
 
-/obj/machinery/computer/update_icon()
-	cut_overlays()
+/obj/machinery/computer/update_overlays()
+	. = ..()
 	SSvis_overlays.remove_vis_overlay(src, managed_vis_overlays)
 	if(stat & NOPOWER)
-		add_overlay("[icon_keyboard]_off")
+		. += "[icon_keyboard]_off"
 		return
-	add_overlay(icon_keyboard)
+	. += icon_keyboard
 
 	// This whole block lets screens ignore lighting and be visible even in the darkest room
 	// We can't do this for many things that emit light unfortunately because it layers over things that would be on top of it

code/game/machinery/computer/aifixer.dm

@@ -103,21 +103,20 @@
 		add_fingerprint(usr)
 	updateUsrDialog()
 
-/obj/machinery/computer/aifixer/update_icon()
-	..()
+/obj/machinery/computer/aifixer/update_overlays()
+	. = ..()
 	if(stat & (NOPOWER|BROKEN))
 		return
+	if(active)
+		. += "ai-fixer-on"
+	if (occupier)
+		switch (occupier.stat)
+			if (0)
+				. += "ai-fixer-full"
+			if (2)
+				. += "ai-fixer-404"
 	else
-		if(active)
-			add_overlay("ai-fixer-on")
-		if (occupier)
-			switch (occupier.stat)
-				if (0)
-					add_overlay("ai-fixer-full")
-				if (2)
-					add_overlay("ai-fixer-404")
-		else
-			add_overlay("ai-fixer-empty")
+		. += "ai-fixer-empty"
 
 /obj/machinery/computer/aifixer/transfer_ai(interaction, mob/user, mob/living/silicon/ai/AI, obj/item/aicard/card)
 	if(!..())

code/game/machinery/computer/atmos_alert.dm

@@ -78,23 +78,20 @@
 	update_icon()
 	return
 
-/obj/machinery/computer/atmos_alert/update_icon()
-	..()
-	cut_overlays()
+/obj/machinery/computer/atmos_alert/update_overlays()
+	. = ..()
 	SSvis_overlays.remove_vis_overlay(src, managed_vis_overlays)
 	var/overlay_state = icon_screen
 	if(stat & (NOPOWER|BROKEN))
-		add_overlay("[icon_keyboard]_off")
+		. |= "[icon_keyboard]_off"
 		return
-	add_overlay(icon_keyboard)
+	. |= icon_keyboard
 	if(priority_alarms.len)
 		overlay_state = "alert:2"
-		add_overlay("alert:2")
 	else if(minor_alarms.len)
 		overlay_state = "alert:1"
-		add_overlay("alert:1")
 	else
 		overlay_state = "alert:0"
-		add_overlay("alert:0")
+	. |= overlay_state
 	SSvis_overlays.add_vis_overlay(src, icon, overlay_state, layer, plane, dir)
 	SSvis_overlays.add_vis_overlay(src, icon, overlay_state, ABOVE_LIGHTING_LAYER, ABOVE_LIGHTING_PLANE, dir, alpha=128)

code/game/machinery/computer/atmos_control.dm

@@ -41,7 +41,7 @@
 	name = "incinerator chamber gas sensor"
 	id_tag = ATMOS_GAS_MONITOR_SENSOR_INCINERATOR
 
-/obj/machinery/air_sensor/update_icon()
+/obj/machinery/air_sensor/update_icon_state()
 		icon_state = "gsensor[on]"
 
 /obj/machinery/air_sensor/process_atmos()

code/game/machinery/computer/camera.dm

@@ -175,11 +175,10 @@
 	clockwork = TRUE //it'd look very weird
 	light_power = 0
 
-/obj/machinery/computer/security/telescreen/update_icon()
+/obj/machinery/computer/security/telescreen/update_icon_state()
 	icon_state = initial(icon_state)
 	if(stat & BROKEN)
 		icon_state += "b"
-	return
 
 /obj/machinery/computer/security/telescreen/entertainment
 	name = "entertainment monitor"

code/game/machinery/computer/station_alert.dm

@@ -75,25 +75,23 @@
 				L -= I
 	return !cleared
 
-/obj/machinery/computer/station_alert/update_icon()
-	..()
-	cut_overlays()
+/obj/machinery/computer/station_alert/update_overlays()
+	. = ..()
 	SSvis_overlays.remove_vis_overlay(src, managed_vis_overlays)
 	var/overlay_state = icon_screen
 	if(stat & (NOPOWER|BROKEN))
-		add_overlay("[icon_keyboard]_off")
+		. |= "[icon_keyboard]_off"
 		return
-	add_overlay(icon_keyboard)
+	. |= icon_keyboard
 	var/active_alarms = FALSE
 	for(var/cat in alarms)
-		var/list/L = alarms[cat]
-		if(L.len)
+		if(length(alarms[cat]))
 			active_alarms = TRUE
+			break
 	if(active_alarms)
 		overlay_state = "alert:2"
-		add_overlay("alert:2")
 	else
 		overlay_state = "alert:0"
-		add_overlay("alert:0")
+	. |= overlay_state
 	SSvis_overlays.add_vis_overlay(src, icon, overlay_state, layer, plane, dir)
-	SSvis_overlays.add_vis_overlay(src, icon, overlay_state, ABOVE_LIGHTING_LAYER, ABOVE_LIGHTING_PLANE, dir, alpha=128)
+	SSvis_overlays.add_vis_overlay(src, icon, overlay_state, ABOVE_LIGHTING_LAYER, ABOVE_LIGHTING_PLANE, dir, alpha=128)

code/game/machinery/computer/telecrystalconsoles.dm

@@ -44,8 +44,8 @@ GLOBAL_LIST_INIT(possible_uplinker_IDs, list("Alfa","Bravo","Charlie","Delta","E
 	else
 		to_chat(user, "<span class='notice'>[I] doesn't appear to be an uplink...</span>")
 
-/obj/machinery/computer/telecrystals/uplinker/update_icon()
-	..()
+/obj/machinery/computer/telecrystals/uplinker/update_overlays()
+	. = ..()
 	if(uplinkholder)
 		add_overlay("[initial(icon_state)]-closed")