Refactors how diagonal smoothing underlays work (#1187)

code/game/turfs/space/space.dm

@@ -160,6 +160,12 @@
 /turf/open/space/acid_act(acidpwr, acid_volume)
 	return 0
 
+/turf/open/space/get_smooth_underlay_icon(mutable_appearance/underlay_appearance, turf/asking_turf, adjacency_dir)
+	underlay_appearance.icon = 'icons/turf/space.dmi'
+	underlay_appearance.icon_state = SPACE_ICON_STATE
+	underlay_appearance.plane = PLANE_SPACE
+	return TRUE
+
 
 /turf/open/space/rcd_vals(mob/user, obj/item/weapon/construction/rcd/the_rcd)
 	if(!CanBuildHere())

code/game/turfs/space/transit.dm

@@ -4,6 +4,11 @@
 	baseturf = /turf/open/space/transit
 	flags = NOJAUNT //This line goes out to every wizard that ever managed to escape the den. I'm sorry.
 
+/turf/open/space/transit/get_smooth_underlay_icon(mutable_appearance/underlay_appearance, turf/asking_turf, adjacency_dir)
+	. = ..()
+	underlay_appearance.icon_state = "speedspace_ns_[get_transit_state(asking_turf)]"
+	underlay_appearance.transform = turn(matrix(), get_transit_angle(asking_turf))
+
 /turf/open/space/transit/south
 	dir = SOUTH
 
@@ -69,25 +74,32 @@
 		throw_atom(AM)
 
 /turf/open/space/transit/proc/update_icon()
-	var/p = 9
-	var/angle = 0
-	var/state = 1
-	switch(dir)
-		if(NORTH)
-			angle = 180
-			state = ((-p*x+y) % 15) + 1
-			if(state < 1)
-				state += 15
-		if(EAST)
-			angle = 90
-			state = ((x+p*y) % 15) + 1
-		if(WEST)
-			angle = -90
-			state = ((x-p*y) % 15) + 1
-			if(state < 1)
-				state += 15
-		else
-			state =	((p*x+y) % 15) + 1
+	icon_state = "speedspace_ns_[get_transit_state(src)]"
+	transform = turn(matrix(), get_transit_angle(src))
 
-	icon_state = "speedspace_ns_[state]"
-	transform = turn(matrix(), angle)
+/proc/get_transit_state(turf/T)
+	var/p = 9
+	. = 1
+	switch(T.dir)
+		if(NORTH)
+			. = ((-p*T.x+T.y) % 15) + 1
+			if(. < 1)
+				. += 15
+		if(EAST)
+			. = ((T.x+p*T.y) % 15) + 1
+		if(WEST)
+			. = ((T.x-p*T.y) % 15) + 1
+			if(. < 1)
+				. += 15
+		else
+			. = ((p*T.x+T.y) % 15) + 1
+
+/proc/get_transit_angle(turf/T)
+	. = 0
+	switch(T.dir)
+		if(NORTH)
+			. = 180
+		if(EAST)
+			. = 90
+		if(WEST)
+			. = -90