Finishes seperating ZAS logic from CanPass().

code/game/gamemodes/meteor/meteors.dm

@@ -147,7 +147,7 @@
 		else
 			die(0)
 
-/obj/effect/meteor/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/effect/meteor/CanPass(atom/movable/mover, turf/target)
 	return istype(mover, /obj/effect/meteor) ? 1 : ..()
 
 /obj/effect/meteor/proc/ram_turf(var/turf/T)

code/game/machinery/deployable.dm

@@ -128,13 +128,10 @@ for reference:
 				dismantle()
 			return
 
-/obj/structure/barricade/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)//So bullets will fly over and stuff.
-	if(air_group || (height==0))
-		return 1
+/obj/structure/barricade/CanPass(atom/movable/mover, turf/target)//So bullets will fly over and stuff.
 	if(istype(mover) && mover.checkpass(PASSTABLE))
-		return 1
-	else
-		return 0
+		return TRUE
+	return FALSE
 
 //Actual Deployable machinery stuff
 /obj/machinery/deployable
@@ -223,13 +220,10 @@ for reference:
 		anchored = !anchored
 		icon_state = "barrier[locked]"
 
-/obj/machinery/deployable/barrier/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)//So bullets will fly over and stuff.
-	if(air_group || (height==0))
-		return 1
+/obj/machinery/deployable/barrier/CanPass(atom/movable/mover, turf/target)//So bullets will fly over and stuff.
 	if(istype(mover) && mover.checkpass(PASSTABLE))
-		return 1
-	else
-		return 0
+		return TRUE
+	return FALSE
 
 /obj/machinery/deployable/barrier/proc/explode()
 

code/game/machinery/doors/blast_door.dm

@@ -264,7 +264,7 @@
 // If for some reason this is actually needed for something important, uncomment this.
 /obj/machinery/door/blast/CanZASPass(turf/T, is_zone)
 	if(is_zone)
-		return TRUE
+		return ATMOS_PASS_YES
 	return ..()
 */
 

code/game/machinery/doors/door.dm

@@ -140,12 +140,12 @@
 	if(istype(mover) && mover.checkpass(PASSGLASS))
 		return !opacity
 	return !density
-/*
+
 /obj/machinery/door/CanZASPass(turf/T, is_zone)
 	if(is_zone)
-		return !block_air_zones
+		return block_air_zones ? ATMOS_PASS_NO : ATMOS_PASS_YES
 	return ..()
-*/
+
 /obj/machinery/door/proc/bumpopen(mob/user as mob)
 	if(operating)	return
 	if(user.last_airflow > world.time - vsc.airflow_delay) //Fakkit

code/game/machinery/doors/firedoor.dm

@@ -471,11 +471,10 @@
 	heat_proof = 1
 	air_properties_vary_with_direction = 1
 
-	CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+	CanPass(atom/movable/mover, turf/target)
 		if(istype(mover) && mover.checkpass(PASSGLASS))
 			return 1
 		if(get_dir(loc, target) == dir) //Make sure looking at appropriate border
-			if(air_group) return 0
 			return !density
 		else
 			return 1

code/game/machinery/doors/windowdoor.dm

@@ -84,14 +84,19 @@
 		open()
 		addtimer(CALLBACK(src, .proc/close), check_access(null)? 50 : 20)
 
-/obj/machinery/door/window/CanPass(atom/movable/mover, turf/target, height, air_group)
+/obj/machinery/door/window/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSGLASS))
-		return 1
+		return TRUE
 	if(get_dir(mover, loc) == turn(dir, 180)) //Make sure looking at appropriate border
-		if(air_group) return 0
 		return !density
-	else
-		return 1
+	return TRUE
+
+/obj/machinery/door/window/CanZASPass(turf/T, is_zone)
+	if(get_dir(T, loc) == turn(dir, 180))
+		if(is_zone) // No merging allowed.
+			return ATMOS_PASS_NO
+		return ..() // Air can flow if open (density == FALSE).
+	return ATMOS_PASS_YES // Windoors don't block if not facing the right way.
 
 /obj/machinery/door/window/CheckExit(atom/movable/mover as mob|obj, turf/target as turf)
 	if(istype(mover) && mover.checkpass(PASSGLASS))

code/game/machinery/iv_drip.dm

@@ -180,7 +180,7 @@
 
 	to_chat(user, "<span class='notice'>[attached ? attached : "No one"] is attached.</span>")
 
-/obj/machinery/iv_drip/CanPass(atom/movable/mover, turf/target, height = 0, air_group = 0)
-	if(height && istype(mover) && mover.checkpass(PASSTABLE)) //allow bullets, beams, thrown objects, mice, drones, and the like through.
-		return 1
+/obj/machinery/iv_drip/CanPass(atom/movable/mover, turf/target)
+	if(istype(mover) && mover.checkpass(PASSTABLE)) //allow bullets, beams, thrown objects, mice, drones, and the like through.
+		return TRUE
 	return ..()

code/game/mecha/mech_sensor.dm

@@ -15,14 +15,14 @@
 	var/frequency = 1379
 	var/datum/radio_frequency/radio_connection
 
-/obj/machinery/mech_sensor/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(!src.enabled()) return 1
-	if(air_group || (height==0)) return 1
+/obj/machinery/mech_sensor/CanPass(atom/movable/mover, turf/target)
+	if(!enabled())
+		return TRUE
 
-	if ((get_dir(loc, target) & dir) && src.is_blocked(mover))
+	if((get_dir(loc, target) & dir) && src.is_blocked(mover))
 		src.give_feedback(mover)
-		return 0
-	return 1
+		return FALSE
+	return TRUE
 
 /obj/machinery/mech_sensor/proc/is_blocked(O as obj)
 	if(istype(O, /obj/mecha/medical/odysseus))

code/game/objects/effects/alien/aliens.dm

@@ -26,6 +26,7 @@
 	density = 1
 	opacity = 1
 	anchored = 1
+	can_atmos_pass = ATMOS_PASS_NO
 	var/health = 200
 	//var/mob/living/affecting = null
 
@@ -128,8 +129,7 @@
 	..()
 	return
 
-/obj/effect/alien/resin/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(air_group) return 0
+/obj/effect/alien/resin/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSGLASS))
 		return !opacity
 	return !density

code/game/objects/effects/chem/foam.dm

@@ -130,6 +130,7 @@
 	anchored = 1
 	name = "foamed metal"
 	desc = "A lightweight foamed metal wall."
+	can_atmos_pass = ATMOS_PASS_NO
 	var/metal = 1 // 1 = aluminum, 2 = iron
 
 /obj/structure/foamedmetal/New()
@@ -178,8 +179,3 @@
 		qdel(src)
 	else
 		user << "<span class='notice'>You hit the metal foam to no effect.</span>"
-
-/obj/structure/foamedmetal/CanPass(atom/movable/mover, turf/target, height=1.5, air_group = 0)
-	if(air_group)
-		return 0
-	return !density

code/game/objects/effects/spiders.dm

@@ -62,17 +62,16 @@
 		icon_state = "stickyweb2"
 	return ..()
 
-/obj/effect/spider/stickyweb/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(air_group || (height==0)) return 1
+/obj/effect/spider/stickyweb/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover, /mob/living/simple_mob/animal/giant_spider))
-		return 1
+		return TRUE
 	else if(istype(mover, /mob/living))
 		if(prob(50))
-			mover << "<span class='warning'>You get stuck in \the [src] for a moment.</span>"
-			return 0
+			to_chat(mover, span("warning", "You get stuck in \the [src] for a moment."))
+			return FALSE
 	else if(istype(mover, /obj/item/projectile))
 		return prob(30)
-	return 1
+	return TRUE
 
 /obj/effect/spider/eggcluster
 	name = "egg cluster"

code/game/objects/effects/zone_divider.dm

@@ -8,13 +8,12 @@
 	density = 0
 	opacity = 0
 
-/obj/effect/zone_divider/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/effect/zone_divider/CanZASPass(turf/T, is_zone)
  	// Special case to prevent us from being part of a zone during the first air master tick.
  	// We must merge ourselves into a zone on next tick.  This will cause a bit of lag on
  	// startup, but it can't really be helped you know?
 	if(air_master && air_master.current_cycle == 0)
 		spawn(1)
 			air_master.mark_for_update(get_turf(src))
-		return 0
-	return !air_group // Anything except zones can pass
-
+		return ATMOS_PASS_NO
+	return is_zone ? ATMOS_PASS_NO : ATMOS_PASS_YES // Anything except zones can pass

code/game/objects/items/weapons/policetape.dm

@@ -286,16 +286,16 @@ var/list/tape_roll_applications = list()
 		update_icon()
 		name = "crumpled [name]"
 
-/obj/item/tape/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/item/tape/CanPass(atom/movable/mover, turf/target)
 	if(!lifted && ismob(mover))
 		var/mob/M = mover
 		add_fingerprint(M)
-		if (!allowed(M))	//only select few learn art of not crumpling the tape
-			M << "<span class='warning'>You are not supposed to go past [src]...</span>"
+		if(!allowed(M))	//only select few learn art of not crumpling the tape
+			to_chat(M, span("warning", "You are not supposed to go past \the [src]..."))
 			if(M.a_intent == I_HELP && !(istype(M, /mob/living/simple_mob)))
-				return 0
+				return FALSE
 			crumple()
-	return ..(mover)
+	return ..()
 
 /obj/item/tape/attackby(obj/item/weapon/W as obj, mob/user as mob)
 	breaktape(user)

code/game/objects/structures/cliff.dm

@@ -132,11 +132,8 @@ two tiles on initialization, and which way a cliff is facing may change during m
 
 // Movement-related code.
 
-/obj/structure/cliff/CanPass(atom/movable/mover, turf/target, height = 0, air_group = 0)
-	if(air_group || height == 0)
-		return TRUE // Airflow can always pass.
-
-	else if(isliving(mover))
+/obj/structure/cliff/CanPass(atom/movable/mover, turf/target)
+	if(isliving(mover))
 		var/mob/living/L = mover
 		if(L.hovering) // Flying mobs can always pass.
 			return TRUE

code/game/objects/structures/coathanger.dm

@@ -27,7 +27,7 @@
 		user << "<span class='notice'>You cannot hang [W] on [src]</span>"
 		return ..()
 
-/obj/structure/coatrack/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/structure/coatrack/CanPass(atom/movable/mover, turf/target)
 	var/can_hang = 0
 	for (var/T in allowed)
 		if(istype(mover,T))

code/game/objects/structures/crates_lockers/closets.dm

@@ -68,7 +68,7 @@
 		else
 			to_chat(user, "It is full.")
 
-/obj/structure/closet/CanPass(atom/movable/mover, turf/target, height, air_group)
+/obj/structure/closet/CanPass(atom/movable/mover, turf/target)
 	if(wall_mounted)
 		return TRUE
 	return ..()

code/game/objects/structures/crates_lockers/closets/coffin.dm

@@ -39,7 +39,7 @@
 							"<span class='notice'>You stop climbing into \the [src.name].</span>")
 	return
 
-/obj/structure/closet/grave/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/structure/closet/grave/CanPass(atom/movable/mover, turf/target)
 	if(opened && ismob(mover))
 		var/mob/M = mover
 		add_fingerprint(M)

code/game/objects/structures/fence.dm

@@ -63,7 +63,7 @@
 	hole_size = LARGE_HOLE
 
 // Projectiles can pass through fences.
-/obj/structure/fence/CanPass(atom/movable/mover, turf/target, height = 0, air_group = 0)
+/obj/structure/fence/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover, /obj/item/projectile))
 		return TRUE
 	return ..()

code/game/objects/structures/gravemarker.dm

@@ -38,15 +38,12 @@
 		if(epitaph)
 			to_chat(user, epitaph)
 
-/obj/structure/gravemarker/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(!mover)
-		return 1
+/obj/structure/gravemarker/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSTABLE))
-		return 1
+		return TRUE
 	if(get_dir(loc, target) & dir)
 		return !density
-	else
-		return 1
+	return TRUE
 
 /obj/structure/gravemarker/CheckExit(atom/movable/O as mob|obj, target as turf)
 	if(istype(O) && O.checkpass(PASSTABLE))

code/game/objects/structures/grille.dm

@@ -49,15 +49,12 @@
 
 	attack_generic(user,damage_dealt,attack_message)
 
-/obj/structure/grille/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(air_group || (height==0)) return 1
+/obj/structure/grille/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSGRILLE))
-		return 1
-	else
-		if(istype(mover, /obj/item/projectile))
-			return prob(30)
-		else
-			return !density
+		return TRUE
+	if(istype(mover, /obj/item/projectile))
+		return prob(30)
+	return !density
 
 /obj/structure/grille/bullet_act(var/obj/item/projectile/Proj)
 	if(!Proj)	return
@@ -235,14 +232,10 @@
 
 /obj/structure/grille/cult
 	name = "cult grille"
-	desc = "A matrice built out of an unknown material, with some sort of force field blocking air around it"
+	desc = "A matrice built out of an unknown material, with some sort of force field blocking air around it."
 	icon_state = "grillecult"
-	health = 40 //Make it strong enough to avoid people breaking in too easily
-
-/obj/structure/grille/cult/CanPass(atom/movable/mover, turf/target, height = 1.5, air_group = 0)
-	if(air_group)
-		return 0 //Make sure air doesn't drain
-	..()
+	health = 40 // Make it strong enough to avoid people breaking in too easily.
+	can_atmos_pass = ATMOS_PASS_NO // Make sure air doesn't drain.
 
 /obj/structure/grille/broken/cult
 	icon_state = "grillecult-b"

code/game/objects/structures/plasticflaps.dm

@@ -64,15 +64,4 @@
 /obj/structure/plasticflaps/mining //A specific type for mining that doesn't allow airflow because of them damn crates
 	name = "airtight plastic flaps"
 	desc = "Heavy duty, airtight, plastic flaps."
-
-/obj/structure/plasticflaps/mining/New() //set the turf below the flaps to block air
-	var/turf/T = get_turf(loc)
-	if(T)
-		T.blocks_air = 1
-	..()
-
-/obj/structure/plasticflaps/mining/Destroy() //lazy hack to set the turf to allow air to pass if it's a simulated floor
-	var/turf/T = get_turf(loc)
-	if(T && istype(T, /turf/simulated/floor))
-		T.blocks_air = 0
-	..()
+	can_atmos_pass = ATMOS_PASS_NO

code/game/objects/structures/railing.dm

@@ -34,15 +34,12 @@
 	for(var/obj/structure/railing/R in orange(location, 1))
 		R.update_icon()
 
-/obj/structure/railing/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(!mover)
-		return 1
+/obj/structure/railing/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSTABLE))
-		return 1
-	if(get_dir(loc, target) == dir)
+		return TRUE
+	if(get_dir(mover, target) == turn(dir, 180))
 		return !density
-	else
-		return 1
+	return TRUE
 
 /obj/structure/railing/examine(mob/user)
 	. = ..()

code/game/objects/structures/simple_doors.dm

@@ -2,6 +2,7 @@
 	name = "door"
 	density = 1
 	anchored = 1
+	can_atmos_pass = ATMOS_PASS_DENSITY
 
 	icon = 'icons/obj/doors/material_doors.dmi'
 	icon_state = "metal"
@@ -36,7 +37,7 @@
 	else
 		set_opacity(1)
 	if(material.products_need_process())
-		START_PROCESSING(SSobj, src)
+		START_PROCESSING(SSobj, src)
 	update_nearby_tiles(need_rebuild=1)
 
 /obj/structure/simple_door/Destroy()
@@ -63,8 +64,7 @@
 /obj/structure/simple_door/attack_hand(mob/user as mob)
 	return TryToSwitchState(user)
 
-/obj/structure/simple_door/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
-	if(air_group) return 0
+/obj/structure/simple_door/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover, /obj/effect/beam))
 		return !opacity
 	return !density

code/game/objects/structures/stool_bed_chair_nest/bed.dm

@@ -68,11 +68,10 @@
 		name = "[material.display_name] [initial(name)]"
 		desc += " It's made of [material.use_name]."
 
-/obj/structure/bed/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/structure/bed/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSTABLE))
-		return 1
-	else
-		return ..()
+		return TRUE
+	return ..()
 
 /obj/structure/bed/ex_act(severity)
 	switch(severity)

code/game/objects/structures/windoor_assembly.dm

@@ -54,14 +54,12 @@ obj/structure/windoor_assembly/Destroy()
 /obj/structure/windoor_assembly/update_icon()
 	icon_state = "[facing]_[secure]windoor_assembly[state]"
 
-/obj/structure/windoor_assembly/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/structure/windoor_assembly/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSGLASS))
-		return 1
+		return TRUE
 	if(get_dir(loc, target) == dir) //Make sure looking at appropriate border
-		if(air_group) return 0
 		return !density
-	else
-		return 1
+	return TRUE
 
 /obj/structure/windoor_assembly/CheckExit(atom/movable/mover as mob|obj, turf/target as turf)
 	if(istype(mover) && mover.checkpass(PASSGLASS))

code/game/objects/structures/window.dm

@@ -3,6 +3,7 @@
 	desc = "A window."
 	icon = 'icons/obj/structures.dmi'
 	density = 1
+	can_atmos_pass = ATMOS_PASS_DENSITY
 	w_class = ITEMSIZE_NORMAL
 
 	layer = WINDOW_LAYER
@@ -129,7 +130,7 @@
 /obj/structure/window/blob_act()
 	take_damage(50)
 
-/obj/structure/window/CanPass(atom/movable/mover, turf/target, height=0, air_group=0)
+/obj/structure/window/CanPass(atom/movable/mover, turf/target)
 	if(istype(mover) && mover.checkpass(PASSGLASS))
 		return TRUE
 	if(is_fulltile())
@@ -139,6 +140,11 @@
 	else
 		return TRUE
 
+/obj/structure/window/CanZASPass(turf/T, is_zone)
+	if(is_fulltile() || get_dir(T, loc) == turn(dir, 180)) // Make sure we're handling the border correctly.
+		return anchored ? ATMOS_PASS_NO : ATMOS_PASS_YES // If it's anchored, it'll block air.
+	return ATMOS_PASS_YES // Don't stop airflow from the other sides.
+
 /obj/structure/window/CheckExit(atom/movable/O as mob|obj, target as turf)
 	if(istype(O) && O.checkpass(PASSGLASS))
 		return 1

code/game/objects/structures/window_spawner.dm

@@ -10,6 +10,7 @@
 	density = 1
 	anchored = 1.0
 	pressure_resistance = 4*ONE_ATMOSPHERE
+	can_atmos_pass = ATMOS_PASS_NO
 	var/win_path = /obj/structure/window/basic
 	var/activated
 
@@ -22,7 +23,7 @@
 /obj/effect/wingrille_spawn/attack_generic()
 	activate()
 
-/obj/effect/wingrille_spawn/CanPass(atom/movable/mover, turf/target, height=1.5, air_group = 0)
+/obj/effect/wingrille_spawn/CanPass(atom/movable/mover, turf/target)
 	return FALSE
 
 /obj/effect/wingrille_spawn/Initialize()

code/game/shuttle_engines.dm

@@ -9,13 +9,15 @@
 	density = 1
 	opacity = 0
 	anchored = 1
+	can_atmos_pass = ATMOS_PASS_NO
 
 	var/window_flags = 0 // Bitflags to indicate connected windows
 	var/wall_flags = 0 // Bitflags to indicate connected walls
 
-/obj/structure/shuttle/window/CanPass(atom/movable/mover, turf/target, height, air_group)
-	if(!height || air_group) return 0
-	else return ..()
+/obj/structure/shuttle/window/CanPass(atom/movable/mover, turf/target)
+	if(istype(mover) && mover.checkpass(PASSGLASS))
+		return TRUE
+	return ..()
 
 /obj/structure/shuttle/window/Initialize()
 	. = ..()