pref for seethrough limbs (#5805)

## About The Pull Request
adds a pref for making limbs partially-seethrough, i kept options for
head and body as disabled prefs because why not
## Why It's Good For The Game
some people want this aspect of customization, could be extra useful for
slimepeople too, or holographic aspects, since it can be partial invis,
does not prevent their hitboxes from working since it's alpha changes
though
## Proof Of Testing
<img width="107" height="92" alt="image"
src="https://github.com/user-attachments/assets/a481771d-a632-469a-946b-602b6b03b93b"
/>

<img width="98" height="99" alt="image"
src="https://github.com/user-attachments/assets/c58f7329-a366-461d-a815-7cb687691e11"
/>

<img width="1100" height="790" alt="qfpaTFo0Bh"
src="https://github.com/user-attachments/assets/710ccb2b-fae4-4a8b-951e-d2bae4f141f1"
/>


## Changelog
🆑
add: pref for limb transparency
/🆑

code/__DEFINES/bodyparts.dm

@@ -1,6 +1,9 @@
 ///The standard amount of bodyparts a carbon has. Currently 6, HEAD/L_ARM/R_ARM/CHEST/L_LEG/R_LEG
 #define BODYPARTS_DEFAULT_MAXIMUM 6
 
+// The lowest alpha a dropped limb's sprite will render at, unlike a attached limb which can be 0
+#define LIMB_DROPPED_MIN_ALPHA 40 /// BUBBER EDIT ADDITION
+
 /// Limb Health
 
 /// The max damage a limb can take before it stops taking damage.

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

@@ -543,6 +543,10 @@
 		. += draw_color
 	if(is_invisible)
 		. += "invisible"
+	// BUBBER EDIT ADDITION START - per-limb alpha
+	if(limb_alpha != 255)
+		. += "alpha_[limb_alpha]"
+	// BUBBER EDIT ADDITION END
 	for(var/datum/bodypart_overlay/overlay as anything in bodypart_overlays)
 		if(!overlay.can_draw_on_bodypart(src, owner, is_husked))
 			continue
@@ -571,6 +575,8 @@
 	. += body_zone
 	if(is_invisible)
 		. += "invisible"
+	if(limb_alpha != 255)
+		. += "alpha_[limb_alpha]" // BUBBER EDIT ADDITION - per-limb alpha
 	. += "[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))

code/modules/surgery/bodyparts/_bodyparts.dm

@@ -1216,6 +1216,14 @@
 	if(owner_species && owner_species.specific_alpha != 255)
 		alpha = owner_species.specific_alpha
 
+	// BUBBER EDIT ADDITION START - per-limb alpha.
+	// preference (stored in dna.features) overrides it for this specific zone if present over species alpha
+	limb_alpha = owner_species?.specific_alpha || 255
+	var/limb_alpha_key = "limb_alpha_[body_zone]"
+	if(limb_alpha_key in human_owner.dna.features)
+		limb_alpha = human_owner.dna.features[limb_alpha_key]
+	// BUBBER EDIT ADDITION END
+
 	if(body_zone in owner_species.body_markings)
 		markings = LAZYCOPY(owner_species.body_markings[body_zone])
 		if(aux_zone && (aux_zone in owner_species.body_markings))
@@ -1327,12 +1335,19 @@
 	var/image/limb = image(used_icon, used_state, -BODYPARTS_LAYER, dir = image_dir)
 	var/image/aux = null
 
+	// BUBBER EDIT ADDITION - per-limb alpha. While worn the chosen alpha is used verbatim (0 = invisible),
+	// while dropped it is floored so the limb stays visible and pickup-able on the ground.
+	var/used_alpha = dropped ? max(limb_alpha, LIMB_DROPPED_MIN_ALPHA) : limb_alpha
+	limb.alpha = used_alpha
+	// BUBBER EDIT ADDITION END
+
 	icon_exists_or_scream(limb.icon, limb.icon_state) //Prints a stack trace on the first failure of a given iconstate.
 
 	. += limb
 
 	if(aux_zone) //Hand shit
 		aux = image(limb.icon, "[limb_id]_[aux_zone]", -aux_layer, dir = image_dir)
+		aux.alpha = used_alpha // BUBBER EDIT ADDITION - per-limb alpha
 		. += aux
 
 	if(dropped && dmg_overlay_type)
@@ -1356,10 +1371,12 @@
 		update_draw_color()
 
 	if(draw_color)
-		var/limb_color = alpha != 255 ? "[draw_color][num2hex(alpha, 2)]" : "[draw_color]" // SKYRAT EDIT ADDITION - Alpha values on limbs. We check if the limb is attached and if the owner has an alpha value to append
-		limb.color = limb_color // SKYRAT EDIT CHANGE - ORIGINAL: limb.color = "[draw_color]"
+		// BUBBER EDIT CHANGE - per-limb transparency is now handled via limb.alpha (see above) rather than
+		// baking an alpha channel into the draw color. ORIGINAL SKYRAT: limb.color = "[draw_color][num2hex(alpha, 2)]"
+		limb.color = "[draw_color]"
 		if(aux_zone)
-			aux.color = limb_color // SKYRAT EDIT CHANGE - ORIGINAL: aux.color = "[draw_color]"
+			aux.color = "[draw_color]"
+		// BUBBER EDIT END
 
 	var/atom/location = loc || owner || src
 	if(blocks_emissive != EMISSIVE_BLOCK_NONE)

modular_skyrat/modules/bodyparts/code/_mutant_bodyparts.dm

@@ -5,6 +5,10 @@
 	var/list/aux_zone_markings
 	/// The alpha override of our markings.
 	var/markings_alpha
+	/// The alpha the limb's sprite overlays are rendered at. Driven by the per-limb alpha
+	/// preferences (and species specific_alpha). 0 is fully invisible while worn; while dropped
+	/// the rendered sprite is floored at LIMB_DROPPED_MIN_ALPHA so the limb stays pickup-able.
+	var/limb_alpha = 255
 	/// What is our normal limb ID? used for squashing legs.
 	var/base_limb_id = SPECIES_MAMMAL
 

modular_zubbers/code/modules/client/preferences/limb_alpha.dm

@@ -0,0 +1,72 @@
+/**
+ * Per-limb alpha (transparency) preferences.
+ */
+
+/// Toggle that reveals the per-limb (arm/leg) alpha sliders.
+/datum/preference/toggle/limb_alpha_per_limb
+	category = PREFERENCE_CATEGORY_SECONDARY_FEATURES
+	savefile_identifier = PREFERENCE_CHARACTER
+	savefile_key = "limb_alpha_per_limb"
+	default_value = FALSE
+	can_randomize = FALSE
+
+/datum/preference/toggle/limb_alpha_per_limb/apply_to_human(mob/living/carbon/human/target, value, datum/preferences/preferences)
+	return
+
+/datum/preference/numeric/limb_alpha
+	abstract_type = /datum/preference/numeric/limb_alpha
+	category = PREFERENCE_CATEGORY_SECONDARY_FEATURES
+	savefile_identifier = PREFERENCE_CHARACTER
+	minimum = 0
+	maximum = 255
+	can_randomize = FALSE
+	/// The BODY_ZONE_* this slider controls. Also forms the dna.features key.
+	var/limb_zone
+	/// If FALSE, the slider is hidden entirely. Kept around so head/chest can be re-enabled later.
+	var/enabled = TRUE
+
+/datum/preference/numeric/limb_alpha/create_default_value()
+	return maximum
+
+/datum/preference/numeric/limb_alpha/is_accessible(datum/preferences/preferences)
+	if(!enabled)
+		return FALSE
+	if(!..())
+		return FALSE
+	if(!preferences.read_preference(/datum/preference/toggle/limb_alpha_per_limb))
+		return FALSE
+	return TRUE
+
+/datum/preference/numeric/limb_alpha/apply_to_human(mob/living/carbon/human/target, value, datum/preferences/preferences)
+	if(!enabled)
+		value = maximum
+	else if(preferences && !preferences.read_preference(/datum/preference/toggle/limb_alpha_per_limb))
+		value = maximum
+	target.dna.features["limb_alpha_[limb_zone]"] = value
+	return TRUE
+
+// Head and chest are intentionally disabled for now (the sliders/keys are kept so they can be
+// re-enabled by simply flipping `enabled` back to TRUE).
+/datum/preference/numeric/limb_alpha/head
+	savefile_key = "limb_alpha_head"
+	limb_zone = BODY_ZONE_HEAD
+
+/datum/preference/numeric/limb_alpha/chest
+	savefile_key = "limb_alpha_chest"
+	limb_zone = BODY_ZONE_CHEST
+
+/datum/preference/numeric/limb_alpha/l_arm
+	savefile_key = "limb_alpha_l_arm"
+	limb_zone = BODY_ZONE_L_ARM
+
+/datum/preference/numeric/limb_alpha/r_arm
+	savefile_key = "limb_alpha_r_arm"
+	limb_zone = BODY_ZONE_R_ARM
+
+/datum/preference/numeric/limb_alpha/l_leg
+	savefile_key = "limb_alpha_l_leg"
+	limb_zone = BODY_ZONE_L_LEG
+
+/datum/preference/numeric/limb_alpha/r_leg
+	savefile_key = "limb_alpha_r_leg"
+	limb_zone = BODY_ZONE_R_LEG

tgstation.dme

@@ -9563,6 +9563,7 @@
 #include "modular_zubbers\code\modules\client\flavor_text\flavor_text.dm"
 #include "modular_zubbers\code\modules\client\preferences\blooper.dm"
 #include "modular_zubbers\code\modules\client\preferences\footstep_sound.dm"
+#include "modular_zubbers\code\modules\client\preferences\limb_alpha.dm"
 #include "modular_zubbers\code\modules\client\preferences\permanent_limp.dm"
 #include "modular_zubbers\code\modules\client\preferences\player_panel.dm"
 #include "modular_zubbers\code\modules\client\preferences\screen.dm"

tgui/packages/tgui/interfaces/PreferencesMenu/preferences/features/character_preferences/bubbers/limb_alpha.tsx

@@ -0,0 +1,53 @@
+import {
+  CheckboxInput,
+  type Feature,
+  FeatureSliderInput,
+  type FeatureToggle,
+} from '../../base';
+
+// Names share the "Limb Transparency" prefix so the panel (which sorts secondary features
+// alphabetically by name) keeps them grouped together, toggle first.
+export const limb_alpha_per_limb: FeatureToggle = {
+  name: 'Limb Transparency',
+  description:
+    'Reveals the per-limb transparency sliders for your arms and legs. While off, those limbs stay fully opaque.',
+  component: CheckboxInput,
+};
+
+export const limb_alpha_head: Feature<number> = {
+  name: 'Limb Transparency: Head',
+  description:
+    'How opaque your head is. 0 is fully invisible while worn; dropped limbs stay faintly visible so they can be picked up.',
+  component: FeatureSliderInput,
+};
+
+export const limb_alpha_chest: Feature<number> = {
+  name: 'Limb Transparency: Chest',
+  description:
+    'How opaque your chest is. 0 is fully invisible while worn; dropped limbs stay faintly visible so they can be picked up.',
+  component: FeatureSliderInput,
+};
+
+export const limb_alpha_l_arm: Feature<number> = {
+  name: 'Limb Transparency: Left Arm',
+  description: 'How opaque your left arm is.',
+  component: FeatureSliderInput,
+};
+
+export const limb_alpha_r_arm: Feature<number> = {
+  name: 'Limb Transparency: Right Arm',
+  description: 'How opaque your right arm is.',
+  component: FeatureSliderInput,
+};
+
+export const limb_alpha_l_leg: Feature<number> = {
+  name: 'Limb Transparency: Left Leg',
+  description: 'How opaque your left leg is.',
+  component: FeatureSliderInput,
+};
+
+export const limb_alpha_r_leg: Feature<number> = {
+  name: 'Limb Transparency: Right Leg',
+  description: 'How opaque your right leg is.',
+  component: FeatureSliderInput,
+};