diff --git a/code/__DEFINES/flags.dm b/code/__DEFINES/flags.dm
index cd6688d095f..6c34d3144b0 100644
--- a/code/__DEFINES/flags.dm
+++ b/code/__DEFINES/flags.dm
@@ -54,6 +54,8 @@
 // LAVA_PROTECT used on the flags_2 variable for both SUIT and HEAD items, and stops lava damage. Must be present in both to stop lava damage.
 #define LAVA_PROTECT_2			2048
 
+#define OVERLAY_QUEUED_2		4096
+
 //Reagent flags
 #define REAGENT_NOREACT			1
 
diff --git a/code/__DEFINES/subsystems.dm b/code/__DEFINES/subsystems.dm
index a03ce11a648..b85677ff777 100644
--- a/code/__DEFINES/subsystems.dm
+++ b/code/__DEFINES/subsystems.dm
@@ -124,3 +124,22 @@
 #define RUNLEVEL_POSTGAME 8
 
 #define RUNLEVELS_DEFAULT (RUNLEVEL_SETUP | RUNLEVEL_GAME | RUNLEVEL_POSTGAME)
+
+#define COMPILE_OVERLAYS(A)\
+	if (TRUE) {\
+		var/list/ad = A.add_overlays;\
+		var/list/rm = A.remove_overlays;\
+		var/list/po = A.priority_overlays;\
+		if(LAZYLEN(rm)){\
+			A.overlays -= rm;\
+			rm.Cut();\
+		}\
+		if(LAZYLEN(ad)){\
+			A.overlays |= ad;\
+			ad.Cut();\
+		}\
+		if(LAZYLEN(po)){\
+			A.overlays |= po;\
+		}\
+		A.flags_2 &= ~OVERLAY_QUEUED_2;\
+}
\ No newline at end of file
diff --git a/code/_onclick/hud/screen_objects.dm b/code/_onclick/hud/screen_objects.dm
index 67f2db660f8..7c38ee1072a 100644
--- a/code/_onclick/hud/screen_objects.dm
+++ b/code/_onclick/hud/screen_objects.dm
@@ -275,8 +275,38 @@
 
 /obj/screen/inventory
 	var/slot_id	//The indentifier for the slot. It has nothing to do with ID cards.
+	var/list/object_overlays = list()
 	layer = 19
 
+/obj/screen/inventory/MouseEntered()
+	..()
+	add_overlays()
+
+/obj/screen/inventory/MouseExited()
+	..()
+	cut_overlay(object_overlays)
+	object_overlays.Cut()
+
+/obj/screen/inventory/proc/add_overlays()
+	var/mob/user = hud.mymob
+
+	if(hud && user && slot_id)
+		var/obj/item/holding = user.get_active_hand()
+
+		if(!holding || user.get_item_by_slot(slot_id))
+			return
+
+		var/image/item_overlay = image(holding)
+		item_overlay.alpha = 92
+
+		if(!user.can_equip(holding, slot_id, disable_warning = TRUE))
+			item_overlay.color = "#ff0000"
+		else
+			item_overlay.color = "#00ff00"
+
+		object_overlays += item_overlay
+		add_overlay(object_overlays)
+
 /obj/screen/inventory/Click()
 	// At this point in client Click() code we have passed the 1/10 sec check and little else
 	// We don't even know if it's a middle click
diff --git a/code/controllers/subsystem/overlays.dm b/code/controllers/subsystem/overlays.dm
new file mode 100644
index 00000000000..154f7bfb8d9
--- /dev/null
+++ b/code/controllers/subsystem/overlays.dm
@@ -0,0 +1,213 @@
+SUBSYSTEM_DEF(overlays)
+	name = "Overlay"
+	flags = SS_TICKER
+	wait = 1
+	priority = FIRE_PRIORITY_OVERLAYS
+	init_order = INIT_ORDER_OVERLAY
+
+	var/list/queue
+	var/list/stats
+	var/list/overlay_icon_state_caches
+	var/list/overlay_icon_cache
+
+/datum/controller/subsystem/overlays/PreInit()
+	overlay_icon_state_caches = list()
+	overlay_icon_cache = list()
+	queue = list()
+	stats = list()
+
+/datum/controller/subsystem/overlays/Initialize()
+	initialized = TRUE
+	fire(mc_check = FALSE)
+	return ..()
+
+
+/datum/controller/subsystem/overlays/stat_entry()
+	..("Ov:[length(queue)]")
+
+/datum/controller/subsystem/overlays/Recover()
+	overlay_icon_state_caches = SSoverlays.overlay_icon_state_caches
+	overlay_icon_cache = SSoverlays.overlay_icon_cache
+	queue = SSoverlays.queue
+
+
+/datum/controller/subsystem/overlays/fire(resumed = FALSE, mc_check = TRUE)
+	var/list/queue = src.queue
+	var/static/count = 0
+	if (count)
+		var/c = count
+		count = 0 //so if we runtime on the Cut, we don't try again.
+		queue.Cut(1,c+1)
+
+	for (var/thing in queue)
+		count++
+		if(thing)
+			var/atom/A = thing
+			COMPILE_OVERLAYS(A)
+		if(mc_check)
+			if(MC_TICK_CHECK)
+				break
+		else
+			CHECK_TICK
+
+	if (count)
+		queue.Cut(1,count+1)
+		count = 0
+
+/proc/iconstate2appearance(icon, iconstate)
+	var/static/image/stringbro = new()
+	var/list/icon_states_cache = SSoverlays.overlay_icon_state_caches
+	var/list/cached_icon = icon_states_cache[icon]
+	if (cached_icon)
+		var/cached_appearance = cached_icon["[iconstate]"]
+		if (cached_appearance)
+			return cached_appearance
+	stringbro.icon = icon
+	stringbro.icon_state = iconstate
+	if (!cached_icon) //not using the macro to save an associated lookup
+		cached_icon = list()
+		icon_states_cache[icon] = cached_icon
+	var/cached_appearance = stringbro.appearance
+	cached_icon["[iconstate]"] = cached_appearance
+	return cached_appearance
+
+/proc/icon2appearance(icon)
+	var/static/image/iconbro = new()
+	var/list/icon_cache = SSoverlays.overlay_icon_cache
+	. = icon_cache[icon]
+	if (!.)
+		iconbro.icon = icon
+		. = iconbro.appearance
+		icon_cache[icon] = .
+
+/atom/proc/build_appearance_list(old_overlays)
+	var/static/image/appearance_bro = new()
+	var/list/new_overlays = list()
+	if (!islist(old_overlays))
+		old_overlays = list(old_overlays)
+	for (var/overlay in old_overlays)
+		if(!overlay)
+			continue
+		if (istext(overlay))
+			new_overlays += iconstate2appearance(icon, overlay)
+		else if(isicon(overlay))
+			new_overlays += icon2appearance(overlay)
+		else
+			if(isloc(overlay))
+				var/atom/A = overlay
+				if (A.flags_2 & OVERLAY_QUEUED_2)
+					COMPILE_OVERLAYS(A)
+			appearance_bro.appearance = overlay //this works for images and atoms too!
+			if(!ispath(overlay))
+				var/image/I = overlay
+				appearance_bro.dir = I.dir
+			new_overlays += appearance_bro.appearance
+	return new_overlays
+
+#define NOT_QUEUED_ALREADY (!(flags_2 & OVERLAY_QUEUED_2))
+#define QUEUE_FOR_COMPILE flags_2 |= OVERLAY_QUEUED_2; SSoverlays.queue += src;
+/atom/proc/cut_overlays(priority = FALSE)
+	LAZYINITLIST(priority_overlays)
+	LAZYINITLIST(remove_overlays)
+	LAZYINITLIST(add_overlays)
+	remove_overlays = overlays.Copy()
+	add_overlays.Cut()
+
+	if(priority)
+		priority_overlays.Cut()
+
+	//If not already queued for work and there are overlays to remove
+	if(NOT_QUEUED_ALREADY && remove_overlays.len)
+		QUEUE_FOR_COMPILE
+
+/atom/proc/cut_overlay(list/overlays, priority)
+	if(!overlays)
+		return
+	overlays = build_appearance_list(overlays)
+	LAZYINITLIST(add_overlays) //always initialized after this point
+	LAZYINITLIST(priority_overlays)
+	LAZYINITLIST(remove_overlays)
+	var/a_len = add_overlays.len
+	var/r_len = remove_overlays.len
+	var/p_len = priority_overlays.len
+	remove_overlays += overlays
+	add_overlays -= overlays
+
+
+	if(priority)
+		var/list/cached_priority = priority_overlays
+		LAZYREMOVE(cached_priority, overlays)
+
+	var/fa_len = add_overlays.len
+	var/fr_len = remove_overlays.len
+	var/fp_len = priority_overlays.len
+
+	//If not already queued and there is work to be done
+	if(NOT_QUEUED_ALREADY && (fa_len != a_len || fr_len != r_len || fp_len != p_len))
+		QUEUE_FOR_COMPILE
+
+/atom/proc/add_overlay(list/overlays, priority = FALSE)
+	if(!overlays)
+		return
+
+	overlays = build_appearance_list(overlays)
+
+	LAZYINITLIST(add_overlays) //always initialized after this point
+	LAZYINITLIST(priority_overlays)
+	var/a_len = add_overlays.len
+	var/p_len = priority_overlays.len
+
+	if(priority)
+		priority_overlays += overlays  //or in the image. Can we use [image] = image?
+		var/fp_len = priority_overlays.len
+		if(NOT_QUEUED_ALREADY && fp_len != p_len)
+			QUEUE_FOR_COMPILE
+	else
+		add_overlays += overlays
+		var/fa_len = add_overlays.len
+		if(NOT_QUEUED_ALREADY && fa_len != a_len)
+			QUEUE_FOR_COMPILE
+
+/atom/proc/copy_overlays(atom/other, cut_old)	//copys our_overlays from another atom
+	if(!other)
+		if(cut_old)
+			cut_overlays()
+		return
+
+	var/list/cached_other = other.overlays.Copy()
+	if(cached_other)
+		if(cut_old || !LAZYLEN(overlays))
+			remove_overlays = overlays
+		add_overlays = cached_other
+		if(NOT_QUEUED_ALREADY)
+			QUEUE_FOR_COMPILE
+	else if(cut_old)
+		cut_overlays()
+
+#undef NOT_QUEUED_ALREADY
+#undef QUEUE_FOR_COMPILE
+
+//TODO: Better solution for these?
+/image/proc/add_overlay(x)
+	overlays |= x
+
+/image/proc/cut_overlay(x)
+	overlays -= x
+
+/image/proc/cut_overlays(x)
+	overlays.Cut()
+
+/image/proc/copy_overlays(atom/other, cut_old)
+	if(!other)
+		if(cut_old)
+			cut_overlays()
+		return
+
+	var/list/cached_other = other.overlays.Copy()
+	if(cached_other)
+		if(cut_old || !overlays.len)
+			overlays = cached_other
+		else
+			overlays |= cached_other
+	else if(cut_old)
+		cut_overlays()
diff --git a/code/game/atoms.dm b/code/game/atoms.dm
index 805e6b8834f..6d8915cdb43 100644
--- a/code/game/atoms.dm
+++ b/code/game/atoms.dm
@@ -44,6 +44,10 @@
 
 	var/initialized = FALSE
 
+	var/list/priority_overlays	//overlays that should remain on top and not normally removed when using cut_overlay functions, like c4.
+	var/list/remove_overlays // a very temporary list of overlays to remove
+	var/list/add_overlays // a very temporary list of overlays to add
+
 /atom/New(loc, ...)
 	if(use_preloader && (src.type == _preloader.target_path))//in case the instanciated atom is creating other atoms in New()
 		_preloader.load(src)
@@ -137,6 +141,8 @@
 
 	QDEL_NULL(reagents)
 	invisibility = 101
+	LAZYCLEARLIST(overlays)
+	LAZYCLEARLIST(priority_overlays)
 	return ..()
 
 //Hook for running code when a dir change occurs
diff --git a/code/modules/food_and_drinks/food/customizables.dm b/code/modules/food_and_drinks/food/customizables.dm
index 70027028344..b0ac9d20d6c 100644
--- a/code/modules/food_and_drinks/food/customizables.dm
+++ b/code/modules/food_and_drinks/food/customizables.dm
@@ -73,7 +73,7 @@
 	bitesize = 4
 	var/top = 1	//Do we have a top?
 	var/obj/item/toptype
-	var/add_overlays = 1	//Do we stack?
+	var/snack_overlays = 1	//Do we stack?
 //	var/offsetstuff = 1 //Do we offset the overlays?
 	var/sandwich_limit = 40
 	var/fullycustom = 0
@@ -87,7 +87,7 @@
 	icon_state = "personal_pizza"
 	baseicon = "personal_pizza"
 	basename = "personal pizza"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/pasta
@@ -96,7 +96,7 @@
 	icon_state = "pasta_bot"
 	baseicon = "pasta_bot"
 	basename = "pasta"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/bread
@@ -105,7 +105,7 @@
 	icon_state = "breadcustom"
 	baseicon = "breadcustom"
 	basename = "bread"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/pie
@@ -114,7 +114,7 @@
 	icon_state = "piecustom"
 	baseicon = "piecustom"
 	basename = "pie"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/cake
@@ -123,7 +123,7 @@
 	icon_state = "cakecustom"
 	baseicon = "cakecustom"
 	basename = "cake"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/jelly
@@ -132,7 +132,7 @@
 	icon_state = "jellycustom"
 	baseicon = "jellycustom"
 	basename = "jelly"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/donkpocket
@@ -141,7 +141,7 @@
 	icon_state = "donkcustom"
 	baseicon = "donkcustom"
 	basename = "donk pocket"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/kebab
@@ -150,7 +150,7 @@
 	icon_state = "kababcustom"
 	baseicon = "kababcustom"
 	basename = "kebab"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/salad
@@ -159,7 +159,7 @@
 	icon_state = "saladcustom"
 	baseicon = "saladcustom"
 	basename = "salad"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/cook/waffles
@@ -168,7 +168,7 @@
 	icon_state = "wafflecustom"
 	baseicon = "wafflecustom"
 	basename = "waffles"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/cookie
@@ -177,7 +177,7 @@
 	icon_state = "cookiecustom"
 	baseicon = "cookiecustom"
 	basename = "cookie"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/cotton
@@ -186,7 +186,7 @@
 	icon_state = "cottoncandycustom"
 	baseicon = "cottoncandycustom"
 	basename = "flavored cotton candy"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/gummybear
@@ -195,7 +195,7 @@
 	icon_state = "gummybearcustom"
 	baseicon = "gummybearcustom"
 	basename = "flavored giant gummy bear"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/gummyworm
@@ -204,7 +204,7 @@
 	icon_state = "gummywormcustom"
 	baseicon = "gummywormcustom"
 	basename = "flavored giant gummy worm"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/jellybean
@@ -213,7 +213,7 @@
 	icon_state = "jellybeancustom"
 	baseicon = "jellybeancustom"
 	basename = "flavored giant jelly bean"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/jawbreaker
@@ -222,7 +222,7 @@
 	icon_state = "jawbreakercustom"
 	baseicon = "jawbreakercustom"
 	basename = "flavored jawbreaker"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/candycane
@@ -231,7 +231,7 @@
 	icon_state = "candycanecustom"
 	baseicon = "candycanecustom"
 	basename = "flavored candy cane"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/gum
@@ -240,7 +240,7 @@
 	icon_state = "gumcustom"
 	baseicon = "gumcustom"
 	basename = "flavored gum"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/donut
@@ -249,7 +249,7 @@
 	icon_state = "donutcustom"
 	baseicon = "donutcustom"
 	basename = "filled donut"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/bar
@@ -258,7 +258,7 @@
 	icon_state = "barcustom"
 	baseicon = "barcustom"
 	basename = "flavored chocolate bar"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/sucker
@@ -267,7 +267,7 @@
 	icon_state = "suckercustom"
 	baseicon = "suckercustom"
 	basename = "flavored sucker"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/cash
@@ -276,7 +276,7 @@
 	icon_state = "cashcustom"
 	baseicon = "cashcustom"
 	basename = "flavored cash"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/candy/coin
@@ -285,7 +285,7 @@
 	icon_state = "coincustom"
 	baseicon = "coincustom"
 	basename = "flavored coin"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 
 /obj/item/reagent_containers/food/snacks/customizable/fullycustom // In the event you fuckers find something I forgot to add a customizable food for.
@@ -294,7 +294,7 @@
 	icon_state = "fullycustom"
 	baseicon = "fullycustom"
 	basename = "on a plate"
-	add_overlays = 0
+	snack_overlays = 0
 	top = 0
 	sandwich_limit = 20
 	fullycustom = 1
@@ -305,7 +305,7 @@
 	icon_state = "soup"
 	baseicon = "soup"
 	basename = "soup"
-	add_overlays = 0
+	snack_overlays = 0
 	trash = /obj/item/trash/bowl
 	top = 0
 
@@ -355,7 +355,7 @@
 					I.color = pick("#FF0000","#0000FF","#008000","#FFFF00")
 			else
 				I.color = pick("#FF0000","#0000FF","#008000","#FFFF00")
-			if(add_overlays)
+			if(snack_overlays)
 				I.pixel_x = pick(list(-1,0,1))
 				I.pixel_y = (i*2)+1
 			overlays += I
diff --git a/paradise.dme b/paradise.dme
index 579a8a6b8f1..a20b8d43042 100644
--- a/paradise.dme
+++ b/paradise.dme
@@ -210,6 +210,7 @@
 #include "code\controllers\subsystem\nightshift.dm"
 #include "code\controllers\subsystem\npcai.dm"
 #include "code\controllers\subsystem\npcpool.dm"
+#include "code\controllers\subsystem\overlays.dm"
 #include "code\controllers\subsystem\shuttles.dm"
 #include "code\controllers\subsystem\spacedrift.dm"
 #include "code\controllers\subsystem\sun.dm"