[READY] Stacks will change item_states and w_class based on how full they are. (#1370)

code/game/objects/items/stacks/stack.dm

@@ -18,6 +18,8 @@
 	var/datum/robot_energy_storage/source
 	var/cost = 1 // How much energy from storage it costs
 	var/merge_type = null // This path and its children should merge with this stack, defaults to src.type
+	var/full_w_class = WEIGHT_CLASS_NORMAL //The weight class the stack should have at amount > 2/3rds max_amount
+	var/novariants = TRUE //Determines whether the item should update it's sprites based on amount.
 
 /obj/item/stack/Initialize(mapload, new_amount=null , merge = TRUE)
 	..()
@@ -29,6 +31,28 @@
 		for(var/obj/item/stack/S in loc)
 			if(S.merge_type == merge_type)
 				merge(S)
+	update_weight()
+	update_icon()
+
+/obj/item/stack/proc/update_weight()
+	if(amount <= (max_amount * (1/3)))
+		w_class = Clamp(full_w_class-2, WEIGHT_CLASS_TINY, full_w_class)
+	else if (amount <= (max_amount * (2/3)))
+		w_class = Clamp(full_w_class-1, WEIGHT_CLASS_TINY, full_w_class)
+	else
+		w_class = full_w_class
+
+/obj/item/stack/update_icon()
+	if(novariants)
+		return ..()
+	if(amount <= (max_amount * (1/3)))
+		icon_state = initial(icon_state)
+	else if (amount <= (max_amount * (2/3)))
+		icon_state = "[initial(icon_state)]_2"
+	else
+		icon_state = "[initial(icon_state)]_3"
+	..()
+
 
 /obj/item/stack/Destroy()
 	if (usr && usr.machine==src)
@@ -188,6 +212,7 @@
 	amount -= used
 	zero_amount()
 	update_icon()
+	update_weight()
 	return 1
 
 /obj/item/stack/proc/zero_amount()
@@ -204,6 +229,7 @@
 	else
 		src.amount += amount
 	update_icon()
+	update_weight()
 
 /obj/item/stack/proc/merge(obj/item/stack/S) //Merge src into S, as much as possible
 	if(QDELETED(S) || QDELETED(src) || S == src) //amusingly this can cause a stack to consume itself, let's not allow that.