[READY]MultiZ stuff - tile atmos, movement backend, falling backend, etc etc - Electric boogaloo (#40428)

Basic multiZ mob movement procs (Observers can always move)
Open space, showing what things are below it, and everything that entails. No complex support for dynamic generation just yet.
Decide how openspace should look :/

    Atoms falling through open space (NO MOB SUPPORT/DAMAGE/ANYTHING YET.)

//CANCELLED FOR ANOTHER PR - [ ] Being able to see upwards? Downwards is going to be handled by open space.

MultiZ tile atmospherics - EDIT: Working demo! https://puu.sh/B7mUs/3f6274740f.mp4
Bugtest the heck out of this trainwreck.

_maps/multiz_debug.dm

@@ -0,0 +1 @@
+#define FORCE_MAP "_maps/multiz_debug.json"

_maps/multiz_debug.json

@@ -0,0 +1,6 @@
+{
+    "map_name": "MultiZ Debug",
+    "map_path": "map_files/debug",
+    "map_file": "multiz.dmm",
+	"traits": [{"Up": 1}, {"Up": 1, "Down": -1}, {"Down": -1}]
+	}

code/__DEFINES/atmospherics.dm

@@ -147,7 +147,9 @@
 #define ATMOS_PASS_NO 0
 #define ATMOS_PASS_PROC -1 //ask CanAtmosPass()
 #define ATMOS_PASS_DENSITY -2 //just check density
+
 #define CANATMOSPASS(A, O) ( A.CanAtmosPass == ATMOS_PASS_PROC ? A.CanAtmosPass(O) : ( A.CanAtmosPass == ATMOS_PASS_DENSITY ? !A.density : A.CanAtmosPass ) )
+#define CANVERTICALATMOSPASS(A, O) ( A.CanAtmosPassVertical == ATMOS_PASS_PROC ? A.CanAtmosPass(O, TRUE) : ( A.CanAtmosPassVertical == ATMOS_PASS_DENSITY ? !A.density : A.CanAtmosPassVertical ) )
 
 //OPEN TURF ATMOS
 #define OPENTURF_DEFAULT_ATMOS		"o2=22;n2=82;TEMP=293.15" //the default air mix that open turfs spawn

code/__DEFINES/components.dm

@@ -103,6 +103,8 @@
 // /turf signals
 #define COMSIG_TURF_CHANGE "turf_change"						//from base of turf/ChangeTurf(): (path, list/new_baseturfs, flags, list/transferring_comps)
 #define COMSIG_TURF_HAS_GRAVITY "turf_has_gravity"				//from base of atom/has_gravity(): (atom/asker, list/forced_gravities)
+#define COMSIG_TURF_MULTIZ_NEW "turf_multiz_new"				//from base of turf/New(): (turf/source, direction)
+
 
 // /atom/movable signals
 #define COMSIG_MOVABLE_MOVED "movable_moved"					//from base of atom/movable/Moved(): (/atom, dir)

code/__DEFINES/layers.dm

@@ -9,6 +9,7 @@
 #define FLOOR_PLANE -2
 #define GAME_PLANE -1
 #define BLACKNESS_PLANE 0 //To keep from conflicts with SEE_BLACKNESS internals
+
 #define SPACE_LAYER 1.8
 //#define TURF_LAYER 2 //For easy recordkeeping; this is a byond define
 #define MID_TURF_LAYER 2.02
@@ -82,11 +83,15 @@
 #define ABOVE_LIGHTING_PLANE 16
 #define ABOVE_LIGHTING_LAYER 16
 
-#define BYOND_LIGHTING_PLANE 17
-#define BYOND_LIGHTING_LAYER 17
+#define FLOOR_OPENSPACE_PLANE 17
+#define OPENSPACE_LAYER 17
+
+#define BYOND_LIGHTING_PLANE 18
+#define BYOND_LIGHTING_LAYER 18
+
+#define CAMERA_STATIC_PLANE 19
+#define CAMERA_STATIC_LAYER 19
 
-#define CAMERA_STATIC_PLANE 18
-#define CAMERA_STATIC_LAYER 18
 //HUD layer defines
 
 #define FULLSCREEN_PLANE 19

code/_globalvars/lists/mapping.dm

@@ -1,6 +1,16 @@
 GLOBAL_LIST_INIT(cardinals, list(NORTH, SOUTH, EAST, WEST))
-GLOBAL_LIST_INIT(alldirs, list(NORTH, SOUTH, EAST, WEST, NORTHEAST, NORTHWEST, SOUTHEAST, SOUTHWEST))
+GLOBAL_LIST_INIT(cardinals_multiz, list(NORTH, SOUTH, EAST, WEST, UP, DOWN))
 GLOBAL_LIST_INIT(diagonals, list(NORTHEAST, NORTHWEST, SOUTHEAST, SOUTHWEST))
+GLOBAL_LIST_INIT(corners_multiz, list(UP|NORTHEAST, UP|NORTHWEST, UP|SOUTHEAST, UP|SOUTHWEST, DOWN|NORTHEAST, DOWN|NORTHWEST, DOWN|SOUTHEAST, DOWN|SOUTHWEST))
+GLOBAL_LIST_INIT(diagonals_multiz, list(
+	NORTHEAST, NORTHWEST, SOUTHEAST, SOUTHWEST,
+	UP|NORTH, UP|SOUTH, UP|EAST, UP|WEST, UP|NORTHEAST, UP|NORTHWEST, UP|SOUTHEAST, UP|SOUTHWEST,
+	DOWN|NORTH, DOWN|SOUTH, DOWN|EAST, DOWN|WEST, DOWN|NORTHEAST, DOWN|NORTHWEST, DOWN|SOUTHEAST, DOWN|SOUTHWEST))
+GLOBAL_LIST_INIT(alldirs_multiz, list(
+	NORTH, SOUTH, EAST, WEST, NORTHEAST, NORTHWEST, SOUTHEAST, SOUTHWEST,
+	UP, UP|NORTH, UP|SOUTH, UP|EAST, UP|WEST, UP|NORTHEAST, UP|NORTHWEST, UP|SOUTHEAST, UP|SOUTHWEST,
+	DOWN, DOWN|NORTH, DOWN|SOUTH, DOWN|EAST, DOWN|WEST, DOWN|NORTHEAST, DOWN|NORTHWEST, DOWN|SOUTHEAST, DOWN|SOUTHWEST))
+GLOBAL_LIST_INIT(alldirs, list(NORTH, SOUTH, EAST, WEST, NORTHEAST, NORTHWEST, SOUTHEAST, SOUTHWEST))
 
 GLOBAL_LIST_EMPTY(landmarks_list)				//list of all landmarks created
 GLOBAL_LIST_EMPTY(start_landmarks_list)			//list of all spawn points created

code/_onclick/hud/plane_master.dm

@@ -16,6 +16,28 @@
 //Trust me, you need one. Period. If you don't think you do, you're doing something extremely wrong.
 /obj/screen/plane_master/proc/backdrop(mob/mymob)
 
+/obj/screen/plane_master/openspace
+	name = "open space plane master"
+	plane = FLOOR_OPENSPACE_PLANE
+	appearance_flags = PLANE_MASTER
+	blend_mode = BLEND_MULTIPLY
+	alpha = 255
+
+/obj/screen/plane_master/openspace/backdrop(mob/mymob)
+	filters = list()
+	filters += filter(type = "drop_shadow", color = "#04080FAA", border = 5, size = -10)
+	filters += filter(type = "drop_shadow", color = "#04080FAA", border = 5, size = -15)
+	filters += filter(type = "drop_shadow", color = "#04080FAA", border = 5, size = -20)
+
+/obj/screen/plane_master/proc/outline(_size, _color)
+	filters += filter(type = "outline", size = _size, color = _color)
+
+/obj/screen/plane_master/proc/shadow(_size, _border, _offset = 0, _x = 0, _y = 0, _color = "#04080FAA")
+	filters += filter(type = "drop_shadow", x = _x, y = _y, color = _color, size = _size, offset = _offset, border = _border)
+
+/obj/screen/plane_master/proc/clear_filters()
+	filters = list()
+
 /obj/screen/plane_master/floor
 	name = "floor plane master"
 	plane = FLOOR_PLANE

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
@@ -728,3 +732,6 @@ Proc for attack log creation, because really why not
 /atom/movable/proc/get_filter(name)
 	if(filter_data && filter_data[name])
 		return filters[filter_data.Find(name)]
+
+/atom/proc/intercept_zImpact(atom/movable/AM, levels = 1)
+	return FALSE

code/game/atoms_movable.dm

@@ -36,6 +36,51 @@
 	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/effects.dm

@@ -58,6 +58,9 @@
 /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/stairs.dm

@@ -0,0 +1,111 @@
+#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/datum/component/redirect/multiz_signal_listener
+
+/obj/structure/stairs/Initialize(mapload)
+	if(force_open_above)
+		force_open_above()
+		build_signal_listener()
+	update_surrounding()
+	return ..()
+
+/obj/structure/stairs/Destroy()
+	QDEL_NULL(multiz_signal_listener)
+	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(isliving(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.
+		AM.forceMove(target)
+
+/obj/structure/stairs/vv_edit_var(var_name, var_value)
+	. = ..()
+	if(.)
+		if(var_name == NAMEOF(src, force_open_above))
+			if(!var_value)
+				QDEL_NULL(multiz_signal_listener)
+			else
+				build_signal_listener()
+				force_open_above()
+
+/obj/structure/stairs/proc/build_signal_listener()
+	QDEL_NULL(multiz_signal_listener)
+	var/turf/open/openspace/T = get_step_multiz(get_turf(src), UP)
+	multiz_signal_listener = T.AddComponent(/datum/component/redirect, list(COMSIG_TURF_MULTIZ_NEW = CALLBACK(src, .proc/on_multiz_new)))
+
+/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/indestructible
 	name = "floor"
 	icon = 'icons/turf/floors.dmi'
@@ -157,43 +173,14 @@
 	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 +1,108 @@
+/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)
+	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>")

code/game/turfs/space/space.dm

@@ -19,7 +19,6 @@
 	dynamic_lighting = DYNAMIC_LIGHTING_DISABLED
 	bullet_bounce_sound = null
 
-
 /turf/open/space/basic/New()	//Do not convert to Initialize
 	//This is used to optimize the map loader
 	return

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)
@@ -193,6 +256,8 @@
 		var/obj/O = AM
 		if(O.obj_flags & FROZEN)
 			O.make_unfrozen()
+	if(!AM.zfalling)
+		zFall(AM)
 
 /turf/proc/is_plasteel_floor()
 	return FALSE

code/modules/atmospherics/environmental/LINDA_system.dm

@@ -1,4 +1,6 @@
 /atom/var/CanAtmosPass = ATMOS_PASS_YES
+/atom/var/CanAtmosPassVertical = ATMOS_PASS_YES
+
 /atom/proc/CanAtmosPass(turf/T)
 	switch (CanAtmosPass)
 		if (ATMOS_PASS_PROC)
@@ -8,42 +10,45 @@
 		else
 			return CanAtmosPass
 
-/turf/closed/CanAtmosPass = ATMOS_PASS_NO
+/turf/CanAtmosPass = ATMOS_PASS_NO
+/turf/CanAtmosPassVertical = ATMOS_PASS_NO
 
 /turf/open/CanAtmosPass = ATMOS_PASS_PROC
-/turf/open/CanAtmosPass(turf/T)
-	var/R
+/turf/open/CanAtmosPassVertical = ATMOS_PASS_PROC
+
+/turf/open/CanAtmosPass(turf/T, vertical = FALSE)
+	var/dir = vertical? get_dir_multiz(src, T) : get_dir(src, T)
+	var/opp = dir_inverse_multiz(dir)
+	var/R = FALSE
+	if(vertical && !(zAirOut(dir, T) && T.zAirIn(dir, src)))
+		R = TRUE
 	if(blocks_air || T.blocks_air)
-		R = 1
+		R = TRUE
 
 	for(var/obj/O in contents+T.contents)
 		var/turf/other = (O.loc == src ? T : src)
-		if(!CANATMOSPASS(O, other))
-			R = 1
+		if(!(vertical? (CANVERTICALATMOSPASS(O, other)) : (CANATMOSPASS(O, other))))
+			R = TRUE
 			if(O.BlockSuperconductivity()) 	//the direction and open/closed are already checked on CanAtmosPass() so there are no arguments
-				var/D = get_dir(src, T)
-				atmos_supeconductivity |= D
-				D = get_dir(T, src)
-				T.atmos_supeconductivity |= D
-				return 0						//no need to keep going, we got all we asked
+				atmos_supeconductivity |= dir
+				T.atmos_supeconductivity |= opp
+				return FALSE						//no need to keep going, we got all we asked
 
-	atmos_supeconductivity &= ~get_dir(src, T)
-	T.atmos_supeconductivity &= ~get_dir(T, src)
+	atmos_supeconductivity &= ~dir
+	T.atmos_supeconductivity &= ~opp
 
 	return !R
 
-
-
 /atom/movable/proc/BlockSuperconductivity() // objects that block air and don't let superconductivity act. Only firelocks atm.
-	return 0
+	return FALSE
 
 /turf/proc/CalculateAdjacentTurfs()
 	var/list/atmos_adjacent_turfs = src.atmos_adjacent_turfs
-	for(var/direction in GLOB.cardinals)
-		var/turf/T = get_step(src, direction)
-		if(!T)
+	for(var/direction in GLOB.cardinals_multiz)
+		var/turf/T = get_step_multiz(src, direction)
+		if(!isopenturf(T))
 			continue
-		if( !(blocks_air || T.blocks_air) && CANATMOSPASS(T, src) )
+		if(!(blocks_air || T.blocks_air) && ((direction & (UP|DOWN))? (CANVERTICALATMOSPASS(T, src)) : (CANATMOSPASS(T, src))) )
 			LAZYINITLIST(atmos_adjacent_turfs)
 			LAZYINITLIST(T.atmos_adjacent_turfs)
 			atmos_adjacent_turfs[T] = TRUE
@@ -72,11 +77,13 @@
 
 	var/turf/curloc = src
 
-	for (var/direction in GLOB.diagonals)
+	for (var/direction in GLOB.diagonals_multiz)
 		var/matchingDirections = 0
-		var/turf/S = get_step(curloc, direction)
+		var/turf/S = get_step_multiz(curloc, direction)
+		if(!S)
+			continue
 
-		for (var/checkDirection in GLOB.cardinals)
+		for (var/checkDirection in GLOB.cardinals_multiz)
 			var/turf/checkTurf = get_step(S, checkDirection)
 			if(!S.atmos_adjacent_turfs || !S.atmos_adjacent_turfs[checkTurf])
 				continue

code/modules/atmospherics/environmental/LINDA_turf_tile.dm

@@ -42,8 +42,7 @@
 
 /turf/open/Destroy()
 	if(active_hotspot)
-		qdel(active_hotspot)
-		active_hotspot = null
+		QDEL_NULL(active_hotspot)
 	// Adds the adjacent turfs to the current atmos processing
 	for(var/T in atmos_adjacent_turfs)
 		SSair.add_to_active(T)

code/modules/mapping/space_management/multiz_helpers.dm

@@ -0,0 +1,47 @@
+/proc/get_step_multiz(ref, dir)
+	if(dir & UP)
+		dir &= ~UP
+		return get_step(SSmapping.get_turf_above(get_turf(ref)), dir)
+	if(dir & DOWN)
+		dir &= ~DOWN
+		return get_step(SSmapping.get_turf_below(get_turf(ref)), dir)
+	return get_step(ref, dir)
+
+/proc/get_dir_multiz(turf/us, turf/them)
+	us = get_turf(us)
+	them = get_turf(them)
+	if(!us || !them)
+		return NONE
+	if(us.z == them.z)
+		return get_dir(us, them)
+	else
+		var/turf/T = us.above()
+		var/dir = NONE
+		if(T && (T.z == them.z))
+			dir = UP
+		else
+			T = us.below()
+			if(T && (T.z == them.z))
+				dir = DOWN
+			else
+				return get_dir(us, them)
+		return (dir | get_dir(us, them))
+
+/turf/proc/above()
+	return get_step_multiz(src, UP)
+
+/turf/proc/below()
+	return get_step_multiz(src, DOWN)
+
+/proc/dir_inverse_multiz(dir)
+	var/holder = dir & (UP|DOWN)
+	if((holder == NONE) || (holder == (UP|DOWN)))
+		return turn(dir, 180)
+	dir &= ~(UP|DOWN)
+	dir = turn(dir, 180)
+	if(holder == UP)
+		holder = DOWN
+	else
+		holder = UP
+	dir |= holder
+	return dir

code/modules/mob/dead/observer/observer.dm

@@ -15,6 +15,7 @@ GLOBAL_VAR_INIT(observer_default_invisibility, INVISIBILITY_OBSERVER)
 	see_in_dark = 100
 	invisibility = INVISIBILITY_OBSERVER
 	hud_type = /datum/hud/ghost
+	movement_type = GROUND | FLYING
 	var/can_reenter_corpse
 	var/datum/hud/living/carbon/hud = null // hud
 	var/bootime = 0

code/modules/mob/dead/observer/observer_movement.dm

@@ -0,0 +1,2 @@
+/mob/dead/observer/canZMove(direction, turf/target)
+	return TRUE

code/modules/mob/living/living.dm

@@ -40,6 +40,15 @@
 	QDEL_LIST(diseases)
 	return ..()
 
+/mob/living/onZImpact(turf/T, levels)
+	ZImpactDamage(T, levels)
+	return ..()
+
+/mob/living/proc/ZImpactDamage(turf/T, levels)
+	visible_message("<span class='danger'>[src] crashes into [T] with a sickening noise!</span>")
+	adjustBruteLoss((levels * 5) ** 1.5)
+	Knockdown(levels * 50)
+
 /mob/living/proc/OpenCraftingMenu()
 	return
 

code/modules/mob/living/living_movement.dm

@@ -25,3 +25,9 @@
 		add_movespeed_modifier(MOVESPEED_ID_LIVING_TURF_SPEEDMOD, TRUE, 100, override = TRUE, multiplicative_slowdown = T.slowdown)
 	else
 		remove_movespeed_modifier(MOVESPEED_ID_LIVING_TURF_SPEEDMOD)
+
+/mob/living/can_zFall(turf/T, levels)
+	return !(movement_type & FLYING)
+
+/mob/living/canZMove(dir, turf/target)
+	return can_zTravel(target, dir) && (movement_type & FLYING)

code/modules/mob/mob_movement.dm

@@ -373,3 +373,35 @@
 	if(hud_used && hud_used.static_inventory)
 		for(var/obj/screen/mov_intent/selector in hud_used.static_inventory)
 			selector.update_icon(src)
+
+/mob/verb/up()
+	set name = "Move Upwards"
+	set category = "IC"
+
+	if(zMove(UP, TRUE))
+		to_chat(src, "<span class='notice'>You move upwards.</span>")
+
+/mob/verb/down()
+	set name = "Move Down"
+	set category = "IC"
+
+	if(zMove(DOWN, TRUE))
+		to_chat(src, "<span class='notice'>You move down.</span>")
+
+/mob/proc/zMove(dir, feedback = FALSE)
+	if(dir != UP && dir != DOWN)
+		return FALSE
+	var/turf/target = get_step_multiz(src, dir)
+	if(!target)
+		if(feedback)
+			to_chat(src, "<span class='warning'>There's nothing in that direction!</span>")
+		return FALSE
+	if(!canZMove(dir, target))
+		if(feedback)
+			to_chat(src, "<span class='warning'>You couldn't move there!</span>")
+		return FALSE
+	forceMove(target)
+	return TRUE
+
+/mob/proc/canZMove(direction, turf/target)
+	return FALSE

code/modules/shuttle/shuttle.dm

@@ -33,6 +33,9 @@
 	else
 		return QDEL_HINT_LETMELIVE
 
+/obj/docking_port/has_gravity(turf/T)
+	return FALSE
+
 /obj/docking_port/take_damage()
 	return
 

config/maps.txt

@@ -42,3 +42,6 @@ endmap
 
 map runtimestation
 endmap
+
+map multiz_debug
+endmap

tgstation.dme

@@ -14,6 +14,7 @@
 
 // BEGIN_INCLUDE
 #include "_maps\_basemap.dm"
+#include "_maps\multiz_debug.dm"
 #include "code\_compile_options.dm"
 #include "code\world.dm"
 #include "code\__DEFINES\_globals.dm"
@@ -995,6 +996,7 @@
 #include "code\game\objects\structures\showcase.dm"
 #include "code\game\objects\structures\spawner.dm"
 #include "code\game\objects\structures\spirit_board.dm"
+#include "code\game\objects\structures\stairs.dm"
 #include "code\game\objects\structures\statues.dm"
 #include "code\game\objects\structures\table_frames.dm"
 #include "code\game\objects\structures\tables_racks.dm"
@@ -1050,6 +1052,7 @@
 #include "code\game\turfs\closed.dm"
 #include "code\game\turfs\open.dm"
 #include "code\game\turfs\turf.dm"
+#include "code\game\turfs\openspace\openspace.dm"
 #include "code\game\turfs\simulated\chasm.dm"
 #include "code\game\turfs\simulated\dirtystation.dm"
 #include "code\game\turfs\simulated\floor.dm"
@@ -1782,6 +1785,7 @@
 #include "code\modules\mapping\reader.dm"
 #include "code\modules\mapping\ruins.dm"
 #include "code\modules\mapping\verify.dm"
+#include "code\modules\mapping\space_management\multiz_helpers.dm"
 #include "code\modules\mapping\space_management\space_level.dm"
 #include "code\modules\mapping\space_management\space_reservation.dm"
 #include "code\modules\mapping\space_management\space_transition.dm"
@@ -1848,6 +1852,7 @@
 #include "code\modules\mob\dead\observer\logout.dm"
 #include "code\modules\mob\dead\observer\notificationprefs.dm"
 #include "code\modules\mob\dead\observer\observer.dm"
+#include "code\modules\mob\dead\observer\observer_movement.dm"
 #include "code\modules\mob\dead\observer\say.dm"
 #include "code\modules\mob\living\blood.dm"
 #include "code\modules\mob\living\bloodcrawl.dm"