emissive blockers are now just an overlay (with kickass fucking graph…

…s). FUCK YOU MAPTICK (tgstation#57934)

currently emissive blockers are objects added to the vis_contents of every item. however mutable appearances as overlays can serve this role perfectly well and according to my tests should cause less maptick per item. for mobs mutable appearances dont work for reasons i dont understand so instead this adds the em_block object to overlays instead of vis_contents. these both use atom/movable/update_icon() now

graphed test results in pr

code/game/atoms_movable.dm

@@ -77,11 +77,15 @@
 	. = ..()
 	switch(blocks_emissive)
 		if(EMISSIVE_BLOCK_GENERIC)
-			update_emissive_block()
+			var/mutable_appearance/gen_emissive_blocker = mutable_appearance(icon, icon_state, EMISSIVE_BLOCKER_LAYER, EMISSIVE_BLOCKER_PLANE)
+			gen_emissive_blocker.dir = dir
+			gen_emissive_blocker.alpha = alpha
+			gen_emissive_blocker.appearance_flags |= appearance_flags
+			add_overlay(list(gen_emissive_blocker))
 		if(EMISSIVE_BLOCK_UNIQUE)
 			render_target = ref(src)
 			em_block = new(src, render_target)
-			vis_contents += em_block
+			add_overlay(list(em_block))
 	if(opacity)
 		AddElement(/datum/element/light_blocking)
 	switch(light_system)
@@ -131,17 +135,24 @@
 
 	vis_contents.Cut()
 
-
 /atom/movable/proc/update_emissive_block()
-	if(blocks_emissive != EMISSIVE_BLOCK_GENERIC)
+	if(!blocks_emissive)
 		return
-	if(length(managed_vis_overlays))
-		for(var/a in managed_vis_overlays)
-			var/obj/effect/overlay/vis/vs
-			if(vs.plane == EMISSIVE_BLOCKER_PLANE)
-				SSvis_overlays.remove_vis_overlay(src, list(vs))
-				break
-	SSvis_overlays.add_vis_overlay(src, icon, icon_state, EMISSIVE_BLOCKER_LAYER, EMISSIVE_BLOCKER_PLANE, dir)
+	else if (blocks_emissive == EMISSIVE_BLOCK_GENERIC)
+		var/mutable_appearance/gen_emissive_blocker = mutable_appearance(icon, icon_state, EMISSIVE_BLOCKER_LAYER, EMISSIVE_BLOCKER_PLANE)
+		gen_emissive_blocker.dir = dir
+		gen_emissive_blocker.alpha = alpha
+		gen_emissive_blocker.appearance_flags |= appearance_flags
+		return gen_emissive_blocker
+	else if(blocks_emissive == EMISSIVE_BLOCK_UNIQUE)
+		if(!em_block)
+			render_target = ref(src)
+			em_block = new(src, render_target)
+		return em_block
+
+/atom/movable/update_overlays()
+	. = ..()
+	. += update_emissive_block()
 
 /atom/movable/proc/can_zFall(turf/source, levels = 1, turf/target, direction)
 	if(!direction)