Ports new zmimic changes/bugfixes/etc from Bay/Nebula. (#14495)

code/__defines/ZAS.dm

@@ -27,18 +27,10 @@ var/list/gzn_check = list(NORTH, SOUTH, EAST, WEST, UP, DOWN)
 	} \
 	else if (B.z != A.z) { \
 		if (B.z < A.z) { \
-			if (!isopenturf(A)) { \
-				ret = BLOCKED; \
-			} else { \
-				ret = ZONE_BLOCKED; \
-			} \
+			ret = (A.z_flags & ZM_ALLOW_ATMOS) ? ZONE_BLOCKED : BLOCKED; \
 		} \
 		else { \
-			if (!isopenturf(B)) { \
-				ret = BLOCKED; \
-			} else { \
-				ret = ZONE_BLOCKED; \
-			} \
+			ret = (B.z_flags & ZM_ALLOW_ATMOS) ? ZONE_BLOCKED : BLOCKED; \
 		} \
 	} \
 	else if (A.blocks_air & ZONE_BLOCKED || B.blocks_air & ZONE_BLOCKED) { \

code/__defines/_layers.dm

@@ -48,6 +48,8 @@
 #define BLOB_NODE_LAYER             4.12
 #define BLOB_CORE_LAYER	            4.13
 
+#define MIMICED_LIGHTING_LAYER      4.21	// Z-Mimic-managed lighting
+
 #define CLICKCATCHER_PLANE -100
 
 #define DEFAULT_APPEARANCE_FLAGS (PIXEL_SCALE)

code/__defines/_macros.dm

@@ -72,6 +72,8 @@
 
 #define isspace(A) istype(A, /area/space)
 
+#define isspaceturf(A) istype(A, /turf/space)
+
 #define isobserver(A) istype(A, /mob/abstract/observer)
 
 #define isorgan(A) istype(A, /obj/item/organ/external)

code/__defines/flags.dm

@@ -1,3 +1,27 @@
 // Movable flags.
 #define MOVABLE_FLAG_EFFECTMOVE       1 //Is this an effect that should move?
 #define MOVABLE_FLAG_DEL_SHUTTLE      2 //Shuttle transition will delete this.
+
+#define TURF_IS_MIMICING(T) (isturf(T) && (T:z_flags & ZM_MIMIC_BELOW))
+#define CHECK_OO_EXISTENCE(OO) if (OO && !TURF_IS_MIMICING(OO.loc)) { qdel(OO); }
+#define UPDATE_OO_IF_PRESENT CHECK_OO_EXISTENCE(bound_overlay); if (bound_overlay) { update_above(); }
+
+// Turf MZ flags.
+#define ZM_MIMIC_BELOW     1	// If this turf should mimic the turf on the Z below.
+#define ZM_MIMIC_OVERWRITE 2	// If this turf is Z-mimicing, overwrite the turf's appearance instead of using a movable. This is faster, but means the turf cannot have its own appearance (say, edges or a translucent sprite).
+#define ZM_ALLOW_ATMOS     4	// If this turf permits passage of air.
+#define ZM_MIMIC_NO_AO    8	// If the turf shouldn't apply regular turf AO and only do Z-mimic AO.
+#define ZM_NO_OCCLUDE     16	// Don't occlude below atoms if we're a non-mimic z-turf.
+
+// Convenience flag.
+#define ZM_MIMIC_DEFAULTS (ZM_MIMIC_BELOW)
+
+// For debug purposes, should contain the above defines in ascending order.
+var/list/mimic_defines = list(
+	"ZM_MIMIC_BELOW",
+	"ZM_MIMIC_OVERWRITE",
+	"ZM_ALLOW_LIGHTING",
+	"ZM_ALLOW_ATMOS",
+	"ZM_MIMIC_NO_AO",
+	"ZM_NO_OCCLUDE"
+)

code/__defines/misc.dm

@@ -6,10 +6,6 @@
 
 // Turf-only flags.
 #define NOJAUNT 1          // This is used in literally one place, turf.dm, to block ethereal jaunt.
-#define MIMIC_BELOW 2      // If this turf should mimic the turf on the Z below.
-#define MIMIC_OVERWRITE 4  // If this turf is Z-mimicing, overwrite the turf's appearance instead of using a movable. This is faster, but means the turf cannot have an icon.
-#define MIMIC_QUEUED 8     // If the turf is currently queued for Z-mimic update.
-#define MIMIC_NO_AO 16     // If the turf shouldn't apply regular turf AO and only do Z-mimic AO.
 
 #define TRANSITIONEDGE 7 // Distance from edge to move to another z-level.
 #define RUIN_MAP_EDGE_PAD 15

code/__defines/subsystem-defines.dm

@@ -85,11 +85,6 @@
 #define STOP_EFFECT(effect) effect.isprocessing = FALSE; SSeffects.effect_systems -= effect;
 #define STOP_VISUAL(visual)	visual.isprocessing = FALSE; SSeffects.visuals -= visual;
 
-// -- SSzcopy --
-#define TURF_IS_MIMICING(T) (isturf(T) && (T.flags & MIMIC_BELOW))
-#define CHECK_OO_EXISTENCE(OO) if (OO && !TURF_IS_MIMICING(OO.loc)) { qdel(OO); }
-#define UPDATE_OO_IF_PRESENT CHECK_OO_EXISTENCE(bound_overlay); if (bound_overlay) { update_above(); }
-
 // -- SSfalling --
 #define ADD_FALLING_ATOM(atom) if (!atom.multiz_falling) { atom.multiz_falling = 1; SSfalling.falling[atom] = 0; }
 

code/controllers/subsystems/zcopy.dm

@@ -2,6 +2,7 @@
 #define OPENTURF_CAP_PLANE -70      // The multiplier goes here so it'll be on top of every other overlay.
 #define OPENTURF_MAX_DEPTH 10		// The maxiumum number of planes deep we'll go before we just dump everything on the same plane.
 #define SHADOWER_DARKENING_FACTOR 0.85	// The multiplication factor for openturf shadower darkness. Lighting will be multiplied by this.
+#define SHADOWER_DARKENING_COLOR "#999999"	// The above, but as an RGB string for lighting-less turfs.
 
 /var/datum/controller/subsystem/zcopy/SSzcopy
 
@@ -17,80 +18,118 @@
 	var/list/queued_overlays = list()
 	var/qo_idex = 1
 
-	var/list/openspace_overlays = list()
-	var/list/openspace_turfs = list()
+	var/openspace_overlays = 0
+	var/openspace_turfs = 0
 
-	var/starlight_enabled = FALSE
+	var/multiqueue_skips_turf = 0
+	var/multiqueue_skips_object = 0
+
+	// Highest Z level in a given Z-group for absolute layering.
+	// zstm[zlev] = group_max
+	var/list/zlev_maximums = list()
 
 /datum/controller/subsystem/zcopy/New()
 	NEW_SS_GLOBAL(SSzcopy)
 
+// for admin proc-call
 /datum/controller/subsystem/zcopy/proc/update_all()
 	disable()
-	for (var/thing in openspace_overlays)
-		var/atom/movable/AM = thing
+	log_debug("SSzcopy: update_all() invoked.")
 
-		var/turf/T = get_turf(AM)
-		if (TURF_IS_MIMICING(T))
-			if (!(T.flags & MIMIC_QUEUED))
+	var/turf/T 	// putting the declaration up here totally speeds it up, right?
+	var/num_upd = 0
+	var/num_del = 0
+	var/num_amupd = 0
+	for (var/atom/A in world)
+		if (isturf(A))
+			T = A
+			if (T.z_flags & ZM_MIMIC_BELOW)
 				T.update_mimic()
+				num_upd += 1
+
+		else if (istype(A, /atom/movable/openspace/mimic))
+			var/turf/Tloc = A.loc
+			if (TURF_IS_MIMICING(Tloc))
+				Tloc.update_mimic()
+				num_amupd += 1
 			else
-			qdel(AM)
+				qdel(A)
+				num_del += 1
 
 		CHECK_TICK
 
-	for (var/thing in openspace_turfs)
-		var/turf/T = thing
-		T.update_mimic()
+	log_debug("SSzcopy: [num_upd + num_amupd] turf updates queued ([num_upd] direct, [num_amupd] indirect), [num_del] orphans destroyed.")
 
 	enable()
 
+// for admin proc-call
 /datum/controller/subsystem/zcopy/proc/hard_reset()
 	disable()
 	log_debug("SSzcopy: hard_reset() invoked.")
 	var/num_deleted = 0
-	var/thing
-	for (thing in openspace_overlays)
-		qdel(thing)
-		num_deleted++
-		CHECK_TICK
-
-	log_debug("SSzcopy: deleted [num_deleted] overlays.")
-
 	var/num_turfs = 0
-	for (thing in turfs)
-		var/turf/T = thing
-		if (T.flags & MIMIC_BELOW)
+
+	var/turf/T
+	for (var/atom/A in world)
+		if (isturf(A))
+			T = A
+			if (T.z_flags & ZM_MIMIC_BELOW)
 				T.update_mimic()
-			num_turfs++
+				num_turfs += 1
+
+		else if (istype(A, /atom/movable/openspace/mimic))
+			qdel(A)
+			num_deleted += 1
 
 		CHECK_TICK
 
-	log_debug("SSzcopy: queued [num_turfs] turfs for update. hard_reset() complete.")
+	log_debug("SSzcopy: deleted [num_deleted] overlays, and queued [num_turfs] turfs for update.")
+
 	enable()
 
-/datum/controller/subsystem/zcopy/stat_entry()
-	..("Q:{T:[queued_turfs.len - (qt_idex - 1)]|O:[queued_overlays.len - (qo_idex - 1)]} T:{T:[openspace_turfs.len]|O:[openspace_overlays.len]}")
+/datum/controller/subsystem/zcopy/stat_entry(text, force)
+		..("\
+			[text]\n\
+			Mx: [json_encode(zlev_maximums)]\n\
+			Queues: \
+			Turfs [queued_turfs.len - (qt_idex - 1)] \
+			Overlays [queued_overlays.len - (qo_idex - 1)]\n\
+			Open Turfs: \
+			Turfs [openspace_turfs] \
+			Overlays [openspace_overlays]\n\
+			Skips: \
+			Turfs [multiqueue_skips_turf] \
+			Objects [multiqueue_skips_object]\
+		")
 
 /datum/controller/subsystem/zcopy/Initialize(timeofday)
-	starlight_enabled = config.starlight && config.openturf_starlight_permitted
+	calculate_zstack_limits()
 	// Flush the queue.
 	fire(FALSE, TRUE)
-	if (starlight_enabled)
-		var/t = REALTIMEOFDAY
-		admin_notice("<span class='danger'>[src] setup completed in [(t - timeofday)/10] seconds!</span>", R_DEBUG)
 
-		SSlighting.fire(FALSE, TRUE)
-		admin_notice("<span class='danger'>Secondary [SSlighting] flush completed in [(REALTIMEOFDAY - t)/10] seconds!</span>", R_DEBUG)
+// If you add a new Zlevel or change Z-connections, call this.
+/datum/controller/subsystem/zcopy/proc/calculate_zstack_limits()
+	zlev_maximums = new(world.maxz)
+	var/start_zlev = 1
+	for (var/z in 1 to world.maxz)
+		if (!HasAbove(z))
+			for (var/member_zlev in start_zlev to z)
+				zlev_maximums[member_zlev] = z
+			if (z - start_zlev > OPENTURF_MAX_DEPTH)
+				log_ss("zcopy", "WARNING: Z-levels [start_zlev] through [z] exceed maximum depth of [OPENTURF_MAX_DEPTH]; layering may behave strangely in this Z-stack.")
+			else if (z - start_zlev > 1)
+				log_ss("zcopy", "Found Z-Stack: [start_zlev] -> [z] = [z - start_zlev + 1] zl")
+			start_zlev = z + 1
 
-		t = REALTIMEOFDAY
+	log_ss("zcopy", "Z-Level maximums: [json_encode(zlev_maximums)]")
 
-		fire(FALSE, TRUE)	// Fire /again/ to flush updates caused by the above.
-		admin_notice("<span class='danger'>Secondary [src] flush completed in [(REALTIMEOFDAY - t)/10] seconds!</span>", R_DEBUG)
+/datum/controller/subsystem/zcopy/StartLoadingMap()
+	suspend()
 
-	..()
+/datum/controller/subsystem/zcopy/StopLoadingMap()
+	wake()
 
-/datum/controller/subsystem/zcopy/fire(resumed = FALSE, no_mc_tick = FALSE)
+/datum/controller/subsystem/zcopy/fire(resumed, no_mc_tick)
 	if (!resumed)
 		qt_idex = 1
 		qo_idex = 1
@@ -105,98 +144,178 @@
 	while (qt_idex <= curr_turfs.len)
 		var/turf/T = curr_turfs[qt_idex]
 		curr_turfs[qt_idex] = null
-		qt_idex++
+		qt_idex += 1
 
-		if (!istype(T) || !T.below)
+		if (!isturf(T) || !(T.z_flags & ZM_MIMIC_BELOW) || !T.z_queued)
 			if (no_mc_tick)
 				CHECK_TICK
 			else if (MC_TICK_CHECK)
 				break
 			continue
 
-		if (!T.shadower)	// If we don't have our shadower yet, create it.
-			T.shadower = new(T)
+		// If we're not at our most recent queue position, don't bother -- we're updating again later anyways.
+		if (T.z_queued > 1)
+			T.z_queued -= 1
+			multiqueue_skips_turf += 1
+			if (no_mc_tick)
+				CHECK_TICK
+			else if (MC_TICK_CHECK)
+				break
+			continue
 
-		// Figure out how many z-levels down we are.
-		var/depth = 0
+		// Z-Turf on the bottom-most level, just fake-copy space.
+		// If this is ever true, that turf should always pass this condition, so don't bother cleaning up beyond the Destroy() hook.
+		if (!T.below)	// Z-turf on the bottom-most level, just fake-copy space.
+			if (T.z_flags & ZM_MIMIC_OVERWRITE)
+				T.appearance = SSskybox.space_appearance_cache[(((T.x + T.y) ^ ~(T.x * T.y) + T.z) % 25) + 1]
+				T.name = initial(T.name)
+				T.desc = initial(T.desc)
+				T.gender = initial(T.gender)
+			else
+				// Some openturfs have icons, so we can't overwrite their appearance.
+				if (!T.mimic_underlay)
+					T.mimic_underlay = new(T)
+				var/atom/movable/openspace/turf_proxy/TO = T.mimic_underlay
+				TO.appearance = SSskybox.space_appearance_cache[(((T.x + T.y) ^ ~(T.x * T.y) + T.z) % 25) + 1]
+				TO.name = T.name
+				TO.gender = T.gender	// Need to grab this too so PLURAL works properly in examine.
+				TO.mouse_opacity = initial(TO.mouse_opacity)
+
+			if (no_mc_tick)
+				CHECK_TICK
+			else if (MC_TICK_CHECK)
+				break
+			continue
+
+		if (!T.shadower)	// If we don't have a shadower yet, something has gone horribly wrong.
+			WARNING("Turf [T] at [T.x],[T.y],[T.z] was queued, but had no shadower.")
+			continue
+
+		T.z_generation += 1
+
+		// Get the bottom-most turf, the one we want to mimic.
 		var/turf/Td = T
-		while (Td && TURF_IS_MIMICING(Td.below))
+		while (Td.below)
 			Td = Td.below
-			depth++
-		if (depth > OPENTURF_MAX_DEPTH)
-			depth = OPENTURF_MAX_DEPTH
 
-		var/oo_target = OPENTURF_MAX_PLANE - depth
-		var/t_target
+		// Depth must be the depth of the *visible* turf, not self.
+		var/turf_depth
+		turf_depth = T.z_depth = zlev_maximums[Td.z] - Td.z
+
+		var/t_target = OPENTURF_MAX_PLANE - turf_depth	// This is where the turf (but not the copied atoms) gets put.
 
 		// Handle space parallax & starlight.
-		if (T.is_above_space())
+		if (T.below.z_eventually_space)
+			T.z_eventually_space = TRUE
 			t_target = PLANE_SPACE_BACKGROUND
-			if (starlight_enabled && !T.light_range)
-				T.set_light(config.starlight, 0.5)
-		else
-			t_target = oo_target
-			if (starlight_enabled && T.light_range)
-				T.set_light(0)
 
-		if (!(T.flags & MIMIC_OVERWRITE))
-			// Some openturfs have icons, so we can't overwrite their appearance.
-			if (!T.below.bound_overlay)
-				T.below.bound_overlay = new(T)
-			var/atom/movable/openspace/turf_overlay/TO = T.below.bound_overlay
-			TO.appearance = T.below
-			TO.name = T.name
-			TO.opacity = FALSE
-			T.desc = TO.desc = "Below seems to be \a [T.below]."
-			TO.plane = t_target
-			TO.mouse_opacity = FALSE
-		else
+		if (T.z_flags & ZM_MIMIC_OVERWRITE)
 			// This openturf doesn't care about its icon, so we can just overwrite it.
-			if (T.below.bound_overlay)
-				QDEL_NULL(T.below.bound_overlay)
+			if (T.below.mimic_proxy)
+				QDEL_NULL(T.below.mimic_proxy)
 			T.appearance = T.below
 			T.name = initial(T.name)
-			T.gender = NEUTER
+			T.desc = initial(T.desc)
+			T.gender = initial(T.gender)
 			T.opacity = FALSE
 			T.plane = t_target
+		else
+			// Some openturfs have icons, so we can't overwrite their appearance.
+			if (!T.below.mimic_proxy)
+				T.below.mimic_proxy = new(T)
+			var/atom/movable/openspace/turf_proxy/TO = T.below.mimic_proxy
+			TO.appearance = Td
+			TO.name = T.name
+			TO.gender = T.gender	// Need to grab this too so PLURAL works properly in examine.
+			TO.opacity = FALSE
+			TO.plane = t_target
+			TO.mouse_opacity = initial(TO.mouse_opacity)
 
-		T.desc = "Below seems to be \a [T.below]."
-		T.queue_ao()	// No need to recalculate ajacencies, shouldn't have changed.
+		T.queue_ao(T.ao_neighbors_mimic == null)	// If ao_neighbors hasn't been set yet, we need to do a rebuild
+
+		// Explicitly copy turf delegates so they show up properly on below levels.
+		//   I think it's possible to get this to work without discrete delegate copy objects, but I'd rather this just work.
+		if ((T.below.z_flags & (ZM_MIMIC_BELOW|ZM_MIMIC_OVERWRITE)) == ZM_MIMIC_BELOW)
+			// Below is a delegate, gotta explicitly copy it for recursive copy.
+			if (!T.below.mimic_above_copy)
+				T.below.mimic_above_copy = new(T)
+			var/atom/movable/openspace/turf_mimic/DC = T.below.mimic_above_copy
+			DC.appearance = T.below
+			DC.mouse_opacity = initial(DC.mouse_opacity)
+			DC.plane = OPENTURF_MAX_PLANE
+
+		else if (T.below.mimic_above_copy)
+			QDEL_NULL(T.below.mimic_above_copy)
+
+		// Handle below atoms.
 
 		// Add everything below us to the update queue.
 		for (var/thing in T.below)
 			var/atom/movable/object = thing
-			if (QDELETED(object) || object.no_z_overlay || object.loc != T.below)
-				// Don't queue deleted stuff or stuff that doesn't need an overlay.
+			if (QDELETED(object) || object.no_z_overlay || object.loc != T.below || object.invisibility == INVISIBILITY_ABSTRACT)
+				// Don't queue deleted stuff, stuff that's not visible, blacklisted stuff, or stuff that's centered on another tile but intersects ours.
+				continue
+
+			// Special case: these are merged into the shadower to reduce memory usage.
+			if (object.type == /atom/movable/lighting_overlay)
+				//T.shadower.copy_lighting(object)
 				continue
 
-			if (object.type == /atom/movable/lighting_overlay)	// Special case.
-				T.shadower.copy_lighting(object)
-			else
 			if (!object.bound_overlay)	// Generate a new overlay if the atom doesn't already have one.
 				object.bound_overlay = new(T)
 				object.bound_overlay.associated_atom = object
 
-				var/atom/movable/openspace/overlay/OO = object.bound_overlay
+			var/override_depth
+			var/original_type = object.type
+			var/original_z = object.z
+			switch (object.type)
+				if (/atom/movable/openspace/mimic)
+					var/atom/movable/openspace/mimic/OOO = object
+					original_type = OOO.mimiced_type
+					override_depth = OOO.override_depth
+					original_z = OOO.original_z
+
+				if (/atom/movable/openspace/turf_proxy, /atom/movable/openspace/turf_mimic)
+					// If we're a turf overlay (the mimic for a non-OVERWRITE turf), we need to make sure copies of us respect space parallax too
+					if (T.z_eventually_space)
+						// Yes, this is an awful hack; I don't want to add yet another override_* var.
+						override_depth = OPENTURF_MAX_PLANE - PLANE_SPACE_BACKGROUND
+
+			var/atom/movable/openspace/mimic/OO = object.bound_overlay
 
 			// If the OO was queued for destruction but was claimed by another OT, stop the destruction timer.
 			if (OO.destruction_timer)
 				deltimer(OO.destruction_timer)
 				OO.destruction_timer = null
 
-				// Cache our already-calculated depth so we don't need to re-calculate it a bunch of times.
-				OO.depth = oo_target
+			OO.depth = override_depth || min(zlev_maximums[T.z] - original_z, OPENTURF_MAX_DEPTH)
 
+			// These types need to be pushed a layer down for bigturfs to function correctly.
+			switch (original_type)
+				if (/atom/movable/openspace/multiplier, /atom/movable/openspace/turf_mimic, /atom/movable/openspace/turf_proxy)
+					if (OO.depth < OPENTURF_MAX_DEPTH)
+						OO.depth += 1
+
+			OO.mimiced_type = original_type
+			OO.override_depth = override_depth
+			OO.original_z = original_z
+
+			// Multi-queue to maintain ordering of updates to these
+			//   queueing it multiple times will result in only the most recent
+			//   actually processing.
+			OO.queued += 1
 			queued_overlays += OO
 
-		T.flags &= ~MIMIC_QUEUED
+		T.z_queued -= 1
+		if (T.above)
+			T.above.update_mimic()
 
 		if (no_mc_tick)
 			CHECK_TICK
 		else if (MC_TICK_CHECK)
 			break
 
-	if (qt_idex > 1 && qt_idex <= curr_turfs.len)
+	if (qt_idex > 1)
 		curr_turfs.Cut(1, qt_idex)
 		qt_idex = 1
 
@@ -204,11 +323,11 @@
 		MC_SPLIT_TICK
 
 	while (qo_idex <= curr_ov.len)
-		var/atom/movable/openspace/overlay/OO = curr_ov[qo_idex]
+		var/atom/movable/openspace/mimic/OO = curr_ov[qo_idex]
 		curr_ov[qo_idex] = null
-		qo_idex++
+		qo_idex += 1
 
-		if (QDELETED(OO))
+		if (QDELETED(OO) || !OO.queued)
 			if (no_mc_tick)
 				CHECK_TICK
 			else if (MC_TICK_CHECK)
@@ -224,12 +343,25 @@
 				break
 			continue
 
+		// Don't update unless we're at the most recent queue occurrence.
+		if (OO.queued > 1)
+			OO.queued -= 1
+			multiqueue_skips_object += 1
+			if (no_mc_tick)
+				CHECK_TICK
+			else if (MC_TICK_CHECK)
+				break
+			continue
+
 		// Actually update the overlay.
-		OO.dir = OO.associated_atom.dir
+		if (OO.dir != OO.associated_atom.dir)
+			OO.set_dir(OO.associated_atom.dir)
+
 		OO.appearance = OO.associated_atom
-		OO.plane = OO.depth
+		OO.plane = OPENTURF_MAX_PLANE - OO.depth
+
 		OO.opacity = FALSE
-		OO.queued = FALSE
+		OO.queued = 0
 
 		if (OO.bound_overlay)	// If we have a bound overlay, queue it too.
 			OO.update_above()
@@ -239,47 +371,125 @@
 		else if (MC_TICK_CHECK)
 			break
 
-		if (qo_idex > 1 && qo_idex <= curr_ov.len)
+	if (qo_idex > 1)
 		curr_ov.Cut(1, qo_idex)
 		qo_idex = 1
 
+#define FMT_DEPTH(X) (X == null ? "(null)" : X)
+
+// This is a dummy object used so overlays can be shown in the analyzer.
+/atom/movable/openspace/debug
 
 /client/proc/analyze_openturf(turf/T)
 	set name = "Analyze Openturf"
 	set desc = "Show the layering of an openturf and everything it's mimicking."
 	set category = "Debug"
 
-	if (!check_rights(R_DEBUG|R_DEV))
+	if (!check_rights(R_DEBUG))
 		return
 
+	var/is_above_space = T.is_above_space()
 	var/list/out = list(
+		"<head><meta charset='utf-8'/></head><body>",
 		"<h1>Analysis of [T] at [T.x],[T.y],[T.z]</h1>",
-		"<b>Z Flags</b>: [english_list(bitfield2list(T.flags, list("NOJAUNT", "MIMIC_BELOW", "MIMIC_OVERWRITE", "MIMIC_QUEUED", "MIMIC_NO_AO")), "(none)")]",
+		"<b>Queue occurrences:</b> [T.z_queued]",
+		"<b>Above space:</b> Apparent [T.z_eventually_space ? "Yes" : "No"], Actual [is_above_space ? "Yes" : "No"] - [T.z_eventually_space == is_above_space ? "<font color='green'>OK</font>" : "<font color='red'>MISMATCH</font>"]",
+		"<b>Z Flags</b>: [english_list(bitfield2list(T.z_flags, global.mimic_defines), "(none)")]",
 		"<b>Has Shadower:</b> [T.shadower ? "Yes" : "No"]",
+		"<b>Has turf proxy:</b> [T.mimic_proxy ? "Yes" : "No"]",
+		"<b>Has above copy:</b> [T.mimic_above_copy ? "Yes" : "No"]",
+		"<b>Has mimic underlay:</b> [T.mimic_underlay ? "Yes" : "No"]",
 		"<b>Below:</b> [!T.below ? "(nothing)" : "[T.below] at [T.below.x],[T.below.y],[T.below.z]"]",
+		"<b>Depth:</b> [FMT_DEPTH(T.z_depth)] [T.z_depth == OPENTURF_MAX_DEPTH ? "(max)" : ""]",
+		"<b>Generation:</b> [T.z_generation]",
 		"<ul>"
 	)
 
 	var/list/found_oo = list(T)
-	for (var/thing in T)
-		if (istype(thing, /atom/movable/openspace))
-			found_oo += thing
+	for (var/atom/movable/openspace/O in T)
+		found_oo += O
+
+	if (T.shadower.overlays.len)
+		for (var/overlay in T.shadower.overlays)
+			var/atom/movable/openspace/debug/D = new
+			D.appearance = overlay
+			if (D.plane < -10000)	// FLOAT_PLANE
+				D.plane = T.shadower.plane
+			found_oo += D
 
 	sortTim(found_oo, /proc/cmp_planelayer)
+
+	var/list/atoms_list_list = list()
 	for (var/thing in found_oo)
 		var/atom/A = thing
-		if (istype(A, /atom/movable/openspace/overlay))
-			var/atom/movable/openspace/overlay/OO = A
+		var/pl = "[A.plane]"
+		LAZYINITLIST(atoms_list_list[pl])
+		atoms_list_list[pl] += A
+
+	if (atoms_list_list["0"])
+		out += "<strong>Non-Z</strong>"
+		SSzcopy.debug_fmt_planelist(atoms_list_list["0"], out, T)
+
+		atoms_list_list -= "0"
+
+	for (var/d in 0 to OPENTURF_MAX_DEPTH)
+		var/pl = OPENTURF_MAX_PLANE - d
+		if (!atoms_list_list["[pl]"])
+			out += "<strong>Depth [d], plane [pl] - empty</strong>"
+			continue
+
+		out += "<strong>Depth [d], plane [pl]</strong>"
+		SSzcopy.debug_fmt_planelist(atoms_list_list["[pl]"], out, T)
+
+		// Flush the list so we can find orphans.
+		atoms_list_list -= "[pl]"
+
+	if (atoms_list_list["[PLANE_SPACE_BACKGROUND]"])	// Space parallax plane
+		out += "<strong>Space parallax plane</strong> ([PLANE_SPACE_BACKGROUND])"
+		SSzcopy.debug_fmt_planelist(atoms_list_list["[PLANE_SPACE_BACKGROUND]"], out, T)
+		atoms_list_list -= "[PLANE_SPACE_BACKGROUND]"
+
+	for (var/key in atoms_list_list)
+		out += "<strong style='color: red;'>Unknown plane: [key]</strong>"
+		SSzcopy.debug_fmt_planelist(atoms_list_list[key], out, T)
+
+		out += "<hr/>"
+
+	out += "</body>"
+
+	show_browser(usr, out.Join("<br>"), "size=980x580;window=openturfanalysis-\ref[T]")
+
+// Yes, I know this proc is a bit of a mess. Feel free to clean it up.
+/datum/controller/subsystem/zcopy/proc/debug_fmt_thing(atom/A, list/out, turf/original)
+	if (istype(A, /atom/movable/openspace/mimic))
+		var/atom/movable/openspace/mimic/OO = A
 		var/atom/movable/AA = OO.associated_atom
-			out += "<li>[icon2html(A, usr)] plane [A.plane], layer [A.layer], depth [OO.depth], associated Z-level [AA.z] - [OO.type] copying [AA] ([AA.type])</li>"
+		var/copied_type = AA.type == OO.mimiced_type ? "[AA.type] \[direct\]" : "[AA.type], eventually [OO.mimiced_type]"
+		return "<li>\icon[A] <b>\[Mimic\]</b> plane [A.plane], layer [A.layer], depth [FMT_DEPTH(OO.depth)], associated Z-level [AA.z] - [OO.type] copying [AA] ([copied_type])</li>"
+	else if (istype(A, /atom/movable/openspace/turf_mimic))
+		var/atom/movable/openspace/turf_mimic/DC = A
+		return "<li>\icon[A] <b>\[Turf Mimic\]</b> plane [A.plane], layer [A.layer], Z-level [A.z], delegate of \icon[DC.delegate] [DC.delegate] ([DC.delegate.type])</li>"
 	else if (isturf(A))
-			if (A == T)
-				out += "<li>[icon2html(A, usr)] plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type]) - <span class='good'>SELF</span></li>"
-			else    // foreign turfs - not visible here, but good for figuring out layering
-				out += "<li>[icon2html(A, usr)] plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type]) - <span class='warning'>FOREIGN</span></li>"
+		if (A == original)
+			return "<li>\icon[A] <b>\[Turf\]</b> plane [A.plane], layer [A.layer], depth [FMT_DEPTH(A:z_depth)], Z-level [A.z] - [A] ([A.type]) - <font color='green'>SELF</font></li>"
+		else	// foreign turfs - not visible here, but sometimes good for figuring out layering -- showing these is currently not enabled
+			return "<li>\icon[A] <b>\[Turf\]</b> <em><font color='#646464'>plane [A.plane], layer [A.layer], depth [FMT_DEPTH(A:z_depth)], Z-level [A.z] - [A] ([A.type])</font></em> - <font color='red'>FOREIGN</font></em></li>"
+	else if (A.type == /atom/movable/openspace/multiplier)
+		return "<li>\icon[A] <b>\[Shadower\]</b> plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type])</li>"
+	else if (A.type == /atom/movable/openspace/debug)	// These are fake objects that exist just to show the shadower's overlays in this list.
+		return "<li>\icon[A] <b>\[Shadower True Overlay\]</b> plane [A.plane], layer [A.layer] - <font color='grey'>VIRTUAL</font></li>"
+	else if (A.type == /atom/movable/openspace/turf_proxy)
+		return "<li>\icon[A] <b>\[Turf Proxy\]</b> plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type])</li>"
 	else
-			out += "<li>[icon2html(A, usr)] plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type])</li>"
+		return "<li>\icon[A] <b>\[?\]</b>  plane [A.plane], layer [A.layer], Z-level [A.z] - [A] ([A.type])</li>"
 
+/datum/controller/subsystem/zcopy/proc/debug_fmt_planelist(list/things, list/out, turf/original)
+	if (things)
+		out += "<ul>"
+		for (var/thing in things)
+			out += debug_fmt_thing(thing, out, original)
 		out += "</ul>"
+	else
+		out += "<em>No atoms.</em>"
 
-	usr << browse(out.Join("<br>"), "window=openturfanalysis-\ref[T]")
+#undef FMT_DEPTH

code/game/atoms_movable.dm

@@ -45,6 +45,9 @@
 			pulledby.pulling = null
 		pulledby = null
 
+	if (bound_overlay)
+		QDEL_NULL(bound_overlay)
+
 // This is called when this atom is prevented from moving by atom/A.
 /atom/movable/proc/Collide(atom/A)
 	if(airflow_speed > 0 && airflow_dest)

code/game/turfs/space/space.dm

@@ -15,6 +15,7 @@
 	is_hole = TRUE
 
 	permit_ao = FALSE
+	z_eventually_space = TRUE
 	var/use_space_appearance = TRUE
 	var/use_starlight = TRUE
 
@@ -45,6 +46,14 @@
 
 	return INITIALIZE_HINT_NORMAL
 
+/turf/space/Destroy()
+	// Cleanup cached z_eventually_space values above us.
+	if (above)
+		var/turf/T = src
+		while ((T = GetAbove(T)))
+			T.z_eventually_space = FALSE
+	return ..()
+
 /turf/space/is_space()
 	return 1
 

code/game/turfs/turf.dm

@@ -92,7 +92,7 @@
 	if (A.flags & SPAWN_ROOF)
 		spawn_roof()
 
-	if (flags & MIMIC_BELOW)
+	if (z_flags & ZM_MIMIC_BELOW)
 		setup_zmimic(mapload)
 
 	return INITIALIZE_HINT_NORMAL
@@ -111,11 +111,11 @@
 		SSocclusion.queue -= src
 		ao_queued = 0
 
-	if (flags & MIMIC_BELOW)
+	if (z_flags & ZM_MIMIC_BELOW)
 		cleanup_zmimic()
 
-	if (bound_overlay)
-		QDEL_NULL(bound_overlay)
+	if (z_flags & ZM_MIMIC_BELOW)
+		cleanup_zmimic()
 
 	..()
 	return QDEL_HINT_IWILLGC

code/modules/ambient_occlusion/ao_turf.dm

@@ -29,9 +29,9 @@
 		return
 
 	var/turf/T
-	if (flags & MIMIC_BELOW)
-		CALCULATE_NEIGHBORS(src, ao_neighbors_mimic, T, (T.flags & MIMIC_BELOW))
-	if (AO_SELF_CHECK(src) && !(flags & MIMIC_NO_AO))
+	if (z_flags & ZM_MIMIC_BELOW)
+		CALCULATE_NEIGHBORS(src, ao_neighbors_mimic, T, (T.z_flags & ZM_MIMIC_BELOW))
+	if (AO_SELF_CHECK(src) && !(z_flags & ZM_MIMIC_NO_AO))
 		CALCULATE_NEIGHBORS(src, ao_neighbors, T, AO_TURF_CHECK(T))
 
 /proc/make_ao_image(corner, i, px = 0, py = 0, pz = 0, pw = 0)
@@ -105,9 +105,9 @@
 	var/list/cache = SSicon_cache.ao_cache
 	CUT_AO(shadower, ao_overlays_mimic)
 	CUT_AO(src, ao_overlays)
-	if (flags & MIMIC_BELOW)
+	if (z_flags & ZM_MIMIC_BELOW)
 		REGEN_AO(shadower, ao_overlays_mimic, ao_neighbors_mimic)
-	if (!has_opaque_atom && !(flags & MIMIC_NO_AO))
+	if (!has_opaque_atom && !(z_flags & ZM_MIMIC_NO_AO))
 		REGEN_AO(src, ao_overlays, ao_neighbors)
 
 #undef REGEN_AO

code/modules/lighting/lighting_overlay.dm

@@ -122,14 +122,6 @@
 				0, 0, 0, 1
 			)
 
-	// If we're on an openturf, update the shadower object too.
-	if (T.above)
-		var/turf/simulated/open/OT = T.above
-		if (OT.shadower)
-			OT.shadower.copy_lighting(src)
-		else
-			OT.update_icon()
-
 #undef ALL_EQUAL
 
 // Variety of overrides so the overlays don't get affected by weird things.

code/modules/lighting/lighting_source.dm

@@ -394,7 +394,7 @@
 		// Note: above is defined on ALL turfs, but below is only defined on OPEN TURFS.
 
 		// Upwards lights are handled at the corner level, so only search down.
-		if (T && (T.flags & MIMIC_BELOW) && T.below)
+		if (T && (T.z_flags & ZM_MIMIC_BELOW) && T.below)
 			T = T.below
 			goto check_t
 

code/modules/lighting/lighting_source_sunlight.dm

@@ -99,7 +99,7 @@
 		CHECK_TICK
 
 		// Sunlight only checks downwards as it has no need to shine upwards, really.
-		if (T && (T.flags & MIMIC_BELOW) && T.below)
+		if (T && (T.z_flags & ZM_MIMIC_BELOW) && T.below)
 			T = T.below
 			goto check_t
 

code/modules/mob/mob.dm

@@ -154,6 +154,10 @@
 	if(intent_message)
 		intent_message(intent_message, intent_range, messagemobs)
 
+	//Multiz, have shadow do same
+	if(bound_overlay)
+		bound_overlay.visible_message(message, blind_message, range)
+
 // Designed for mobs contained inside things, where a normal visible message wont actually be visible
 // Useful for visible actions by pAIs, and held mobs
 // Broadcaster is the place the action will be seen/heard from, mobs in sight of THAT will see the message. This is generally the object or mob that src is contained in

code/modules/multiz/movement.dm

@@ -803,7 +803,7 @@
 	forceMove(get_step(owner, UP))
 	if(isturf(src.loc))
 		var/turf/T = src.loc
-		if(T.flags & MIMIC_BELOW)
+		if(T.z_flags & ZM_MIMIC_BELOW)
 			return
 	owner.reset_view(null)
 	owner.z_eye = null
@@ -812,7 +812,7 @@
 /atom/movable/z_observer/z_down/follow()
 	forceMove(get_step(tile_shifted ? src : owner, DOWN))
 	var/turf/T = get_turf(tile_shifted ? get_step(owner, owner.dir) : owner)
-	if(T && (T.flags & MIMIC_BELOW))
+	if(T && (T.z_flags & ZM_MIMIC_BELOW))
 		return
 	owner.reset_view(null)
 	owner.z_eye = null

code/modules/multiz/turfs/open_space.dm

@@ -11,9 +11,9 @@
 	density = 0
 	pathweight = 100000 //Seriously, don't try and path over this one numbnuts
 	is_hole = TRUE
-	flags = MIMIC_BELOW | MIMIC_OVERWRITE | MIMIC_NO_AO
 	roof_type = null
 	footstep_sound = null
+	z_flags = ZM_MIMIC_DEFAULTS | ZM_MIMIC_OVERWRITE | ZM_MIMIC_NO_AO | ZM_ALLOW_ATMOS
 
 	// A lazy list to contain a list of mobs who are currently scaling
 	// up this turf. Used in human/can_fall.
@@ -30,6 +30,34 @@
 
 	return ..()
 
+/turf/proc/CanZPass(atom/A, direction)
+	if(z == A.z) //moving FROM this turf
+		return direction == UP //can't go below
+	else
+		if(direction == UP) //on a turf below, trying to enter
+			return 0
+		if(direction == DOWN) //on a turf above, trying to enter
+			return !density
+
+/turf/simulated/open/CanZPass(atom/A, direction)
+	if(locate(/obj/structure/lattice/catwalk, src))
+		if(z == A.z)
+			if(direction == DOWN)
+				return 0
+		else if(direction == UP)
+			return 0
+	return 1
+
+/turf/space/CanZPass(atom/A, direction)
+	if(locate(/obj/structure/lattice/catwalk, src))
+		if(z == A.z)
+			if(direction == DOWN)
+				return 0
+		else if(direction == UP)
+			return 0
+	return 1
+
+
 // Add a falling atom by default. Even if it's not an atom that can actually fall.
 // SSfalling will check this on its own and remove if necessary. This is saner, as it
 // centralizes control to SSfalling.
@@ -105,7 +133,7 @@
 	icon_state = "debug"
 	smooth = SMOOTH_TRUE | SMOOTH_BORDER | SMOOTH_NO_CLEAR_ICON
 	smoothing_hints = SMOOTHHINT_CUT_F | SMOOTHHINT_ONLY_MATCH_TURF | SMOOTHHINT_TARGETS_NOT_UNIQUE
-	flags = MIMIC_BELOW
+	z_flags = ZM_MIMIC_BELOW
 	name = "hole"
 
 /turf/simulated/open/chasm/airless

code/modules/multiz/zmimic/mimic_common.dm

@@ -2,39 +2,17 @@
 /atom/proc/update_above()
 	return
 
-/**
- * Used to check wether or not an atom can pass through a turf.
- *
- * @param	A The atom that's moving either up or down from this turf or to it.
- * @param	direction The direction of the atom's movement in relation to its
- * current position.
- *
- * @return	TRUE if A can pass in the movement direction, FALSE if not.
- */
-/turf/proc/CanZPass(atom/A, direction)
-	var/turf/T = get_turf(A)
-	if(z == T.z) //moving FROM this turf
-		return direction == UP //can't go below
-	else
-		if(direction == UP) //on a turf below, trying to enter
-			return FALSE
-		if(direction == DOWN) //on a turf above, trying to enter
-			return !density
-
-/**
- * Used to check whether or not the specific open turf eventually leads into spess.
- *
- * @return	TRUE if the turf eventually leads into space. FALSE otherwise.
- */
 /turf/proc/is_above_space()
 	var/turf/T = GetBelow(src)
-	while (T && (T.flags & MIMIC_BELOW))
+	while (T && (T.z_flags & ZM_MIMIC_BELOW))
 		T = GetBelow(T)
+	return isspaceturf(T)
 
-	return istype(T, /turf/space)
+/turf/update_icon()
+	..()
+	if (above)
+		update_above()
 
-/turf/simulated/open/CanZPass(atom, direction)
-	return TRUE
-
-/turf/space/CanZPass(atom, direction)
-	return TRUE
+/atom/movable/update_icon()
+	..()
+	UPDATE_OO_IF_PRESENT

code/modules/multiz/zmimic/mimic_movable.dm

@@ -1,36 +1,41 @@
 /atom/movable
-	var/tmp/atom/movable/openspace/overlay/bound_overlay	// The overlay that is directly mirroring us that we proxy movement to.
-	var/no_z_overlay	// If TRUE, this atom will not be drawn on open turfs.
-
-/atom/movable/Destroy()
-	. = ..()
-	if (bound_overlay)
-		QDEL_NULL(bound_overlay)
+	/// The mimic (if any) that's *directly* copying us.
+	var/tmp/atom/movable/openspace/mimic/bound_overlay
+	/// If TRUE, this atom is ignored by Z-Mimic.
+	var/no_z_overlay
 
 /atom/movable/forceMove(atom/dest)
 	. = ..(dest)
-	if (bound_overlay)
+	if (. && bound_overlay)
 		// The overlay will handle cleaning itself up on non-openspace turfs.
 		if (isturf(dest))
 			bound_overlay.forceMove(get_step(src, UP))
+			if (dir != bound_overlay.dir)
 				bound_overlay.set_dir(dir)
 		else	// Not a turf, so we need to destroy immediately instead of waiting for the destruction timer to proc.
 			qdel(bound_overlay)
 
+/atom/movable/Move()
+	. = ..()
+	if (. && bound_overlay)
+		bound_overlay.forceMove(get_step(src, UP))
+		if (bound_overlay.dir != dir)
+			bound_overlay.set_dir(dir)
+
 /atom/movable/set_dir(ndir)
 	. = ..()
 	if (. && bound_overlay)
 		bound_overlay.set_dir(ndir)
 
 /atom/movable/update_above()
-	if (!bound_overlay)
+	if (!bound_overlay || !isturf(loc))
 		return
 
 	var/turf/T = loc
+
 	if (TURF_IS_MIMICING(T.above))
-		if (!bound_overlay.queued)
 		SSzcopy.queued_overlays += bound_overlay
-			bound_overlay.queued = TRUE
+		bound_overlay.queued += 1
 	else
 		qdel(bound_overlay)
 
@@ -55,6 +60,7 @@
 
 // No blowing up abstract objects.
 /atom/movable/openspace/ex_act(ex_sev)
+	SHOULD_CALL_PARENT(FALSE)
 	return
 
 /atom/movable/openspace/singularity_act()
@@ -66,17 +72,16 @@
 /atom/movable/openspace/singuloCanEat()
 	return
 
-/atom/movable/openspace/shuttle_move()
-	return
+// -- MULTIPLIER / SHADOWER --
 
 // Holder object used for dimming openspaces & copying lighting of below turf.
 /atom/movable/openspace/multiplier
 	name = "openspace multiplier"
 	desc = "You shouldn't see this."
 	icon = 'icons/effects/lighting_overlay.dmi'
-	icon_state = "blank"
-	plane = OPENTURF_CAP_PLANE
-	layer = LIGHTING_LAYER
+	icon_state = "dark"
+	plane = OPENTURF_MAX_PLANE
+	layer = MIMICED_LIGHTING_LAYER
 	blend_mode = BLEND_MULTIPLY
 	color = list(
 		SHADOWER_DARKENING_FACTOR, 0, 0,
@@ -93,53 +98,65 @@
 
 /atom/movable/openspace/multiplier/proc/copy_lighting(atom/movable/lighting_overlay/LO)
 	appearance = LO
-	layer = EFFECTS_ABOVE_LIGHTING_LAYER
-	plane = OPENTURF_CAP_PLANE
+	layer = MIMICED_LIGHTING_LAYER
+	plane = OPENTURF_MAX_PLANE
 	invisibility = 0
-	if (icon_state == LIGHTING_BASE_ICON_STATE)
+	blend_mode = BLEND_MULTIPLY
+	if (icon_state == null)
 		// We're using a color matrix, so just darken the colors across the board.
+		// Bay stores lights as inverted so the lighting PM can invert it for darksight, but
+		//   we don't have a plane master, so invert it again.
 		var/list/c_list = color
-		c_list[CL_MATRIX_RR] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_RG] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_RB] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_GR] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_GG] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_GB] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_BR] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_BG] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_BB] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_AR] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_AG] *= SHADOWER_DARKENING_FACTOR
-		c_list[CL_MATRIX_AB] *= SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_RR] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_RG] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_RB] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_GR] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_GG] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_GB] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_BR] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_BG] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_BB] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_AR] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_AG] *= -SHADOWER_DARKENING_FACTOR
+		c_list[CL_MATRIX_AB] *= -SHADOWER_DARKENING_FACTOR
 		color = c_list
 	else
-		// Not a color matrix, so we can just use the color var ourselves.
+		// Not a color matrix, so we just ignore the lighting values.
+		icon_state = "dark"	// this is actually just a white sprite, which is what this blending needs
 		color = list(
 			SHADOWER_DARKENING_FACTOR, 0, 0,
 			0, SHADOWER_DARKENING_FACTOR, 0,
 			0, 0, SHADOWER_DARKENING_FACTOR
 		)
 
-	if (our_overlays || priority_overlays)
-		compile_overlays()
-	else if (bound_overlay)
-		// compile_overlays() calls update_above().
+	var/turf/parent = loc
+	ASSERT(isturf(parent))
+	if (LAZYLEN(parent.ao_overlays_mimic))
+		overlays += parent.ao_overlays_mimic
+
+	if (bound_overlay)
 		update_above()
 
+// -- OPENSPACE OVERLAY --
+// todo: rename
+
 // Object used to hold a mimiced atom's appearance.
-/atom/movable/openspace/overlay
+/atom/movable/openspace/mimic
 	plane = OPENTURF_MAX_PLANE
 	var/atom/movable/associated_atom
 	var/depth
-	var/queued = FALSE
+	var/queued = 0
 	var/destruction_timer
+	var/mimiced_type
+	var/original_z
+	var/override_depth
 
-/atom/movable/openspace/overlay/New()
+/atom/movable/openspace/mimic/New()
 	initialized = TRUE
-	SSzcopy.openspace_overlays += src
+	SSzcopy.openspace_overlays += 1
 
-/atom/movable/openspace/overlay/Destroy()
-	SSzcopy.openspace_overlays -= src
+/atom/movable/openspace/mimic/Destroy()
+	SSzcopy.openspace_overlays -= 1
 
 	if (associated_atom)
 		associated_atom.bound_overlay = null
@@ -150,44 +167,74 @@
 
 	return ..()
 
-/atom/movable/openspace/overlay/attackby(obj/item/W, mob/user)
+/atom/movable/openspace/mimic/attackby(obj/item/W, mob/user)
 	to_chat(user, SPAN_NOTICE("\The [src] is too far away."))
 
-/atom/movable/openspace/overlay/attack_hand(mob/user as mob)
+/atom/movable/openspace/mimic/attack_hand(mob/user)
 	to_chat(user, SPAN_NOTICE("You cannot reach \the [src] from here."))
 
-/atom/movable/openspace/overlay/attack_generic(mob/user as mob)
-	to_chat(user, SPAN_NOTICE("You cannot reach \the [src] from here."))
+/atom/movable/openspace/mimic/examine(...)
+	SHOULD_CALL_PARENT(FALSE)
+	. = associated_atom.examine(arglist(args))	// just pass all the args to the copied atom
 
-/atom/movable/openspace/overlay/examine(mob/examiner)
-	associated_atom.examine(examiner)
-
-/atom/movable/openspace/overlay/forceMove(turf/dest)
+/atom/movable/openspace/mimic/forceMove(turf/dest)
 	. = ..()
 	if (TURF_IS_MIMICING(dest))
 		if (destruction_timer)
 			deltimer(destruction_timer)
 			destruction_timer = null
 	else if (!destruction_timer)
-		destruction_timer = addtimer(CALLBACK(GLOBAL_PROC, /proc/qdel, src), 10 SECONDS, TIMER_STOPPABLE)
+		destruction_timer = addtimer(CALLBACK(src, /datum/.proc/qdel_self), 10 SECONDS, TIMER_STOPPABLE)
 
 // Called when the turf we're on is deleted/changed.
-/atom/movable/openspace/overlay/proc/owning_turf_changed()
+/atom/movable/openspace/mimic/proc/owning_turf_changed()
 	if (!destruction_timer)
-		destruction_timer = addtimer(CALLBACK(GLOBAL_PROC, /proc/qdel, src), 10 SECONDS, TIMER_STOPPABLE)
+		destruction_timer = addtimer(CALLBACK(src, /datum/.proc/qdel_self), 10 SECONDS, TIMER_STOPPABLE)
 
-// This one's a little different because it's mimicing a turf.
-/atom/movable/openspace/turf_overlay
+// -- TURF PROXY --
+
+// This thing holds the mimic appearance for non-OVERWRITE turfs.
+/atom/movable/openspace/turf_proxy
 	plane = OPENTURF_MAX_PLANE
+	mouse_opacity = 0
+	no_z_overlay = TRUE  // Only one of these should ever be visible at a time, the mimic logic will handle that.
 
-/atom/movable/openspace/turf_overlay/attackby(obj/item/W, mob/user)
+/atom/movable/openspace/turf_proxy/attackby(obj/item/W, mob/user)
 	loc.attackby(W, user)
 
-/atom/movable/openspace/turf_overlay/attack_hand(mob/user as mob)
+/atom/movable/openspace/turf_proxy/attack_hand(mob/user as mob)
 	loc.attack_hand(user)
 
-/atom/movable/openspace/turf_overlay/attack_generic(mob/user as mob)
+/atom/movable/openspace/turf_proxy/attack_generic(mob/user as mob)
 	loc.attack_generic(user)
 
-/atom/movable/openspace/turf_overlay/examine(mob/examiner)
-	loc.examine(examiner)
+/atom/movable/openspace/turf_proxy/examine(mob/examiner)
+	SHOULD_CALL_PARENT(FALSE)
+	. = loc.examine(examiner)
+
+
+// -- TURF MIMIC --
+
+// A type for copying non-overwrite turfs' self-appearance.
+/atom/movable/openspace/turf_mimic
+	plane = OPENTURF_MAX_PLANE	// These *should* only ever be at the top?
+	mouse_opacity = 0
+	var/turf/delegate
+
+/atom/movable/openspace/turf_mimic/Initialize(mapload, ...)
+	. = ..()
+	ASSERT(isturf(loc))
+	delegate = loc:below
+
+/atom/movable/openspace/turf_mimic/attackby(obj/item/W, mob/user)
+	loc.attackby(W, user)
+
+/atom/movable/openspace/turf_mimic/attack_hand(mob/user as mob)
+	to_chat(user, SPAN_NOTICE("You cannot reach \the [src] from here."))
+
+/atom/movable/openspace/turf_mimic/attack_generic(mob/user as mob)
+	to_chat(user, SPAN_NOTICE("You cannot reach \the [src] from here."))
+
+/atom/movable/openspace/turf_mimic/examine(mob/examiner)
+	SHOULD_CALL_PARENT(FALSE)
+	. = delegate.examine(examiner)

code/modules/multiz/zmimic/mimic_turf.dm

@@ -1,12 +1,26 @@
-/turf
-	// Reference to any open turf that might be above us to speed up atom Entered() updates.
-	var/tmp/turf/above
-	var/tmp/turf/below
-	var/tmp/atom/movable/openspace/turf_overlay/bound_overlay
-	var/tmp/atom/movable/openspace/multiplier/shadower		// Overlay used to multiply color of all OO overlays at once.
+/// Reference to any open turf that might be above us to speed up atom Entered() updates.
+/turf/var/tmp/turf/above
+/turf/var/tmp/turf/below
+/// If we're a non-overwrite z-turf, this holds the appearance of the bottom-most Z-turf in the z-stack.
+/turf/var/tmp/atom/movable/openspace/turf_proxy/mimic_proxy
+/// Overlay used to multiply color of all OO overlays at once.
+/turf/var/tmp/atom/movable/openspace/multiplier/shadower
+/// If this is a delegate (non-overwrite) Z-turf with a z-turf above, this is the delegate copy that's copying us.
+/turf/var/tmp/atom/movable/openspace/turf_mimic/mimic_above_copy
+/// If we're at the bottom of the stack, a proxy used to fake a below space turf.
+/turf/var/tmp/atom/movable/openspace/turf_proxy/mimic_underlay
+/// How many times this turf is currently queued - multiple queue occurrences are allowed to ensure update consistency.
+/turf/var/tmp/z_queued = 0
+/// If this Z-turf leads to space, uninterrupted.
+/turf/var/tmp/z_eventually_space = FALSE
+/turf/var/z_flags = 0
+
+// debug
+/turf/var/tmp/z_depth
+/turf/var/tmp/z_generation = 0
 
 /turf/Entered(atom/movable/thing, turf/oldLoc)
-	. = ..(thing, oldLoc)
+	. = ..()
 	if (thing.bound_overlay || thing.no_z_overlay || !TURF_IS_MIMICING(above))
 		return
 	above.update_mimic()
@@ -15,57 +29,59 @@
 	if (TURF_IS_MIMICING(above))
 		above.update_mimic()
 
-/turf/proc/update_mimic(recurse = TRUE)
-	if (!(flags & MIMIC_BELOW))
+/turf/proc/update_mimic()
+	if (!(z_flags & ZM_MIMIC_BELOW))
 		return
 
-	if (below && !(flags & MIMIC_QUEUED))	
-		flags |= MIMIC_QUEUED
+	z_queued += 1
 	SSzcopy.queued_turfs += src
 
-	if (recurse)
-		update_above()	// Even if we're already updating, the turf above us might not be.
-
-// Enables Z-mimic for a turf that didn't already have it enabled.
+/// Enables Z-mimic for a turf that didn't already have it enabled.
 /turf/proc/enable_zmimic(additional_flags = 0)
-	if (flags & MIMIC_BELOW)
+	if (z_flags & ZM_MIMIC_BELOW)
 		return FALSE
 
-	flags |= MIMIC_BELOW | additional_flags
+	z_flags |= ZM_MIMIC_BELOW | additional_flags
 	setup_zmimic(FALSE)
 	return TRUE
 
-// Disables Z-mimic for a turf.
+/// Disables Z-mimic for a turf.
 /turf/proc/disable_zmimic()
-	if (!(flags & MIMIC_BELOW))
+	if (!(z_flags & ZM_MIMIC_BELOW))
 		return FALSE
 
-	flags &= ~MIMIC_BELOW
+	z_flags &= ~ZM_MIMIC_BELOW
 	cleanup_zmimic()
+	return TRUE
 
-// Sets up Z-mimic for this turf. You shouldn't call this directly 99% of the time.
+/// Sets up Z-mimic for this turf. You shouldn't call this directly 99% of the time.
 /turf/proc/setup_zmimic(mapload)
 	if (shadower)
 		CRASH("Attempt to enable Z-mimic on already-enabled turf!")
 	shadower = new(src)
-	SSzcopy.openspace_turfs += src
+	SSzcopy.openspace_turfs += 1
 	var/turf/under = GetBelow(src)
 	if (under)
 		below = under
 		below.above = src
 
+	if (!(z_flags & (ZM_MIMIC_OVERWRITE|ZM_NO_OCCLUDE)) && mouse_opacity)
+		mouse_opacity = 2
+
 	update_mimic(!mapload)	// Only recursively update if the map isn't loading.
 
-// Cleans up Z-mimic objects for this turf. You shouldn't call this directly 99% of the time.
+/// Cleans up Z-mimic objects for this turf. You shouldn't call this directly 99% of the time.
 /turf/proc/cleanup_zmimic()
-	SSzcopy.openspace_turfs -= src
-	if (flags & MIMIC_QUEUED)
-		SSzcopy.queued_turfs -= src
+	SSzcopy.openspace_turfs -= 1
+	// Don't remove ourselves from the queue, the subsystem will explode. We'll naturally fall out of the queue.
+	z_queued = 0
 
 	QDEL_NULL(shadower)
+	QDEL_NULL(mimic_above_copy)
+	QDEL_NULL(mimic_underlay)
 
-	for (var/atom/movable/openspace/overlay/OwO in src)	// wats this~?
-		OwO.owning_turf_changed()
+	for (var/atom/movable/openspace/mimic/OO in src)
+		OO.owning_turf_changed()
 
 	if (above)
 		above.update_mimic()
@@ -73,19 +89,3 @@
 	if (below)
 		below.above = null
 		below = null
-
-// Movable for mimicing turfs that don't allow appearance mutation.
-/atom/movable/openspace/turf_overlay
-	plane = OPENTURF_MAX_PLANE
-
-/atom/movable/openspace/turf_overlay/attackby(obj/item/W, mob/user)
-	loc.attackby(W, user)
-
-/atom/movable/openspace/turf_overlay/attack_hand(mob/user as mob)
-	loc.attack_hand(user)
-
-/atom/movable/openspace/turf_overlay/attack_generic(mob/user as mob)
-	loc.attack_generic(user)
-
-/atom/movable/openspace/turf_overlay/examine(mob/examiner)
-	loc.examine(examiner)

html/changelogs/mattatlas-yet_again_another_bayport.yml

@@ -0,0 +1,41 @@
+################################
+# Example Changelog File
+#
+# Note: This file, and files beginning with ".", and files that don't end in ".yml" will not be read. If you change this file, you will look really dumb.
+#
+# Your changelog will be merged with a master changelog. (New stuff added only, and only on the date entry for the day it was merged.)
+# When it is, any changes listed below will disappear.
+#
+# Valid Prefixes:
+#   bugfix
+#   wip (For works in progress)
+#   tweak
+#   soundadd
+#   sounddel
+#   rscadd (general adding of nice things)
+#   rscdel (general deleting of nice things)
+#   imageadd
+#   imagedel
+#   maptweak
+#   spellcheck (typo fixes)
+#   experiment
+#   balance
+#   admin
+#   backend
+#   security
+#   refactor
+#################################
+
+# Your name.
+author: Lohikar, CrimsonShrike, MattAtlas
+
+# Optional: Remove this file after generating master changelog.  Useful for PR changelogs that won't get used again.
+delete-after: True
+
+# Any changes you've made.  See valid prefix list above.
+# INDENT WITH TWO SPACES.  NOT TABS.  SPACES.
+# SCREW THIS UP AND IT WON'T WORK.
+# Also, all entries are changed into a single [] after a master changelog generation. Just remove the brackets when you add new entries.
+# Please surround your changes in  double quotes ("), as certain characters otherwise screws up compiling. The quotes will not show up in the changelog.
+changes:
+  - backend: "Ported some Z-Mimic changes/improvements/bugfixes from Nebula/Bay."