Porting multi-z support updates.

code/game/atoms.dm

@@ -186,6 +186,10 @@
 			else
 				M.forceMove(src)
 
+//common name
+/atom/proc/update_multiz(prune_on_fail = FALSE)
+	return FALSE
+
 /atom/proc/assume_air(datum/gas_mixture/giver)
 	qdel(giver)
 	return null
@@ -266,7 +270,7 @@
 	if(SEND_SIGNAL(src, COMSIG_ATOM_GET_EXAMINE_NAME, user, override) & COMPONENT_EXNAME_CHANGED)
 		should_override = TRUE
 
-	
+
 	if(blood_DNA && !istype(src, /obj/effect/decal))
 		override[EXAMINE_POSITION_BEFORE] = " blood-stained "
 		should_override = TRUE
@@ -832,4 +836,7 @@ Proc for attack log creation, because really why not
 	if(filter_data[name])
 		filter_data -= name
 		update_filters()
-		return TRUE
+		return TRUE
+
+/atom/proc/intercept_zImpact(atom/movable/AM, levels = 1)
+	return FALSE

code/game/atoms_movable.dm

@@ -35,6 +35,51 @@
 	var/datum/component/orbiter/orbiting
 	var/can_be_z_moved = TRUE
 
+	var/zfalling = FALSE
+
+/atom/movable/proc/can_zFall(turf/source, levels = 1, turf/target, direction)
+	if(!direction)
+		direction = DOWN
+	if(!source)
+		source = get_turf(src)
+		if(!source)
+			return FALSE
+	if(!target)
+		target = get_step_multiz(source, direction)
+		if(!target)
+			return FALSE
+	return !(movement_type & FLYING) && has_gravity(source) && !throwing
+
+/atom/movable/proc/onZImpact(turf/T, levels)
+	var/atom/highest = T
+	for(var/i in T.contents)
+		var/atom/A = i
+		if(!A.density)
+			continue
+		if(isobj(A) || ismob(A))
+			if(A.layer > highest.layer)
+				highest = A
+	INVOKE_ASYNC(src, .proc/SpinAnimation, 5, 2)
+	throw_impact(highest)
+	return TRUE
+
+//For physical constraints to travelling up/down.
+/atom/movable/proc/can_zTravel(turf/destination, direction)
+	var/turf/T = get_turf(src)
+	if(!T)
+		return FALSE
+	if(!direction)
+		if(!destination)
+			return FALSE
+		direction = get_dir(T, destination)
+	if(direction != UP && direction != DOWN)
+		return FALSE
+	if(!destination)
+		destination = get_step_multiz(src, direction)
+		if(!destination)
+			return FALSE
+	return T.zPassOut(src, direction, destination) && destination.zPassIn(src, direction, T)
+
 /atom/movable/vv_edit_var(var_name, var_value)
 	var/static/list/banned_edits = list("step_x", "step_y", "step_size")
 	var/static/list/careful_edits = list("bound_x", "bound_y", "bound_width", "bound_height")

code/game/objects/effects/decals/decal.dm

@@ -15,7 +15,7 @@
 		qdel(src)
 
 /obj/effect/decal/proc/NeverShouldHaveComeHere(turf/T)
-	return isspaceturf(T) || isclosedturf(T) || islava(T) || istype(T, /turf/open/water) || ischasm(T)
+	return isclosedturf(T) || isgroundlessturf(T)
 
 /obj/effect/decal/ex_act(severity, target)
 	qdel(src)

code/game/objects/effects/effects.dm

@@ -57,6 +57,9 @@
 /obj/effect/abstract/singularity_act()
 	return
 
+/obj/effect/abstract/has_gravity(turf/T)
+	return FALSE
+
 /obj/effect/dummy/singularity_pull()
 	return
 

code/game/objects/structures/lattice.dm

@@ -100,6 +100,7 @@
 	number_of_rods = 2
 	smooth = SMOOTH_TRUE
 	canSmoothWith = null
+	obj_flags = CAN_BE_HIT | BLOCK_Z_FALL
 
 /obj/structure/lattice/catwalk/deconstruction_hints(mob/user)
 	to_chat(user, "<span class='notice'>The supporting rods look like they could be <b>cut</b>.</span>")

code/game/objects/structures/stairs.dm

@@ -0,0 +1,125 @@
+#define STAIR_TERMINATOR_AUTOMATIC 0
+#define STAIR_TERMINATOR_NO 1
+#define STAIR_TERMINATOR_YES 2
+
+/obj/structure/stairs
+	name = "stairs"
+	icon = 'icons/obj/stairs.dmi'
+	icon_state = "stairs"
+	anchored = TRUE
+	//dir = direction of travel to go upwards
+
+	var/force_open_above = FALSE
+	var/terminator_mode = STAIR_TERMINATOR_AUTOMATIC
+	var/turf/listeningTo
+
+/obj/structure/stairs/Initialize(mapload)
+	if(force_open_above)
+		force_open_above()
+		build_signal_listener()
+	update_surrounding()
+	return ..()
+
+/obj/structure/stairs/Destroy()
+	listeningTo = null
+	return ..()
+
+/obj/structure/stairs/Move()			//Look this should never happen but...
+	. = ..()
+	if(force_open_above)
+		build_signal_listener()
+	update_surrounding()
+
+/obj/structure/stairs/proc/update_surrounding()
+	update_icon()
+	for(var/i in GLOB.cardinals)
+		var/turf/T = get_step(get_turf(src), i)
+		var/obj/structure/stairs/S = locate() in T
+		if(S)
+			S.update_icon()
+
+/obj/structure/stairs/Uncross(atom/movable/AM, turf/newloc)
+	if(!newloc || !AM)
+		return ..()
+	if(!isobserver(AM) && isTerminator() && (get_dir(src, newloc) == dir))
+		stair_ascend(AM)
+		return FALSE
+	return ..()
+
+/obj/structure/stairs/Cross(atom/movable/AM)
+	if(isTerminator() && (get_dir(src, AM) == dir))
+		return FALSE
+	return ..()
+
+/obj/structure/stairs/update_icon()
+	if(isTerminator())
+		icon_state = "stairs_t"
+	else
+		icon_state = "stairs"
+
+/obj/structure/stairs/proc/stair_ascend(atom/movable/AM)
+	var/turf/checking = get_step_multiz(get_turf(src), UP)
+	if(!istype(checking))
+		return
+	if(!checking.zPassIn(AM, UP, get_turf(src)))
+		return
+	var/turf/target = get_step_multiz(get_turf(src), (dir|UP))
+	if(istype(target) && !target.can_zFall(AM, null, get_step_multiz(target, DOWN)))			//Don't throw them into a tile that will just dump them back down.
+		if(isliving(AM))
+			var/mob/living/L = AM
+			var/pulling = L.pulling
+			if(pulling)
+				L.pulling.forceMove(target)
+			L.forceMove(target)
+			L.start_pulling(pulling)
+		else
+			AM.forceMove(target)
+
+/obj/structure/stairs/vv_edit_var(var_name, var_value)
+	. = ..()
+	if(!.)
+		return
+	if(var_name != NAMEOF(src, force_open_above))
+		return
+	if(!var_value)
+		if(listeningTo)
+			UnregisterSignal(listeningTo, COMSIG_TURF_MULTIZ_NEW)
+			listeningTo = null
+	else
+		build_signal_listener()
+		force_open_above()
+
+/obj/structure/stairs/proc/build_signal_listener()
+	if(listeningTo)
+		UnregisterSignal(listeningTo, COMSIG_TURF_MULTIZ_NEW)
+	var/turf/open/openspace/T = get_step_multiz(get_turf(src), UP)
+	RegisterSignal(T, COMSIG_TURF_MULTIZ_NEW, .proc/on_multiz_new)
+	listeningTo = T
+
+/obj/structure/stairs/proc/force_open_above()
+	var/turf/open/openspace/T = get_step_multiz(get_turf(src), UP)
+	if(T && !istype(T))
+		T.ChangeTurf(/turf/open/openspace)
+
+/obj/structure/stairs/proc/on_multiz_new(turf/source, dir)
+	if(dir == UP)
+		var/turf/open/openspace/T = get_step_multiz(get_turf(src), UP)
+		if(T && !istype(T))
+			T.ChangeTurf(/turf/open/openspace)
+
+/obj/structure/stairs/intercept_zImpact(atom/movable/AM, levels = 1)
+	return isTerminator()
+
+/obj/structure/stairs/proc/isTerminator()			//If this is the last stair in a chain and should move mobs up
+	if(terminator_mode != STAIR_TERMINATOR_AUTOMATIC)
+		return (terminator_mode == STAIR_TERMINATOR_YES)
+	var/turf/T = get_turf(src)
+	if(!T)
+		return FALSE
+	var/turf/them = get_step(T, dir)
+	if(!them)
+		return FALSE
+	for(var/obj/structure/stairs/S in them)
+		if(S.dir == dir)
+			return FALSE
+	return TRUE

code/game/turfs/open.dm

@@ -16,6 +16,22 @@
 	if(wet)
 		AddComponent(/datum/component/wet_floor, wet, INFINITY, 0, INFINITY, TRUE)
 
+//direction is direction of travel of A
+/turf/open/zPassIn(atom/movable/A, direction, turf/source)
+	return (direction == DOWN)
+
+//direction is direction of travel of A
+/turf/open/zPassOut(atom/movable/A, direction, turf/destination)
+	return (direction == UP)
+
+//direction is direction of travel of air
+/turf/open/zAirIn(direction, turf/source)
+	return (direction == DOWN)
+
+//direction is direction of travel of air
+/turf/open/zAirOut(direction, turf/source)
+	return (direction == UP)
+
 /turf/open/MouseDrop_T(atom/dropping, mob/user)
 	. = ..()
 	if(dropping == user && isliving(user))
@@ -184,43 +200,14 @@
 	update_visuals()
 
 	current_cycle = times_fired
-
-	//cache some vars
-	var/list/atmos_adjacent_turfs = src.atmos_adjacent_turfs
-
-	for(var/direction in GLOB.cardinals)
-		var/turf/open/enemy_tile = get_step(src, direction)
-		if(!istype(enemy_tile))
-			if (atmos_adjacent_turfs)
-				atmos_adjacent_turfs -= enemy_tile
-			continue
+	CalculateAdjacentTurfs()
+	for(var/i in atmos_adjacent_turfs)
+		var/turf/open/enemy_tile = i
 		var/datum/gas_mixture/enemy_air = enemy_tile.return_air()
-
-		//only check this turf, if it didn't check us when it was initalized
-		if(enemy_tile.current_cycle < times_fired)
-			if(CANATMOSPASS(src, enemy_tile))
-				LAZYINITLIST(atmos_adjacent_turfs)
-				LAZYINITLIST(enemy_tile.atmos_adjacent_turfs)
-				atmos_adjacent_turfs[enemy_tile] = TRUE
-				enemy_tile.atmos_adjacent_turfs[src] = TRUE
-			else
-				if (atmos_adjacent_turfs)
-					atmos_adjacent_turfs -= enemy_tile
-				if (enemy_tile.atmos_adjacent_turfs)
-					enemy_tile.atmos_adjacent_turfs -= src
-				UNSETEMPTY(enemy_tile.atmos_adjacent_turfs)
-				continue
-		else
-			if (!atmos_adjacent_turfs || !atmos_adjacent_turfs[enemy_tile])
-				continue
-
 		if(!excited && air.compare(enemy_air))
 			//testing("Active turf found. Return value of compare(): [is_active]")
 			excited = TRUE
 			SSair.active_turfs |= src
-	UNSETEMPTY(atmos_adjacent_turfs)
-	if (atmos_adjacent_turfs)
-		src.atmos_adjacent_turfs = atmos_adjacent_turfs
 
 /turf/open/proc/GetHeatCapacity()
 	. = air.heat_capacity()

code/game/turfs/openspace/openspace.dm

@@ -0,0 +1,134 @@
+/turf/open/openspace
+	name = "open space"
+	desc = "Watch your step!"
+	icon_state = "grey"
+	baseturfs = /turf/open/openspace
+	CanAtmosPassVertical = ATMOS_PASS_YES
+	plane = FLOOR_OPENSPACE_PLANE
+	layer = OPENSPACE_LAYER
+	//mouse_opacity = MOUSE_OPACITY_TRANSPARENT
+	var/can_cover_up = TRUE
+	var/can_build_on = TRUE
+
+/turf/open/openspace/debug/update_multiz()
+	..()
+	return TRUE
+
+/turf/open/openspace/Initialize()
+	. = ..()
+	return INITIALIZE_HINT_LATELOAD
+
+/turf/open/openspace/LateInitialize()
+	update_multiz(TRUE, TRUE)
+
+/turf/open/openspace/Destroy()
+	vis_contents.len = 0
+	return ..()
+
+/turf/open/openspace/update_multiz(prune_on_fail = FALSE, init = FALSE)
+	. = ..()
+	var/turf/T = below()
+	if(!T)
+		vis_contents.len = 0
+		if(prune_on_fail)
+			ChangeTurf(/turf/open/floor/plating)
+		return FALSE
+	if(init)
+		vis_contents += T
+	return TRUE
+
+/turf/open/openspace/multiz_turf_del(turf/T, dir)
+	if(dir != DOWN)
+		return
+	update_multiz()
+
+/turf/open/openspace/multiz_turf_new(turf/T, dir)
+	if(dir != DOWN)
+		return
+	update_multiz()
+
+/turf/open/openspace/zAirIn()
+	return TRUE
+
+/turf/open/openspace/zAirOut()
+	return TRUE
+
+/turf/open/openspace/zPassIn(atom/movable/A, direction, turf/source)
+	return TRUE
+
+/turf/open/openspace/zPassOut(atom/movable/A, direction, turf/destination)
+	if(A.anchored)
+		return FALSE
+	for(var/obj/O in contents)
+		if(O.obj_flags & BLOCK_Z_FALL)
+			return FALSE
+	return TRUE
+
+/turf/open/openspace/proc/CanCoverUp()
+	return can_cover_up
+
+/turf/open/openspace/proc/CanBuildHere()
+	return can_build_on
+
+/turf/open/openspace/attackby(obj/item/C, mob/user, params)
+	..()
+	if(!CanBuildHere())
+		return
+	if(istype(C, /obj/item/stack/rods))
+		var/obj/item/stack/rods/R = C
+		var/obj/structure/lattice/L = locate(/obj/structure/lattice, src)
+		var/obj/structure/lattice/catwalk/W = locate(/obj/structure/lattice/catwalk, src)
+		if(W)
+			to_chat(user, "<span class='warning'>There is already a catwalk here!</span>")
+			return
+		if(L)
+			if(R.use(1))
+				to_chat(user, "<span class='notice'>You construct a catwalk.</span>")
+				playsound(src, 'sound/weapons/genhit.ogg', 50, 1)
+				new/obj/structure/lattice/catwalk(src)
+			else
+				to_chat(user, "<span class='warning'>You need two rods to build a catwalk!</span>")
+			return
+		if(R.use(1))
+			to_chat(user, "<span class='notice'>You construct a lattice.</span>")
+			playsound(src, 'sound/weapons/genhit.ogg', 50, 1)
+			ReplaceWithLattice()
+		else
+			to_chat(user, "<span class='warning'>You need one rod to build a lattice.</span>")
+		return
+	if(istype(C, /obj/item/stack/tile/plasteel))
+		if(!CanCoverUp())
+			return
+		var/obj/structure/lattice/L = locate(/obj/structure/lattice, src)
+		if(L)
+			var/obj/item/stack/tile/plasteel/S = C
+			if(S.use(1))
+				qdel(L)
+				playsound(src, 'sound/weapons/genhit.ogg', 50, 1)
+				to_chat(user, "<span class='notice'>You build a floor.</span>")
+				PlaceOnTop(/turf/open/floor/plating)
+			else
+				to_chat(user, "<span class='warning'>You need one floor tile to build a floor!</span>")
+		else
+			to_chat(user, "<span class='warning'>The plating is going to need some support! Place metal rods first.</span>")
+
+/turf/open/openspace/rcd_vals(mob/user, obj/item/construction/rcd/the_rcd)
+	if(!CanBuildHere())
+		return FALSE
+
+	switch(the_rcd.mode)
+		if(RCD_FLOORWALL)
+			var/obj/structure/lattice/L = locate(/obj/structure/lattice, src)
+			if(L)
+				return list("mode" = RCD_FLOORWALL, "delay" = 0, "cost" = 1)
+			else
+				return list("mode" = RCD_FLOORWALL, "delay" = 0, "cost" = 3)
+	return FALSE
+
+/turf/open/openspace/rcd_act(mob/user, obj/item/construction/rcd/the_rcd, passed_mode)
+	switch(passed_mode)
+		if(RCD_FLOORWALL)
+			to_chat(user, "<span class='notice'>You build a floor.</span>")
+			PlaceOnTop(/turf/open/floor/plating, flags = CHANGETURF_INHERIT_AIR)
+			return TRUE
+	return FALSE

code/game/turfs/turf.dm

@@ -39,7 +39,7 @@
 		return FALSE
 	. = ..()
 
-/turf/Initialize()
+/turf/Initialize(mapload)
 	if(flags_1 & INITIALIZED_1)
 		stack_trace("Warning: [src]([type]) initialized multiple times!")
 	flags_1 |= INITIALIZED_1
@@ -68,6 +68,15 @@
 	if (light_power && light_range)
 		update_light()
 
+	var/turf/T = SSmapping.get_turf_above(src)
+	if(T)
+		T.multiz_turf_new(src, DOWN)
+		SEND_SIGNAL(T, COMSIG_TURF_MULTIZ_NEW, src, DOWN)
+	T = SSmapping.get_turf_below(src)
+	if(T)
+		T.multiz_turf_new(src, UP)
+		SEND_SIGNAL(T, COMSIG_TURF_MULTIZ_NEW, src, UP)
+
 	if (opacity)
 		has_opaque_atom = TRUE
 
@@ -83,6 +92,12 @@
 	if(!changing_turf)
 		stack_trace("Incorrect turf deletion")
 	changing_turf = FALSE
+	var/turf/T = SSmapping.get_turf_above(src)
+	if(T)
+		T.multiz_turf_del(src, DOWN)
+	T = SSmapping.get_turf_below(src)
+	if(T)
+		T.multiz_turf_del(src, UP)
 	if(force)
 		..()
 		//this will completely wipe turf state
@@ -105,6 +120,54 @@
 		return
 	user.Move_Pulled(src)
 
+/turf/proc/multiz_turf_del(turf/T, dir)
+
+/turf/proc/multiz_turf_new(turf/T, dir)
+
+//zPassIn doesn't necessarily pass an atom!
+//direction is direction of travel of air
+/turf/proc/zPassIn(atom/movable/A, direction, turf/source)
+	return FALSE
+
+//direction is direction of travel of air
+/turf/proc/zPassOut(atom/movable/A, direction, turf/destination)
+	return FALSE
+
+//direction is direction of travel of air
+/turf/proc/zAirIn(direction, turf/source)
+	return FALSE
+
+//direction is direction of travel of air
+/turf/proc/zAirOut(direction, turf/source)
+	return FALSE
+
+/turf/proc/zImpact(atom/movable/A, levels = 1)
+	for(var/i in contents)
+		var/atom/thing = i
+		if(thing.intercept_zImpact(A, levels))
+			return FALSE
+	if(zFall(A, ++levels))
+		return FALSE
+	A.visible_message("<span class='danger'>[A] crashes into [src]!</span>")
+	A.onZImpact(src, levels)
+	return TRUE
+
+/turf/proc/can_zFall(atom/movable/A, levels = 1, turf/target)
+	return zPassOut(A, DOWN, target) && target.zPassIn(A, DOWN, src)
+
+/turf/proc/zFall(atom/movable/A, levels = 1, force = FALSE)
+	var/turf/target = get_step_multiz(src, DOWN)
+	if(!target || (!isobj(A) && !ismob(A)))
+		return FALSE
+	if(!force && (!can_zFall(A, levels, target) || !A.can_zFall(src, levels, target, DOWN)))
+		return FALSE
+	A.visible_message("<span class='danger'>[A] falls through [src]!</span>")
+	A.zfalling = TRUE
+	A.forceMove(target)
+	A.zfalling = FALSE
+	target.zImpact(A, levels)
+	return TRUE
+
 /turf/proc/handleRCL(obj/item/twohanded/rcl/C, mob/user)
 	if(C.loaded)
 		for(var/obj/structure/cable/LC in src)
@@ -196,6 +259,9 @@
 		if(O.obj_flags & FROZEN)
 			O.make_unfrozen()
 
+	if(!AM.zfalling)
+		zFall(AM)
+
 /turf/proc/is_plasteel_floor()
 	return FALSE