Height and minor bodypart overlay refactor (#96570)

## About The Pull Request

### Main changes

Height is no longer applied in `apply_overlay`

There is now a proc titled `apply_height()` which is passed an
appearance and a body area, and handles either applying a filter or
adjusting the offset of the appearance up or down

`apply_height` is now called directly when applying item appearances
(ie, `update_worn_x`)
`apply_height` is also called directly in `get_limb_icon` (as height is
included in limb render keys).

### Other changes

Bodypart overlays were cleaned up a bit. You can now apply and remove
bodypart overlays directly with just the typepath, which is a bit more
convenient.

Bodypart textures were split into a separate type. Previously, textures
relied on insertion order to be "correctly" added (any bodypart overlays
added later would not be modified by the bodypart texture). Now

Fixed a bug with cybernetics while I was there. They reskin by changing
DMI so they needed to have their DMI included in their render keys.

## Why It's Good For The Game

This allows us to be more specific and less wasteful about applying
height filters and whatnot - We can now specify whether certain overlays
are offset or given a filter.

For example: In the past, horns and frills were filtered solely because
they were attached to the head and the head was filtered.
We couldn't independently say "Offsets the horns and frills, they don't
need filters".
But now, not only are we able to say "rather than filter the head, just
apply an offset", we can also say "horns and frills should be offset
rather than filtered".

TL;DR fixes the issue where horns or cat ears are cut off by height
filters, yippee.

## Changelog

🆑 Melbert
fix: Cybernetic reskinning should break less. 
fix: Horns and cat ears should be cut off less by height.
fix: Bodypart textures should apply more consistently. 
refactor: Mutant parts like moth wings, lizard tails, cat eats, etc.
have been refactored a tiny bit, report any oddities.
refactor: Bodypart textures were refactored a tiny bit, report any
oddities.
refactor: Refactored the way height works, report anything weird looking
things involving that.
/🆑

code/__DEFINES/bodyparts.dm

@@ -54,8 +54,6 @@
 #define LIMB_COLOR_FISH_INFUSION 15
 /// Carp infusion color priority
 #define LIMB_COLOR_CARP_INFUSION 20
-/// Untextured fish suicide color priority
-#define LIMB_COLOR_CS_SOURCE_SUICIDE 30
 /// Base priority for atom colors, gets atom priorities added to it
 #define LIMB_COLOR_ATOM_COLOR 40
 /// Voidwalker effect color priority

code/__DEFINES/mobs.dm

@@ -734,6 +734,16 @@
 #define GRADIENT_APPLIES_TO_HAIR (1<<0)
 #define GRADIENT_APPLIES_TO_FACIAL_HAIR (1<<1)
 
+// Used in applying height
+/// Used for overlays centered around the upper half of the human sprite
+#define UPPER_BODY "upper body"
+/// Used for overlays centered around the lower half of the human sprite
+#define LOWER_BODY "lower body"
+/// Used for overlays that should not offset at all
+#define NO_MODIFY "do not modify"
+/// Used for overlays that stretch the full body and thus need a filter
+#define ENTIRE_BODY "full body"
+
 // Height defines
 // - They are numbers so you can compare height values (x height < y height)
 // - They do not start at 0 for futureproofing
@@ -749,20 +759,19 @@
 #define HUMAN_HEIGHT_TALL 14
 #define HUMAN_HEIGHT_TALLER 16
 #define HUMAN_HEIGHT_TALLEST 18
+// If you add a height here update human_heights_to_offsets as well!
 
-/// Assoc list of all heights, cast to strings, to """"tuples"""""
-/// The first """tuple""" index is the upper body offset
-/// The second """tuple""" index is the lower body offset
-GLOBAL_LIST_INIT(human_heights_to_offsets, list(
-	"[MONKEY_HEIGHT_DWARF]" = list(-9, -3),
-	"[MONKEY_HEIGHT_MEDIUM]" = list(-7, -4),
-	"[HUMAN_HEIGHT_DWARF]" = list(-5, -4),
-	"[HUMAN_HEIGHT_SHORTEST]" = list(-2, -1),
-	"[HUMAN_HEIGHT_SHORT]" = list(-1, -1),
-	"[HUMAN_HEIGHT_MEDIUM]" = list(0, 0),
-	"[HUMAN_HEIGHT_TALL]" = list(1, 1),
-	"[HUMAN_HEIGHT_TALLER]" = list(2, 1),
-	"[HUMAN_HEIGHT_TALLEST]" = list(3, 2),
+/// Assoc list of all heights, to offset values
+GLOBAL_ALIST_INIT(human_heights_to_offsets, alist(
+	MONKEY_HEIGHT_DWARF   = list("[UPPER_BODY]" = -9, "[LOWER_BODY]" = -3),
+	MONKEY_HEIGHT_MEDIUM  = list("[UPPER_BODY]" = -7, "[LOWER_BODY]" = -4),
+	HUMAN_HEIGHT_DWARF    = list("[UPPER_BODY]" = -5, "[LOWER_BODY]" = -4),
+	HUMAN_HEIGHT_SHORTEST = list("[UPPER_BODY]" = -2, "[LOWER_BODY]" = -1),
+	HUMAN_HEIGHT_SHORT    = list("[UPPER_BODY]" = -1, "[LOWER_BODY]" = -1),
+	HUMAN_HEIGHT_MEDIUM   = list("[UPPER_BODY]" =  0, "[LOWER_BODY]" =  0),
+	HUMAN_HEIGHT_TALL     = list("[UPPER_BODY]" =  1, "[LOWER_BODY]" =  1),
+	HUMAN_HEIGHT_TALLER   = list("[UPPER_BODY]" =  2, "[LOWER_BODY]" =  1),
+	HUMAN_HEIGHT_TALLEST  = list("[UPPER_BODY]" =  3, "[LOWER_BODY]" =  2),
 ))
 
 /*
@@ -869,34 +878,6 @@ GLOBAL_LIST_INIT(human_heights_to_offsets, list(
 /// (You ONLY need to update this if you add a standing overlay, adding an integer.)
 #define TOTAL_LAYERS 23
 
-#define UPPER_BODY "upper body"
-#define LOWER_BODY "lower body"
-#define NO_MODIFY "do not modify"
-
-/// Used for human height overlay adjustments
-/// Certain standing overlay layers shouldn't have a filter applied and should instead just offset by a pixel y
-/// This list contains all the layers that must offset, with its value being whether it's a part of the upper half of the body (TRUE) or not (FALSE)
-GLOBAL_LIST_INIT(layers_to_offset, list(
-	// Weapons commonly cross the middle of the sprite so they get cut in half by the filter
-	"[HANDS_LAYER]" = LOWER_BODY,
-	// Very tall hats will get cut off by filter
-	"[HEAD_LAYER]" = UPPER_BODY,
-	// Hair will get cut off by filter
-	"[HAIR_LAYER]" = UPPER_BODY,
-	// Doesn't do much
-	"[EYES_LAYER]" = UPPER_BODY,
-	// Long belts (sabre sheathe) will get cut off by filter
-	"[BELT_LAYER]" = LOWER_BODY,
-	// Everything below looks fine with or without a filter, so we can skip it and just offset
-	// (In practice they'd be fine if they got a filter but we can optimize a bit by not.)
-	"[NECK_LAYER]" = UPPER_BODY,
-	"[GLASSES_LAYER]" = UPPER_BODY,
-	"[GLOVES_LAYER]" = LOWER_BODY,
-	"[HANDCUFF_LAYER]" = LOWER_BODY,
-	"[ID_LAYER]" = UPPER_BODY,
-	"[FACEMASK_LAYER]" = UPPER_BODY,
-))
-
 //Bitflags for the layers a bodypart overlay can draw on (can be drawn on multiple layers)
 /// Draws overlay on the BODY_FRONT_LAYER
 #define EXTERNAL_FRONT (1 << 0)
@@ -904,8 +885,6 @@ GLOBAL_LIST_INIT(layers_to_offset, list(
 #define EXTERNAL_ADJACENT (1 << 1)
 /// Draws overlay on the BODY_BEHIND_LAYER
 #define EXTERNAL_BEHIND (1 << 2)
-/// Draws organ on all EXTERNAL layers
-#define ALL_EXTERNAL_OVERLAYS EXTERNAL_FRONT | EXTERNAL_ADJACENT | EXTERNAL_BEHIND
 
 // Bitflags for external organs restylability
 #define EXTERNAL_RESTYLE_ALL ALL

code/datums/bodypart_overlays/bodypart_overlay.dm

@@ -3,34 +3,36 @@
 /datum/bodypart_overlay
 	/// Sometimes we need multiple layers, for like the back, middle and front of the person (EXTERNAL_FRONT, EXTERNAL_ADJACENT, EXTERNAL_BEHIND)
 	var/layers
-	/// List of all possible layers. Used for looping through in drawing
-	var/static/list/all_layers = list(EXTERNAL_FRONT, EXTERNAL_ADJACENT, EXTERNAL_BEHIND)
+	/// List of all possible layers to their real layer. Used for looping through in drawing
+	var/static/alist/all_layers = alist(
+		EXTERNAL_FRONT = -BODY_FRONT_LAYER,
+		EXTERNAL_ADJACENT = -BODY_ADJ_LAYER,
+		EXTERNAL_BEHIND = -BODY_BEHIND_LAYER,
+	)
 	/// Key of the icon states of all the sprite_datums for easy caching
 	var/cache_key = ""
 	/// Whether the overlay blocks emissive light
 	var/blocks_emissive = EMISSIVE_BLOCK_UNIQUE
 	/// Can this overlay be drawn on husked mobs?
 	var/draw_on_husks = HUSK_OVERLAY_NONE
+	/// Determines body area of the overlay for height offsets
+	var/offset_location = NO_MODIFY
 
 ///Wrapper for getting the proper image, colored and everything
-/datum/bodypart_overlay/proc/get_overlay(layer, obj/item/bodypart/limb, is_husked = FALSE)
-	layer = bitflag_to_layer(layer)
+/datum/bodypart_overlay/proc/get_overlay(layer, obj/item/bodypart/limb)
 	var/image/main_image = get_image(layer, limb)
 
-	if (is_husked && draw_on_husks != HUSK_OVERLAY_NORMAL)
+	if (limb?.is_husked && draw_on_husks != HUSK_OVERLAY_NORMAL)
 		main_image = huskify_image(main_image)
 		main_image.color = limb.husk_color
 	else
 		color_image(main_image, layer, limb)
 
-	if(blocks_emissive == EMISSIVE_BLOCK_NONE || !limb)
-		return main_image
+	var/list/created_overlays = list(main_image)
+	if(blocks_emissive != EMISSIVE_BLOCK_NONE && !isnull(limb))
+		created_overlays += emissive_blocker(main_image.icon, main_image.icon_state, limb, layer = main_image.layer, alpha = main_image.alpha)
 
-	var/list/all_images = list(
-		main_image,
-		emissive_blocker(main_image.icon, main_image.icon_state, limb, layer = main_image.layer, alpha = main_image.alpha)
-	)
-	return all_images
+	return created_overlays
 
 /datum/bodypart_overlay/proc/huskify_image(image/main_image)
 	var/icon/husk_icon = new(main_image.icon)
@@ -70,29 +72,15 @@
 		if(-BODY_FRONT_LAYER)
 			return "FRONT"
 
-///Converts a bitflag to the right layer. I'd love to make this a static index list, but byond made an attempt on my life when i did
-/datum/bodypart_overlay/proc/bitflag_to_layer(layer)
-	switch(layer)
-		if(EXTERNAL_BEHIND)
-			return -BODY_BEHIND_LAYER
-		if(EXTERNAL_ADJACENT)
-			return -BODY_ADJ_LAYER
-		if(EXTERNAL_FRONT)
-			return -BODY_FRONT_LAYER
-
 ///Check whether we can draw the overlays. You generally don't want lizard snouts to draw over an EVA suit
-/datum/bodypart_overlay/proc/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/proc/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	SHOULD_CALL_PARENT(TRUE)
-	return !is_husked || draw_on_husks
+	return !bodypart_owner.is_husked || draw_on_husks
 
 ///Colorizes the limb it's inserted to, if required.
 /datum/bodypart_overlay/proc/override_color(obj/item/bodypart/bodypart_owner)
 	CRASH("External organ color set to override with no override proc.")
 
 ///Generate a unique identifier to cache with. If you change something about the image, but the icon cache stays the same, it'll simply pull the unchanged image out of the cache
-/datum/bodypart_overlay/proc/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/proc/icon_render_key(obj/item/bodypart/limb)
 	return list()
-
-/// Additionally color or texture the limb
-/datum/bodypart_overlay/proc/modify_bodypart_appearance(datum/appearance)
-	return

code/datums/bodypart_overlays/emote_bodypart_overlay.dm

@@ -1,6 +1,7 @@
 ///Variant of bodypart_overlay for displaying emote overlays. See [/datum/emote/living/blush/run_emote] for an example on how to use one of these.
 /datum/bodypart_overlay/simple/emote
 	icon = 'icons/mob/human/emote_visuals.dmi'
+	offset_location = UPPER_BODY
 	///The body zone to attach the overlay to, overlay won't be added if no bodypart can be found with this
 	var/attached_body_zone = BODY_ZONE_CHEST
 	///The feature key used to figure out what specific bodily feature we offset this to follow
@@ -25,10 +26,8 @@
 
 ///Removes the overlay from the attached bodypart and updates the necessary sprites
 /datum/bodypart_overlay/simple/emote/Destroy()
-	var/obj/item/bodypart/referenced_bodypart = attached_bodypart.resolve()
-	if(!referenced_bodypart)
-		return ..()
-	referenced_bodypart.remove_bodypart_overlay(src)
+	var/obj/item/bodypart/referenced_bodypart = attached_bodypart?.resolve()
+	referenced_bodypart?.remove_bodypart_overlay(src)
 	return ..()
 
 /**
@@ -41,13 +40,7 @@
  */
 /mob/living/carbon/human/proc/give_emote_overlay(datum/bodypart_overlay/simple/emote/overlay_typepath)
 	var/obj/item/bodypart/bodypart = get_bodypart(overlay_typepath::attached_body_zone)
-	if(!bodypart)
-		return null
-	if(locate(overlay_typepath) in bodypart.bodypart_overlays)
-		return null
-	var/datum/bodypart_overlay/simple/emote/overlay = new overlay_typepath()
-	bodypart.add_bodypart_overlay(overlay)
-	return overlay
+	return bodypart?.add_bodypart_overlay(overlay_typepath)
 
 /datum/bodypart_overlay/simple/emote/tongue
 	icon_state = "tongue"

code/datums/bodypart_overlays/markings_bodypart_overlay.dm

@@ -1,6 +1,7 @@
 /// For body markings applied on the species, which need some extra code
 /datum/bodypart_overlay/simple/body_marking
 	layers = EXTERNAL_ADJACENT
+	offset_location = ENTIRE_BODY
 	/// Listen to the gendercode, if the limb is bimorphic
 	var/use_gender = FALSE
 	/// Which dna feature key to draw from
@@ -29,12 +30,12 @@
 	use_gender = accessory.gender_specific
 	draw_color = accessory.color_src ? set_color : null
 
-/datum/bodypart_overlay/simple/body_marking/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/simple/body_marking/icon_render_key(obj/item/bodypart/limb)
 	. = ..()
 	. += use_gender
 	. += draw_color
 
-/datum/bodypart_overlay/simple/body_marking/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/simple/body_marking/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && icon_state != SPRITE_ACCESSORY_NONE
 
 /datum/bodypart_overlay/simple/body_marking/get_image(layer, obj/item/bodypart/limb)

code/datums/bodypart_overlays/mutant_bodypart_overlay.dm

@@ -106,7 +106,7 @@
 	sprite_datum = fetch_sprite_datum_from_name(accessory_name)
 
 ///Generate a unique key based on our sprites. So that if we've aleady drawn these sprites, they can be found in the cache and wont have to be drawn again (blessing and curse, but mostly curse)
-/datum/bodypart_overlay/mutant/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/mutant/icon_render_key(obj/item/bodypart/limb)
 	. = list()
 	. += "[get_base_icon_state()]"
 	. += "[feature_key]"

code/datums/bodypart_overlays/simple_bodypart_overlay.dm

@@ -15,7 +15,7 @@
 
 	overlay.color = draw_color
 
-/datum/bodypart_overlay/simple/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/simple/icon_render_key(obj/item/bodypart/limb)
 	. = ..()
 	. += icon_state
 
@@ -24,14 +24,17 @@
 	icon_state = "sixpack"
 	layers = EXTERNAL_ADJACENT
 	draw_on_husks = HUSK_OVERLAY_GRAYSCALE
+	offset_location = ENTIRE_BODY
 
 ///bags drawn beneath the eyes
 /datum/bodypart_overlay/simple/bags
 	icon_state = "bags"
 	draw_color = COLOR_WEBSAFE_DARK_GRAY
 	layers = EXTERNAL_ADJACENT
+	offset_location = UPPER_BODY
 
 ///PENDING eyes drawn on the face
 /datum/bodypart_overlay/simple/soul_pending_eyes
 	icon_state = "soul_pending_eyes"
 	layers = EXTERNAL_FRONT
+	offset_location = UPPER_BODY

code/datums/bodypart_overlays/texture_bodypart_overlay.dm

@@ -1,5 +1,5 @@
 /// Bodypart overlays focused on texturing limbs
-/datum/bodypart_overlay/texture
+/datum/bodypart_texture
 	/// icon file for the texture
 	var/texture_icon
 	/// icon state for the texture
@@ -9,42 +9,42 @@
 	/// Priority of this texture - all textures with a lower priority will not be rendered
 	var/overlay_priority = 0
 
-/datum/bodypart_overlay/texture/New()
+/datum/bodypart_texture/New()
 	. = ..()
 	cached_texture_icon = icon(texture_icon, texture_icon_state)
 
-/datum/bodypart_overlay/texture/modify_bodypart_appearance(datum/appearance)
+/datum/bodypart_texture/proc/modify_bodypart_appearance(image/appearance)
 	appearance.add_filter("bodypart_texture_[texture_icon_state]", 1, layering_filter(icon = cached_texture_icon, blend_mode = BLEND_INSET_OVERLAY))
 
-/datum/bodypart_overlay/texture/generate_icon_cache(obj/item/bodypart/limb)
-	. = ..()
-	. += type
+/datum/bodypart_texture/proc/icon_render_key()
+	return type
 
-/datum/bodypart_overlay/texture/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
-	if (!..())
-		return FALSE
-	for (var/datum/bodypart_overlay/texture/other_texture in bodypart_owner.bodypart_overlays)
+/datum/bodypart_texture/proc/can_texture_bodypart(obj/item/bodypart/bodypart_owner)
+	for (var/datum/bodypart_texture/other_texture as anything in bodypart_owner.bodypart_textures)
 		if (other_texture.overlay_priority > overlay_priority)
 			return FALSE
 	return TRUE
 
-/datum/bodypart_overlay/texture/spacey
-	blocks_emissive = EMISSIVE_BLOCK_NONE
+/datum/bodypart_texture/spacey
 	texture_icon_state = "spacey"
 	texture_icon = 'icons/mob/human/textures.dmi'
 	overlay_priority = BODYPART_OVERLAY_VOIDWALKER_CURSE
 
-/datum/bodypart_overlay/texture/carpskin
+/datum/bodypart_texture/carpskin
 	texture_icon_state = "carpskin"
 	texture_icon = 'icons/mob/human/textures.dmi'
 	overlay_priority = BODYPART_OVERLAY_CARP_INFUSION
 
-/datum/bodypart_overlay/texture/checkered
+/datum/bodypart_texture/checkered
 	texture_icon_state = "checkered"
 	texture_icon = 'icons/mob/human/textures.dmi'
 	overlay_priority = BODYPART_OVERLAY_CSS_SUICIDE
 
-/datum/bodypart_overlay/texture/fishscale
+/datum/bodypart_texture/checkered/modify_bodypart_appearance(image/appearance)
+	. = ..()
+	appearance.color = COLOR_WHITE
+
+/datum/bodypart_texture/fishscale
 	texture_icon_state = "fishscale"
 	texture_icon = 'icons/mob/human/textures.dmi'
 	overlay_priority = BODYPART_OVERLAY_FISH_INFUSION

code/datums/components/ghostrole_on_revive.dm

@@ -77,10 +77,7 @@
 
 	// we might have some lingering blinking eyes
 	var/obj/item/bodypart/head/head = source.get_bodypart(BODY_ZONE_HEAD)
-	if(head)
-		var/soul_eyes = locate(/datum/bodypart_overlay/simple/soul_pending_eyes) in head.bodypart_overlays
-		if(soul_eyes)
-			head.remove_bodypart_overlay(soul_eyes)
+	head?.remove_bodypart_overlay(/datum/bodypart_overlay/simple/soul_pending_eyes)
 
 	prepare_brain(removed_brain)
 

code/datums/elements/organ_set_bonus.dm

@@ -61,9 +61,9 @@
 	var/bonus_biotype
 	/// If the biotype was added - used to check if we should remove the biotype or not, on organ set loss.
 	var/biotype_added = FALSE
-	/// Limb overlay to apply upon activation
-	var/limb_overlay
-	/// Color priority for limb overlay
+	/// Limb texture to apply upon activation
+	var/limb_texture
+	/// Color priority for limb limb_texture
 	var/color_overlay_priority
 
 /datum/status_effect/organ_set_bonus/proc/set_organs(new_value, obj/item/organ/organ)
@@ -97,22 +97,21 @@
 	if(bonus_activate_text)
 		to_chat(owner, bonus_activate_text)
 
-	// Add limb overlay
-	if(!iscarbon(owner) || !limb_overlay)
+	// Add limb texture
+	if(!limb_texture)
 		return TRUE
 
-	var/mob/living/carbon/carbon_owner = owner
-	RegisterSignal(carbon_owner, COMSIG_CARBON_ATTACH_LIMB, PROC_REF(texture_limb))
-	RegisterSignal(carbon_owner, COMSIG_CARBON_REMOVE_LIMB, PROC_REF(untexture_limb))
+	RegisterSignal(owner, COMSIG_CARBON_ATTACH_LIMB, PROC_REF(texture_limb))
+	RegisterSignal(owner, COMSIG_CARBON_REMOVE_LIMB, PROC_REF(untexture_limb))
 
-	for(var/obj/item/bodypart/limb as anything in carbon_owner.get_bodyparts())
+	for(var/obj/item/bodypart/limb as anything in owner.get_bodyparts())
 		if (!(limb.bodytype & BODYTYPE_ORGANIC))
 			continue
-		limb.add_bodypart_overlay(new limb_overlay(), update = FALSE)
+		limb.add_bodypart_texture(limb_texture, update = FALSE)
 		if (color_overlay_priority)
 			limb.add_color_override(COLOR_WHITE, color_overlay_priority)
 
-	carbon_owner.update_body()
+	owner.update_body()
 	return TRUE
 
 /datum/status_effect/organ_set_bonus/proc/disable_bonus(obj/item/organ/removed_organ)
@@ -130,24 +129,20 @@
 		to_chat(owner, bonus_deactivate_text)
 
 	// Remove limb overlay
-	if(!iscarbon(owner) || !limb_overlay)
+	if(!limb_texture)
 		return
 
-	var/mob/living/carbon/carbon_owner = owner
-	UnregisterSignal(carbon_owner, list(COMSIG_CARBON_ATTACH_LIMB, COMSIG_CARBON_REMOVE_LIMB))
+	UnregisterSignal(owner, list(COMSIG_CARBON_ATTACH_LIMB, COMSIG_CARBON_REMOVE_LIMB))
 
-	if(QDELETED(carbon_owner))
+	if(QDELETED(owner))
 		return
 
-	for(var/obj/item/bodypart/limb as anything in carbon_owner.get_bodyparts())
-		var/overlay = locate(limb_overlay) in limb.bodypart_overlays
-		if(!overlay)
-			continue
-		limb.remove_bodypart_overlay(overlay, update = FALSE)
+	for(var/obj/item/bodypart/limb as anything in owner.get_bodyparts())
+		limb.remove_bodypart_texture(limb_texture, update = FALSE)
 		if (color_overlay_priority)
 			limb.remove_color_override(color_overlay_priority)
 
-	carbon_owner.update_body()
+	owner.update_body()
 
 /datum/status_effect/organ_set_bonus/proc/texture_limb(atom/source, obj/item/bodypart/limb)
 	SIGNAL_HANDLER
@@ -156,16 +151,13 @@
 		return
 
 	// Not updating because enable/disable_bonus(obj/item/organ/removed_organ) call it down the line, and calls coming from comsigs update the owner's body themselves
-	limb.add_bodypart_overlay(new limb_overlay(), update = FALSE)
+	limb.add_bodypart_texture(limb_texture, update = FALSE)
 	if(color_overlay_priority)
 		limb.add_color_override(COLOR_WHITE, color_overlay_priority)
 
 /datum/status_effect/organ_set_bonus/proc/untexture_limb(atom/source, obj/item/bodypart/limb)
 	SIGNAL_HANDLER
 
-	var/overlay = locate(limb_overlay) in limb.bodypart_overlays
-	if(!overlay)
-		return
-	limb.remove_bodypart_overlay(overlay, update = FALSE)
+	limb.remove_bodypart_texture(limb_texture, update = FALSE)
 	if(color_overlay_priority)
 		limb.remove_color_override(color_overlay_priority)

code/datums/mutations/_mutations.dm

@@ -175,7 +175,7 @@
 	SIGNAL_HANDLER
 
 	var/mutable_appearance/mutation_appearance = mutable_appearance(mutation_icon, mutation_icon_state, -layer_used)
-	owner.apply_height_offsets(mutation_appearance, offset_location)
+	owner.apply_height(mutation_appearance, offset_location)
 
 	overlay_list += mutation_appearance
 

code/datums/mutations/adaptation.dm

@@ -8,7 +8,7 @@
 	locked = TRUE // fake parent
 	conflicts = list(/datum/mutation/adaptation)
 	mutation_traits = list(TRAIT_WADDLING)
-	mutation_icon = 'icons/mob/effects/genetics.dmi'
+	offset_location = FULL_BODY
 
 /datum/mutation/adaptation/New(datum/mutation/copymut)
 	. = ..()

code/datums/mutations/radioactive.dm

@@ -7,6 +7,7 @@
 	difficulty = 8
 	power_coeff = 1
 	mutation_icon_state = "radiation"
+	offset_location = FULL_BODY
 	/// Weakref to our radiation emitter component
 	var/datum/weakref/radioactivity_source_ref
 

code/datums/proximity_monitor/fields/heretic_arena.dm

@@ -158,7 +158,7 @@ GLOBAL_LIST_EMPTY(heretic_arenas)
 	crown_overlay.pixel_z = 24
 	if(ishuman(owner))
 		var/mob/living/carbon/human/human_parent = owner
-		human_parent.apply_height_offsets(crown_overlay, UPPER_BODY)
+		human_parent.apply_height(crown_overlay, UPPER_BODY)
 		var/obj/item/bodypart/head/human_head = human_parent.get_bodypart(BODY_ZONE_HEAD)
 		human_head?.worn_head_offset?.apply_offset(crown_overlay)
 	owner.add_overlay(crown_overlay)
@@ -210,7 +210,7 @@ GLOBAL_LIST_EMPTY(heretic_arenas)
 	crown_overlay.pixel_z = 24
 	if(ishuman(owner))
 		var/mob/living/carbon/human/human_parent = owner
-		human_parent.apply_height_offsets(crown_overlay, UPPER_BODY)
+		human_parent.apply_height(crown_overlay, UPPER_BODY)
 		var/obj/item/bodypart/head/human_head = human_parent.get_bodypart(BODY_ZONE_HEAD)
 		human_head?.worn_head_offset?.apply_offset(crown_overlay)
 	owner.add_overlay(crown_overlay)

code/datums/status_effects/buffs/cult_halo.dm

@@ -44,7 +44,7 @@
 	halo_overlay.pixel_w = 0
 	if (ishuman(owner))
 		var/mob/living/carbon/human/human_parent = owner
-		human_parent.apply_height_offsets(halo_overlay, UPPER_BODY)
+		human_parent.apply_height(halo_overlay, UPPER_BODY)
 
 		var/obj/item/bodypart/head/human_head = human_parent.get_bodypart(BODY_ZONE_HEAD)
 		human_head?.worn_head_offset?.apply_offset(halo_overlay)

code/game/machinery/dna_infuser/organ_sets/carp_organs.dm

@@ -11,7 +11,7 @@
 	bonus_deactivate_text = span_notice("Your DNA is once again mostly yours, and so fades your ability to space-swim...")
 	bonus_traits = list(TRAIT_SPACEWALK)
 	bonus_biotype = MOB_AQUATIC
-	limb_overlay = /datum/bodypart_overlay/texture/carpskin
+	limb_texture = /datum/bodypart_texture/carpskin
 	color_overlay_priority = LIMB_COLOR_CARP_INFUSION
 
 ///Carp lungs! You can breathe in space! Oh... you can't breathe on the station, you need low oxygen environments.

code/game/machinery/dna_infuser/organ_sets/fish_organs.dm

@@ -26,7 +26,7 @@
 		TRAIT_WATER_ADAPTATION,
 		)
 	bonus_biotype = MOB_AQUATIC
-	limb_overlay = /datum/bodypart_overlay/texture/fishscale
+	limb_texture = /datum/bodypart_texture/fishscale
 	/// Are we at all five organs?
 	var/color_active = FALSE
 
@@ -301,15 +301,6 @@
 	else //otherwise get one from a set of faded out blue and some greys colors.
 		return pick("#B4B8DD", "#85C7D0", "#67BBEE", "#2F4450", "#55CCBB", "#999FD0", "#345066", "#585B69", "#7381A0", "#B6DDE5", "#4E4E50")
 
-/datum/bodypart_overlay/mutant/tail/fish/get_image(image_layer, obj/item/bodypart/limb)
-	var/mutable_appearance/appearance = ..()
-	// We add all appearances the parent bodypart has to the tail to inherit scales and fancy effects
-	// but most other organs don't want to inherit those so we do it here and not on parent
-	for (var/datum/bodypart_overlay/texture/texture in limb.bodypart_overlays)
-		if(texture.can_draw_on_bodypart(limb, limb.owner, limb.is_husked))
-			texture.modify_bodypart_appearance(appearance)
-	return appearance
-
 ///Lungs that replace the need of oxygen with water vapor or being wet
 /obj/item/organ/lungs/fish
 	name = "mutated gills"

code/game/machinery/dna_infuser/organ_sets/roach_organs.dm

@@ -144,6 +144,7 @@
 	icon_state = "roach_shell"
 	layers = EXTERNAL_FRONT|EXTERNAL_BEHIND
 	draw_on_husks = HUSK_OVERLAY_GRAYSCALE
+	offset_location = ENTIRE_BODY
 
 /datum/bodypart_overlay/simple/roach_shell/get_image(image_layer, obj/item/bodypart/limb)
 	return image(

code/game/objects/items/stacks/golem_food/golem_status_effects.dm

@@ -123,7 +123,8 @@
 /// Body part overlays applied by golem status effects
 /datum/bodypart_overlay/simple/golem_overlay
 	icon = 'icons/mob/human/species/golems.dmi'
-	layers = ALL_EXTERNAL_OVERLAYS
+	layers = EXTERNAL_FRONT | EXTERNAL_ADJACENT | EXTERNAL_BEHIND
+	offset_location = ENTIRE_BODY
 	///The bodypart that the overlay is currently applied to
 	var/datum/weakref/attached_bodypart
 
@@ -134,9 +135,7 @@
 
 /datum/bodypart_overlay/simple/golem_overlay/Destroy(force)
 	var/obj/item/bodypart/referenced_bodypart = attached_bodypart.resolve()
-	if(!referenced_bodypart)
-		return ..()
-	referenced_bodypart.remove_bodypart_overlay(src)
+	referenced_bodypart?.remove_bodypart_overlay(src)
 	return ..()
 
 /// Freezes hunger for the duration

code/modules/antagonists/voidwalker/voidwalker_traumas.dm

@@ -9,7 +9,7 @@
 	random_gain = FALSE
 	known_trauma = FALSE
 	/// Type for the bodypart texture we add
-	var/bodypart_overlay_type = /datum/bodypart_overlay/texture/spacey
+	var/bodypart_texture_type = /datum/bodypart_texture/spacey
 	/// Color in which we paint the space texture
 	var/space_color = COLOR_WHITE
 	///traits we give on gain
@@ -90,7 +90,7 @@
 	SIGNAL_HANDLER
 
 	// Not updating because on_gain/on_lose() call it down the line, and calls coming from comsigs update the owner's body themselves
-	limb.add_bodypart_overlay(new bodypart_overlay_type(), update = FALSE)
+	limb.add_bodypart_texture(bodypart_texture_type, update = FALSE)
 	limb.add_color_override(space_color, LIMB_COLOR_VOIDWALKER_CURSE)
 	if(istype(limb, /obj/item/bodypart/head))
 		var/obj/item/bodypart/head/head = limb
@@ -99,10 +99,9 @@
 /datum/brain_trauma/voided/proc/untexture_limb(atom/source, obj/item/bodypart/limb)
 	SIGNAL_HANDLER
 
-	var/overlay = locate(bodypart_overlay_type) in limb.bodypart_overlays
-	if(overlay)
-		limb.remove_bodypart_overlay(overlay, update = FALSE)
-		limb.remove_color_override(LIMB_COLOR_VOIDWALKER_CURSE)
+
+	limb.remove_bodypart_texture(bodypart_texture_type, update = FALSE)
+	limb.remove_color_override(LIMB_COLOR_VOIDWALKER_CURSE)
 
 	if(istype(limb, /obj/item/bodypart/head))
 		var/obj/item/bodypart/head/head = limb

code/modules/fishing/fish/types/holographic.dm

@@ -116,8 +116,7 @@
 		return ..()
 
 	for(var/obj/item/bodypart/limb in user.get_bodyparts())
-		limb.add_color_override(COLOR_WHITE, LIMB_COLOR_CS_SOURCE_SUICIDE)
-		limb.add_bodypart_overlay(new /datum/bodypart_overlay/texture/checkered(), update = FALSE)
+		limb.add_bodypart_overlay(/datum/bodypart_texture/checkered, update = FALSE)
 
 	var/obj/item/bodypart/head/head = user.get_bodypart(BODY_ZONE_HEAD)
 	if(!isnull(head))

code/modules/fishing/fish/types/rift.dm

@@ -722,8 +722,9 @@
 /datum/bodypart_overlay/simple/babbearfish
 	icon_state = "babbearfish"
 	draw_on_husks = HUSK_OVERLAY_NORMAL
+	offset_location = UPPER_BODY
 
-/datum/bodypart_overlay/simple/babbearfish/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/simple/babbearfish/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEEARS)
 
 /obj/item/organ/ears/babbelfish/Initialize(mapload)

code/modules/hallucination/shock.dm

@@ -32,7 +32,7 @@
 	electrocution_skeleton_anim.appearance_flags |= RESET_COLOR|KEEP_APART
 	if(ishuman(hallucinator))
 		var/mob/living/carbon/human/human_hallucinator = hallucinator
-		human_hallucinator.apply_height_filters(electrocution_skeleton_anim)
+		human_hallucinator.apply_height(electrocution_skeleton_anim, ENTIRE_BODY)
 
 	SET_PLANE_EXPLICIT(shock_image, ABOVE_GAME_PLANE, hallucinator)
 	SET_PLANE_EXPLICIT(electrocution_skeleton_anim, ABOVE_GAME_PLANE, hallucinator)

code/modules/mob/living/basic/lavaland/raptor/raptor_color.dm

@@ -271,7 +271,8 @@ GLOBAL_LIST_INIT(raptor_colors, init_raptor_colors())
 	// Raptors won't have the best of times keeping up tall humans or fatties up in the air
 	var/struggling = HAS_TRAIT(user, TRAIT_FAT) || user.mob_height > HUMAN_HEIGHT_SHORTEST
 	if (wings_open)
-		wings_underlay = user.apply_height_offsets(mutable_appearance(worn_icon, "raptor_purple_wings", -BODY_BEHIND_LAYER, user), UPPER_BODY)
+		wings_underlay = mutable_appearance(worn_icon, "raptor_purple_wings", -BODY_BEHIND_LAYER, user)
+		user.apply_height(wings_underlay, UPPER_BODY)
 		user.add_overlay(wings_underlay)
 		user.physiology.stun_mod *= 2
 		user.add_traits(list(TRAIT_MOVE_FLOATING, TRAIT_IGNORING_GRAVITY, TRAIT_NOGRAV_ALWAYS_DRIFT), REF(src))

code/modules/mob/living/carbon/carbon_update_icons.dm

@@ -302,6 +302,7 @@
 	if(isnull(damage_overlay))
 		return
 
+	apply_height(damage_overlay, ENTIRE_BODY)
 	overlays_standing[DAMAGE_LAYER] = damage_overlay
 	apply_overlay(DAMAGE_LAYER)
 
@@ -324,6 +325,7 @@
 	if(isnull(wound_overlay))
 		return
 
+	apply_height(wound_overlay, ENTIRE_BODY)
 	overlays_standing[WOUND_LAYER] = wound_overlay
 	apply_overlay(WOUND_LAYER)
 
@@ -387,7 +389,7 @@
 		var/mutable_appearance/handcuff_overlay = mutable_appearance('icons/mob/simple/mob.dmi', "handcuff1", -HANDCUFF_LAYER)
 		if(handcuffed.blocks_emissive != EMISSIVE_BLOCK_NONE)
 			handcuff_overlay.overlays += emissive_blocker(handcuff_overlay.icon, handcuff_overlay.icon_state, src, alpha = handcuff_overlay.alpha)
-
+		apply_height(handcuff_overlay, LOWER_BODY) // low hanging
 		overlays_standing[HANDCUFF_LAYER] = handcuff_overlay
 		apply_overlay(HANDCUFF_LAYER)
 
@@ -498,9 +500,11 @@
 	if(is_invisible)
 		. += "invisible"
 	for(var/datum/bodypart_overlay/overlay as anything in bodypart_overlays)
-		if(!overlay.can_draw_on_bodypart(src, owner, is_husked))
-			continue
-		. += overlay.generate_icon_cache(src)
+		if(overlay.can_draw_on_bodypart(src, owner))
+			. += overlay.icon_render_key(src)
+	for(var/datum/bodypart_texture/texture as anything in bodypart_textures)
+		if(texture.can_texture_bodypart(src))
+			. += texture.icon_render_key()
 	if(ishuman(owner))
 		var/mob/living/carbon/human/human_owner = owner
 		. += "[human_owner.mob_height]"
@@ -525,11 +529,10 @@
 	. += body_zone
 	if(is_invisible)
 		. += "invisible"
-	. += "[LAZYLEN(blood_dna_info) ? get_color_from_blood_list(blood_dna_info) : BLOOD_COLOR_RED]"
 	for(var/datum/bodypart_overlay/overlay as anything in bodypart_overlays)
-		if(!overlay.can_draw_on_bodypart(src, owner, TRUE))
-			continue
-		. += overlay.generate_icon_cache(src)
+		if(overlay.can_draw_on_bodypart(src, owner))
+			. += overlay.icon_render_key(src)
+	. += "[LAZYLEN(blood_dna_info) ? get_color_from_blood_list(blood_dna_info) : BLOOD_COLOR_RED]"
 	if(ishuman(owner))
 		var/mob/living/carbon/human/human_owner = owner
 		. += "[human_owner.mob_height]"

code/modules/mob/living/carbon/human/_species.dm

@@ -2047,9 +2047,14 @@ GLOBAL_LIST_EMPTY(features_by_species)
 
 /// Remove body markings
 /datum/species/proc/remove_body_markings(mob/living/carbon/human/hooman)
+	var/needs_update = FALSE
 	for(var/obj/item/bodypart/part as anything in hooman.get_bodyparts())
 		for(var/datum/bodypart_overlay/simple/body_marking/marking in part.bodypart_overlays)
-			part.remove_bodypart_overlay(marking)
+			part.remove_bodypart_overlay(marking, update = FALSE)
+			needs_update = TRUE
+
+	if(needs_update && !(hooman.living_flags & STOP_OVERLAY_UPDATE_BODY_PARTS))
+		hooman.update_body_parts()
 
 /**
  * Calculates the expected height values for this species

code/modules/mob/living/carbon/human/dummy.dm

@@ -95,19 +95,17 @@ INITIALIZE_IMMEDIATE(/mob/living/carbon/human/dummy)
 /mob/living/carbon/human/dummy/log_mob_tag(text)
 	return
 
-// To speed up the preference menu, we apply 1 filter to the entire mob
+// To speed up the preference menu, we apply one height filter to the entire mob,
+// rather than independently applying offsets and filters to each individual overlay
+// This looks good enough to pass the sniff test and saves a lot of time
 /mob/living/carbon/human/dummy/regenerate_icons()
 	. = ..()
-	apply_height_filters(src, TRUE)
+	apply_height(src, ENTIRE_BODY)
 
-/mob/living/carbon/human/dummy/apply_height_filters(image/appearance, only_apply_in_prefs = FALSE)
-	if(only_apply_in_prefs)
+/mob/living/carbon/human/dummy/apply_height(image/appearance, upper_torso)
+	if(appearance == src)
 		return ..()
 
-// Not necessary with above
-/mob/living/carbon/human/dummy/apply_height_offsets(image/appearance, upper_torso)
-	return
-
 /// Takes in an accessory list and returns the first entry from that list, ensuring that we dont return SPRITE_ACCESSORY_NONE in the process.
 /proc/get_consistent_feature_entry(list/accessory_feature_list)
 	var/consistent_entry = (accessory_feature_list- SPRITE_ACCESSORY_NONE)[1]

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

@@ -637,7 +637,7 @@
 	if(dna?.species)
 		add_atom_colour(COLOR_BLACK, TEMPORARY_COLOUR_PRIORITY)
 		var/mutable_appearance/shock_animation_dna = mutable_appearance(icon, "electrocuted_base", appearance_flags = RESET_COLOR|KEEP_APART)
-		apply_height_filters(shock_animation_dna)
+		apply_height(shock_animation_dna, ENTIRE_BODY)
 		zap_appearance = shock_animation_dna
 
 	// Otherwise do a generic animation

code/modules/mob/living/carbon/human/human_update_icons.dm

@@ -85,7 +85,7 @@ There are several things that need to be remembered:
 		if(uniform.adjusted == ALT_STYLE)
 			target_overlay = "[target_overlay]_d"
 
-		var/mutable_appearance/uniform_overlay
+
 		//This is how non-humanoid clothing works. You check if the mob has the right bodyflag, and the clothing has the corresponding clothing flag.
 		//handled_by_bodyshape is used to track whether or not we successfully used an alternate sprite. It's set to TRUE to ease up on copy-paste.
 		//icon_file MUST be set to null by default, or it causes issues.
@@ -107,7 +107,7 @@ There are several things that need to be remembered:
 			handled_by_bodyshape = FALSE
 
 		//END SPECIES HANDLING
-		uniform_overlay = uniform.build_worn_icon(
+		var/mutable_appearance/uniform_overlay = uniform.build_worn_icon(
 			default_layer = UNIFORM_LAYER,
 			default_icon_file = icon_file,
 			isinhands = FALSE,
@@ -117,6 +117,7 @@ There are several things that need to be remembered:
 			bodyshape = bodyshape,
 		)
 
+		apply_height(uniform_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_uniform_offset?.apply_offset(uniform_overlay)
 		overlays_standing[UNIFORM_LAYER] = uniform_overlay
@@ -127,8 +128,6 @@ There are several things that need to be remembered:
 	remove_overlay(ID_LAYER)
 	hud_used?.update_inventory_slot(ITEM_SLOT_ID)
 
-	var/mutable_appearance/id_overlay = overlays_standing[ID_LAYER]
-
 	if(wear_id)
 		var/obj/item/worn_item = wear_id
 
@@ -136,12 +135,9 @@ There are several things that need to be remembered:
 			return
 
 		var/icon_file = 'icons/mob/clothing/id.dmi'
+		var/mutable_appearance/id_overlay = wear_id.build_worn_icon(default_layer = ID_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
 
-		id_overlay = wear_id.build_worn_icon(default_layer = ID_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
-
-		if(!id_overlay)
-			return
-
+		apply_height(id_overlay, UPPER_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_id_offset?.apply_offset(id_overlay)
 		overlays_standing[ID_LAYER] = id_overlay
@@ -167,6 +163,8 @@ There are several things that need to be remembered:
 			var/mutable_appearance/blood_overlay = mutable_appearance('icons/effects/blood.dmi', "bloodyhands_right")
 			blood_overlay.color = get_blood_dna_color()
 			hands_combined.overlays += blood_overlay
+
+		apply_height(hands_combined, LOWER_BODY)
 		overlays_standing[GLOVES_LAYER] = hands_combined
 		apply_overlay(GLOVES_LAYER)
 		return
@@ -183,11 +181,10 @@ There are several things that need to be remembered:
 	var/feature_y_offset = 0
 	//needs to be typed, hand_bodyparts can have nulls
 	for (var/obj/item/bodypart/arm/my_hand in hand_bodyparts)
-		var/list/glove_offset = my_hand.worn_glove_offset?.get_offset()
-		if (glove_offset && (!feature_y_offset || glove_offset["y"] > feature_y_offset))
-			feature_y_offset = glove_offset["y"]
+		feature_y_offset = max(my_hand.worn_glove_offset?.get_offset()["y"], feature_y_offset)
 
 	gloves_overlay.pixel_z += feature_y_offset
+	apply_height(gloves_overlay, LOWER_BODY)
 
 	// We dont have any >2 hands human species (and likely wont ever), so theres no point in splitting this because:
 	// It will only run if the left hand OR the right hand is missing, and it wont run if both are missing because you cant wear gloves with no arms
@@ -221,6 +218,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/eyes.dmi'
 
 		var/mutable_appearance/glasses_overlay = glasses.build_worn_icon(default_layer = GLASSES_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(glasses_overlay, UPPER_BODY)
 		my_head.worn_glasses_offset?.apply_offset(glasses_overlay)
 		overlays_standing[GLASSES_LAYER] = glasses_overlay
 	apply_overlay(GLASSES_LAYER)
@@ -242,6 +240,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/ears.dmi'
 
 		var/mutable_appearance/ears_overlay = ears.build_worn_icon(default_layer = EARS_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(ears_overlay, UPPER_BODY)
 		my_head.worn_ears_offset?.apply_offset(ears_overlay)
 		overlays_standing[EARS_LAYER] = ears_overlay
 	apply_overlay(EARS_LAYER)
@@ -259,6 +258,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/neck.dmi'
 
 		var/mutable_appearance/neck_overlay = worn_item.build_worn_icon(default_layer = NECK_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(neck_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_neck_offset?.apply_offset(neck_overlay)
 		overlays_standing[NECK_LAYER] = neck_overlay
@@ -281,19 +281,13 @@ There are several things that need to be remembered:
 		var/icon_file = DEFAULT_SHOES_FILE
 
 		var/mutable_appearance/shoes_overlay = shoes.build_worn_icon(default_layer = SHOES_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
-		if(!shoes_overlay)
-			return
-
 		var/feature_y_offset = 0
-		for (var/body_zone in list(BODY_ZONE_L_LEG, BODY_ZONE_R_LEG))
+		for (var/body_zone in GLOB.leg_zones)
 			var/obj/item/bodypart/leg/my_leg = get_bodypart(body_zone)
-			if(isnull(my_leg))
-				continue
-			var/list/foot_offset = my_leg.worn_foot_offset?.get_offset()
-			if (foot_offset && foot_offset["y"] > feature_y_offset)
-				feature_y_offset = foot_offset["y"]
+			feature_y_offset = max(my_leg?.worn_foot_offset?.get_offset()["y"], feature_y_offset)
 
 		shoes_overlay.pixel_z += feature_y_offset
+		// apply_height(shoes_overlay, NO_MODIFY) // Shoes are rooted
 		overlays_standing[SHOES_LAYER] = shoes_overlay
 
 	apply_overlay(SHOES_LAYER)
@@ -308,6 +302,7 @@ There are several things that need to be remembered:
 			return
 
 		var/mutable_appearance/s_store_overlay = worn_item.build_worn_icon(default_layer = SUIT_STORE_LAYER, default_icon_file = 'icons/mob/clothing/belt_mirror.dmi')
+		apply_height(s_store_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_suit_storage_offset?.apply_offset(s_store_overlay)
 		overlays_standing[SUIT_STORE_LAYER] = s_store_overlay
@@ -325,6 +320,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/head/default.dmi'
 
 		var/mutable_appearance/head_overlay = head.build_worn_icon(default_layer = HEAD_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(head_overlay, UPPER_BODY)
 		var/obj/item/bodypart/head/my_head = get_bodypart(BODY_ZONE_HEAD)
 		my_head?.worn_head_offset?.apply_offset(head_overlay)
 		overlays_standing[HEAD_LAYER] = head_overlay
@@ -343,6 +339,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/belt.dmi'
 
 		var/mutable_appearance/belt_overlay = belt.build_worn_icon(default_layer = BELT_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(belt_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_belt_offset?.apply_offset(belt_overlay)
 		overlays_standing[BELT_LAYER] = belt_overlay
@@ -362,6 +359,7 @@ There are several things that need to be remembered:
 		var/icon_file = DEFAULT_SUIT_FILE
 
 		var/mutable_appearance/suit_overlay = wear_suit.build_worn_icon(default_layer = SUIT_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(suit_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_suit_offset?.apply_offset(suit_overlay)
 		overlays_standing[SUIT_LAYER] = suit_overlay
@@ -389,6 +387,7 @@ There are several things that need to be remembered:
 		var/icon_file = 'icons/mob/clothing/mask.dmi'
 
 		var/mutable_appearance/mask_overlay = wear_mask.build_worn_icon(default_layer = FACEMASK_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(mask_overlay, LOWER_BODY)
 		my_head.worn_mask_offset?.apply_offset(mask_overlay)
 		overlays_standing[FACEMASK_LAYER] = mask_overlay
 
@@ -399,18 +398,13 @@ There are several things that need to be remembered:
 	hud_used?.update_inventory_slot(ITEM_SLOT_BACK)
 
 	if(back)
-		var/obj/item/worn_item = back
-		var/mutable_appearance/back_overlay
-
-		if(HAS_TRAIT(worn_item, TRAIT_NO_WORN_ICON))
+		if(HAS_TRAIT(back, TRAIT_NO_WORN_ICON))
 			return
 
 		var/icon_file = 'icons/mob/clothing/back.dmi'
 
-		back_overlay = back.build_worn_icon(default_layer = BACK_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
-
-		if(!back_overlay)
-			return
+		var/mutable_appearance/back_overlay = back.build_worn_icon(default_layer = BACK_LAYER, default_icon_file = icon_file, bodyshape = bodyshape)
+		apply_height(back_overlay, ENTIRE_BODY)
 		var/obj/item/bodypart/chest/my_chest = get_bodypart(BODY_ZONE_CHEST)
 		my_chest?.worn_back_offset?.apply_offset(back_overlay)
 		overlays_standing[BACK_LAYER] = back_overlay
@@ -425,9 +419,10 @@ There are several things that need to be remembered:
 		if(!t_state)
 			t_state = worn_item.icon_state
 
-		var/mutable_appearance/hand_overlay
+
 		var/icon_file = IS_RIGHT_INDEX(held_index) ? worn_item.righthand_file : worn_item.lefthand_file
-		hand_overlay = worn_item.build_worn_icon(default_layer = HANDS_LAYER, default_icon_file = icon_file, isinhands = TRUE, bodyshape = bodyshape)
+		var/mutable_appearance/hand_overlay = worn_item.build_worn_icon(default_layer = HANDS_LAYER, default_icon_file = icon_file, isinhands = TRUE, bodyshape = bodyshape)
+		apply_height(hand_overlay, LOWER_BODY)
 		var/obj/item/bodypart/arm/held_in_hand = hand_bodyparts[held_index]
 		held_in_hand?.held_hand_offset?.apply_offset(hand_overlay)
 
@@ -667,14 +662,12 @@ generate/load female uniform sprites matching all previously decided variables
 
 /mob/living/carbon/human/update_body(is_creating = FALSE)
 	remove_overlay(BODY_LAYER)
-
-	var/list/body_overlays = list()
-	body_overlays += get_underwear_overlays()
-
-	if(length(body_overlays))
-		overlays_standing[BODY_LAYER] = body_overlays
+	var/list/clothing_overlays = get_underwear_overlays()
+	if(length(clothing_overlays))
+		for(var/image/overlay as anything in clothing_overlays)
+			apply_height(overlay, ENTIRE_BODY)
+		overlays_standing[BODY_LAYER] = clothing_overlays
 		apply_overlay(BODY_LAYER)
-
 	// parent call will update the actual bodyparts
 	return ..()
 
@@ -722,6 +715,8 @@ generate/load female uniform sprites matching all previously decided variables
 
 	var/list/eye_overlays = noggin.get_eye_overlays()
 	if(length(eye_overlays))
+		for(var/image/overlay as anything in eye_overlays)
+			apply_height(overlay, UPPER_BODY)
 		overlays_standing[EYES_LAYER] = eye_overlays
 		apply_overlay(EYES_LAYER)
 
@@ -735,6 +730,8 @@ generate/load female uniform sprites matching all previously decided variables
 	var/obj/item/bodypart/head/head = get_bodypart(BODY_ZONE_HEAD)
 	var/list/head_overlays = head?.get_hair_overlays()
 	if(length(head_overlays))
+		for(var/image/overlay as anything in head_overlays)
+			apply_height(overlay, UPPER_BODY)
 		overlays_standing[HAIR_LAYER] = head_overlays
 		apply_overlay(HAIR_LAYER)
 
@@ -751,6 +748,7 @@ generate/load female uniform sprites matching all previously decided variables
 	for (var/mutable_appearance/overlay as anything in eye_overlays)
 		overlay.pixel_w = 0
 		overlay.pixel_z = 0
+		apply_height(overlay, UPPER_BODY)
 		noggin.worn_face_offset.apply_offset(overlay)
 
 	overlays_standing[EYES_LAYER] = eye_overlays
@@ -775,56 +773,37 @@ generate/load female uniform sprites matching all previously decided variables
 	update_eyes()
 	update_hair()
 
-// Hooks into human apply overlay so that we can modify all overlays applied through standing overlays to our height system.
-// Some of our overlays will be passed through a displacement filter to make our mob look taller or shorter.
-// Some overlays can't be displaced as they're too close to the edge of the sprite or cross the middle point in a weird way.
-// So instead we have to pass them through an offset, which is close enough to look good.
-/mob/living/carbon/human/apply_overlay(cache_index)
-	if(mob_height == HUMAN_HEIGHT_MEDIUM)
-		return ..()
-
-	var/raw_applied = overlays_standing[cache_index]
-	var/string_form_index = num2text(cache_index)
-	var/offset_type = GLOB.layers_to_offset[string_form_index]
-	if(isnull(offset_type))
-		if(islist(raw_applied))
-			for(var/image/applied_appearance in raw_applied)
-				apply_height_filters(applied_appearance)
-		else if(isimage(raw_applied))
-			apply_height_filters(raw_applied)
-	else
-		if(islist(raw_applied))
-			for(var/image/applied_appearance in raw_applied)
-				apply_height_offsets(applied_appearance, offset_type)
-		else if(isimage(raw_applied))
-			apply_height_offsets(raw_applied, offset_type)
-
-	return ..()
-
 /**
- * Used in some circumstances where appearances can get cut off from the mob sprite from being too tall
+ * Applies an offset or a filter to an appearance accordance to the height of our mob
  *
- * upper_torso is to specify whether the appearance is locate in the upper half of the mob rather than the lower half,
- * higher up things (hats for example) need to be offset more due to the location of the filter displacement
+ * * appearance - The appearance to apply the height changes to
+ * * body_area - The body area this appearance is on, used to determine what offsets/filters to apply
  */
-/mob/living/carbon/human/proc/apply_height_offsets(image/appearance, upper_torso)
-	var/height_to_use = num2text(mob_height)
-	var/final_offset = 0
-	switch(upper_torso)
-		if(UPPER_BODY)
-			final_offset = GLOB.human_heights_to_offsets[height_to_use][1]
-		if(LOWER_BODY)
-			final_offset = GLOB.human_heights_to_offsets[height_to_use][2]
-		else
+/mob/living/carbon/proc/apply_height(image/appearance, body_area)
+	return
+
+/mob/living/carbon/human/apply_height(image/appearance, body_area)
+	if(mob_height == HUMAN_HEIGHT_MEDIUM)
+		return // default, no handling needed
+
+	switch(body_area)
+		if(LOWER_BODY, UPPER_BODY)
+			appearance.pixel_z += GLOB.human_heights_to_offsets[mob_height][body_area]
+			return
+		if(ENTIRE_BODY)
+			apply_height_filter(appearance)
+			return
+		if(NO_MODIFY)
 			return
 
-	appearance.pixel_z += final_offset
-	return appearance
+	stack_trace("Invalid height body_area specified ([body_area || "null"])")
 
 /**
  * Applies a filter to an appearance according to mob height
  */
-/mob/living/carbon/human/proc/apply_height_filters(image/appearance)
+/mob/living/carbon/human/proc/apply_height_filter(image/appearance)
+	PRIVATE_PROC(TRUE)
+
 	var/static/icon/cut_torso_mask = icon('icons/effects/cut.dmi', "Cut1")
 	var/static/icon/cut_legs_mask = icon('icons/effects/cut.dmi', "Cut2")
 	var/static/icon/lenghten_torso_mask = icon('icons/effects/cut.dmi', "Cut3")
@@ -953,8 +932,8 @@ generate/load female uniform sprites matching all previously decided variables
 	// Kinda gross but because many humans overlays do not use KEEP_TOGETHER we need to manually propogate the filter
 	// Otherwise overlays, such as worn overlays on icons, won't have the filter "applied", and the effect kinda breaks
 	if(!(appearance.appearance_flags & KEEP_TOGETHER))
-		for(var/image/overlay in list() + appearance.underlays + appearance.overlays)
-			apply_height_filters(overlay)
+		for(var/mutable_appearance/child_overlay as anything in appearance.underlays + appearance.overlays)
+			apply_height_filter(child_overlay)
 
 	return appearance
 

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

@@ -105,8 +105,9 @@
 	layers = EXTERNAL_ADJACENT
 	feature_key = FEATURE_MUSH_CAP
 	dyable = TRUE
+	offset_location = UPPER_BODY
 
-/datum/bodypart_overlay/mutant/mushroom_cap/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/mushroom_cap/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEHAIR)
 
 /datum/bodypart_overlay/mutant/mushroom_cap/override_color(obj/item/bodypart/bodypart_owner)

code/modules/surgery/bodyparts/_bodyparts.dm

@@ -160,7 +160,9 @@
 	var/list/applied_items
 
 	///A list of all bodypart overlays to draw
-	var/list/bodypart_overlays = list()
+	var/list/bodypart_overlays
+	///A list of all bodypart textures to apply
+	var/list/bodypart_textures
 
 	/// Type of an attack from this limb does. Arms will do punches, Legs for kicks, and head for bites. (TO ADD: tactical chestbumps)
 	var/attack_type = BRUTE
@@ -215,7 +217,7 @@
 	/// get_damage() / total_damage must surpass this to allow our limb to be disabled, even temporarily, by an EMP.
 	var/robotic_emp_paralyze_damage_percent_threshold = 0.3
 	/// A potential texturing overlay to put on the limb
-	var/datum/bodypart_overlay/texture/texture_bodypart_overlay
+	var/datum/bodypart_texture/texture_bodypart_overlay
 	/// Lazylist of /datum/status_effect/grouped/bodypart_effect types. Instances of this are applied to the carbon when added the limb is attached, and merged with similair limbs
 	var/list/bodypart_effects
 	/// The cached info about the blood this organ belongs to, set during on_removal()
@@ -301,6 +303,14 @@
 		QDEL_LIST_ASSOC_VAL(applied_items)
 	QDEL_LAZYLIST(scars)
 
+	// Overlays and textures may be owned by something else like a status effect,
+	// so we'll just remove them all rather than delete them
+	// Worst case scenario they'll just get swept up by GC and which is fine
+	for(var/datum/bodypart_overlay/remaining_overlay in bodypart_overlays)
+		remove_bodypart_overlay(remaining_overlay, update = FALSE)
+	for(var/datum/bodypart_texture/remaining_texture in bodypart_textures)
+		remove_bodypart_texture(remaining_texture, update = FALSE)
+
 	for(var/atom/movable/movable in contents)
 		qdel(movable)
 
@@ -1369,30 +1379,43 @@
 			// Add two masked images based on the old one
 			. += leg_source.generate_masked_leg(limb_image)
 
+	// Apply height to the overlays we generated so far
+	// This is done before collecting bodypart overlays so we don't apply height twice to the same overlays
+	if(!dropped && !isnull(owner))
+		for(var/image/generated_overlay as anything in .)
+			// While you may think that heads could be applied with UPPER_BODY instead of ENTIRE_BODY to save us one filter,
+			// it's more important to keep it consistent for things like getflaticon
+			owner.apply_height(generated_overlay, ENTIRE_BODY)
+
 	// Draw external organs like horns and frills
+	// Height is applied again in here so we can specify where the overlay is set (ie offset_location)
 	for(var/datum/bodypart_overlay/overlay as anything in bodypart_overlays)
-		if(!overlay.can_draw_on_bodypart(src, owner, is_husked))
+		if(!overlay.can_draw_on_bodypart(src, owner))
 			continue
 
 		// Some externals have multiple layers for background, foreground and between
-		for(var/external_layer in overlay.all_layers)
+		for(var/external_layer, actual_layer in overlay.all_layers)
 			if(!(overlay.layers & external_layer))
 				continue
 
-			var/external_overlay = overlay.get_overlay(external_layer, src, is_husked)
-			if (!dropped)
-				. += external_overlay
+			for (var/mutable_appearance/actual_overlay as anything in overlay.get_overlay(actual_layer, src))
+				if(dropped || isnull(owner))
+					. += image(actual_overlay, dir = SOUTH)
+					continue
+
+				owner.apply_height(actual_overlay, overlay.offset_location)
+				. += actual_overlay
+
+	// Then texture everything at once, including bodypart overlays
+	for(var/datum/bodypart_texture/texture as anything in bodypart_textures)
+		if(!texture.can_texture_bodypart(src))
+			continue
+		for(var/image/generated_overlay as anything in .)
+			var/appearance_plane = PLANE_TO_TRUE(generated_overlay.plane)
+			if(appearance_plane != FLOAT_PLANE && appearance_plane != GAME_PLANE)
 				continue
 
-			if (!islist(external_overlay))
-				. += image(external_overlay, dir = SOUTH)
-				continue
-
-			for (var/mutable_appearance/actual_overlay as anything in external_overlay)
-				. += image(actual_overlay, dir = SOUTH)
-
-		for(var/datum/layer in .)
-			overlay.modify_bodypart_appearance(layer)
+			texture.modify_bodypart_appearance(generated_overlay)
 
 	SEND_SIGNAL(src, COMSIG_BODYPART_GET_LIMB_ICON, ., dropped)
 	return .
@@ -1409,24 +1432,92 @@
 	husk_blood.color = LAZYLEN(blood_dna_info) ? get_color_from_blood_list(blood_dna_info) : BLOOD_COLOR_RED
 	return husk_blood
 
-///Add a bodypart overlay and call the appropriate update procs
+/**
+ * Adds a bodypart overlay to the limb
+ *
+ * * overlay: The overlay to add. Either an instance of a bodypart overlay or a typepath of a bodypart overlay.
+ * If you pass a typepath, the proc will avoid creating duplicates.
+ * * update: Whether to call update procs after adding the overlay.
+ * Set this to FALSE if you are adding multiple overlays at once.
+ */
 /obj/item/bodypart/proc/add_bodypart_overlay(datum/bodypart_overlay/overlay, update = TRUE)
-	bodypart_overlays += overlay
+	if(ispath(overlay, /datum/bodypart_overlay))
+		if(locate(overlay) in bodypart_overlays)
+			return
+		overlay = new overlay()
+
+	LAZYADD(bodypart_overlays, overlay)
 	overlay.added_to_limb(src)
 	if(!update)
 		return
-	if(!owner)
+	if(isnull(owner))
 		update_icon_dropped()
 	else if(!(owner.living_flags & STOP_OVERLAY_UPDATE_BODY_PARTS))
 		owner.update_body_parts()
 
-///Remove a bodypart overlay and call the appropriate update procs
+/**
+ * Removes a bodypart overlay from the limb
+ *
+ * * overlay: The overlay to remove. Either an instance of a bodypart overlay or a typepath of a bodypart overlay.
+ * If you pass a typepath, the first overlay of that typepath found will be removed.
+ * * update: Whether to call update procs after removing the overlay.
+ * Set this to FALSE if you are removing multiple overlays at once.
+ */
 /obj/item/bodypart/proc/remove_bodypart_overlay(datum/bodypart_overlay/overlay, update = TRUE)
-	bodypart_overlays -= overlay
+	if(ispath(overlay, /datum/bodypart_overlay))
+		overlay = locate(overlay) in bodypart_overlays
+		if(isnull(overlay))
+			return
+
+	LAZYREMOVE(bodypart_overlays, overlay)
 	overlay.removed_from_limb(src)
 	if(!update)
 		return
-	if(!owner)
+	if(isnull(owner))
+		update_icon_dropped()
+	else if(!(owner.living_flags & STOP_OVERLAY_UPDATE_BODY_PARTS))
+		owner.update_body_parts()
+
+/**
+ * Adds a bodypart texture to the limb
+ *
+ * * texture: The texture to add. Either an instance of a bodypart texture or a typepath of a bodypart texture.
+ * If you pass a typepath, the proc will avoid creating duplicates.
+ * * update: Whether to call update procs after adding the texture.
+ * Set this to FALSE if you are adding multiple textures at once.
+ */
+/obj/item/bodypart/proc/add_bodypart_texture(datum/bodypart_texture/texture, update = TRUE)
+	if(ispath(texture, /datum/bodypart_texture))
+		if(locate(texture) in bodypart_textures)
+			return
+		texture = new texture()
+
+	LAZYADD(bodypart_textures, texture)
+	if(!update)
+		return
+	if(isnull(owner))
+		update_icon_dropped()
+	else if(!(owner.living_flags & STOP_OVERLAY_UPDATE_BODY_PARTS))
+		owner.update_body_parts()
+
+/**
+ * Removes a bodypart texture from the limb
+ *
+ * * texture: The texture to remove. Either an instance of a bodypart texture or a typepath of a bodypart texture.
+ * If you pass a typepath, the first texture of that typepath found will be removed.
+ * * update: Whether to call update procs after removing the texture.
+ * Set this to FALSE if you are removing multiple textures at once.
+ */
+/obj/item/bodypart/proc/remove_bodypart_texture(datum/bodypart_texture/texture, update = TRUE)
+	if(ispath(texture, /datum/bodypart_texture))
+		texture = locate(texture) in bodypart_textures
+		if(isnull(texture))
+			return
+
+	LAZYREMOVE(bodypart_textures, texture)
+	if(!update)
+		return
+	if(isnull(owner))
 		update_icon_dropped()
 	else if(!(owner.living_flags & STOP_OVERLAY_UPDATE_BODY_PARTS))
 		owner.update_body_parts()

code/modules/surgery/bodyparts/robot_bodyparts.dm

@@ -46,6 +46,11 @@
 	bodypart_flags = BODYPART_UNHUSKABLE
 	butcher_replacement = null
 
+/obj/item/bodypart/arm/left/robot/generate_icon_key()
+	. = ..()
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 /obj/item/bodypart/arm/right/robot
 	name = "cyborg right arm"
 	desc = "A skeletal limb wrapped in pseudomuscles, with a low-conductivity case."
@@ -82,6 +87,11 @@
 	bodypart_flags = BODYPART_UNHUSKABLE
 	butcher_replacement = null
 
+/obj/item/bodypart/arm/right/robot/generate_icon_key()
+	. = ..()
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 /obj/item/bodypart/leg/left/robot
 	name = "cyborg left leg"
 	desc = "A skeletal limb wrapped in pseudomuscles, with a low-conductivity case."
@@ -118,6 +128,11 @@
 	bodypart_flags = BODYPART_UNHUSKABLE
 	butcher_replacement = null
 
+/obj/item/bodypart/leg/left/robot/generate_icon_key()
+	. = ..()
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 /obj/item/bodypart/leg/left/robot/emp_effect(severity, protection)
 	. = ..()
 	if(!. || isnull(owner))
@@ -168,6 +183,11 @@
 	bodypart_flags = BODYPART_UNHUSKABLE
 	butcher_replacement = null
 
+/obj/item/bodypart/leg/right/robot/generate_icon_key()
+	. = ..()
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 /obj/item/bodypart/leg/right/robot/emp_effect(severity, protection)
 	. = ..()
 	if(!. || isnull(owner))
@@ -222,6 +242,13 @@
 	var/wired = FALSE
 	var/obj/item/stock_parts/power_store/cell = null
 
+/obj/item/bodypart/chest/robot/generate_icon_key()
+	. = ..()
+	// When we reskin cybernetic limbs, we solely change their icon, nothing else
+	// So we need to include the relevant icon in the cache key
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 /obj/item/bodypart/chest/robot/emp_effect(severity, protection)
 	. = ..()
 	if(!. || isnull(owner))
@@ -398,6 +425,11 @@
 	var/obj/item/assembly/flash/handheld/flash1 = null
 	var/obj/item/assembly/flash/handheld/flash2 = null
 
+/obj/item/bodypart/head/robot/generate_icon_key()
+	. = ..()
+	if(limb_id == BODYPART_ID_ROBOTIC)
+		. += should_draw_greyscale ? icon_greyscale : icon_static
+
 #define EMP_GLITCH "EMP_GLITCH"
 
 /obj/item/bodypart/head/robot/emp_effect(severity, protection)

code/modules/surgery/bodyparts/worn_feature_offset.dm

@@ -37,7 +37,7 @@
 	return ..()
 
 /// Returns the current offset which should be used for this feature
-/datum/worn_feature_offset/proc/get_offset()
+/datum/worn_feature_offset/proc/get_offset() as /list
 	var/current_dir = owner ? owner.dir : SOUTH
 	if(ISDIAGONALDIR(current_dir))
 		current_dir = current_dir & (EAST|WEST)

code/modules/surgery/organs/external/_visual_organs.dm

@@ -94,9 +94,9 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 		return
 
 	//Build the mob sprite and use it as our overlay
-	for(var/external_layer in bodypart_overlay.all_layers)
+	for(var/external_layer, actual_layer in bodypart_overlay.all_layers)
 		if(bodypart_overlay.layers & external_layer)
-			. += bodypart_overlay.get_overlay(external_layer, bodypart_owner, bodypart_owner?.is_husked)
+			. += bodypart_overlay.get_overlay(actual_layer, bodypart_owner)
 
 ///The horns of a lizard!
 /obj/item/organ/horns
@@ -119,8 +119,9 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	feature_key = FEATURE_HORNS
 	dyable = TRUE
 	draw_on_husks = HUSK_OVERLAY_NORMAL
+	offset_location = UPPER_BODY
 
-/datum/bodypart_overlay/mutant/horns/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/horns/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEHAIR)
 
 ///The frills of a lizard (like weird fin ears)
@@ -142,11 +143,12 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 /datum/bodypart_overlay/mutant/frills
 	layers = EXTERNAL_ADJACENT
 	feature_key = FEATURE_FRILLS
+	offset_location = UPPER_BODY
 
-/datum/bodypart_overlay/mutant/frills/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/frills/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEHAIR)
 
-/datum/bodypart_overlay/mutant/frills/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/mutant/frills/icon_render_key(obj/item/bodypart/limb)
 	. = ..()
 	if(LAZYLEN(limb?.owner?.hair_masks))
 		. += jointext(limb.owner.hair_masks, ",")
@@ -211,8 +213,9 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	layers = EXTERNAL_ADJACENT
 	feature_key = FEATURE_SNOUT
 	draw_on_husks = HUSK_OVERLAY_GRAYSCALE
+	offset_location = UPPER_BODY
 
-/datum/bodypart_overlay/mutant/snout/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/snout/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDESNOUT)
 
 ///A moth's antennae
@@ -280,6 +283,7 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	layers = EXTERNAL_FRONT | EXTERNAL_BEHIND
 	feature_key = FEATURE_MOTH_ANTENNAE
 	dyable = TRUE
+	offset_location = UPPER_BODY
 	///Accessory datum of the burn sprite
 	var/datum/sprite_accessory/burn_datum = /datum/sprite_accessory/moth_antennae/burnt_off
 	///Are we burned? If so we draw differently
@@ -293,7 +297,7 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 /datum/bodypart_overlay/mutant/antennae/get_base_icon_state()
 	return burnt ? burn_datum.icon_state : sprite_datum.icon_state
 
-/datum/bodypart_overlay/mutant/antennae/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/antennae/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEANTENNAE)
 
 ///The leafy hair of a podperson
@@ -318,6 +322,7 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	layers = EXTERNAL_FRONT|EXTERNAL_ADJACENT
 	feature_key = FEATURE_POD_HAIR
 	dyable = TRUE
+	offset_location = UPPER_BODY
 
 	///This layer will be colored differently than the rest of the organ. So we can get differently colored flowers or something
 	var/color_swapped_layer = EXTERNAL_FRONT
@@ -325,7 +330,7 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	var/color_inverse_base = 255
 
 /datum/bodypart_overlay/mutant/pod_hair/color_image(image/overlay, draw_layer, obj/item/bodypart/limb)
-	if(draw_layer != bitflag_to_layer(color_swapped_layer))
+	if(draw_layer != all_layers[color_swapped_layer])
 		return ..()
 
 	var/color_to_use = dye_color || draw_color
@@ -335,5 +340,5 @@ Unlike normal organs, we're actually inside a persons limbs at all times
 	else
 		overlay.color = null
 
-/datum/bodypart_overlay/mutant/pod_hair/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/pod_hair/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEHAIR)

code/modules/surgery/organs/external/spines.dm

@@ -32,8 +32,9 @@
 	feature_key = FEATURE_SPINES
 	dyable = TRUE
 	draw_on_husks = HUSK_OVERLAY_GRAYSCALE
+	offset_location = ENTIRE_BODY
 
-/datum/bodypart_overlay/mutant/spines/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/spines/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEJUMPSUIT)
 
 /datum/bodypart_overlay/mutant/spines/set_dye_color(new_color, obj/item/organ/tail/organ)

code/modules/surgery/organs/external/tails.dm

@@ -142,12 +142,13 @@
 /datum/bodypart_overlay/mutant/tail
 	layers = EXTERNAL_FRONT|EXTERNAL_BEHIND
 	dyable = TRUE
+	offset_location = ENTIRE_BODY
 	var/wagging = FALSE
 
 /datum/bodypart_overlay/mutant/tail/get_base_icon_state()
 	return "[wagging ? "wagging_" : ""][sprite_datum.icon_state]" //add the wagging tag if we be wagging
 
-/datum/bodypart_overlay/mutant/tail/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/tail/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEJUMPSUIT)
 
 /obj/item/organ/tail/cat
@@ -254,6 +255,7 @@
 	layers = EXTERNAL_ADJACENT|EXTERNAL_BEHIND
 	feature_key = FEATURE_TAILSPINES
 	draw_on_husks = HUSK_OVERLAY_GRAYSCALE
+	offset_location = ENTIRE_BODY
 	///Spines wag when the tail does
 	var/wagging = FALSE
 	/// Key for tail spine states, depends on the shape of the tail. Defined in the tail sprite datum.
@@ -262,7 +264,7 @@
 /datum/bodypart_overlay/mutant/tail_spines/get_base_icon_state()
 	return (!isnull(tail_spine_key) ? "[tail_spine_key]_" : "") + (wagging ? "wagging_" : "") + sprite_datum.icon_state // Select the wagging state if appropriate
 
-/datum/bodypart_overlay/mutant/tail_spines/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/tail_spines/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEJUMPSUIT)
 
 /datum/bodypart_overlay/mutant/tail_spines/set_dye_color(new_color, obj/item/organ/organ)

code/modules/surgery/organs/external/wings/functional_wings.dm

@@ -183,7 +183,7 @@
 	feature_key = initial(feature_key)
 	set_appearance_from_name(sprite_datum.name)
 
-/datum/bodypart_overlay/mutant/wings/functional/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/mutant/wings/functional/icon_render_key(obj/item/bodypart/limb)
 	. = ..()
 	. += wings_open ? "open" : "closed"
 

code/modules/surgery/organs/external/wings/wings.dm

@@ -22,10 +22,11 @@
 
 ///Bodypart overlay of default wings. Does not have any wing functionality
 /datum/bodypart_overlay/mutant/wings
-	layers = ALL_EXTERNAL_OVERLAYS
+	layers = EXTERNAL_FRONT | EXTERNAL_ADJACENT | EXTERNAL_BEHIND
 	feature_key = FEATURE_WINGS
+	offset_location = ENTIRE_BODY
 	/// Slot we check against
 	var/slot_blocker = HIDEJUMPSUIT
 
-/datum/bodypart_overlay/mutant/wings/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/wings/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & slot_blocker)

code/modules/surgery/organs/internal/cyberimp/augments_internal.dm

@@ -47,6 +47,7 @@
 /datum/bodypart_overlay/augment
 	layers = EXTERNAL_ADJACENT
 	draw_on_husks = HUSK_OVERLAY_NORMAL
+	offset_location = ENTIRE_BODY
 	/// Implant that owns this overlay
 	var/obj/item/organ/cyberimp/implant
 
@@ -58,12 +59,11 @@
 	implant = null
 	return ..()
 
-/datum/bodypart_overlay/augment/generate_icon_cache(obj/item/bodypart/limb)
+/datum/bodypart_overlay/augment/icon_render_key(obj/item/bodypart/limb)
 	. = ..()
 	. += implant.get_overlay_state()
 
 /datum/bodypart_overlay/augment/get_overlay(layer, obj/item/bodypart/limb)
-	layer = bitflag_to_layer(layer)
 	var/list/imageset = implant.get_overlay(layer, limb)
 	if(blocks_emissive == EMISSIVE_BLOCK_NONE || !limb)
 		return imageset

code/modules/surgery/organs/internal/ears/_ears.dm

@@ -162,11 +162,12 @@
 	color_source = ORGAN_COLOR_HAIR
 	feature_key = FEATURE_EARS
 	dyable = TRUE
+	offset_location = UPPER_BODY
 
 	/// Layer upon which we add the inner ears overlay
 	var/inner_layer = EXTERNAL_FRONT
 
-/datum/bodypart_overlay/mutant/cat_ears/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner, is_husked = FALSE)
+/datum/bodypart_overlay/mutant/cat_ears/can_draw_on_bodypart(obj/item/bodypart/bodypart_owner, mob/living/carbon/owner)
 	return ..() && !(bodypart_owner.owner?.obscured_slots & HIDEHAIR)
 
 /datum/bodypart_overlay/mutant/cat_ears/get_image(image_layer, obj/item/bodypart/limb)
@@ -174,7 +175,7 @@
 	base_ears.color = (dye_color || draw_color)
 
 	// Only add inner ears on the inner layer
-	if(image_layer != bitflag_to_layer(inner_layer))
+	if(image_layer != all_layers[inner_layer])
 		return base_ears
 
 	// Construct image of inner ears, apply to base ears as an overlay
@@ -237,7 +238,7 @@
 	var/inner_color = "#F0004A"
 
 /datum/bodypart_overlay/mutant/cat_ears/cybernetic/get_image(image_layer, obj/item/bodypart/limb)
-	if (image_layer != bitflag_to_layer(inner_layer))
+	if (image_layer != all_layers[inner_layer])
 		return ..()
 	var/mutable_appearance/ear_holder = ..()
 	var/mutable_appearance/inner = ear_holder.overlays[2]
@@ -245,7 +246,7 @@
 	return ear_holder
 
 /datum/bodypart_overlay/mutant/cat_ears/cybernetic/get_overlay(layer, obj/item/bodypart/limb)
-	if (layer != inner_layer)
+	if (layer != all_layers[inner_layer])
 		return ..()
 	var/list/all_images = ..()
 	var/mutable_appearance/ear_holder = all_images[1]