Cache tiers rather than recalculating them constantly

code/modules/research/rdconsole.dm

@@ -553,48 +553,21 @@ doesn't have toxins access.
 
 /obj/machinery/computer/rdconsole/proc/ui_techweb()		//Legacy code.
 	var/list/l = list()
-	var/list/backlog = list()
-	for(var/v in stored_research.researched_nodes)
-		backlog += stored_research.researched_nodes[v]
-
-	var/list/tiers = list()
-	var/list/current = list()
-	for(var/v in stored_research.available_nodes)
-		if(stored_research.researched_nodes[v])
-			continue
-		current += stored_research.available_nodes[v]
-
-	while (current.len)
-		var/list/next = list()
-		for (var/node_ in current)
-			var/datum/techweb_node/node = node_
-			var/current_value = tiers[node]
-			if (!current_value)
-				current_value = tiers[node] = 1
-			for (var/id in node.unlocks)
-				var/datum/techweb_node/follows = node.unlocks[id]
-				if (tiers[follows] < current_value + 1)
-					tiers[follows] = current_value + 1
-					next += follows
-		current = next
-
 	var/list/columns = list()
 	var/max_tier = 0
-	for (var/node_ in tiers)
+	for (var/node_ in stored_research.tiers)
 		var/datum/techweb_node/node = node_
-		var/tier = tiers[node]
+		var/tier = stored_research.tiers[node]
 		LAZYINITLIST(columns["[tier]"])  // String hackery to make the numbers associative
 		columns["[tier]"] += ui_techweb_single_node(node, minimal=(tier != 1))
 		max_tier = max(max_tier, tier)
 
 	l += "<table><tr><th align='left'>Researched</th><th align='left'>Available</th><th align='left'>Future</th></tr><tr>[RDSCREEN_NOBREAK]"
-	l += "<td valign='top'>[RDSCREEN_NOBREAK]"
-	for(var/datum/techweb_node/N in backlog)
-		l += ui_techweb_single_node(N, minimal=TRUE)
-	for(var/tier in 1 to max_tier)
-		l += "</td><td valign='top'>[RDSCREEN_NOBREAK]"
+	for(var/tier in 0 to max_tier)
+		l += "<td valign='top'>[RDSCREEN_NOBREAK]"
 		l += columns["[tier]"]
-	l += "</td></tr></table>[RDSCREEN_NOBREAK]"
+		l += "</td>[RDSCREEN_NOBREAK]"
+	l += "</tr></table>[RDSCREEN_NOBREAK]"
 	return l
 
 /obj/machinery/computer/rdconsole/proc/build_path_icon(atom/item, user)

code/modules/research/techweb/_techweb.dm

@@ -19,6 +19,7 @@
 	var/max_bomb_value = 0
 	var/organization = "Third-Party"							//Organization name, used for display.
 	var/last_bitcoins = 0										//Current per-second production, used for display only.
+	var/list/tiers = list()										//Assoc list, datum = number, 1 is available, 2 is all reqs are 1, so on
 
 /datum/techweb/New()
 	for(var/i in SSresearch.techweb_nodes_starting)
@@ -161,6 +162,24 @@
 			hidden_nodes -= N.id
 	return TRUE
 
+/datum/techweb/proc/update_tiers(datum/techweb_node/base)
+	var/list/current = list(base)
+	while (current.len)
+		var/list/next = list()
+		for (var/node_ in current)
+			var/datum/techweb_node/node = node_
+			var/tier = 0
+			if (!researched_nodes[node.id])  // researched is tier 0
+				for (var/id in node.prereq_ids)
+					var/prereq_tier = tiers[node.prerequisites[id]]
+					tier = max(tier, prereq_tier + 1)
+
+			if (tier != tiers[node])
+				tiers[node] = tier
+				for (var/id in node.unlocks)
+					next += node.unlocks[id]
+		current = next
+
 /datum/techweb/proc/update_node_status(datum/techweb_node/node, autoupdate_consoles = TRUE)
 	var/researched = FALSE
 	var/available = FALSE
@@ -189,6 +208,7 @@
 		else
 			if(visible)
 				visible_nodes[node.id] = node
+	update_tiers(node)
 	if(autoupdate_consoles)
 		for(var/v in consoles_accessing)
 			var/obj/machinery/computer/rdconsole/V = v