Hud Image Culling By Z Level: Theft edition (#65189)

* makes hud images only apply by z level

* makes some of the atom_hud procs have better names

* fixes warning with the hud_user list and adds better documentation

* better docs for hud_images

* removes TODOs

* docs for hud_list

* adds support for linked z levels so mobs can see lower ones

* fixes merge conflict and shittily makes only shocked airlocks get added

* adds support for setting images in the hud as active and inactive

* gets rid of unatomic spatial grid change

* maybe i should actually try COMPILING my changes

* fixes merge skew and makes it compile again

* fixes huds refusing to remove from users who changed z level

* improves z level and registration logic

* fixes antag huds not appearing

* Fixes antag huds not properly setting. We now use hud_list in init, so it needs to be set before the new call, not after. Not sure why the use of appearance key was split like this, but none else knows either so none can stop me

* Ensures that hiding a basic appearance also hides the atom's active list too

* Fixes antag huds going poof

Ensures that remove_atom_from_hud will return false if the passed atom
isn't managed by it

This fixes antag huds disappearing randomly, since they assumed that if
the parent call of remove_atom_from_hud returned true, we should delete
ourselves. This is a safe assumption for them to make, since they should
only ever have one atom.

Does kinda bork if we call remove_atom_from_hud in a way that is unsure
if the passed atom is actually in that list. We were forced into doing
this by how atom huds use the qdeleting signal.

* makes basic alternate_appearance's only update themselves when setting their hud image to active and makes them not add themselves to the global huds_by_category list

* fixes mistake with hud_users list being set non associatively (bad)

* as anything in bot path loops

* Fixes merge skew problems

* Makes bot paths non global

This way they can show themselves to only the bot that "owns" them, ya
feel me?

* Fixes huds not showing up sometimes, cleans up some code

Post Kapu's limb refactor, we were calling prepare_huds twice in a human
init call chain. What was happening was this:

call prepare_huds() // Human
I gained a new hud image
I set active hud icons to mirror it
call prepare_huds() // Living
I overwrote the new hud image
I attempted to set active hud icons, which failed because it assumes
this can never happen

*cries*

* Renames add_hud_to_atom to show_to

My hope is this will make understanding hud code a bit easier, by tying
the behavior to a "verb" more closely. Also renamed a few vars

* remove_hud_from_mob -> hide_from

* Nitpicks a few comments

* Whoops/fuck/shit/damn it all/hhhhhhhhhhhh

* Moves check down, improves stack trace a bit

Co-authored-by: KylerAce <kylerlumpkin1@gmail.com>

code/__DEFINES/atom_hud.dm

@@ -2,6 +2,7 @@
 // note: if you add more HUDs, even for non-human atoms, make sure to use unique numbers for the defines!
 // /datum/atom_hud expects these to be unique
 // these need to be strings in order to make them associative lists
+
 /// dead, alive, sick, health status
 #define HEALTH_HUD "1"
 /// a simple line rounding the mob's number health

code/__DEFINES/icon_smoothing.dm

@@ -26,8 +26,7 @@ DEFINE_BITFIELD(smoothing_flags, list(
 
 #define QUEUE_SMOOTH(thing_to_queue) if(thing_to_queue.smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK)) {SSicon_smooth.add_to_queue(thing_to_queue)}
 
-#define QUEUE_SMOOTH_NEIGHBORS(thing_to_queue) for(var/neighbor in orange(1, thing_to_queue)) {var/atom/atom_neighbor = neighbor; QUEUE_SMOOTH(atom_neighbor)}
-
+#define QUEUE_SMOOTH_NEIGHBORS(thing_to_queue) for(var/atom/atom_neighbor as anything in orange(1, thing_to_queue)) {QUEUE_SMOOTH(atom_neighbor)}
 
 /**SMOOTHING GROUPS
  * Groups of things to smooth with.

code/__DEFINES/spatial_gridmap.dm

@@ -14,3 +14,29 @@
 
 ///whether movable is itself or containing something which should be in one of the spatial grid channels.
 #define HAS_SPATIAL_GRID_CONTENTS(movable) (movable.important_recursive_contents && (movable.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE] || movable.important_recursive_contents[RECURSIVE_CONTENTS_CLIENT_MOBS]))
+
+// macros meant specifically to add/remove movables from lazy content lists in the spatial grid.
+// when empty they become references to a single list in SSspatial_grid and when filled they become their own list
+// this is to save memory without making them lazylists as that slows down iteration through them
+#define GRID_CELL_ADD(cell_contents_list, movable_or_list) \
+	if(!length(cell_contents_list)) { \
+		cell_contents_list = list(); \
+		cell_contents_list += movable_or_list; \
+	} else { \
+		cell_contents_list += movable_or_list; \
+	};
+
+#define GRID_CELL_SET(cell_contents_list, movable_or_list) \
+	if(!length(cell_contents_list)) { \
+		cell_contents_list = list(); \
+		cell_contents_list += movable_or_list; \
+	} else { \
+		cell_contents_list |= movable_or_list; \
+	};
+
+//dont use these outside of SSspatial_grid's scope use the procs it has for this purpose
+#define GRID_CELL_REMOVE(cell_contents_list, movable_or_list) \
+	cell_contents_list -= movable_or_list; \
+	if(!length(cell_contents_list)) {\
+		cell_contents_list = dummy_list; \
+	};

code/__HELPERS/icon_smoothing.dm

@@ -309,8 +309,7 @@ DEFINE_BITFIELD(smoothing_junction, list(
 			return ADJ_FOUND
 
 	if(smoothing_flags & SMOOTH_OBJ)
-		for(var/am in target_turf)
-			var/atom/movable/thing = am
+		for(var/atom/movable/thing as anything in target_turf)
 			if(!thing.anchored || isnull(thing.smoothing_groups))
 				continue
 			for(var/target in canSmoothWith)
@@ -402,20 +401,18 @@ DEFINE_BITFIELD(smoothing_junction, list(
 //Icon smoothing helpers
 /proc/smooth_zlevel(zlevel, now = FALSE)
 	var/list/away_turfs = block(locate(1, 1, zlevel), locate(world.maxx, world.maxy, zlevel))
-	for(var/V in away_turfs)
-		var/turf/T = V
-		if(T.smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
+	for(var/turf/turf_to_smooth as anything in away_turfs)
+		if(turf_to_smooth.smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
 			if(now)
-				T.smooth_icon()
+				turf_to_smooth.smooth_icon()
 			else
-				QUEUE_SMOOTH(T)
-		for(var/R in T)
-			var/atom/A = R
-			if(A.smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
+				QUEUE_SMOOTH(turf_to_smooth)
+		for(var/atom/movable/movable_to_smooth as anything in turf_to_smooth)
+			if(movable_to_smooth.smoothing_flags & (SMOOTH_CORNERS|SMOOTH_BITMASK))
 				if(now)
-					A.smooth_icon()
+					movable_to_smooth.smooth_icon()
 				else
-					QUEUE_SMOOTH(A)
+					QUEUE_SMOOTH(movable_to_smooth)
 
 
 /atom/proc/clear_smooth_overlays()

code/__HELPERS/roundend.dm

@@ -231,7 +231,7 @@
 	// Add AntagHUD to everyone, see who was really evil the whole time!
 	for(var/datum/atom_hud/alternate_appearance/basic/antagonist_hud/antagonist_hud in GLOB.active_alternate_appearances)
 		for(var/mob/player as anything in GLOB.player_list)
-			antagonist_hud.add_hud_to(player)
+			antagonist_hud.show_to(player)
 
 	CHECK_TICK
 

code/controllers/subsystem/icon_smooth.dm

@@ -11,10 +11,10 @@ SUBSYSTEM_DEF(icon_smooth)
 	var/list/deferred = list()
 
 /datum/controller/subsystem/icon_smooth/fire()
-	var/list/cached = smooth_queue
-	while(length(cached))
-		var/atom/smoothing_atom = cached[length(cached)]
-		cached.len--
+	var/list/smooth_queue_cache = smooth_queue
+	while(length(smooth_queue_cache))
+		var/atom/smoothing_atom = smooth_queue_cache[length(smooth_queue_cache)]
+		smooth_queue_cache.len--
 		if(QDELETED(smoothing_atom) || !(smoothing_atom.smoothing_flags & SMOOTH_QUEUED))
 			continue
 		if(smoothing_atom.flags_1 & INITIALIZED_1)
@@ -24,10 +24,10 @@ SUBSYSTEM_DEF(icon_smooth)
 		if (MC_TICK_CHECK)
 			return
 
-	if (!cached.len)
+	if (!length(smooth_queue_cache))
 		if (deferred.len)
 			smooth_queue = deferred
-			deferred = cached
+			deferred = smooth_queue_cache
 		else
 			can_fire = FALSE
 
@@ -49,8 +49,7 @@ SUBSYSTEM_DEF(icon_smooth)
 	queue = blueprint_queue
 	blueprint_queue = null
 
-	for(var/item in queue)
-		var/atom/movable/movable_item = item
+	for(var/atom/movable/movable_item as anything in queue)
 		if(!isturf(movable_item.loc))
 			continue
 		var/turf/item_loc = movable_item.loc

code/controllers/subsystem/mapping.dm

@@ -40,6 +40,7 @@ SUBSYSTEM_DEF(mapping)
 	// Z-manager stuff
 	var/station_start  // should only be used for maploading-related tasks
 	var/space_levels_so_far = 0
+	///list of all the z level datums created representing the z levels in the world
 	var/list/z_list
 	var/datum/space_level/transit
 	var/datum/space_level/empty_space

code/controllers/subsystem/spatial_gridmap.dm

@@ -1,32 +1,6 @@
 ///the subsystem creates this many [/mob/oranges_ear] mob instances during init. allocations that require more than this create more.
 #define NUMBER_OF_PREGENERATED_ORANGES_EARS 2500
 
-// macros meant specifically to add/remove movables from the hearing_contents and client_contents lists of
-// /datum/spatial_grid_cell, when empty they become references to a single list in SSspatial_grid and when filled they become their own list
-// this is to save memory without making them lazylists as that slows down iteration through them
-#define GRID_CELL_ADD(cell_contents_list, movable_or_list) \
-	if(!length(cell_contents_list)) { \
-		cell_contents_list = list(); \
-		cell_contents_list += movable_or_list; \
-	} else { \
-		cell_contents_list += movable_or_list; \
-	};
-
-#define GRID_CELL_SET(cell_contents_list, movable_or_list) \
-	if(!length(cell_contents_list)) { \
-		cell_contents_list = list(); \
-		cell_contents_list += movable_or_list; \
-	} else { \
-		cell_contents_list |= movable_or_list; \
-	};
-
-//dont use these outside of SSspatial_grid's scope use the procs it has for this purpose
-#define GRID_CELL_REMOVE(cell_contents_list, movable_or_list) \
-	cell_contents_list -= movable_or_list; \
-	if(!length(cell_contents_list)) {\
-		cell_contents_list = dummy_list; \
-	};
-
 /**
  * # Spatial Grid Cell
  *
@@ -64,7 +38,6 @@
 	if(length(dummy_list))
 		dummy_list.Cut()
 		stack_trace("SSspatial_grid.dummy_list had something inserted into it at some point! this is a problem as it is supposed to stay empty")
-
 	hearing_contents = dummy_list
 	client_contents = dummy_list
 
@@ -296,6 +269,7 @@ SUBSYSTEM_DEF(spatial_grid)
 
 	//technically THIS list only contains lists, but inside those lists are grid cell datums and we can go without a SINGLE var init if we do this
 	var/list/datum/spatial_grid_cell/grid_level = grids_by_z_level[center_turf.z]
+
 	switch(type)
 		if(SPATIAL_GRID_CONTENTS_TYPE_CLIENTS)
 			for(var/row in BOUNDING_BOX_MIN(center_y) to BOUNDING_BOX_MAX(center_y, cells_on_y_axis))
@@ -363,15 +337,15 @@ SUBSYSTEM_DEF(spatial_grid)
 
 	var/datum/spatial_grid_cell/intersecting_cell = grids_by_z_level[z_index][y_index][x_index]
 
-	if(new_target.important_recursive_contents[RECURSIVE_CONTENTS_CLIENT_MOBS])
+	if(new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
 		GRID_CELL_SET(intersecting_cell.client_contents, new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
 
-		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_ENTERED(RECURSIVE_CONTENTS_CLIENT_MOBS), new_target)
+		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_ENTERED(SPATIAL_GRID_CONTENTS_TYPE_CLIENTS), new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
 
-	if(new_target.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE])
-		GRID_CELL_SET(intersecting_cell.hearing_contents, new_target.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE])
+	if(new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
+		GRID_CELL_SET(intersecting_cell.hearing_contents, new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
 
-		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_ENTERED(RECURSIVE_CONTENTS_HEARING_SENSITIVE), new_target)
+		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_ENTERED(SPATIAL_GRID_CONTENTS_TYPE_HEARING), new_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
 
 /**
  * find the spatial map cell that target used to belong to, then subtract target's important_recusive_contents from it.
@@ -385,35 +359,54 @@ SUBSYSTEM_DEF(spatial_grid)
 	if(!initialized)
 		return
 	if(!target_turf || !old_target?.important_recursive_contents)
-		CRASH("/datum/controller/subsystem/spatial_grid/proc/exit_cell() was given null arguments or a new_target without important_recursive_contents!")
+		stack_trace("/datum/controller/subsystem/spatial_grid/proc/exit_cell() was given null arguments or a new_target without important_recursive_contents!")
+		return FALSE
 
 	var/x_index = ROUND_UP(target_turf.x / SPATIAL_GRID_CELLSIZE)
 	var/y_index = ROUND_UP(target_turf.y / SPATIAL_GRID_CELLSIZE)
 	var/z_index = target_turf.z
 
-	var/list/grid = grids_by_z_level[z_index]
-	var/datum/spatial_grid_cell/intersecting_cell = grid[y_index][x_index]
+	var/datum/spatial_grid_cell/intersecting_cell = grids_by_z_level[z_index][y_index][x_index]
+	var/list/old_target_contents = old_target.important_recursive_contents //cache for sanic speeds (lists are references anyways)
 
-	if(exclusive_type && old_target.important_recursive_contents[exclusive_type])
-		switch(exclusive_type)
-			if(RECURSIVE_CONTENTS_CLIENT_MOBS)
-				GRID_CELL_REMOVE(intersecting_cell.client_contents, old_target.important_recursive_contents[RECURSIVE_CONTENTS_CLIENT_MOBS])
+	if(old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
+		GRID_CELL_REMOVE(intersecting_cell.client_contents, old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
 
-			if(RECURSIVE_CONTENTS_HEARING_SENSITIVE)
-				GRID_CELL_REMOVE(intersecting_cell.hearing_contents, old_target.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE])
+		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(SPATIAL_GRID_CONTENTS_TYPE_CLIENTS), old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
 
-		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(exclusive_type), old_target)
-		return
+	if(old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
+		GRID_CELL_REMOVE(intersecting_cell.hearing_contents, old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
 
-	if(old_target.important_recursive_contents[RECURSIVE_CONTENTS_CLIENT_MOBS])
-		GRID_CELL_REMOVE(intersecting_cell.client_contents, old_target.important_recursive_contents[RECURSIVE_CONTENTS_CLIENT_MOBS])
+		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(SPATIAL_GRID_CONTENTS_TYPE_HEARING), old_target_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
 
-		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(SPATIAL_GRID_CONTENTS_TYPE_CLIENTS), old_target)
+	return TRUE
 
-	if(old_target.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE])
-		GRID_CELL_REMOVE(intersecting_cell.hearing_contents, old_target.important_recursive_contents[RECURSIVE_CONTENTS_HEARING_SENSITIVE])
+///acts like exit_cell() but only removes the target from the specified type of grid cell contents list
+/datum/controller/subsystem/spatial_grid/proc/remove_single_contents_type(atom/movable/old_target, turf/target_turf, exclusive_type)
+	if(!target_turf || !old_target?.important_recursive_contents || !exclusive_type)
+		stack_trace("/datum/controller/subsystem/spatial_grid/proc/remove_single_contents_type() was given null arguments or a new_target without important_recursive_contents!")
+		return FALSE
+
+	if(!old_target.important_recursive_contents[exclusive_type])
+		return FALSE
+
+	var/x_index = ROUND_UP(target_turf.x / SPATIAL_GRID_CELLSIZE)
+	var/y_index = ROUND_UP(target_turf.y / SPATIAL_GRID_CELLSIZE)
+	var/z_index = target_turf.z
+
+	var/datum/spatial_grid_cell/intersecting_cell = grids_by_z_level[z_index][y_index][x_index]
+
+	switch(exclusive_type)
+		if(SPATIAL_GRID_CONTENTS_TYPE_CLIENTS)
+			GRID_CELL_REMOVE(intersecting_cell.client_contents, old_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_CLIENTS])
+
+		if(SPATIAL_GRID_CONTENTS_TYPE_HEARING)
+			GRID_CELL_REMOVE(intersecting_cell.hearing_contents, old_target.important_recursive_contents[SPATIAL_GRID_CONTENTS_TYPE_HEARING])
+
+	SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(exclusive_type), old_target)
+
+	return TRUE
 
-		SEND_SIGNAL(intersecting_cell, SPATIAL_GRID_CELL_EXITED(RECURSIVE_CONTENTS_HEARING_SENSITIVE), old_target)
 
 ///find the cell this movable is associated with and removes it from all lists
 /datum/controller/subsystem/spatial_grid/proc/force_remove_from_cell(atom/movable/to_remove, datum/spatial_grid_cell/input_cell)

code/datums/hud.dm

@@ -2,6 +2,10 @@
 
 GLOBAL_LIST_EMPTY(all_huds)
 
+///gets filled by each /datum/atom_hud/New().
+///associative list of the form: list(hud category = list(all global atom huds that use that category))
+GLOBAL_LIST_EMPTY(huds_by_category)
+
 //GLOBAL HUD LIST
 GLOBAL_LIST_INIT(huds, list(
 	DATA_HUD_SECURITY_BASIC = new/datum/atom_hud/data/human/security/basic(),
@@ -17,116 +21,354 @@ GLOBAL_LIST_INIT(huds, list(
 ))
 
 /datum/atom_hud
-	var/list/atom/hudatoms = list() //list of all atoms which display this hud
-	var/list/hudusers = list() //list with all mobs who can see the hud
-	var/list/hud_icons = list() //these will be the indexes for the atom's hud_list
+	///associative list of the form: list(z level = list(hud atom)).
+	///tracks what hud atoms for this hud exists in what z level so we can only give users
+	///the hud images that they can actually see.
+	var/list/atom/hud_atoms = list()
 
-	var/list/next_time_allowed = list() //mobs associated with the next time this hud can be added to them
-	var/list/queued_to_see = list() //mobs that have triggered the cooldown and are queued to see the hud, but do not yet
-	var/hud_exceptions = list() // huduser = list(ofatomswiththeirhudhidden) - aka everyone hates targeted invisiblity
+	///associative list of the form: list(z level = list(hud user client mobs)).
+	///tracks mobs that can "see" us
+	// by z level so when they change z's we can adjust what images they see from this hud.
+	var/list/hud_users = list()
+
+	///used for signal tracking purposes, associative list of the form: list(hud atom = TRUE) that isnt separated by z level
+	var/list/atom/hud_atoms_all_z_levels = list()
+
+	///used for signal tracking purposes, associative list of the form: list(hud user = number of times this hud was added to this user).
+	///that isnt separated by z level
+	var/list/mob/hud_users_all_z_levels = list()
+
+	///these will be the indexes for the atom's hud_list
+	var/list/hud_icons = list()
+
+	///mobs associated with the next time this hud can be added to them
+	var/list/next_time_allowed = list()
+	///mobs that have triggered the cooldown and are queued to see the hud, but do not yet
+	var/list/queued_to_see = list()
+	/// huduser = list(atoms with their hud hidden) - aka everyone hates targeted invisiblity
+	var/list/hud_exceptions = list()
+	///whether or not this atom_hud type updates the global huds_by_category list.
+	///some subtypes cant work like this since theyre supposed to "belong" to
+	///one target atom each. it will still go in the other global hud lists.
+	var/uses_global_hud_category = TRUE
 
 /datum/atom_hud/New()
 	GLOB.all_huds += src
+	for(var/z_level in 1 to world.maxz)
+		hud_atoms += list(list())
+		hud_users += list(list())
+
+	RegisterSignal(SSdcs, COMSIG_GLOB_NEW_Z, .proc/add_z_level_huds)
+
+	if(uses_global_hud_category)
+		for(var/hud_icon in hud_icons)
+			GLOB.huds_by_category[hud_icon] += list(src)
 
 /datum/atom_hud/Destroy()
-	for(var/v in hudusers)
-		remove_hud_from(v)
-	for(var/v in hudatoms)
-		remove_from_hud(v)
+	for(var/mob/mob as anything in hud_users_all_z_levels)
+		hide_from(mob)
+
+	for(var/atom/atom as anything in hud_atoms_all_z_levels)
+		remove_atom_from_hud(atom)
+
+	if(uses_global_hud_category)
+		for(var/hud_icon in hud_icons)
+			LAZYREMOVEASSOC(GLOB.huds_by_category, hud_icon, src)
+
 	GLOB.all_huds -= src
 	return ..()
 
-/datum/atom_hud/proc/remove_hud_from(mob/M, absolute = FALSE)
-	if(!M || !hudusers[M])
-		return
-	if (absolute || !--hudusers[M])
-		UnregisterSignal(M, COMSIG_PARENT_QDELETING)
-		hudusers -= M
-		if(next_time_allowed[M])
-			next_time_allowed -= M
-		if(queued_to_see[M])
-			queued_to_see -= M
-		else
-			for(var/atom/A in hudatoms)
-				remove_from_single_hud(M, A)
+/datum/atom_hud/proc/add_z_level_huds()
+	SIGNAL_HANDLER
+	hud_atoms += list(list())
+	hud_users += list(list())
 
-/datum/atom_hud/proc/remove_from_hud(atom/A)
-	if(!A)
+///returns a list of all hud atoms in the given z level and linked lower z levels (because hud users in higher z levels can see below)
+/datum/atom_hud/proc/get_hud_atoms_for_z_level(z_level)
+	if(z_level <= 0)
 		return FALSE
-	for(var/mob/M in hudusers)
-		remove_from_single_hud(M, A)
-	hudatoms -= A
+	if(z_level > length(hud_atoms))
+		stack_trace("get_hud_atoms_for_z_level() was given a z level index out of bounds of hud_atoms!")
+		return FALSE
+
+	. = list()
+	. += hud_atoms[z_level]
+
+	var/max_number_of_linked_z_levels_i_care_to_support_here = 10
+
+	while(max_number_of_linked_z_levels_i_care_to_support_here)
+		var/lower_z_level_exists = SSmapping.level_trait(z_level, ZTRAIT_DOWN)
+
+		if(lower_z_level_exists)
+			z_level--
+			. += hud_atoms[z_level]
+			max_number_of_linked_z_levels_i_care_to_support_here--
+			continue
+
+		else
+			break
+
+///returns a list of all hud users in the given z level and linked upper z levels (because hud users in higher z levels can see below)
+/datum/atom_hud/proc/get_hud_users_for_z_level(z_level)
+	if(z_level > length(hud_users) || z_level <= 0)
+		stack_trace("get_hud_atoms_for_z_level() was given a z level index [z_level] out of bounds 1->[length(hud_users)] of hud_atoms!")
+		return FALSE
+
+	. = list()
+	. += hud_users[z_level]
+
+	var/max_number_of_linked_z_levels_i_care_to_support_here = 10
+
+	while(max_number_of_linked_z_levels_i_care_to_support_here)
+		var/upper_level_exists = SSmapping.level_trait(z_level, ZTRAIT_UP)
+
+		if(upper_level_exists)
+			z_level++
+			. += hud_users[z_level]
+			max_number_of_linked_z_levels_i_care_to_support_here--
+			continue
+
+		else
+			break
+
+///show this hud to the passed in user
+/datum/atom_hud/proc/show_to(mob/new_viewer)
+	if(!new_viewer)
+		return
+
+	var/turf/their_turf = get_turf(new_viewer)
+	if(!their_turf)
+		return
+
+	if(!hud_users[their_turf.z][new_viewer])
+		hud_users[their_turf.z][new_viewer] = TRUE
+		hud_users_all_z_levels[new_viewer] = 1
+
+		RegisterSignal(new_viewer, COMSIG_PARENT_QDELETING, .proc/unregister_atom, override = TRUE) //both hud users and hud atoms use these signals
+		RegisterSignal(new_viewer, COMSIG_MOVABLE_Z_CHANGED, .proc/on_atom_or_user_z_level_changed, override = TRUE)
+
+		if(next_time_allowed[new_viewer] > world.time)
+			if(!queued_to_see[new_viewer])
+				addtimer(CALLBACK(src, .proc/show_hud_images_after_cooldown, new_viewer), next_time_allowed[new_viewer] - world.time)
+				queued_to_see[new_viewer] = TRUE
+
+		else
+			next_time_allowed[new_viewer] = world.time + ADD_HUD_TO_COOLDOWN
+			for(var/atom/hud_atom_to_add as anything in get_hud_atoms_for_z_level(their_turf.z))
+				add_atom_to_single_mob_hud(new_viewer, hud_atom_to_add)
+	else
+		hud_users_all_z_levels[new_viewer] += 1 //increment the number of times this hud has been added to this hud user
+
+///Hides the images in this hud from former_viewer
+///If absolute is set to true, this will forcefully remove the hud, even if sources in theory remain
+/datum/atom_hud/proc/hide_from(mob/former_viewer, absolute = FALSE)
+	if(!former_viewer || !hud_users_all_z_levels[former_viewer])
+		return
+
+	var/turf/their_turf = get_turf(former_viewer)
+	if(!their_turf)
+		return
+
+	hud_users_all_z_levels[former_viewer] -= 1//decrement number of sources for this hud on this user (bad way to track i know)
+
+	if (absolute || hud_users_all_z_levels[former_viewer] <= 0)//if forced or there arent any sources left, remove the user
+
+		if(!hud_atoms_all_z_levels[former_viewer])//make sure we arent unregistering changes on a mob thats also a hud atom for this hud
+			UnregisterSignal(former_viewer, COMSIG_MOVABLE_Z_CHANGED)
+			UnregisterSignal(former_viewer, COMSIG_PARENT_QDELETING)
+
+		hud_users[their_turf.z] -= former_viewer
+		hud_users_all_z_levels -= former_viewer
+
+		if(next_time_allowed[former_viewer])
+			next_time_allowed -= former_viewer
+
+		if(queued_to_see[former_viewer])
+			queued_to_see -= former_viewer
+		else
+			for(var/atom/hud_atom as anything in get_hud_atoms_for_z_level(their_turf.z))
+				remove_atom_from_single_hud(former_viewer, hud_atom)
+
+/// add new_hud_atom to this hud
+/datum/atom_hud/proc/add_atom_to_hud(atom/new_hud_atom)
+	if(!new_hud_atom)
+		return FALSE
+	var/turf/atom_turf = get_turf(new_hud_atom)
+	if(!atom_turf)
+		return
+
+	RegisterSignal(new_hud_atom, COMSIG_MOVABLE_Z_CHANGED, .proc/on_atom_or_user_z_level_changed, override = TRUE)
+	RegisterSignal(new_hud_atom, COMSIG_PARENT_QDELETING, .proc/unregister_atom, override = TRUE) //both hud atoms and hud users use these signals
+
+	hud_atoms[atom_turf.z] |= new_hud_atom
+	hud_atoms_all_z_levels[new_hud_atom] = TRUE
+
+	for(var/mob/mob_to_show as anything in get_hud_users_for_z_level(atom_turf.z))
+		if(!queued_to_see[mob_to_show])
+			add_atom_to_single_mob_hud(mob_to_show, new_hud_atom)
 	return TRUE
 
-/datum/atom_hud/proc/remove_from_single_hud(mob/M, atom/A) //unsafe, no sanity apart from client
-	if(!M || !M.client || !A)
-		return
-	for(var/i in hud_icons)
-		M.client.images -= A.hud_list[i]
+/// remove this atom from this hud completely
+/datum/atom_hud/proc/remove_atom_from_hud(atom/hud_atom_to_remove)
+	if(!hud_atom_to_remove || !hud_atoms_all_z_levels[hud_atom_to_remove])
+		return FALSE
 
-/datum/atom_hud/proc/add_hud_to(mob/M)
-	if(!M)
-		return
-	if(!hudusers[M])
-		hudusers[M] = 1
-		RegisterSignal(M, COMSIG_PARENT_QDELETING, .proc/unregister_mob)
-		if(next_time_allowed[M] > world.time)
-			if(!queued_to_see[M])
-				addtimer(CALLBACK(src, .proc/show_hud_images_after_cooldown, M), next_time_allowed[M] - world.time)
-				queued_to_see[M] = TRUE
-		else
-			next_time_allowed[M] = world.time + ADD_HUD_TO_COOLDOWN
-			for(var/atom/A in hudatoms)
-				add_to_single_hud(M, A)
-	else
-		hudusers[M]++
+	//make sure we arent unregistering a hud atom thats also a hud user mob
+	if(!hud_users_all_z_levels[hud_atom_to_remove])
+		UnregisterSignal(hud_atom_to_remove, COMSIG_MOVABLE_Z_CHANGED)
+		UnregisterSignal(hud_atom_to_remove, COMSIG_PARENT_QDELETING)
 
-/datum/atom_hud/proc/unregister_mob(datum/source, force)
+	for(var/mob/mob_to_remove as anything in hud_users_all_z_levels)
+		remove_atom_from_single_hud(mob_to_remove, hud_atom_to_remove)
+
+	var/turf/atom_turf = get_turf(hud_atom_to_remove)
+	if(!atom_turf)
+		return
+
+	hud_atoms[atom_turf.z] -= hud_atom_to_remove
+	hud_atoms_all_z_levels -= hud_atom_to_remove
+
+	return TRUE
+
+///adds a newly active hud category's image on a hud atom to every mob that could see it
+/datum/atom_hud/proc/add_single_hud_category_on_atom(atom/hud_atom, hud_category_to_add)
+	if(!hud_atom?.active_hud_list?[hud_category_to_add] || QDELING(hud_atom) || !(hud_category_to_add in hud_icons))
+		return FALSE
+
+	var/turf/atom_turf = get_turf(hud_atom)
+	if(!atom_turf)
+		return FALSE
+
+	if(!hud_atoms_all_z_levels[hud_atom])
+		add_atom_to_hud(hud_atom)
+		return TRUE
+
+	for(var/mob/hud_user as anything in get_hud_users_for_z_level(atom_turf.z))
+		if(!hud_user.client)
+			continue
+		if(!hud_exceptions[hud_user] || !(hud_atom in hud_exceptions[hud_user]))
+			hud_user.client.images |= hud_atom.active_hud_list[hud_category_to_add]
+
+	return TRUE
+
+///removes the image or images in hud_atom.hud_list[hud_category_to_remove] from every mob that can see it but leaves every other image
+///from that atom there.
+/datum/atom_hud/proc/remove_single_hud_category_on_atom(atom/hud_atom, hud_category_to_remove)
+	if(QDELETED(hud_atom) || !(hud_category_to_remove in hud_icons) || !hud_atoms_all_z_levels[hud_atom])
+		return FALSE
+
+	if(!hud_atom.active_hud_list)
+		remove_atom_from_hud(hud_atom)
+		return TRUE
+
+	var/turf/atom_turf = get_turf(hud_atom)
+	if(!atom_turf)
+		return FALSE
+
+	for(var/mob/hud_user as anything in get_hud_users_for_z_level(atom_turf.z))
+		if(!hud_user.client)
+			continue
+		hud_user.client.images -= hud_atom.active_hud_list[hud_category_to_remove]//by this point it shouldnt be in active_hud_list
+
+	return TRUE
+
+///when a hud atom or hud user changes z levels this makes sure it gets the images it needs and removes the images it doesnt need.
+///because of how signals work we need the same proc to handle both use cases because being a hud atom and being a hud user arent mutually exclusive
+/datum/atom_hud/proc/on_atom_or_user_z_level_changed(atom/movable/moved_atom, turf/old_turf, turf/new_turf)
 	SIGNAL_HANDLER
-	remove_hud_from(source, TRUE)
 
-/datum/atom_hud/proc/hide_single_atomhud_from(hud_user,hidden_atom)
-	if(hudusers[hud_user])
-		remove_from_single_hud(hud_user,hidden_atom)
+	if(old_turf)
+		if(hud_users_all_z_levels[moved_atom])
+			hud_users[old_turf.z] -= moved_atom
+
+			for(var/atom/formerly_seen_hud_atom as anything in get_hud_atoms_for_z_level(old_turf.z))
+				remove_atom_from_single_hud(moved_atom, formerly_seen_hud_atom)
+
+		if(hud_atoms_all_z_levels[moved_atom])
+			hud_atoms[old_turf.z] -= moved_atom
+
+			for(var/mob/formerly_seeing as anything in get_hud_users_for_z_level(old_turf.z))//this wont include moved_atom since its removed
+				remove_atom_from_single_hud(formerly_seeing, moved_atom)
+
+	if(new_turf)
+		if(hud_users_all_z_levels[moved_atom])
+			hud_users[new_turf.z][moved_atom] = TRUE //hud users is associative, hud atoms isnt
+
+			for(var/atom/newly_seen_hud_atom as anything in get_hud_atoms_for_z_level(new_turf.z))
+				add_atom_to_single_mob_hud(moved_atom, newly_seen_hud_atom)
+
+		if(hud_atoms_all_z_levels[moved_atom])
+			hud_atoms[new_turf.z] |= moved_atom
+
+			for(var/mob/newly_seeing as anything in get_hud_users_for_z_level(new_turf.z))
+				add_atom_to_single_mob_hud(newly_seeing, moved_atom)
+
+/// add just hud_atom's hud images (that are part of this atom_hud) to requesting_mob's client.images list
+/datum/atom_hud/proc/add_atom_to_single_mob_hud(mob/requesting_mob, atom/hud_atom) //unsafe, no sanity apart from client
+	if(!requesting_mob || !requesting_mob.client || !hud_atom)
+		return
+
+	for(var/hud_category in (hud_icons & hud_atom.active_hud_list))
+		if(!hud_exceptions[requesting_mob] || !(hud_atom in hud_exceptions[requesting_mob]))
+			requesting_mob.client.images |= hud_atom.active_hud_list[hud_category]
+
+/// remove every hud image for this hud on atom_to_remove from client_mob's client.images list
+/datum/atom_hud/proc/remove_atom_from_single_hud(mob/client_mob, atom/atom_to_remove)
+	if(!client_mob || !client_mob.client || !atom_to_remove?.active_hud_list)
+		return
+	for(var/hud_image in hud_icons)
+		client_mob.client.images -= atom_to_remove.active_hud_list[hud_image]
+
+/datum/atom_hud/proc/unregister_atom(datum/source, force)
+	SIGNAL_HANDLER
+	hide_from(source, TRUE)
+	remove_atom_from_hud(source)
+
+/datum/atom_hud/proc/hide_single_atomhud_from(mob/hud_user, atom/hidden_atom)
+
+	if(hud_users_all_z_levels[hud_user])
+		remove_atom_from_single_hud(hud_user, hidden_atom)
+
 	if(!hud_exceptions[hud_user])
 		hud_exceptions[hud_user] = list(hidden_atom)
 	else
 		hud_exceptions[hud_user] += hidden_atom
 
-/datum/atom_hud/proc/unhide_single_atomhud_from(hud_user,hidden_atom)
+/datum/atom_hud/proc/unhide_single_atomhud_from(mob/hud_user, atom/hidden_atom)
 	hud_exceptions[hud_user] -= hidden_atom
-	if(hudusers[hud_user])
-		add_to_single_hud(hud_user,hidden_atom)
 
-/datum/atom_hud/proc/show_hud_images_after_cooldown(M)
-	if(queued_to_see[M])
-		queued_to_see -= M
-		next_time_allowed[M] = world.time + ADD_HUD_TO_COOLDOWN
-		for(var/atom/A in hudatoms)
-			add_to_single_hud(M, A)
+	var/turf/hud_atom_turf = get_turf(hidden_atom)
 
-/datum/atom_hud/proc/add_to_hud(atom/A)
-	if(!A)
-		return FALSE
-	hudatoms |= A
-	for(var/mob/M in hudusers)
-		if(!queued_to_see[M])
-			add_to_single_hud(M, A)
-	return TRUE
-
-/datum/atom_hud/proc/add_to_single_hud(mob/M, atom/A) //unsafe, no sanity apart from client
-	if(!M || !M.client || !A)
+	if(!hud_atom_turf)
 		return
-	for(var/i in hud_icons)
-		if(A.hud_list[i] && (!hud_exceptions[M] || !(A in hud_exceptions[M])))
-			M.client.images |= A.hud_list[i]
+
+	if(hud_users[hud_atom_turf.z][hud_user])
+		add_atom_to_single_mob_hud(hud_user, hidden_atom)
+
+/datum/atom_hud/proc/show_hud_images_after_cooldown(mob/queued_hud_user)
+	if(!queued_to_see[queued_hud_user])
+		return
+
+	queued_to_see -= queued_hud_user
+	next_time_allowed[queued_hud_user] = world.time + ADD_HUD_TO_COOLDOWN
+
+	var/turf/user_turf = get_turf(queued_hud_user)
+	if(!user_turf)
+		return
+
+	for(var/atom/hud_atom_to_show as anything in get_hud_atoms_for_z_level(user_turf.z))
+		add_atom_to_single_mob_hud(queued_hud_user, hud_atom_to_show)
 
 //MOB PROCS
 /mob/proc/reload_huds()
+	var/turf/our_turf = get_turf(src)
+	if(!our_turf)
+		return
+
 	for(var/datum/atom_hud/hud in GLOB.all_huds)
-		if(hud?.hudusers[src])
-			for(var/atom/A in hud.hudatoms)
-				hud.add_to_single_hud(src, A)
+		if(hud?.hud_users_all_z_levels[src])
+			for(var/atom/hud_atom as anything in hud.get_hud_atoms_for_z_level(our_turf.z))
+				hud.add_atom_to_single_mob_hud(src, hud_atom)
 
 /mob/dead/new_player/reload_huds()
 	return

code/datums/mind.dm

@@ -52,11 +52,14 @@
 	var/static/default_martial_art = new/datum/martial_art
 	var/miming = FALSE // Mime's vow of silence
 	var/list/antag_datums
-	var/antag_hud_icon_state = null //this mind's ANTAG_HUD should have this icon_state
-	var/datum/atom_hud/alternate_appearance/basic/antagonist_hud/antag_hud = null //this mind's antag HUD
+	///this mind's ANTAG_HUD should have this icon_state
+	var/antag_hud_icon_state = null
+	///this mind's antag HUD
+	var/datum/atom_hud/alternate_appearance/basic/antagonist_hud/antag_hud = null
 	var/holy_role = NONE //is this person a chaplain or admin role allowed to use bibles, Any rank besides 'NONE' allows for this.
 
-	var/mob/living/enslaved_to //If this mind's master is another mob (i.e. adamantine golems)
+	///If this mind's master is another mob (i.e. adamantine golems)
+	var/mob/living/enslaved_to
 	var/datum/language_holder/language_holder
 	var/unconvertable = FALSE
 	var/late_joiner = FALSE

code/datums/quirks/good.dm

@@ -76,7 +76,7 @@
 
 /datum/quirk/item_quirk/clown_enjoyer/add()
 	var/datum/atom_hud/fan = GLOB.huds[DATA_HUD_FAN]
-	fan.add_hud_to(quirk_holder)
+	fan.show_to(quirk_holder)
 
 /datum/quirk/item_quirk/mime_fan
 	name = "Mime Fan"
@@ -93,7 +93,7 @@
 
 /datum/quirk/item_quirk/mime_fan/add()
 	var/datum/atom_hud/fan = GLOB.huds[DATA_HUD_FAN]
-	fan.add_hud_to(quirk_holder)
+	fan.show_to(quirk_holder)
 
 /datum/quirk/freerunning
 	name = "Freerunning"

code/datums/status_effects/buffs.dm

@@ -237,15 +237,15 @@
 
 	//Makes the user passive, it's in their oath not to harm!
 	ADD_TRAIT(owner, TRAIT_PACIFISM, HIPPOCRATIC_OATH_TRAIT)
-	var/datum/atom_hud/H = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	H.add_hud_to(owner)
+	var/datum/atom_hud/med_hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
+	med_hud.show_to(owner)
 	return ..()
 
 /datum/status_effect/hippocratic_oath/on_remove()
 	QDEL_NULL(aura_healing)
 	REMOVE_TRAIT(owner, TRAIT_PACIFISM, HIPPOCRATIC_OATH_TRAIT)
-	var/datum/atom_hud/H = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	H.remove_hud_from(owner)
+	var/datum/atom_hud/med_hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
+	med_hud.hide_from(owner)
 
 /datum/status_effect/hippocratic_oath/get_examine_text()
 	return span_notice("[owner.p_they(TRUE)] seem[owner.p_s()] to have an aura of healing and helpfulness about [owner.p_them()].")

code/game/alternate_appearance.dm

@@ -5,7 +5,7 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 		for(var/K in alternate_appearances)
 			var/datum/atom_hud/alternate_appearance/AA = alternate_appearances[K]
 			if(AA.appearance_key == key)
-				AA.remove_from_hud(src)
+				AA.remove_atom_from_hud(src)
 				break
 
 /atom/proc/add_alt_appearance(type, key, ...)
@@ -24,13 +24,16 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 	var/transfer_overlays = FALSE
 
 /datum/atom_hud/alternate_appearance/New(key)
-	..()
-	GLOB.active_alternate_appearances += src
+	// We use hud_icons to register our hud, so we need to do this before the parent call
 	appearance_key = key
+	hud_icons = list(appearance_key)
+	..()
+
+	GLOB.active_alternate_appearances += src
 
 	for(var/mob in GLOB.player_list)
 		if(mobShouldSee(mob))
-			add_hud_to(mob)
+			show_to(mob)
 
 /datum/atom_hud/alternate_appearance/Destroy()
 	GLOB.active_alternate_appearances -= src
@@ -38,18 +41,18 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 
 /datum/atom_hud/alternate_appearance/proc/onNewMob(mob/M)
 	if(mobShouldSee(M))
-		add_hud_to(M)
+		show_to(M)
 
 /datum/atom_hud/alternate_appearance/proc/mobShouldSee(mob/M)
 	return FALSE
 
-/datum/atom_hud/alternate_appearance/add_to_hud(atom/A, image/I)
+/datum/atom_hud/alternate_appearance/add_atom_to_hud(atom/A, image/I)
 	. = ..()
 	if(.)
 		LAZYINITLIST(A.alternate_appearances)
 		A.alternate_appearances[appearance_key] = src
 
-/datum/atom_hud/alternate_appearance/remove_from_hud(atom/A)
+/datum/atom_hud/alternate_appearance/remove_atom_from_hud(atom/A)
 	. = ..()
 	if(.)
 		LAZYREMOVE(A.alternate_appearances, appearance_key)
@@ -63,6 +66,7 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 	var/image/image
 	var/add_ghost_version = FALSE
 	var/ghost_appearance
+	uses_global_hud_category = FALSE
 
 /datum/atom_hud/alternate_appearance/basic/New(key, image/I, options = AA_TARGET_SEE_APPEARANCE)
 	..()
@@ -72,10 +76,11 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 	if(transfer_overlays)
 		I.copy_overlays(target)
 
-	hud_icons = list(appearance_key)
-	add_to_hud(target, I)
+	add_atom_to_hud(target)
+	target.set_hud_image_active(appearance_key, exclusive_hud = src)
+
 	if((options & AA_TARGET_SEE_APPEARANCE) && ismob(target))
-		add_hud_to(target)
+		show_to(target)
 	if(add_ghost_version)
 		var/image/ghost_image = image(icon = I.icon , icon_state = I.icon_state, loc = I.loc)
 		ghost_image.override = FALSE
@@ -89,14 +94,15 @@ GLOBAL_LIST_EMPTY(active_alternate_appearances)
 	if(ghost_appearance)
 		QDEL_NULL(ghost_appearance)
 
-/datum/atom_hud/alternate_appearance/basic/add_to_hud(atom/A)
+/datum/atom_hud/alternate_appearance/basic/add_atom_to_hud(atom/A)
 	LAZYINITLIST(A.hud_list)
 	A.hud_list[appearance_key] = image
 	. = ..()
 
-/datum/atom_hud/alternate_appearance/basic/remove_from_hud(atom/A)
+/datum/atom_hud/alternate_appearance/basic/remove_atom_from_hud(atom/A)
 	. = ..()
 	A.hud_list -= appearance_key
+	A.set_hud_image_inactive(appearance_key)
 	if(. && !QDELETED(src))
 		qdel(src)
 

code/game/atoms.dm

@@ -30,8 +30,12 @@
 	///Reagents holder
 	var/datum/reagents/reagents = null
 
-	///This atom's HUD (med/sec, etc) images. Associative list.
+	///all of this atom's HUD (med/sec, etc) images. Associative list of the form: list(hud category = hud image or images for that category).
+	///most of the time hud category is associated with a single image, sometimes its associated with a list of images.
+	///not every hud in this list is actually used. for ones available for others to see, look at active_hud_list.
 	var/list/image/hud_list = null
+	///all of this atom's HUD images which can actually be seen by players with that hud
+	var/list/image/active_hud_list = null
 	///HUD images that this atom can provide.
 	var/list/hud_possible
 
@@ -300,7 +304,7 @@
 	if(alternate_appearances)
 		for(var/current_alternate_appearance in alternate_appearances)
 			var/datum/atom_hud/alternate_appearance/selected_alternate_appearance = alternate_appearances[current_alternate_appearance]
-			selected_alternate_appearance.remove_from_hud(src)
+			selected_alternate_appearance.remove_atom_from_hud(src)
 
 	if(reagents)
 		QDEL_NULL(reagents)

code/game/atoms_movable.dm

@@ -842,7 +842,7 @@
 	var/turf/our_turf = get_turf(src)
 
 	if(our_turf && SSspatial_grid.initialized)
-		SSspatial_grid.exit_cell(src, our_turf, RECURSIVE_CONTENTS_CLIENT_MOBS)
+		SSspatial_grid.remove_single_contents_type(src, our_turf, RECURSIVE_CONTENTS_CLIENT_MOBS)
 	else if(our_turf && !SSspatial_grid.initialized)
 		SSspatial_grid.remove_from_pre_init_queue(src, RECURSIVE_CONTENTS_CLIENT_MOBS)
 

code/game/data_huds.dm

@@ -9,11 +9,11 @@
 
 /atom/proc/add_to_all_human_data_huds()
 	for(var/datum/atom_hud/data/human/hud in GLOB.huds)
-		hud.add_to_hud(src)
+		hud.add_atom_to_hud(src)
 
 /atom/proc/remove_from_all_data_huds()
 	for(var/datum/atom_hud/data/hud in GLOB.huds)
-		hud.remove_from_hud(src)
+		hud.remove_atom_from_hud(src)
 
 /datum/atom_hud/data
 
@@ -32,12 +32,12 @@
 		return FALSE
 	return TRUE
 
-/datum/atom_hud/data/human/medical/basic/add_to_single_hud(mob/M, mob/living/carbon/H)
+/datum/atom_hud/data/human/medical/basic/add_atom_to_single_mob_hud(mob/M, mob/living/carbon/H)
 	if(check_sensors(H))
 		..()
 
 /datum/atom_hud/data/human/medical/basic/proc/update_suit_sensors(mob/living/carbon/H)
-	check_sensors(H) ? add_to_hud(H) : remove_from_hud(H)
+	check_sensors(H) ? add_atom_to_hud(H) : remove_atom_from_hud(H)
 
 /datum/atom_hud/data/human/medical/advanced
 
@@ -61,6 +61,8 @@
 	hud_icons = list(DIAG_HUD, DIAG_STAT_HUD, DIAG_BATT_HUD, DIAG_MECH_HUD, DIAG_BOT_HUD, DIAG_CIRCUIT_HUD, DIAG_TRACK_HUD, DIAG_AIRLOCK_HUD, DIAG_LAUNCHPAD_HUD, DIAG_PATH_HUD)
 
 /datum/atom_hud/data/bot_path
+	// This hud exists so the bot can see itself, that's all
+	uses_global_hud_category = FALSE
 	hud_icons = list(DIAG_PATH_HUD)
 
 /datum/atom_hud/abductor
@@ -72,12 +74,12 @@
 /datum/atom_hud/ai_detector
 	hud_icons = list(AI_DETECT_HUD)
 
-/datum/atom_hud/ai_detector/add_hud_to(mob/M)
+/datum/atom_hud/ai_detector/show_to(mob/new_viewer)
 	..()
-	if(M && (hudusers.len == 1))
-		for(var/V in GLOB.aiEyes)
-			var/mob/camera/ai_eye/E = V
-			E.update_ai_detect_hud()
+	if(!new_viewer || hud_users.len != 1)
+		return
+	for(var/mob/camera/ai_eye/eye as anything in GLOB.aiEyes)
+		eye.update_ai_detect_hud()
 
 /* MED/SEC/DIAG HUD HOOKS */
 
@@ -229,11 +231,19 @@ FAN HUDs! For identifying other fans on-sight.
 	holder.pixel_y = I.Height() - world.icon_size
 	holder.icon_state = "hudfan_no"
 	var/obj/item/clothing/under/U = get_item_by_slot(ITEM_SLOT_ICLOTHING)
-	if(U)
-		if(istype(U.attached_accessory, /obj/item/clothing/accessory/mime_fan_pin))
-			holder.icon_state = "mime_fan_pin"
-		else if(istype(U.attached_accessory, /obj/item/clothing/accessory/clown_enjoyer_pin))
-			holder.icon_state = "clown_enjoyer_pin"
+	if(!U)
+		set_hud_image_inactive(FAN_HUD)
+		return
+
+	if(istype(U.attached_accessory, /obj/item/clothing/accessory/mime_fan_pin))
+		holder.icon_state = "mime_fan_pin"
+
+	else if(istype(U.attached_accessory, /obj/item/clothing/accessory/clown_enjoyer_pin))
+		holder.icon_state = "clown_enjoyer_pin"
+	set_hud_image_active(FAN_HUD)
+	return
+
+
 
 /***********************************************
 Security HUDs! Basic mode shows only the job.
@@ -256,22 +266,29 @@ Security HUDs! Basic mode shows only the job.
 	for(var/i in list(IMPTRACK_HUD, IMPLOYAL_HUD, IMPCHEM_HUD))
 		holder = hud_list[i]
 		holder.icon_state = null
+		set_hud_image_inactive(i)
+
 	for(var/obj/item/implant/I in implants)
 		if(istype(I, /obj/item/implant/tracking))
 			holder = hud_list[IMPTRACK_HUD]
 			var/icon/IC = icon(icon, icon_state, dir)
 			holder.pixel_y = IC.Height() - world.icon_size
 			holder.icon_state = "hud_imp_tracking"
+			set_hud_image_active(IMPTRACK_HUD)
+
 		else if(istype(I, /obj/item/implant/chem))
 			holder = hud_list[IMPCHEM_HUD]
 			var/icon/IC = icon(icon, icon_state, dir)
 			holder.pixel_y = IC.Height() - world.icon_size
 			holder.icon_state = "hud_imp_chem"
+			set_hud_image_active(IMPCHEM_HUD)
+
 	if(HAS_TRAIT(src, TRAIT_MINDSHIELD))
 		holder = hud_list[IMPLOYAL_HUD]
 		var/icon/IC = icon(icon, icon_state, dir)
 		holder.pixel_y = IC.Height() - world.icon_size
 		holder.icon_state = "hud_imp_loyal"
+		set_hud_image_active(IMPLOYAL_HUD)
 
 /mob/living/carbon/human/proc/sec_hud_set_security_status()
 	var/image/holder = hud_list[WANTED_HUD]
@@ -281,23 +298,26 @@ Security HUDs! Basic mode shows only the job.
 	if(perpname && GLOB.data_core)
 		var/datum/data/record/R = find_record("name", perpname, GLOB.data_core.security)
 		if(R)
+			var/has_criminal_entry = TRUE
 			switch(R.fields["criminal"])
 				if("*Arrest*")
 					holder.icon_state = "hudwanted"
-					return
 				if("Incarcerated")
 					holder.icon_state = "hudincarcerated"
-					return
 				if("Suspected")
 					holder.icon_state = "hudsuspected"
-					return
 				if("Paroled")
 					holder.icon_state = "hudparolled"
-					return
 				if("Discharged")
 					holder.icon_state = "huddischarged"
-					return
+				else
+					has_criminal_entry = FALSE
+			if(has_criminal_entry)
+				set_hud_image_active(WANTED_HUD)
+				return
+
 	holder.icon_state = null
+	set_hud_image_inactive(WANTED_HUD)
 
 /***********************************************
 Diagnostic HUDs!
@@ -361,10 +381,13 @@ Diagnostic HUDs!
 	holder.pixel_y = I.Height() - world.icon_size
 	if(!shell) //Not an AI shell
 		holder.icon_state = null
+		set_hud_image_inactive(DIAG_TRACK_HUD)
+		return
 	else if(deployed) //AI shell in use by an AI
 		holder.icon_state = "hudtrackingai"
 	else //Empty AI shell
 		holder.icon_state = "hudtracking"
+	set_hud_image_active(DIAG_TRACK_HUD)
 
 //AI side tracking of AI shell control
 /mob/living/silicon/ai/proc/diag_hud_set_deployed() //Shows tracking beacons on the mech
@@ -373,8 +396,10 @@ Diagnostic HUDs!
 	holder.pixel_y = I.Height() - world.icon_size
 	if(!deployed_shell)
 		holder.icon_state = null
+		set_hud_image_inactive(DIAG_TRACK_HUD)
 	else //AI is currently controlling a shell
 		holder.icon_state = "hudtrackingai"
+		set_hud_image_active(DIAG_TRACK_HUD)
 
 /*~~~~~~~~~~~~~~~~~~~~
 	BIG STOMPY MECHS
@@ -401,11 +426,14 @@ Diagnostic HUDs!
 	var/image/holder = hud_list[DIAG_STAT_HUD]
 	var/icon/I = icon(icon, icon_state, dir)
 	holder.pixel_y = I.Height() - world.icon_size
-	holder.icon_state = null
 	if(internal_damage)
 		holder.icon_state = "hudwarn"
+		set_hud_image_active(DIAG_STAT_HUD)
+	holder.icon_state = null
+	set_hud_image_inactive(DIAG_STAT_HUD)
 
-/obj/vehicle/sealed/mecha/proc/diag_hud_set_mechtracking() //Shows tracking beacons on the mech
+///Shows tracking beacons on the mech
+/obj/vehicle/sealed/mecha/proc/diag_hud_set_mechtracking()
 	var/image/holder = hud_list[DIAG_TRACK_HUD]
 	var/icon/I = icon(icon, icon_state, dir)
 	holder.pixel_y = I.Height() - world.icon_size
@@ -474,8 +502,10 @@ Diagnostic HUDs!
 	Airlocks!
 ~~~~~~~~~~~~~*/
 /obj/machinery/door/airlock/proc/diag_hud_set_electrified()
+	if(secondsElectrified == MACHINE_NOT_ELECTRIFIED)
+		set_hud_image_inactive(DIAG_AIRLOCK_HUD)
+		return
+
 	var/image/holder = hud_list[DIAG_AIRLOCK_HUD]
-	if(secondsElectrified != MACHINE_NOT_ELECTRIFIED)
-		holder.icon_state = "electrified"
-	else
-		holder.icon_state = ""
+	holder.icon_state = "electrified"
+	set_hud_image_active(DIAG_AIRLOCK_HUD)

code/game/machinery/doors/airlock.dm

@@ -161,9 +161,11 @@
 		max_integrity = normal_integrity
 	if(damage_deflection == AIRLOCK_DAMAGE_DEFLECTION_N && security_level > AIRLOCK_SECURITY_IRON)
 		damage_deflection = AIRLOCK_DAMAGE_DEFLECTION_R
+
 	prepare_huds()
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
+
 	diag_hud_set_electrified()
 
 	RegisterSignal(src, COMSIG_MACHINERY_BROKEN, .proc/on_break)
@@ -333,7 +335,7 @@
 	QDEL_NULL(note)
 	QDEL_NULL(seal)
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.remove_from_hud(src)
+		diag_hud.remove_atom_from_hud(src)
 	return ..()
 
 /obj/machinery/door/airlock/handle_atom_del(atom/A)

code/game/machinery/launch_pad.dm

@@ -35,7 +35,7 @@
 	. = ..()
 	prepare_huds()
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 
 	var/image/holder = hud_list[DIAG_LAUNCHPAD_HUD]
 	var/mutable_appearance/MA = new /mutable_appearance()
@@ -49,7 +49,7 @@
 
 /obj/machinery/launchpad/Destroy()
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.remove_from_hud(src)
+		diag_hud.remove_atom_from_hud(src)
 	return ..()
 
 /obj/machinery/launchpad/examine(mob/user)

code/game/objects/items/devices/multitool.dm

@@ -106,8 +106,8 @@
 		var/atom/movable/screen/plane_master/camera_static/ai_detect_plane = user.hud_used.plane_masters["[CAMERA_STATIC_PLANE]"]
 		ai_detect_plane.alpha = 64
 		var/datum/atom_hud/hud = GLOB.huds[hud_type]
-		if(!hud.hudusers[user])
-			hud.add_hud_to(user)
+		if(!hud.hud_users[user])
+			hud.show_to(user)
 		eye.eye_user = user
 		eye.setLoc(get_turf(src))
 
@@ -116,7 +116,7 @@
 		var/atom/movable/screen/plane_master/camera_static/ai_detect_plane = user.hud_used.plane_masters["[CAMERA_STATIC_PLANE]"]
 		ai_detect_plane.alpha = 255
 		var/datum/atom_hud/hud = GLOB.huds[hud_type]
-		hud.remove_hud_from(user)
+		hud.hide_from(user)
 		if(eye)
 			eye.setLoc(null)
 			eye.eye_user = null

code/modules/admin/verbs/admingame.dm

@@ -385,10 +385,10 @@ Traitors and the like can also be revived with the previous role mostly intact.
 
 	for (var/hudtype in list(DATA_HUD_SECURITY_ADVANCED, DATA_HUD_MEDICAL_ADVANCED, DATA_HUD_DIAGNOSTIC_ADVANCED))
 		var/datum/atom_hud/atom_hud = GLOB.huds[hudtype]
-		atom_hud.add_hud_to(mob)
+		atom_hud.show_to(mob)
 
 	for (var/datum/atom_hud/alternate_appearance/basic/antagonist_hud/antag_hud in GLOB.active_alternate_appearances)
-		antag_hud.add_hud_to(mob)
+		antag_hud.show_to(mob)
 
 	mob.lighting_alpha = mob.default_lighting_alpha()
 	mob.update_sight()
@@ -401,10 +401,10 @@ Traitors and the like can also be revived with the previous role mostly intact.
 
 	for (var/hudtype in list(DATA_HUD_SECURITY_ADVANCED, DATA_HUD_MEDICAL_ADVANCED, DATA_HUD_DIAGNOSTIC_ADVANCED))
 		var/datum/atom_hud/atom_hud = GLOB.huds[hudtype]
-		atom_hud.remove_hud_from(mob)
+		atom_hud.hide_from(mob)
 
 	for (var/datum/atom_hud/alternate_appearance/basic/antagonist_hud/antag_hud in GLOB.active_alternate_appearances)
-		antag_hud.remove_hud_from(mob)
+		antag_hud.hide_from(mob)
 
 	mob.lighting_alpha = mob.default_lighting_alpha()
 	mob.update_sight()

code/modules/antagonists/_common/antag_datum.dm

@@ -220,7 +220,7 @@ GLOBAL_LIST_EMPTY(antagonists)
 	var/mob/living/current = owner.current
 	for (var/datum/atom_hud/alternate_appearance/basic/has_antagonist/antag_hud as anything in GLOB.has_antagonist_huds)
 		if (!antag_hud.mobShouldSee(current))
-			antag_hud.remove_hud_from(current)
+			antag_hud.hide_from(current)
 
 	qdel(src)
 
@@ -424,7 +424,7 @@ GLOBAL_LIST_EMPTY(antagonists)
 	// Add HUDs that they couldn't see before
 	for (var/datum/atom_hud/alternate_appearance/basic/has_antagonist/antag_hud as anything in GLOB.has_antagonist_huds)
 		if (antag_hud.mobShouldSee(owner.current))
-			antag_hud.add_hud_to(owner.current)
+			antag_hud.show_to(owner.current)
 
 //This one is created by admin tools for custom objectives
 /datum/antagonist/custom

code/modules/antagonists/abductor/equipment/gland.dm

@@ -85,7 +85,7 @@
 	if(initial(uses) == 1)
 		uses = initial(uses)
 	var/datum/atom_hud/abductor/hud = GLOB.huds[DATA_HUD_ABDUCTOR]
-	hud.remove_from_hud(owner)
+	hud.remove_atom_from_hud(owner)
 	clear_mind_control()
 	..()
 
@@ -94,7 +94,7 @@
 	if(special != 2 && uses) // Special 2 means abductor surgery
 		Start()
 	var/datum/atom_hud/abductor/hud = GLOB.huds[DATA_HUD_ABDUCTOR]
-	hud.add_to_hud(owner)
+	hud.add_atom_to_hud(owner)
 	update_gland_hud()
 
 /obj/item/organ/heart/gland/on_life(delta_time, times_fired)

code/modules/antagonists/blob/structures/_blob.dm

@@ -317,7 +317,7 @@
 /obj/structure/blob/examine(mob/user)
 	. = ..()
 	var/datum/atom_hud/hud_to_check = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	if(HAS_TRAIT(user, TRAIT_RESEARCH_SCANNER) || hud_to_check.hudusers[user])
+	if(HAS_TRAIT(user, TRAIT_RESEARCH_SCANNER) || hud_to_check.hud_users[user])
 		. += "<b>Your HUD displays an extensive report...</b><br>"
 		if(overmind)
 			. += overmind.blobstrain.examine(user)

code/modules/antagonists/cult/runes.dm

@@ -925,6 +925,7 @@ structure_check() searches for nearby cultist structures required for the invoca
 	if(rune_in_use)
 		return
 	. = ..()
+
 	var/area/place = get_area(src)
 	var/mob/living/user = invokers[1]
 	var/datum/antagonist/cult/user_antag = user.mind.has_antag_datum(/datum/antagonist/cult,TRUE)
@@ -935,8 +936,10 @@ structure_check() searches for nearby cultist structures required for the invoca
 	if(!(place in summon_objective.summon_spots))
 		to_chat(user, span_cultlarge("The Apocalypse rune will remove a ritual site, where Nar'Sie can be summoned, it can only be scribed in [english_list(summon_objective.summon_spots)]!"))
 		return
+
 	summon_objective.summon_spots -= place
 	rune_in_use = TRUE
+
 	var/turf/T = get_turf(src)
 	new /obj/effect/temp_visual/dir_setting/curse/grasp_portal/fading(T)
 	var/intensity = 0
@@ -945,20 +948,23 @@ structure_check() searches for nearby cultist structures required for the invoca
 			intensity++
 	intensity = max(60, 360 - (360*(intensity/length(GLOB.player_list) + 0.3)**2)) //significantly lower intensity for "winning" cults
 	var/duration = intensity*10
+
 	playsound(T, 'sound/magic/enter_blood.ogg', 100, TRUE)
 	visible_message(span_warning("A colossal shockwave of energy bursts from the rune, disintegrating it in the process!"))
+
 	for(var/mob/living/target in range(src, 3))
 		target.Paralyze(30)
 	empulse(T, 0.42*(intensity), 1)
+
 	var/list/images = list()
 	var/zmatch = T.z
-	var/datum/atom_hud/AH = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
+	var/datum/atom_hud/sec_hud = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
 	for(var/mob/living/M in GLOB.alive_mob_list)
 		if(M.z != zmatch)
 			continue
 		if(ishuman(M))
 			if(!IS_CULTIST(M))
-				AH.remove_hud_from(M)
+				sec_hud.hide_from(M)
 				addtimer(CALLBACK(GLOBAL_PROC, .proc/hudFix, M), duration)
 			var/image/A = image('icons/mob/cult.dmi',M,"cultist", ABOVE_MOB_LAYER)
 			A.override = 1
@@ -1050,5 +1056,5 @@ structure_check() searches for nearby cultist structures required for the invoca
 		return
 	var/obj/O = target.get_item_by_slot(ITEM_SLOT_EYES)
 	if(istype(O, /obj/item/clothing/glasses/hud/security))
-		var/datum/atom_hud/AH = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
-		AH.add_hud_to(target)
+		var/datum/atom_hud/sec_hud = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
+		sec_hud.show_to(target)

code/modules/antagonists/disease/disease_mob.dm

@@ -66,7 +66,7 @@ the new instance inside the host to be updated to the template's stats.
 	SSdisease.archive_diseases[disease_template.GetDiseaseID()] = disease_template //important for stuff that uses disease IDs
 
 	var/datum/atom_hud/my_hud = GLOB.huds[DATA_HUD_SENTIENT_DISEASE]
-	my_hud.add_hud_to(src)
+	my_hud.show_to(src)
 
 	browser = new /datum/browser(src, "disease_menu", "Adaptation Menu", 1000, 770, src)
 
@@ -163,7 +163,7 @@ the new instance inside the host to be updated to the template's stats.
 	if(!mind.has_antag_datum(/datum/antagonist/disease))
 		mind.add_antag_datum(/datum/antagonist/disease)
 	var/datum/atom_hud/medsensor = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	medsensor.add_hud_to(src)
+	medsensor.show_to(src)
 
 /mob/camera/disease/proc/pick_name()
 	var/static/list/taken_names
@@ -255,7 +255,7 @@ the new instance inside the host to be updated to the template's stats.
 	MA.alpha = 200
 	holder.appearance = MA
 	var/datum/atom_hud/my_hud = GLOB.huds[DATA_HUD_SENTIENT_DISEASE]
-	my_hud.add_to_hud(V.affected_mob)
+	my_hud.add_atom_to_hud(V.affected_mob)
 
 	to_chat(src, span_notice("A new host, <b>[V.affected_mob.real_name]</b>, has been infected."))
 
@@ -271,7 +271,7 @@ the new instance inside the host to be updated to the template's stats.
 		to_chat(src, span_notice("One of your hosts, <b>[V.affected_mob.real_name]</b>, has been purged of your infection."))
 
 		var/datum/atom_hud/my_hud = GLOB.huds[DATA_HUD_SENTIENT_DISEASE]
-		my_hud.remove_from_hud(V.affected_mob)
+		my_hud.remove_atom_from_hud(V.affected_mob)
 
 		if(following_host == V.affected_mob)
 			follow_next()

code/modules/atmospherics/machinery/atmosmachinery.dm

@@ -57,8 +57,8 @@
 
 	///The bitflag that's being checked on ventcrawling. Default is to allow ventcrawling and seeing pipes.
 	var/vent_movement = VENTCRAWL_ALLOWED | VENTCRAWL_CAN_SEE
-	
-	///keeps the name of the object from being overridden if it's vareditted. 
+
+	///keeps the name of the object from being overridden if it's vareditted.
 	var/override_naming
 
 /obj/machinery/atmospherics/LateInitialize()
@@ -89,7 +89,7 @@
 /obj/machinery/atmospherics/Initialize(mapload)
 	if(mapload && name != initial(name))
 		override_naming = TRUE
-	return ..()	
+	return ..()
 
 /obj/machinery/atmospherics/Destroy()
 	for(var/i in 1 to device_type)

code/modules/client/client_procs.dm

@@ -1125,7 +1125,6 @@ GLOBAL_LIST_INIT(blacklisted_builds, list(
 		holder.filteriffic = new /datum/filter_editor(in_atom)
 		holder.filteriffic.ui_interact(mob)
 
-
 /client/proc/set_right_click_menu_mode(shift_only)
 	if(shift_only)
 		winset(src, "mapwindow.map", "right-click=true")

code/modules/clothing/glasses/_glasses.dm

@@ -557,8 +557,8 @@
 		return
 	if(ishuman(user))
 		for(var/hud in hudlist)
-			var/datum/atom_hud/H = GLOB.huds[hud]
-			H.add_hud_to(user)
+			var/datum/atom_hud/our_hud = GLOB.huds[hud]
+			our_hud.show_to(user)
 		ADD_TRAIT(user, TRAIT_MEDICAL_HUD, GLASSES_TRAIT)
 		ADD_TRAIT(user, TRAIT_SECURITY_HUD, GLASSES_TRAIT)
 		if(xray)
@@ -571,8 +571,8 @@
 	REMOVE_TRAIT(user, TRAIT_XRAY_VISION, GLASSES_TRAIT)
 	if(ishuman(user))
 		for(var/hud in hudlist)
-			var/datum/atom_hud/H = GLOB.huds[hud]
-			H.remove_hud_from(user)
+			var/datum/atom_hud/our_hud = GLOB.huds[hud]
+			our_hud.hide_from(user)
 
 /obj/item/clothing/glasses/debug/AltClick(mob/user)
 	. = ..()

code/modules/clothing/glasses/hud.dm

@@ -12,8 +12,8 @@
 	if(slot != ITEM_SLOT_EYES)
 		return
 	if(hud_type)
-		var/datum/atom_hud/H = GLOB.huds[hud_type]
-		H.add_hud_to(user)
+		var/datum/atom_hud/our_hud = GLOB.huds[hud_type]
+		our_hud.show_to(user)
 	if(hud_trait)
 		ADD_TRAIT(user, hud_trait, GLASSES_TRAIT)
 
@@ -22,8 +22,8 @@
 	if(!istype(user) || user.glasses != src)
 		return
 	if(hud_type)
-		var/datum/atom_hud/H = GLOB.huds[hud_type]
-		H.remove_hud_from(user)
+		var/datum/atom_hud/our_hud = GLOB.huds[hud_type]
+		our_hud.hide_from(user)
 	if(hud_trait)
 		REMOVE_TRAIT(user, hud_trait, GLASSES_TRAIT)
 
@@ -197,8 +197,8 @@
 		return
 
 	if (hud_type)
-		var/datum/atom_hud/H = GLOB.huds[hud_type]
-		H.remove_hud_from(user)
+		var/datum/atom_hud/our_hud = GLOB.huds[hud_type]
+		our_hud.hide_from(user)
 
 	if (hud_type == DATA_HUD_MEDICAL_ADVANCED)
 		hud_type = null
@@ -208,8 +208,8 @@
 		hud_type = DATA_HUD_SECURITY_ADVANCED
 
 	if (hud_type)
-		var/datum/atom_hud/H = GLOB.huds[hud_type]
-		H.add_hud_to(user)
+		var/datum/atom_hud/our_hud = GLOB.huds[hud_type]
+		our_hud.show_to(user)
 
 /obj/item/clothing/glasses/hud/toggle/thermal
 	name = "thermal HUD scanner"

code/modules/clothing/masks/boxing.dm

@@ -31,15 +31,15 @@
 		return
 	to_chat(user, "You roll the balaclava over your face, and a data display appears before your eyes.")
 	ADD_TRAIT(user, TRAIT_DIAGNOSTIC_HUD, MASK_TRAIT)
-	var/datum/atom_hud/H = GLOB.huds[DATA_HUD_DIAGNOSTIC_BASIC]
-	H.add_hud_to(user)
+	var/datum/atom_hud/diag_hud = GLOB.huds[DATA_HUD_DIAGNOSTIC_BASIC]
+	diag_hud.show_to(user)
 	voice_unknown = TRUE
 
 /obj/item/clothing/mask/infiltrator/dropped(mob/living/carbon/human/user)
 	to_chat(user, "You pull off the balaclava, and the mask's internal hud system switches off quietly.")
 	REMOVE_TRAIT(user, TRAIT_DIAGNOSTIC_HUD, MASK_TRAIT)
-	var/datum/atom_hud/H = GLOB.huds[DATA_HUD_DIAGNOSTIC_BASIC]
-	H.remove_hud_from(user)
+	var/datum/atom_hud/diag_hud = GLOB.huds[DATA_HUD_DIAGNOSTIC_BASIC]
+	diag_hud.hide_from(user)
 	voice_unknown = FALSE
 	return ..()
 

code/modules/clothing/suits/ablativecoat.dm

@@ -40,7 +40,7 @@
 	var/mob/living/carbon/user = loc
 	var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
 	ADD_TRAIT(user, TRAIT_SECURITY_HUD, HELMET_TRAIT)
-	hud.add_hud_to(user)
+	hud.show_to(user)
 	balloon_alert(user, "you put on the hood, and enable the hud")
 	return ..()
 
@@ -48,8 +48,8 @@
 	if (!hood_up)
 		return ..()
 	var/mob/living/carbon/user = loc
-	var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
+	var/datum/atom_hud/sec_hud = GLOB.huds[DATA_HUD_SECURITY_ADVANCED]
 	REMOVE_TRAIT(user, TRAIT_SECURITY_HUD, HELMET_TRAIT)
-	hud.remove_hud_from(user)
+	sec_hud.hide_from(user)
 	balloon_alert(user, "you take off the hood, and disable the hud")
 	return ..()

code/modules/jobs/job_types/clown.dm

@@ -96,4 +96,4 @@
 	for(var/datum/mutation/human/clumsy/M in H.dna.mutations)
 		M.mutadone_proof = TRUE
 	var/datum/atom_hud/fan = GLOB.huds[DATA_HUD_FAN]
-	fan.add_hud_to(H)
+	fan.show_to(H)

code/modules/jobs/job_types/mime.dm

@@ -77,7 +77,7 @@
 		H.mind.miming = TRUE
 
 	var/datum/atom_hud/fan = GLOB.huds[DATA_HUD_FAN]
-	fan.add_hud_to(H)
+	fan.show_to(H)
 
 /obj/item/book/mimery
 	name = "Guide to Dank Mimery"

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

@@ -734,13 +734,13 @@ This is the proc mobs get to turn into a ghost. Forked from ghostize due to comp
 
 /mob/dead/observer/proc/show_data_huds()
 	for(var/hudtype in datahuds)
-		var/datum/atom_hud/H = GLOB.huds[hudtype]
-		H.add_hud_to(src)
+		var/datum/atom_hud/data_hud = GLOB.huds[hudtype]
+		data_hud.show_to(src)
 
 /mob/dead/observer/proc/remove_data_huds()
 	for(var/hudtype in datahuds)
-		var/datum/atom_hud/H = GLOB.huds[hudtype]
-		H.remove_hud_from(src)
+		var/datum/atom_hud/data_hud = GLOB.huds[hudtype]
+		data_hud.hide_from(src)
 
 /mob/dead/observer/verb/toggle_data_huds()
 	set name = "Toggle Sec/Med/Diag HUD"

code/modules/mob/living/carbon/human/species_types/abductors.dm

@@ -28,11 +28,11 @@
 /datum/species/abductor/on_species_gain(mob/living/carbon/C, datum/species/old_species)
 	. = ..()
 	var/datum/atom_hud/abductor_hud = GLOB.huds[DATA_HUD_ABDUCTOR]
-	abductor_hud.add_hud_to(C)
+	abductor_hud.show_to(C)
 
 	C.set_safe_hunger_level()
 
 /datum/species/abductor/on_species_loss(mob/living/carbon/C)
 	. = ..()
 	var/datum/atom_hud/abductor_hud = GLOB.huds[DATA_HUD_ABDUCTOR]
-	abductor_hud.remove_hud_from(C)
+	abductor_hud.hide_from(C)

code/modules/mob/living/living.dm

@@ -4,9 +4,9 @@
 	if(unique_name)
 		set_name()
 	var/datum/atom_hud/data/human/medical/advanced/medhud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	medhud.add_to_hud(src)
+	medhud.add_atom_to_hud(src)
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 	faction += "[REF(src)]"
 	GLOB.mob_living_list += src
 	SSpoints_of_interest.make_point_of_interest(src)

code/modules/mob/living/silicon/ai/freelook/eye.dm

@@ -35,14 +35,14 @@
 	var/datum/atom_hud/ai_detector/hud = GLOB.huds[DATA_HUD_AI_DETECT]
 	var/list/old_images = hud_list[AI_DETECT_HUD]
 	if(!ai_detector_visible)
-		hud.remove_from_hud(src)
+		hud.remove_atom_from_hud(src)
 		QDEL_LIST(old_images)
 		return
 
-	if(!length(hud.hudusers))
+	if(!length(hud.hud_users))
 		return //no one is watching, do not bother updating anything
 
-	hud.remove_from_hud(src)
+	hud.remove_atom_from_hud(src)
 
 	var/static/list/vis_contents_opaque = list()
 	var/obj/effect/overlay/ai_detect_hud/hud_obj = vis_contents_opaque[ai_detector_color]
@@ -61,7 +61,7 @@
 	for(var/i in (new_images.len + 1) to old_images.len)
 		qdel(old_images[i])
 	hud_list[AI_DETECT_HUD] = new_images
-	hud.add_to_hud(src)
+	hud.add_atom_to_hud(src)
 
 /mob/camera/ai_eye/proc/get_visible_turfs()
 	if(!isturf(loc))
@@ -124,7 +124,7 @@
 	GLOB.aiEyes -= src
 	if(ai_detector_visible)
 		var/datum/atom_hud/ai_detector/hud = GLOB.huds[DATA_HUD_AI_DETECT]
-		hud.remove_from_hud(src)
+		hud.remove_atom_from_hud(src)
 		var/list/L = hud_list[AI_DETECT_HUD]
 		QDEL_LIST(L)
 	return ..()

code/modules/mob/living/silicon/pai/software.dm

@@ -119,10 +119,10 @@
 			medHUD = !medHUD
 			if(medHUD)
 				var/datum/atom_hud/med = GLOB.huds[med_hud]
-				med.add_hud_to(src)
+				med.show_to(src)
 			else
 				var/datum/atom_hud/med = GLOB.huds[med_hud]
-				med.remove_hud_from(src)
+				med.hide_from(src)
 		if("newscaster")
 			newscaster.ui_interact(src)
 		if("photography_module")
@@ -147,10 +147,10 @@
 			secHUD = !secHUD
 			if(secHUD)
 				var/datum/atom_hud/sec = GLOB.huds[sec_hud]
-				sec.add_hud_to(src)
+				sec.show_to(src)
 			else
 				var/datum/atom_hud/sec = GLOB.huds[sec_hud]
-				sec.remove_hud_from(src)
+				sec.hide_from(src)
 		if("universal_translator")
 			if(!languages_granted)
 				grant_all_languages(TRUE, TRUE, TRUE, LANGUAGE_SOFTWARE)

code/modules/mob/living/silicon/silicon.dm

@@ -57,7 +57,7 @@
 	if(ispath(radio))
 		radio = new radio(src)
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 	diag_hud_set_status()
 	diag_hud_set_health()
 	add_sensors()
@@ -377,17 +377,17 @@
 	var/datum/atom_hud/secsensor = GLOB.huds[sec_hud]
 	var/datum/atom_hud/medsensor = GLOB.huds[med_hud]
 	var/datum/atom_hud/diagsensor = GLOB.huds[d_hud]
-	secsensor.remove_hud_from(src)
-	medsensor.remove_hud_from(src)
-	diagsensor.remove_hud_from(src)
+	secsensor.hide_from(src)
+	medsensor.hide_from(src)
+	diagsensor.hide_from(src)
 
 /mob/living/silicon/proc/add_sensors()
 	var/datum/atom_hud/secsensor = GLOB.huds[sec_hud]
 	var/datum/atom_hud/medsensor = GLOB.huds[med_hud]
 	var/datum/atom_hud/diagsensor = GLOB.huds[d_hud]
-	secsensor.add_hud_to(src)
-	medsensor.add_hud_to(src)
-	diagsensor.add_hud_to(src)
+	secsensor.show_to(src)
+	medsensor.show_to(src)
+	diagsensor.show_to(src)
 
 /mob/living/silicon/proc/toggle_sensors()
 	if(incapacitated())

code/modules/mob/living/simple_animal/bot/bot.dm

@@ -104,7 +104,7 @@
 	var/beacon_freq = FREQ_NAV_BEACON
 	///The type of data HUD the bot uses. Diagnostic by default.
 	var/data_hud_type = DATA_HUD_DIAGNOSTIC_BASIC
-	var/datum/atom_hud/data/bot_path/path_hud = new /datum/atom_hud/data/bot_path()
+	var/datum/atom_hud/data/bot_path/path_hud
 	var/path_image_icon = 'icons/mob/aibots.dmi'
 	var/path_image_icon_state = "path_indicator"
 	var/path_image_color = "#FFFFFF"
@@ -164,6 +164,11 @@
 /mob/living/simple_animal/bot/Initialize(mapload)
 	. = ..()
 	GLOB.bots_list += src
+
+	path_hud = new /datum/atom_hud/data/bot_path()
+	for(var/hud in path_hud.hud_icons) // You get to see your own path
+		set_hud_image_active(hud, exclusive_hud = path_hud)
+
 	// Give bots a fancy new ID card that can hold any access.
 	access_card = new /obj/item/card/id/advanced/simple_bot(src)
 	// This access is so bots can be immediately set to patrol and leave Robotics, instead of having to be let out first.
@@ -178,7 +183,7 @@
 	//Adds bot to the diagnostic HUD system
 	prepare_huds()
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 	diag_hud_set_bothealth()
 	diag_hud_set_botstat()
 	diag_hud_set_botmode()
@@ -186,10 +191,10 @@
 	//If a bot has its own HUD (for player bots), provide it.
 	if(!isnull(data_hud_type))
 		var/datum/atom_hud/datahud = GLOB.huds[data_hud_type]
-		datahud.add_hud_to(src)
+		datahud.show_to(src)
 	if(path_hud)
-		path_hud.add_to_hud(src)
-		path_hud.add_hud_to(src)
+		path_hud.add_atom_to_hud(src)
+		path_hud.show_to(src)
 
 
 /mob/living/simple_animal/bot/Destroy()
@@ -1022,11 +1027,10 @@ Pass a positive integer as an argument to override a bot's default speed.
 	var/list/path_huds_watching_me = list(GLOB.huds[DATA_HUD_DIAGNOSTIC_ADVANCED])
 	if(path_hud)
 		path_huds_watching_me += path_hud
-	for(var/V in path_huds_watching_me)
-		var/datum/atom_hud/H = V
-		H.remove_from_hud(src)
+	for(var/datum/atom_hud/hud as anything in path_huds_watching_me)
+		hud.remove_atom_from_hud(src)
 
-	var/list/path_images = hud_list[DIAG_PATH_HUD]
+	var/list/path_images = active_hud_list[DIAG_PATH_HUD]
 	QDEL_LIST(path_images)
 	if(newpath)
 		for(var/i in 1 to newpath.len)
@@ -1065,9 +1069,8 @@ Pass a positive integer as an argument to override a bot's default speed.
 			path[T] = I
 			path_images += I
 
-	for(var/V in path_huds_watching_me)
-		var/datum/atom_hud/H = V
-		H.add_to_hud(src)
+	for(var/datum/atom_hud/hud as anything in path_huds_watching_me)
+		hud.add_atom_to_hud(src)
 
 /mob/living/simple_animal/bot/proc/increment_path()
 	if(!length(path))

code/modules/mob/living/simple_animal/constructs.dm

@@ -306,7 +306,7 @@
 /mob/living/simple_animal/hostile/construct/artificer/Initialize(mapload)
 	. = ..()
 	var/datum/atom_hud/datahud = GLOB.huds[health_hud]
-	datahud.add_hud_to(src)
+	datahud.show_to(src)
 
 /mob/living/simple_animal/hostile/construct/artificer/Found(atom/A) //what have we found here?
 	if(isconstruct(A)) //is it a construct?

code/modules/mob/living/simple_animal/friendly/drone/_drone.dm

@@ -182,7 +182,7 @@
 	alert_drones(DRONE_NET_CONNECT)
 
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 
 	ADD_TRAIT(src, TRAIT_VENTCRAWLER_ALWAYS, INNATE_TRAIT)
 	ADD_TRAIT(src, TRAIT_NEGATES_GRAVITY, INNATE_TRAIT)

code/modules/mob/living/simple_animal/friendly/robot_customer.dm

@@ -57,11 +57,11 @@
 
 /mob/living/simple_animal/robot_customer/MouseEntered(location, control, params)
 	. = ..()
-	hud_to_show_on_hover?.add_hud_to(usr)
+	hud_to_show_on_hover?.show_to(usr)
 
 /mob/living/simple_animal/robot_customer/MouseExited(location, control, params)
 	. = ..()
-	hud_to_show_on_hover?.remove_hud_from(usr)
+	hud_to_show_on_hover?.hide_from(usr)
 
 /mob/living/simple_animal/robot_customer/update_overlays()
 	. = ..()

code/modules/mob/living/simple_animal/guardian/types/support.dm

@@ -20,7 +20,7 @@
 /mob/living/simple_animal/hostile/guardian/healer/Initialize(mapload)
 	. = ..()
 	var/datum/atom_hud/medsensor = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	medsensor.add_hud_to(src)
+	medsensor.show_to(src)
 
 /mob/living/simple_animal/hostile/guardian/healer/get_status_tab_items()
 	. = ..()

code/modules/mob/living/simple_animal/hostile/giant_spider.dm

@@ -142,7 +142,7 @@
 /mob/living/simple_animal/hostile/giant_spider/nurse/Initialize(mapload)
 	. = ..()
 	var/datum/atom_hud/datahud = GLOB.huds[health_hud]
-	datahud.add_hud_to(src)
+	datahud.show_to(src)
 
 /mob/living/simple_animal/hostile/giant_spider/nurse/AttackingTarget()
 	if(is_busy)

code/modules/mob/living/simple_animal/hostile/megafauna/colossus.dm

@@ -506,7 +506,7 @@
 	remove_verb(src, /mob/living/verb/pulled)
 	remove_verb(src, /mob/verb/me_verb)
 	var/datum/atom_hud/medsensor = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-	medsensor.add_hud_to(src)
+	medsensor.show_to(src)
 
 	ADD_TRAIT(src, TRAIT_VENTCRAWLER_ALWAYS, INNATE_TRAIT)
 

code/modules/mob/mob.dm

@@ -94,23 +94,69 @@
 /mob/GenerateTag()
 	tag = "mob_[next_mob_id++]"
 
+/**
+ * set every hud image in the given category active so other people with the given hud can see it.
+ * Arguments:
+ * * hud_category - the index in our active_hud_list corresponding to an image now being shown.
+ * * update_huds - if FALSE we will just put the hud_category into active_hud_list without actually updating the atom_hud datums subscribed to it
+ * * exclusive_hud - if given a reference to an atom_hud, will just update that hud instead of all global ones attached to that category.
+ * This is because some atom_hud subtypes arent supposed to work via global categories, updating normally would affect all of these which we dont want.
+ */
+/atom/proc/set_hud_image_active(hud_category, update_huds = TRUE, datum/atom_hud/exclusive_hud)
+	if(!istext(hud_category) || !hud_list?[hud_category] || active_hud_list?[hud_category])
+		return FALSE
+
+	LAZYSET(active_hud_list, hud_category, hud_list[hud_category])
+
+	if(!update_huds)
+		return TRUE
+
+	if(exclusive_hud)
+		exclusive_hud.add_single_hud_category_on_atom(src, hud_category)
+	else
+		for(var/datum/atom_hud/hud_to_update as anything in GLOB.huds_by_category[hud_category])
+			hud_to_update.add_single_hud_category_on_atom(src, hud_category)
+
+	return TRUE
+
+///sets every hud image in the given category inactive so no one can see it
+/atom/proc/set_hud_image_inactive(hud_category, update_huds = TRUE, datum/atom_hud/exclusive_hud)
+	if(!istext(hud_category))
+		return FALSE
+
+	LAZYREMOVE(active_hud_list, hud_category)
+
+	if(!update_huds)
+		return TRUE
+
+	if(exclusive_hud)
+		exclusive_hud.remove_single_hud_category_on_atom(src, hud_category)
+	else
+		for(var/datum/atom_hud/hud_to_update as anything in GLOB.huds_by_category[hud_category])
+			hud_to_update.remove_single_hud_category_on_atom(src, hud_category)
+
+	return TRUE
+
 /**
  * Prepare the huds for this atom
  *
- * Goes through hud_possible list and adds the images to the hud_list variable (if not already
- * cached)
+ * Goes through hud_possible list and adds the images to the hud_list variable (if not already cached)
  */
 /atom/proc/prepare_huds()
+	if(hud_list) // I choose to be lienient about people calling this proc more then once
+		return
 	hud_list = list()
 	for(var/hud in hud_possible)
 		var/hint = hud_possible[hud]
-		switch(hint)
-			if(HUD_LIST_LIST)
-				hud_list[hud] = list()
-			else
-				var/image/I = image('icons/mob/huds/hud.dmi', src, "")
-				I.appearance_flags = RESET_COLOR|RESET_TRANSFORM
-				hud_list[hud] = I
+
+		if(hint == HUD_LIST_LIST)
+			hud_list[hud] = list()
+
+		else
+			var/image/I = image('icons/mob/huds/hud.dmi', src, "")
+			I.appearance_flags = RESET_COLOR|RESET_TRANSFORM
+			hud_list[hud] = I
+		set_hud_image_active(hud, update_huds = FALSE) //by default everything is active. but dont add it to huds to keep control.
 
 /**
  * Some kind of debug verb that gives atmosphere environment details

code/modules/mod/modules/modules_visor.dm

@@ -20,7 +20,7 @@
 		return
 	if(hud_type)
 		var/datum/atom_hud/hud = GLOB.huds[hud_type]
-		hud.add_hud_to(mod.wearer)
+		hud.show_to(mod.wearer)
 	for(var/trait in visor_traits)
 		ADD_TRAIT(mod.wearer, trait, MOD_TRAIT)
 	mod.wearer.update_sight()
@@ -31,7 +31,7 @@
 		return
 	if(hud_type)
 		var/datum/atom_hud/hud = GLOB.huds[hud_type]
-		hud.remove_hud_from(mod.wearer)
+		hud.hide_from(mod.wearer)
 	for(var/trait in visor_traits)
 		REMOVE_TRAIT(mod.wearer, trait, MOD_TRAIT)
 	mod.wearer.update_sight()

code/modules/surgery/organs/augments_eyes.dm

@@ -19,14 +19,14 @@
 	..()
 	if(HUD_type)
 		var/datum/atom_hud/hud = GLOB.huds[HUD_type]
-		hud.add_hud_to(eye_owner)
+		hud.show_to(eye_owner)
 	if(HUD_trait)
 		ADD_TRAIT(eye_owner, HUD_trait, ORGAN_TRAIT)
 
 /obj/item/organ/cyberimp/eyes/hud/Remove(mob/living/carbon/eye_owner, special = 0)
 	if(HUD_type)
 		var/datum/atom_hud/hud = GLOB.huds[HUD_type]
-		hud.remove_hud_from(eye_owner)
+		hud.hide_from(eye_owner)
 	if(HUD_trait)
 		REMOVE_TRAIT(eye_owner, HUD_trait, ORGAN_TRAIT)
 	..()

code/modules/vehicles/mecha/_mecha.dm

@@ -231,7 +231,7 @@
 	GLOB.mechas_list += src //global mech list
 	prepare_huds()
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.add_to_hud(src)
+		diag_hud.add_atom_to_hud(src)
 	diag_hud_set_mechhealth()
 	diag_hud_set_mechcell()
 	diag_hud_set_mechstat()
@@ -277,7 +277,7 @@
 
 	GLOB.mechas_list -= src //global mech list
 	for(var/datum/atom_hud/data/diagnostic/diag_hud in GLOB.huds)
-		diag_hud.remove_from_hud(src) //YEET
+		diag_hud.remove_atom_from_hud(src) //YEET
 	return ..()
 
 /obj/vehicle/sealed/mecha/atom_destruction()

code/modules/vehicles/mecha/medical/odysseus.dm

@@ -15,13 +15,13 @@
 	. = ..()
 	if(. && !HAS_TRAIT(H, TRAIT_MEDICAL_HUD))
 		var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-		hud.add_hud_to(H)
+		hud.show_to(H)
 		ADD_TRAIT(H, TRAIT_MEDICAL_HUD, VEHICLE_TRAIT)
 
 /obj/vehicle/sealed/mecha/medical/odysseus/remove_occupant(mob/living/carbon/human/H)
 	if(isliving(H) && HAS_TRAIT_FROM(H, TRAIT_MEDICAL_HUD, VEHICLE_TRAIT))
-		var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-		hud.remove_hud_from(H)
+		var/datum/atom_hud/med_hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
+		med_hud.hide_from(H)
 		REMOVE_TRAIT(H, TRAIT_MEDICAL_HUD, VEHICLE_TRAIT)
 	return ..()
 
@@ -30,4 +30,4 @@
 	if(. && !HAS_TRAIT(M, TRAIT_MEDICAL_HUD))
 		var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
 		var/mob/living/brain/B = M.brainmob
-		hud.add_hud_to(B)
+		hud.show_to(B)

code/modules/wiremod/components/bci/hud/bar_overlay.dm

@@ -59,7 +59,7 @@
 		cool_overlay,
 		owner,
 	)
-	alt_appearance.add_hud_to(owner)
+	alt_appearance.show_to(owner)
 
 	active_overlays[target_atom] = WEAKREF(alt_appearance)
 

code/modules/wiremod/components/bci/hud/counter_overlay.dm

@@ -78,7 +78,7 @@
 		counter,
 		owner,
 	)
-	alt_appearance.add_hud_to(owner)
+	alt_appearance.show_to(owner)
 
 	counter_appearance = WEAKREF(alt_appearance)
 
@@ -103,7 +103,7 @@
 			number,
 			owner,
 		)
-		number_alt_appearance.add_hud_to(owner)
+		number_alt_appearance.show_to(owner)
 
 		numbers += WEAKREF(number_alt_appearance)
 
@@ -115,7 +115,7 @@
 	numbers = list()
 
 	var/datum/atom_hud/overlay = counter_appearance?.resolve()
-	overlay.remove_hud_from(owner)
+	overlay.hide_from(owner)
 	QDEL_NULL(overlay)
 
 /obj/item/circuit_component/counter_overlay/Destroy()

code/modules/wiremod/components/bci/hud/object_overlay.dm

@@ -119,7 +119,7 @@
 		cool_overlay,
 		owner,
 	)
-	alt_appearance.add_hud_to(owner)
+	alt_appearance.show_to(owner)
 
 	active_overlays[target_atom] = WEAKREF(alt_appearance)