Misc. Optimizations (#3993)

changes:

Overlays now creates less temporary lists.
Falling no longer queues unsimulated atoms that wouldn't fall anyways (incl. LOs).
Pixel-shifted AO is now cached too.
Changed some references to get_map_cell() to macro equivalents in random maps.
Added smoothing hinting to the icon smoother, allowing for major performance improvements in common cases.
Space initialization no longer involves appearance churn (and is much faster as a result).

code/controllers/subsystems/icon_cache.dm

@@ -2,7 +2,8 @@
 
 /datum/controller/subsystem/icon_cache
 	name = "Icon Cache"
-	flags = SS_NO_FIRE | SS_NO_INIT
+	flags = SS_NO_FIRE
+	init_order = SS_INIT_MISC_FIRST
 
 	// Cached bloody overlays, key is object type.
 	var/list/bloody_cache = list()
@@ -67,9 +68,20 @@
 
 	var/list/rgb_blend_cache = list()	// not an icon per-se, but this proc could be expensive so we might as well cache it.
 
+	var/list/space_dust_cache = list()
+
+	var/list/space_cache = list()
+
 /datum/controller/subsystem/icon_cache/New()
 	NEW_SS_GLOBAL(SSicon_cache)
 
+/datum/controller/subsystem/icon_cache/Initialize()
+	build_dust_cache()
+	build_space_cache()
+	setup_collar_mappings()
+	setup_uniform_mappings()
+	..()
+
 /datum/controller/subsystem/icon_cache/proc/setup_collar_mappings()
 	collar_states = list()
 	for (var/i in icon_states('icons/mob/collar.dmi'))
@@ -94,3 +106,20 @@
 	var/image/I = new(icon, icon_state)
 	I.color = color
 	return I
+
+/datum/controller/subsystem/icon_cache/proc/build_dust_cache()
+	for (var/i in 0 to 25)
+		var/image/im = image('icons/turf/space_parallax1.dmi',"[i]")
+		im.plane = PLANE_SPACE_DUST
+		im.alpha = 80
+		im.blend_mode = BLEND_ADD
+		space_dust_cache["[i]"] = im
+
+/datum/controller/subsystem/icon_cache/proc/build_space_cache()
+	for (var/i in 0 to 25)
+		var/image/I = new()
+		I.appearance = /turf/space
+		var/istr = "[i]"
+		I.icon_state = istr
+		I.overlays += space_dust_cache[istr]
+		space_cache[istr] = I