MODLink System (+ NWTLMM) (#77639)

## About The Pull Request
A pact made with `@Kapu1178`
Small changes you should not care about:
RD MODsuit outfit (admin only) no longer has a beret that blocks the
activation of the suit
The beret used by death squad officers no longer is blocked from being
put on a hat stabilizer module
Admins can now Shear matrices of objects in Modify Transform
Multitool buffers have been a little refactored to use a setter proc
that saves them from causing hard dels
Cooler stuff:
A revival and remake of [Nobody Wants To Learn Matrix
Math](https://github.com/tgstation/tgstation/pull/59103), this time with
additional tooling for quick matrix calculations.

![image](https://github.com/tgstation/tgstation/assets/23585223/eb387738-0839-463a-aed8-4703d139b11a)
The MODLink system, available through every MODsuit and MODLink scryers
(a neck item obtainable from advanced modsuit research or
charliestation)
Let's you make a holographic call with any other MODLink user, where you
can chat in realtime and see what's up with em

![image](https://github.com/tgstation/tgstation/assets/23585223/5a822f9f-e823-497e-b766-40055f2fc0d6)
![image](https://github.com/tgstation/tgstation/assets/23585223/062983ee-6058-4e78-a3aa-bccda1a3e224)


## Why It's Good For The Game
Adds a fun way for the crew to communicate with each other that can be
done in real-time with relative privacy compared to radio.

## Changelog
🆑 Fikou, Armhulen, Sheets (+rep for Mothblocks and Potato)
fix: RD MODsuit outfit (admin only) no longer has a beret that blocks
the activation of the suit
fix: The beret used by death squad officers no longer is blocked from
being put on a hat stabilizer module
admin: Admins can now Shear matrices of objects in Modify Transform
admin: Admins now have access to Test Matrices in the VV dropdown, an
all-in-one tool for editing transforms.
add: MODLink system, available through scryers (from RnD and Charlie
Station) and through MODsuits. Lets you call people with holographs!
/🆑

_maps/RandomRuins/SpaceRuins/oldstation.dmm

@@ -157,6 +157,7 @@
 /obj/effect/decal/cleanable/dirt,
 /obj/structure/table,
 /obj/effect/decal/cleanable/dirt,
+/obj/item/clothing/neck/link_scryer/loaded/charlie,
 /turf/open/floor/iron,
 /area/ruin/space/ancientstation/charlie/bridge)
 "aS" = (
@@ -2468,6 +2469,7 @@
 /obj/machinery/light/small/directional/west,
 /obj/effect/decal/cleanable/dirt,
 /obj/effect/spawner/random/decoration/glowstick,
+/obj/item/clothing/neck/link_scryer/loaded/charlie,
 /turf/open/floor/iron,
 /area/ruin/space/ancientstation/charlie/dorms)
 "kO" = (
@@ -6712,6 +6714,7 @@
 /obj/effect/decal/cleanable/dirt,
 /obj/effect/spawner/random/decoration/glowstick,
 /obj/structure/mirror/directional/west,
+/obj/item/clothing/neck/link_scryer/loaded/charlie,
 /turf/open/floor/iron,
 /area/ruin/space/ancientstation/charlie/dorms)
 "Mu" = (

_maps/map_files/Birdshot/birdshot.dmm

@@ -25025,19 +25025,8 @@
 /turf/open/floor/iron/textured_half,
 /area/station/hallway/primary/aft)
 "jif" = (
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = 4
-	},
-/obj/item/mod/core/standard{
-	pixel_y = 4
-	},
-/obj/structure/closet/crate/science{
-	name = "MOD core crate"
-	},
 /obj/effect/turf_decal/tile/neutral/fourcorners,
+/obj/structure/closet/crate/mod,
 /turf/open/floor/iron/white,
 /area/station/science/robotics/augments)
 "jig" = (

_maps/map_files/Deltastation/DeltaStation2.dmm

@@ -87774,18 +87774,6 @@
 /turf/open/floor/iron/dark,
 /area/station/ai_monitored/turret_protected/ai_upload)
 "vWV" = (
-/obj/structure/closet/crate/science{
-	anchored = 1
-	},
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = 4
-	},
-/obj/item/mod/core/standard{
-	pixel_y = 4
-	},
 /obj/effect/turf_decal/bot,
 /obj/machinery/requests_console/directional/north{
 	department = "Robotics";
@@ -87794,6 +87782,7 @@
 /obj/effect/mapping_helpers/requests_console/ore_update,
 /obj/effect/mapping_helpers/requests_console/supplies,
 /obj/machinery/light/cold/directional/north,
+/obj/structure/closet/crate/mod,
 /turf/open/floor/iron,
 /area/station/science/robotics/lab)
 "vXh" = (

_maps/map_files/IceBoxStation/IceBoxStation.dmm

@@ -33855,19 +33855,10 @@
 /turf/open/floor/iron,
 /area/station/hallway/primary/aft)
 "kKI" = (
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = 4
-	},
-/obj/item/mod/core/standard{
-	pixel_y = 4
-	},
-/obj/structure/table,
 /obj/effect/turf_decal/tile/red/half/contrasted{
 	dir = 1
 	},
+/obj/structure/closet/crate/mod,
 /turf/open/floor/iron/white,
 /area/station/science/robotics/lab)
 "kKL" = (

_maps/map_files/MetaStation/MetaStation.dmm

@@ -8368,18 +8368,7 @@
 	name = "Robotics Privacy Control";
 	req_access = list("robotics")
 	},
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = 4
-	},
-/obj/item/mod/core/standard{
-	pixel_y = 4
-	},
-/obj/structure/closet/crate/science{
-	name = "MOD core crate"
-	},
+/obj/structure/closet/crate/mod,
 /obj/structure/disposalpipe/segment{
 	dir = 4
 	},

_maps/map_files/NorthStar/north_star.dmm

@@ -66820,16 +66820,7 @@
 /turf/open/floor/pod/light,
 /area/station/maintenance/floor2/port/fore)
 "rwV" = (
-/obj/structure/rack,
-/obj/item/mod/core/standard{
-	pixel_x = 4;
-	pixel_y = -4
-	},
-/obj/item/mod/core/standard,
-/obj/item/mod/core/standard{
-	pixel_x = -4;
-	pixel_y = 4
-	},
+/obj/structure/closet/crate/mod,
 /turf/open/floor/iron/dark/smooth_large,
 /area/station/science/robotics/lab)
 "rwY" = (

_maps/map_files/tramstation/tramstation.dmm

@@ -26202,24 +26202,13 @@
 /turf/open/floor/catwalk_floor,
 /area/station/maintenance/port/central)
 "ixu" = (
-/obj/structure/closet/crate/science{
-	name = "MOD core crate"
-	},
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
-/obj/item/mod/core/standard{
-	pixel_x = -4
-	},
 /obj/structure/noticeboard/directional/north,
 /obj/machinery/camera/directional/north{
 	c_tag = "Science - Robotics";
 	network = list("ss13","rd")
 	},
 /obj/effect/turf_decal/tile/neutral/fourcorners,
+/obj/structure/closet/crate/mod,
 /turf/open/floor/iron/dark,
 /area/station/science/robotics/lab)
 "ixC" = (

code/__DEFINES/dcs/signals/signals_mob/signals_mob_carbon.dm

@@ -108,6 +108,10 @@
 	#define COMSIG_CARBON_BLOCK_EAT (1 << 0)
 ///Called when a carbon vomits : (distance, force)
 #define COMSIG_CARBON_VOMITED "carbon_vomited"
+///Called from apply_overlay(cache_index, overlay)
+#define COMSIG_CARBON_APPLY_OVERLAY "carbon_apply_overlay"
+///Called from remove_overlay(cache_index, overlay)
+#define COMSIG_CARBON_REMOVE_OVERLAY "carbon_remove_overlay"
 
 // /mob/living/carbon/human signals
 

code/__DEFINES/mod.dm

@@ -43,5 +43,13 @@
 #define MOD_ICON_OVERRIDE "mod_icon_override"
 #define MOD_WORN_ICON_OVERRIDE "mod_worn_icon_override"
 
+//Defines for MODlink frequencies
+#define MODLINK_FREQ_NANOTRASEN "NT"
+#define MODLINK_FREQ_SYNDICATE "SYND"
+#define MODLINK_FREQ_CHARLIE "CHRL"
+#define MODLINK_FREQ_CENTCOM "CC"
+
 /// Global list of all /datum/mod_theme
 GLOBAL_LIST_INIT(mod_themes, setup_mod_themes())
+/// Global list of all ids associated to a /datum/mod_link instance
+GLOBAL_LIST_EMPTY(mod_link_ids)

code/__DEFINES/traits.dm

@@ -573,6 +573,9 @@ Remember to update _globalvars/traits.dm if you're adding/removing/renaming trai
 /// Mobs with this trait do care about a few grisly things, such as digging up graves. They also really do not like bringing people back to life or tending wounds, but love autopsies and amputations.
 #define TRAIT_MORBID "morbid"
 
+/// Whether or not the user is in a MODlink call, prevents making more calls
+#define TRAIT_IN_CALL "in_call"
+
 // METABOLISMS
 // Various jobs on the station have historically had better reactions
 // to various drinks and foodstuffs. Security liking donuts is a classic
@@ -760,7 +763,7 @@ Remember to update _globalvars/traits.dm if you're adding/removing/renaming trai
 #define TRAIT_CUSTOM_TAP_SOUND "no_tap_sound"
 /// Makes the feedback message when someone else is putting this item on you more noticeable
 #define TRAIT_DANGEROUS_OBJECT "dangerous_object"
-// determines whether or not objects are haunted and teleport/attack randomly
+/// determines whether or not objects are haunted and teleport/attack randomly
 #define TRAIT_HAUNTED "haunted"
 
 //quirk traits

code/__DEFINES/vv.dm

@@ -98,6 +98,7 @@
 #define VV_HK_EDIT_FILTERS "edit_filters"
 #define VV_HK_EDIT_PARTICLES "edit_particles"
 #define VV_HK_EDIT_COLOR_MATRIX "edit_color_matrix"
+#define VV_HK_TEST_MATRIXES "test_matrixes"
 #define VV_HK_ADD_AI "add_ai"
 #define VV_HK_ARMOR_MOD "mod_obj_armor"
 

code/datums/actions/items/toggles.dm

@@ -101,3 +101,7 @@
 
 /datum/action/item_action/flip
 	name = "Flip"
+
+/datum/action/item_action/call_link
+	name = "Call MODlink"
+

code/datums/chatmessage.dm

@@ -193,7 +193,7 @@
 /datum/chatmessage/proc/finish_image_generation(mheight, atom/target, mob/owner, complete_text, lifespan)
 	var/rough_time = REALTIMEOFDAY
 	approx_lines = max(1, mheight / CHAT_MESSAGE_APPROX_LHEIGHT)
-
+	var/starting_height = target.maptext_height
 	// Translate any existing messages upwards, apply exponential decay factors to timers
 	message_loc = isturf(target) ? target : get_atom_on_turf(target)
 	if (owned_by.seen_messages)
@@ -208,7 +208,12 @@
 			// When choosing to update the remaining time we have to be careful not to update the
 			// scheduled time once the EOL has been executed.
 			if (time_spent >= time_before_fade)
-				animate(m.message, pixel_y = m.message.pixel_y + mheight, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
+				if(m.message.pixel_y < starting_height)
+					var/max_height = m.message.pixel_y + m.approx_lines * CHAT_MESSAGE_APPROX_LHEIGHT - starting_height
+					if(max_height > 0)
+						animate(m.message, pixel_y = m.message.pixel_y + max_height, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
+				else if(mheight + starting_height >= m.message.pixel_y)
+					animate(m.message, pixel_y = m.message.pixel_y + mheight, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
 				continue
 
 			var/remaining_time = time_before_fade * (CHAT_MESSAGE_EXP_DECAY ** idx++) * (CHAT_MESSAGE_HEIGHT_DECAY ** combined_height)
@@ -225,7 +230,12 @@
 				animate(alpha = 0, time = CHAT_MESSAGE_EOL_FADE)
 			// We run this after the alpha animate, because we don't want to interrup it, but also don't want to block it by running first
 			// Sooo instead we do this. bit messy but it fuckin works
-			animate(m.message, pixel_y = m.message.pixel_y + mheight, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
+			if(m.message.pixel_y < starting_height)
+				var/max_height = m.message.pixel_y + m.approx_lines * CHAT_MESSAGE_APPROX_LHEIGHT - starting_height
+				if(max_height > 0)
+					animate(m.message, pixel_y = m.message.pixel_y + max_height, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
+			else if(mheight + starting_height >= m.message.pixel_y)
+				animate(m.message, pixel_y = m.message.pixel_y + mheight, time = CHAT_MESSAGE_SPAWN_TIME, flags = ANIMATION_PARALLEL)
 
 	// Reset z index if relevant
 	if (current_z_idx >= CHAT_LAYER_MAX_Z)
@@ -236,7 +246,7 @@
 	SET_PLANE_EXPLICIT(message, RUNECHAT_PLANE, message_loc)
 	message.appearance_flags = APPEARANCE_UI_IGNORE_ALPHA | KEEP_APART
 	message.alpha = 0
-	message.pixel_y = target.maptext_height
+	message.pixel_y = starting_height
 	message.pixel_x = -target.base_pixel_x
 	message.maptext_width = CHAT_MESSAGE_WIDTH
 	message.maptext_height = mheight * 1.25 // We add extra because some characters are superscript, like actions

code/game/atoms.dm

@@ -1271,6 +1271,7 @@
 	VV_DROPDOWN_OPTION(VV_HK_TRIGGER_EXPLOSION, "Explosion")
 	VV_DROPDOWN_OPTION(VV_HK_EDIT_FILTERS, "Edit Filters")
 	VV_DROPDOWN_OPTION(VV_HK_EDIT_COLOR_MATRIX, "Edit Color as Matrix")
+	VV_DROPDOWN_OPTION(VV_HK_TEST_MATRIXES, "Test Matrices")
 	VV_DROPDOWN_OPTION(VV_HK_ADD_AI, "Add AI controller")
 	VV_DROPDOWN_OPTION(VV_HK_ARMOR_MOD, "Modify Armor")
 	if(greyscale_colors)
@@ -1354,7 +1355,7 @@
 		ai_controller = new result(src)
 
 	if(href_list[VV_HK_MODIFY_TRANSFORM] && check_rights(R_VAREDIT))
-		var/result = input(usr, "Choose the transformation to apply","Transform Mod") as null|anything in list("Scale","Translate","Rotate")
+		var/result = input(usr, "Choose the transformation to apply","Transform Mod") as null|anything in list("Scale","Translate","Rotate","Shear")
 		var/matrix/M = transform
 		if(!result)
 			return
@@ -1371,6 +1372,12 @@
 				if(isnull(x) || isnull(y))
 					return
 				transform = M.Translate(x,y)
+			if("Shear")
+				var/x = input(usr, "Choose x mod","Transform Mod") as null|num
+				var/y = input(usr, "Choose y mod","Transform Mod") as null|num
+				if(isnull(x) || isnull(y))
+					return
+				transform = M.Shear(x,y)
 			if("Rotate")
 				var/angle = input(usr, "Choose angle to rotate","Transform Mod") as null|num
 				if(isnull(angle))
@@ -1413,12 +1420,13 @@
 			vv_auto_rename(newname)
 
 	if(href_list[VV_HK_EDIT_FILTERS] && check_rights(R_VAREDIT))
-		var/client/C = usr.client
-		C?.open_filter_editor(src)
+		usr.client?.open_filter_editor(src)
 
 	if(href_list[VV_HK_EDIT_COLOR_MATRIX] && check_rights(R_VAREDIT))
-		var/client/C = usr.client
-		C?.open_color_matrix_editor(src)
+		usr.client?.open_color_matrix_editor(src)
+
+	if(href_list[VV_HK_TEST_MATRIXES] && check_rights(R_VAREDIT))
+		usr.client?.open_matrix_tester(src)
 
 /atom/vv_get_header()
 	. = ..()
@@ -1605,7 +1613,7 @@
 /atom/proc/multitool_act_secondary(mob/living/user, obj/item/tool)
 	return
 
-///Check if the multitool has an item in it's data buffer
+///Check if an item supports a data buffer (is a multitool)
 /atom/proc/multitool_check_buffer(user, obj/item/multitool, silent = FALSE)
 	if(!istype(multitool, /obj/item/multitool))
 		if(user && !silent)
@@ -2098,16 +2106,18 @@
 	// Now we're gonna do a scanline effect
 	// Gonna take this atom and give it a render target, then use it as a source for a filter
 	// (We use an atom because it seems as if setting render_target on an MA is just invalid. I hate this engine)
-	var/static/atom/movable/scanline
-	if(!scanline)
-		scanline = new(null)
-		scanline.icon = 'icons/effects/effects.dmi'
-		scanline.icon_state = "scanline"
-		// * so it doesn't render
-		scanline.render_target = "*HoloScanline"
+	var/atom/movable/scanline = new(null)
+	scanline.icon = 'icons/effects/effects.dmi'
+	scanline.icon_state = "scanline"
+	scanline.appearance_flags |= RESET_TRANSFORM
+	// * so it doesn't render
+	var/static/uid_scan = 0
+	scanline.render_target = "*HoloScanline [uid_scan]"
+	uid_scan++
 	// Now we add it as a filter, and overlay the appearance so the render source is always around
 	add_filter("HOLO: Scanline", 2, alpha_mask_filter(render_source = scanline.render_target))
 	add_overlay(scanline)
+	qdel(scanline)
 	// Annd let's make the sucker emissive, so it glows in the dark
 	if(!render_target)
 		var/static/uid = 0

code/game/machinery/botlaunchpad.dm

@@ -26,7 +26,7 @@
 	if(!multitool_check_buffer(user, tool))
 		return
 	var/obj/item/multitool/multitool = tool
-	multitool.buffer = src
+	multitool.set_buffer(src)
 	to_chat(user, span_notice("You save the data in the [multitool.name]'s buffer."))
 	return TOOL_ACT_TOOLTYPE_SUCCESS
 

code/game/machinery/computer/atmos_computers/_air_sensor.dm

@@ -91,7 +91,7 @@
 	if(istype(multi_tool.buffer, /obj/machinery/atmospherics/components/unary/outlet_injector))
 		var/obj/machinery/atmospherics/components/unary/outlet_injector/input = multi_tool.buffer
 		inlet_id = input.id_tag
-		multi_tool.buffer = null
+		multi_tool.set_buffer(null)
 		balloon_alert(user, "connected to input")
 
 	else if(istype(multi_tool.buffer, /obj/machinery/atmospherics/components/unary/vent_pump))
@@ -105,11 +105,11 @@
 		output.external_pressure_bound = 0
 		//finally assign it to this sensor
 		outlet_id = output.id_tag
-		multi_tool.buffer = null
+		multi_tool.set_buffer(null)
 		balloon_alert(user, "connected to output")
 
 	else
-		multi_tool.buffer = src
+		multi_tool.set_buffer(src)
 		balloon_alert(user, "added to multitool buffer")
 
 	return TRUE

code/game/machinery/computer/launchpad_control.dm

@@ -66,7 +66,7 @@
 		if(M.buffer && istype(M.buffer, /obj/machinery/launchpad))
 			if(LAZYLEN(launchpads) < maximum_pads)
 				launchpads |= M.buffer
-				M.buffer = null
+				M.set_buffer(null)
 				to_chat(user, span_notice("You upload the data from the [W.name]'s buffer."))
 			else
 				to_chat(user, span_warning("[src] cannot handle any more connections!"))

code/game/machinery/computer/mechlaunchpad.dm

@@ -100,11 +100,11 @@
 			if(buffered_pad in mechpads)
 				remove_pad(buffered_pad)
 			connect_launchpad(buffered_pad)
-			multitool.buffer = null
+			multitool.set_buffer(null)
 			to_chat(user, span_notice("You connect the console to the pad with data from the [multitool.name]'s buffer."))
 		else
 			add_pad(buffered_pad)
-			multitool.buffer = null
+			multitool.set_buffer(null)
 			to_chat(user, span_notice("You upload the data from the [multitool.name]'s buffer."))
 	return TRUE
 

code/game/machinery/launch_pad.dm

@@ -77,7 +77,7 @@
 				if(!multitool_check_buffer(user, I))
 					return
 				var/obj/item/multitool/M = I
-				M.buffer = src
+				M.set_buffer(src)
 				to_chat(user, span_notice("You save the data in the [I.name]'s buffer."))
 				return 1
 

code/game/machinery/mechlaunchpad.dm

@@ -36,7 +36,7 @@
 	if(!multitool_check_buffer(user, tool))
 		return
 	var/obj/item/multitool/multitool = tool
-	multitool.buffer = src
+	multitool.set_buffer(src)
 	to_chat(user, span_notice("You save the data in the [multitool.name]'s buffer."))
 	return TRUE
 

code/game/machinery/porta_turret/portable_turret.dm

@@ -350,7 +350,7 @@ DEFINE_BITFIELD(turret_flags, list(
 		if(!multitool_check_buffer(user, I))
 			return
 		var/obj/item/multitool/M = I
-		M.buffer = src
+		M.set_buffer(src)
 		to_chat(user, span_notice("You add [src] to multitool buffer."))
 	else
 		return ..()

code/game/machinery/porta_turret/portable_turret_cover.dm

@@ -65,7 +65,7 @@
 		if(!multitool_check_buffer(user, I))
 			return
 		var/obj/item/multitool/M = I
-		M.buffer = parent_turret
+		M.set_buffer(parent_turret)
 		to_chat(user, span_notice("You add [parent_turret] to multitool buffer."))
 		return
 	return ..()

code/game/machinery/quantum_pad.dm

@@ -62,7 +62,7 @@
 			if(!multitool_check_buffer(user, I))
 				return
 			var/obj/item/multitool/M = I
-			M.buffer = src
+			M.set_buffer(src)
 			to_chat(user, span_notice("You save the data in [I]'s buffer. It can now be saved to pads with closed panels."))
 			return TRUE
 	else if(I.tool_behaviour == TOOL_MULTITOOL)

code/game/machinery/telecomms/machine_interactions.dm

@@ -153,10 +153,10 @@
 				var/obj/machinery/telecomms/T = heldmultitool.buffer
 				. = add_new_link(T, operator)
 		if("buffer")
-			heldmultitool.buffer = src
+			heldmultitool.set_buffer(src)
 			. = TRUE
 		if("flush")
-			heldmultitool.buffer = null
+			heldmultitool.set_buffer(null)
 			. = TRUE
 
 	add_act(action, params)

code/game/machinery/teleporter.dm

@@ -165,13 +165,13 @@
 			return
 		var/obj/item/multitool/M = W
 		if(panel_open)
-			M.buffer = src
+			M.set_buffer(src)
 			to_chat(user, span_notice("You download the data to the [W.name]'s buffer."))
 		else
 			if(M.buffer && istype(M.buffer, /obj/machinery/teleport/station) && M.buffer != src)
 				if(linked_stations.len < efficiency)
 					linked_stations.Add(M.buffer)
-					M.buffer = null
+					M.set_buffer(null)
 					to_chat(user, span_notice("You upload the data from the [W.name]'s buffer."))
 				else
 					to_chat(user, span_alert("This station can't hold more information, try to use better parts."))

code/game/objects/items/botpad_remote.dm

@@ -40,7 +40,7 @@
 			connected_botpad = buffered_remote
 			connected_botpad.connected_remote = src
 			connected_botpad.id = id
-			multitool.buffer = null
+			multitool.set_buffer(null)
 			to_chat(user, span_notice("You connect the controller to the pad with data from the [multitool.name]'s buffer."))
 		else
 			to_chat(user, span_warning("Unable to upload!"))

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

@@ -30,7 +30,7 @@
 	custom_premium_price = PAYCHECK_COMMAND * 3
 	toolspeed = 1
 	usesound = 'sound/weapons/empty.ogg'
-	var/obj/machinery/buffer // simple machine buffer for device linkage
+	var/datum/buffer // simple machine buffer for device linkage
 	var/mode = 0
 
 /obj/item/multitool/examine(mob/user)
@@ -41,6 +41,17 @@
 	user.visible_message(span_suicide("[user] puts the [src] to [user.p_their()] chest. It looks like [user.p_theyre()] trying to pulse [user.p_their()] heart off!"))
 	return OXYLOSS//theres a reason it wasn't recommended by doctors
 
+/obj/item/multitool/proc/set_buffer(datum/buffer)
+	if(buffer)
+		UnregisterSignal(buffer, COMSIG_QDELETING)
+	if(QDELETED(buffer))
+		return
+	src.buffer = buffer
+	RegisterSignal(buffer, COMSIG_QDELETING, PROC_REF(on_buffer_del))
+
+/obj/item/multitool/proc/on_buffer_del(datum/source)
+	SIGNAL_HANDLER
+	buffer = null
 
 // Syndicate device disguised as a multitool; it will turn red when an AI camera is nearby.
 

code/game/objects/structures/crates_lockers/crates.dm

@@ -298,6 +298,18 @@
 	icon_state = "scicrate"
 	base_icon_state = "scicrate"
 
+/obj/structure/closet/crate/mod
+	name = "MOD crate"
+	icon_state = "scicrate"
+	base_icon_state = "scicrate"
+
+/obj/structure/closet/crate/mod/PopulateContents()
+	..()
+	for(var/i in 1 to 3)
+		new /obj/item/mod/core/standard(src)
+	for(var/i in 1 to 2)
+		new /obj/item/clothing/neck/link_scryer(src)
+
 /obj/structure/closet/crate/solarpanel_small
 	name = "budget solar panel crate"
 	icon_state = "engi_e_crate"

code/modules/admin/view_variables/nobody_wants_to_learn_matrix_math.dm

@@ -0,0 +1,80 @@
+
+/**
+ * ## nobody wants to learn matrix math!
+ *
+ * More than just a completely true statement, this datum is created as a tgui interface
+ * allowing you to modify each vector until you know what you're doing.
+ * Much like filteriffic, 'nobody wants to learn matrix math' is meant for developers like you and I
+ * to implement interesting matrix transformations without the hassle if needing to know... algebra? Damn, i'm stupid.
+ */
+/datum/nobody_wants_to_learn_matrix_math
+	var/atom/target
+	var/matrix/testing_matrix
+
+/datum/nobody_wants_to_learn_matrix_math/New(atom/target)
+	src.target = target
+	testing_matrix = matrix(target.transform)
+
+/datum/nobody_wants_to_learn_matrix_math/Destroy(force, ...)
+	QDEL_NULL(testing_matrix)
+	return ..()
+
+/datum/nobody_wants_to_learn_matrix_math/ui_state(mob/user)
+	return GLOB.admin_state
+
+/datum/nobody_wants_to_learn_matrix_math/ui_close(mob/user)
+	qdel(src)
+
+/datum/nobody_wants_to_learn_matrix_math/ui_interact(mob/user, datum/tgui/ui)
+	ui = SStgui.try_update_ui(user, src, ui)
+	if(!ui)
+		ui = new(user, src, "MatrixMathTester")
+		ui.open()
+
+/datum/nobody_wants_to_learn_matrix_math/ui_data()
+	var/list/data = list()
+	data["matrix_a"] = testing_matrix.a
+	data["matrix_b"] = testing_matrix.b
+	data["matrix_c"] = testing_matrix.c
+	data["matrix_d"] = testing_matrix.d
+	data["matrix_e"] = testing_matrix.e
+	data["matrix_f"] = testing_matrix.f
+	data["pixelated"] = target.appearance_flags & PIXEL_SCALE
+	return data
+
+/datum/nobody_wants_to_learn_matrix_math/ui_act(action, list/params)
+	. = ..()
+	if(.)
+		return
+
+	switch(action)
+		if("change_var")
+			var/matrix_var_name = params["var_name"]
+			var/matrix_var_value = params["var_value"]
+			if(testing_matrix.vv_edit_var(matrix_var_name, matrix_var_value) == FALSE)
+				to_chat(src, "Your edit was rejected by the object. This is a bug with the matrix tester, not your fault, so report it on github.", confidential = TRUE)
+				return
+			set_transform()
+		if("scale")
+			testing_matrix.Scale(params["x"], params["y"])
+			set_transform()
+		if("translate")
+			testing_matrix.Translate(params["x"], params["y"])
+			set_transform()
+		if("shear")
+			testing_matrix.Shear(params["x"], params["y"])
+			set_transform()
+		if("turn")
+			testing_matrix.Turn(params["angle"])
+			set_transform()
+		if("toggle_pixel")
+			target.appearance_flags ^= PIXEL_SCALE
+
+/datum/nobody_wants_to_learn_matrix_math/proc/set_transform()
+	animate(target, transform = testing_matrix, time = 0.5 SECONDS)
+	testing_matrix = matrix(target.transform)
+
+/client/proc/open_matrix_tester(atom/in_atom)
+	if(holder)
+		var/datum/nobody_wants_to_learn_matrix_math/matrix_tester = new(in_atom)
+		matrix_tester.ui_interact(mob)

code/modules/antagonists/pirate/pirate_shuttle_equipment.dm

@@ -183,7 +183,7 @@
 	. = ..()
 	if (istype(I))
 		to_chat(user, span_notice("You register [src] in [I]s buffer."))
-		I.buffer = src
+		I.set_buffer(src)
 		return TRUE
 
 /obj/machinery/piratepad/screwdriver_act_secondary(mob/living/user, obj/item/screwdriver/screw)

code/modules/atmospherics/machinery/components/unary_devices/bluespace_sender.dm

@@ -122,7 +122,7 @@ GLOBAL_LIST_EMPTY_TYPED(bluespace_senders, /obj/machinery/atmospherics/component
 
 /obj/machinery/atmospherics/components/unary/bluespace_sender/multitool_act(mob/living/user, obj/item/item)
 	var/obj/item/multitool/multitool = item
-	multitool.buffer = src
+	multitool.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [item]'s buffer."))
 	return TRUE
 

code/modules/atmospherics/machinery/components/unary_devices/outlet_injector.dm

@@ -48,12 +48,12 @@
 	if(istype(multi_tool.buffer, /obj/machinery/air_sensor))
 		var/obj/machinery/air_sensor/sensor = multi_tool.buffer
 		sensor.inlet_id = id_tag
-		multi_tool.buffer = null
+		multi_tool.set_buffer(null)
 		balloon_alert(user, "input linked to sensor")
 		return TOOL_ACT_TOOLTYPE_SUCCESS
 
 	balloon_alert(user, "saved in buffer")
-	multi_tool.buffer = src
+	multi_tool.set_buffer(src)
 	return TOOL_ACT_TOOLTYPE_SUCCESS
 
 /obj/machinery/atmospherics/components/unary/outlet_injector/CtrlClick(mob/user)

code/modules/atmospherics/machinery/components/unary_devices/vent_pump.dm

@@ -58,12 +58,12 @@
 	if(istype(multi_tool.buffer, /obj/machinery/air_sensor))
 		var/obj/machinery/air_sensor/sensor = multi_tool.buffer
 		sensor.outlet_id = id_tag
-		multi_tool.buffer = null
+		multi_tool.set_buffer(null)
 		balloon_alert(user, "output linked to sensor")
 		return TOOL_ACT_TOOLTYPE_SUCCESS
 
 	balloon_alert(user, "saved in buffer")
-	multi_tool.buffer = src
+	multi_tool.set_buffer(src)
 	return TOOL_ACT_TOOLTYPE_SUCCESS
 
 /obj/machinery/atmospherics/components/unary/vent_pump/Destroy()

code/modules/clothing/spacesuits/specialops.dm

@@ -6,7 +6,7 @@
 	icon_state = "beret_badge"
 	inhand_icon_state = null
 	greyscale_colors = "#397F3F#FFCE5B"
-
+	clothing_flags = STOPSPRESSUREDAMAGE | THICKMATERIAL | SNUG_FIT
 	flags_inv = 0
 	armor_type = /datum/armor/space_beret
 	strip_delay = 130

code/modules/food_and_drinks/machinery/monkeyrecycler.dm

@@ -99,5 +99,5 @@ GLOBAL_LIST_EMPTY(monkey_recyclers)
 	. = ..()
 	if(istype(I))
 		to_chat(user, span_notice("You log [src] in the multitool's buffer."))
-		I.buffer = src
+		I.set_buffer(src)
 		return TRUE

code/modules/jobs/job_types/research_director.dm

@@ -82,5 +82,6 @@
 	suit_store = /obj/item/tank/internals/oxygen
 	back = /obj/item/mod/control/pre_equipped/research
 	suit = null
+	head = null
 	mask = /obj/item/clothing/mask/breath
 	internals_slot = ITEM_SLOT_SUITSTORE

code/modules/mining/machine_silo.dm

@@ -183,7 +183,7 @@ GLOBAL_LIST_EMPTY(silo_access_logs)
 	. = ..()
 	if (istype(I))
 		to_chat(user, span_notice("You log [src] in the multitool's buffer."))
-		I.buffer = src
+		I.set_buffer(src)
 		return TRUE
 
 /**

code/modules/mining/machine_stacking.dm

@@ -26,7 +26,7 @@
 	if(!multitool_check_buffer(user, I))
 		return
 	var/obj/item/multitool/M = I
-	M.buffer = src
+	M.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [I]'s buffer."))
 	return TRUE
 

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

@@ -75,12 +75,14 @@
 /mob/living/carbon/proc/apply_overlay(cache_index)
 	if((. = overlays_standing[cache_index]))
 		add_overlay(.)
+	SEND_SIGNAL(src, COMSIG_CARBON_APPLY_OVERLAY, cache_index, .)
 
 /mob/living/carbon/proc/remove_overlay(cache_index)
 	var/I = overlays_standing[cache_index]
 	if(I)
 		cut_overlay(I)
 		overlays_standing[cache_index] = null
+	SEND_SIGNAL(src, COMSIG_CARBON_REMOVE_OVERLAY, cache_index, I)
 
 //used when putting/removing clothes that hide certain mutant body parts to just update those and not update the whole body.
 /mob/living/carbon/human/proc/update_mutant_bodyparts()

code/modules/mod/mod_activation.dm

@@ -158,6 +158,7 @@
 		if(!module.active || (module.allow_flags & MODULE_ALLOW_INACTIVE))
 			continue
 		module.on_deactivation(display_message = FALSE)
+	mod_link.end_call()
 	activating = TRUE
 	to_chat(wearer, span_notice("MODsuit [active ? "shutting down" : "starting up"]."))
 	if (ai_assistant)
@@ -227,17 +228,15 @@
 		if (!seal && wearer?.invalid_internals())
 			wearer.cutoff_internals()
 
-/// Finishes the suit's activation, starts processing
+/// Finishes the suit's activation
 /obj/item/mod/control/proc/finish_activation(on)
 	active = on
 	if(active)
 		for(var/obj/item/mod/module/module as anything in modules)
 			module.on_suit_activation()
-		START_PROCESSING(SSobj, src)
 	else
 		for(var/obj/item/mod/module/module as anything in modules)
 			module.on_suit_deactivation()
-		STOP_PROCESSING(SSobj, src)
 	update_speed()
 	update_icon_state()
 	wearer.update_clothing(slot_flags)

code/modules/mod/mod_control.dm

@@ -84,6 +84,10 @@
 	var/obj/item/mod/module/selected_module
 	/// AI or pAI mob inhabiting the MOD.
 	var/mob/living/silicon/ai_assistant
+	/// The MODlink datum, letting us call people from the suit.
+	var/datum/mod_link/mod_link
+	/// The starting MODlink frequency, overridden on subtypes that want it to be something.
+	var/starting_frequency = null
 	/// Delay between moves as AI.
 	var/static/movedelay = 0
 	/// Cooldown for AI moves.
@@ -141,10 +145,10 @@
 	for(var/obj/item/mod/module/module as anything in theme.inbuilt_modules)
 		module = new module(src)
 		install(module)
+	START_PROCESSING(SSobj, src)
 
 /obj/item/mod/control/Destroy()
-	if(active)
-		STOP_PROCESSING(SSobj, src)
+	STOP_PROCESSING(SSobj, src)
 	for(var/obj/item/mod/module/module as anything in modules)
 		uninstall(module, deleting = TRUE)
 	for(var/obj/item/part as anything in mod_parts)
@@ -173,6 +177,7 @@
 	if(core)
 		QDEL_NULL(core)
 	QDEL_NULL(wires)
+	QDEL_NULL(mod_link)
 	return ..()
 
 /obj/item/mod/control/atom_destruction(damage_flag)
@@ -217,6 +222,7 @@
 			. += span_notice("You could install an AI or pAI using their <b>storage card</b>.")
 		else if(isAI(ai_assistant))
 			. += span_notice("You could remove [ai_assistant] with an <b>intellicard</b>.")
+	. += span_notice("You could copy/set link frequency with a <b>multitool</b>.")
 	. += span_notice("<i>You could examine it more thoroughly...</i>")
 
 /obj/item/mod/control/examine_more(mob/user)
@@ -226,13 +232,17 @@
 /obj/item/mod/control/process(seconds_per_tick)
 	if(seconds_electrified > MACHINE_NOT_ELECTRIFIED)
 		seconds_electrified--
+	if(mod_link.link_call)
+		subtract_charge((DEFAULT_CHARGE_DRAIN * 0.25) * seconds_per_tick)
+	if(!active)
+		return
 	if(!get_charge() && active && !activating)
 		power_off()
-		return PROCESS_KILL
+		return
 	var/malfunctioning_charge_drain = 0
 	if(malfunctioning)
 		malfunctioning_charge_drain = rand(1,20)
-	subtract_charge((charge_drain + malfunctioning_charge_drain)*seconds_per_tick)
+	subtract_charge((charge_drain + malfunctioning_charge_drain) * seconds_per_tick)
 	update_charge_alert()
 	for(var/obj/item/mod/module/module as anything in modules)
 		if(malfunctioning && module.active && SPT_PROB(5, seconds_per_tick))
@@ -493,6 +503,7 @@
 		retract(null, part)
 	if(active)
 		finish_activation(on = FALSE)
+		mod_link?.end_call()
 	var/mob/old_wearer = wearer
 	unset_wearer()
 	old_wearer.temporarilyRemoveItemFromInventory(src)
@@ -587,6 +598,10 @@
 	QDEL_LIST_ASSOC_VAL(old_module.pinned_to)
 	old_module.mod = null
 
+/// Intended for callbacks, don't use normally, just get wearer by itself.
+/obj/item/mod/control/proc/get_wearer()
+	return wearer
+
 /obj/item/mod/control/proc/update_access(mob/user, obj/item/card/id/card)
 	if(!allowed(user))
 		balloon_alert(user, "insufficient access!")

code/modules/mod/mod_link.dm

@@ -0,0 +1,520 @@
+/proc/make_link_visual_generic(datum/mod_link/mod_link, proc_path)
+	var/mob/living/user = mod_link.get_user_callback.Invoke()
+	var/obj/effect/overlay/link_visual = new()
+	link_visual.name = "holocall ([mod_link.id])"
+	link_visual.mouse_opacity = MOUSE_OPACITY_TRANSPARENT
+	LAZYADD(mod_link.holder.update_on_z, link_visual)
+	link_visual.appearance_flags |= KEEP_TOGETHER
+	link_visual.makeHologram(0.75)
+	mod_link.visual_overlays = user.overlays - user.active_thinking_indicator
+	link_visual.add_overlay(mod_link.visual_overlays)
+	mod_link.visual = link_visual
+	mod_link.holder.become_hearing_sensitive(REF(mod_link))
+	mod_link.holder.RegisterSignals(user, list(COMSIG_CARBON_APPLY_OVERLAY, COMSIG_CARBON_REMOVE_OVERLAY), proc_path)
+	return link_visual
+
+/proc/get_link_visual_generic(datum/mod_link/mod_link, atom/movable/visuals, proc_path)
+	var/mob/living/user = mod_link.get_user_callback.Invoke()
+	playsound(mod_link.holder, 'sound/machines/terminal_processing.ogg', 50, vary = TRUE)
+	visuals.add_overlay(mutable_appearance('icons/effects/effects.dmi', "static_base", TURF_LAYER))
+	visuals.add_overlay(mutable_appearance('icons/effects/effects.dmi', "modlink", ABOVE_ALL_MOB_LAYER))
+	visuals.add_filter("crop_square", 1, alpha_mask_filter(icon = icon('icons/effects/effects.dmi', "modlink_filter")))
+	visuals.maptext_height = 6
+	visuals.alpha = 0
+	user.vis_contents += visuals
+	visuals.forceMove(user)
+	animate(visuals, 0.5 SECONDS, alpha = 255)
+	var/datum/callback/setdir_callback = CALLBACK(mod_link.holder, proc_path)
+	setdir_callback.Invoke(user, user.dir, user.dir)
+	mod_link.holder.RegisterSignal(mod_link.holder.loc, COMSIG_ATOM_DIR_CHANGE, proc_path)
+
+/proc/delete_link_visual_generic(datum/mod_link/mod_link)
+	var/mob/living/user = mod_link.get_user_callback.Invoke()
+	playsound(mod_link.get_other().holder, 'sound/machines/terminal_processing.ogg', 50, vary = TRUE, frequency = -1)
+	LAZYREMOVE(mod_link.holder.update_on_z, mod_link.visual)
+	mod_link.holder.lose_hearing_sensitivity(REF(mod_link))
+	mod_link.holder.UnregisterSignal(user, list(COMSIG_CARBON_APPLY_OVERLAY, COMSIG_CARBON_REMOVE_OVERLAY, COMSIG_ATOM_DIR_CHANGE))
+	QDEL_NULL(mod_link.visual)
+
+/proc/on_user_set_dir_generic(datum/mod_link/mod_link, newdir)
+	var/atom/other_visual = mod_link.get_other().visual
+	if(!newdir) //can sometimes be null or 0
+		return
+	other_visual.setDir(SOUTH)
+	other_visual.pixel_x = 0
+	other_visual.pixel_y = 0
+	var/matrix/new_transform = matrix()
+	if(newdir & NORTH)
+		other_visual.pixel_y = 13
+		other_visual.layer = BELOW_MOB_LAYER
+		SET_PLANE_IMPLICIT(other_visual, GAME_PLANE_FOV_HIDDEN)
+	if(newdir & SOUTH)
+		other_visual.pixel_y = -24
+		other_visual.layer = ABOVE_ALL_MOB_LAYER
+		SET_PLANE_IMPLICIT(other_visual, GAME_PLANE_UPPER_FOV_HIDDEN)
+		new_transform.Scale(-1, 1)
+		new_transform.Translate(-1, 0)
+	if(newdir & EAST)
+		other_visual.pixel_x = 14
+		other_visual.layer = BELOW_MOB_LAYER
+		SET_PLANE_IMPLICIT(other_visual, GAME_PLANE_FOV_HIDDEN)
+		new_transform.Shear(0.5, 0)
+		new_transform.Scale(0.65, 1)
+	if(newdir & WEST)
+		other_visual.pixel_x = -14
+		other_visual.layer = BELOW_MOB_LAYER
+		SET_PLANE_IMPLICIT(other_visual, GAME_PLANE_FOV_HIDDEN)
+		new_transform.Shear(-0.5, 0)
+		new_transform.Scale(0.65, 1)
+	other_visual.transform = new_transform
+
+/obj/item/mod/control/Initialize(mapload, datum/mod_theme/new_theme, new_skin, obj/item/mod/core/new_core)
+	. = ..()
+	mod_link = new(
+		src,
+		starting_frequency,
+		CALLBACK(src, PROC_REF(get_wearer)),
+		CALLBACK(src, PROC_REF(can_call)),
+		CALLBACK(src, PROC_REF(make_link_visual)),
+		CALLBACK(src, PROC_REF(get_link_visual)),
+		CALLBACK(src, PROC_REF(delete_link_visual))
+	)
+
+/obj/item/mod/control/multitool_act_secondary(mob/living/user, obj/item/multitool/tool)
+	if(!multitool_check_buffer(user, tool))
+		return
+	var/tool_frequency = null
+	if(istype(tool.buffer, /datum/mod_link))
+		var/datum/mod_link/buffer_link = tool.buffer
+		tool_frequency = buffer_link.frequency
+	if(!tool_frequency && mod_link.frequency)
+		tool.set_buffer(mod_link)
+	else if(tool_frequency && !mod_link.frequency)
+		mod_link.frequency = tool_frequency
+	else if(tool_frequency && mod_link.frequency)
+		var/response = tgui_alert(user, "Would you like to copy or imprint the frequency?", "MODlink Frequency", list("Copy", "Imprint"))
+		if(!user.is_holding(tool))
+			return
+		switch(response)
+			if("Copy")
+				tool.set_buffer(mod_link)
+			if("Imprint")
+				mod_link.frequency = tool_frequency
+
+/obj/item/mod/control/proc/can_call()
+	return wearer && wearer.stat < DEAD
+
+/obj/item/mod/control/proc/make_link_visual()
+	return make_link_visual_generic(mod_link, PROC_REF(on_overlay_change))
+
+/obj/item/mod/control/proc/get_link_visual(atom/movable/visuals)
+	return get_link_visual_generic(mod_link, visuals, PROC_REF(on_wearer_set_dir))
+
+/obj/item/mod/control/proc/delete_link_visual()
+	return delete_link_visual_generic(mod_link)
+
+/obj/item/mod/control/Hear(message, atom/movable/speaker, message_language, raw_message, radio_freq, list/spans, list/message_mods, message_range)
+	. = ..()
+	if(speaker != wearer && speaker != ai_assistant)
+		return
+	mod_link.visual.say(raw_message, sanitize = FALSE, message_range = 2)
+
+/obj/item/mod/control/proc/on_overlay_change(atom/source, cache_index, overlay)
+	SIGNAL_HANDLER
+	addtimer(CALLBACK(src, PROC_REF(update_link_visual)), 1 TICKS, TIMER_UNIQUE)
+
+/obj/item/mod/control/proc/update_link_visual()
+	if(QDELETED(mod_link.link_call))
+		return
+	mod_link.visual.cut_overlay(mod_link.visual_overlays)
+	mod_link.visual_overlays = wearer.overlays - wearer.active_thinking_indicator
+	mod_link.visual.add_overlay(mod_link.visual_overlays)
+
+/obj/item/mod/control/proc/on_wearer_set_dir(atom/source, dir, newdir)
+	SIGNAL_HANDLER
+	on_user_set_dir_generic(mod_link, newdir)
+
+/obj/item/clothing/neck/link_scryer
+	name = "\improper MODlink scryer"
+	desc = "An intricate piece of machinery that creates a holographic video call with another MODlink-compatible device. Essentially a video necklace."
+	icon_state = "modlink"
+	actions_types = list(/datum/action/item_action/call_link)
+	/// The installed power cell.
+	var/obj/item/stock_parts/cell/cell
+	/// The MODlink datum we operate.
+	var/datum/mod_link/mod_link
+	/// Initial frequency of the MODlink.
+	var/starting_frequency = "NT"
+	/// An additional name tag for the scryer, seen as "MODlink scryer - [label]"
+	var/label
+
+/obj/item/clothing/neck/link_scryer/Initialize(mapload)
+	. = ..()
+	mod_link = new(
+		src,
+		starting_frequency,
+		CALLBACK(src, PROC_REF(get_user)),
+		CALLBACK(src, PROC_REF(can_call)),
+		CALLBACK(src, PROC_REF(make_link_visual)),
+		CALLBACK(src, PROC_REF(get_link_visual)),
+		CALLBACK(src, PROC_REF(delete_link_visual))
+	)
+	START_PROCESSING(SSobj, src)
+
+/obj/item/clothing/neck/link_scryer/Destroy()
+	QDEL_NULL(cell)
+	QDEL_NULL(mod_link)
+	STOP_PROCESSING(SSobj, src)
+	return ..()
+
+/obj/item/clothing/neck/link_scryer/examine(mob/user)
+	. = ..()
+	if(cell)
+		. += span_notice("The battery charge reads [cell.percent()]%. <b>Right-click</b> with an empty hand to remove it.")
+	else
+		. += span_notice("It is missing a battery, one can be installed by clicking with a power cell on it.")
+	. += span_notice("The MODlink ID is [mod_link.id], frequency is [mod_link.frequency]. <b>Right-click</b> with multitool to copy/imprint frequency.")
+	. += span_notice("Use in hand to set name.")
+
+/obj/item/clothing/neck/link_scryer/equipped(mob/living/user, slot)
+	. = ..()
+	if(slot != ITEM_SLOT_NECK)
+		mod_link?.end_call()
+
+/obj/item/clothing/neck/link_scryer/dropped(mob/living/user)
+	. = ..()
+	mod_link?.end_call()
+
+/obj/item/clothing/neck/link_scryer/attack_self(mob/user, modifiers)
+	var/new_label = reject_bad_text(tgui_input_text(user, "Change the visible name", "Set Name", label, MAX_NAME_LEN))
+	if(!new_label)
+		balloon_alert(user, "invalid name!")
+		return
+	label = new_label
+	balloon_alert(user, "name set")
+	update_name()
+
+/obj/item/clothing/neck/link_scryer/process(seconds_per_tick)
+	if(!mod_link.link_call)
+		return
+	cell.use(min(20 * seconds_per_tick, cell.charge))
+
+/obj/item/clothing/neck/link_scryer/attackby(obj/item/attacked_by, mob/user, params)
+	. = ..()
+	if(cell || !istype(attacked_by, /obj/item/stock_parts/cell))
+		return
+	if(!user.transferItemToLoc(attacked_by, src))
+		return
+	cell = attacked_by
+	balloon_alert(user, "installed [cell.name]")
+
+/obj/item/clothing/neck/link_scryer/update_name(updates)
+	. = ..()
+	name = "[initial(name)][label ? " - [label]" : ""]"
+
+/obj/item/clothing/neck/link_scryer/Exited(atom/movable/gone, direction)
+	. = ..()
+	if(gone == cell)
+		cell = null
+
+/obj/item/clothing/neck/link_scryer/attack_hand_secondary(mob/user, list/modifiers)
+	if(!cell)
+		return SECONDARY_ATTACK_CONTINUE_CHAIN
+	balloon_alert(user, "removed [cell.name]")
+	user.put_in_hands(cell)
+	return SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN
+
+/obj/item/clothing/neck/link_scryer/multitool_act_secondary(mob/living/user, obj/item/multitool/tool)
+	if(!multitool_check_buffer(user, tool))
+		return
+	var/tool_frequency = null
+	if(istype(tool.buffer, /datum/mod_link))
+		var/datum/mod_link/buffer_link = tool.buffer
+		tool_frequency = buffer_link.frequency
+	if(!tool_frequency && mod_link.frequency)
+		tool.set_buffer(mod_link)
+	else if(tool_frequency && !mod_link.frequency)
+		mod_link.frequency = tool_frequency
+	else if(tool_frequency && mod_link.frequency)
+		var/response = tgui_alert(user, "Would you like to copy or imprint the frequency?", "MODlink Frequency", list("Copy", "Imprint"))
+		switch(response)
+			if("Copy")
+				tool.set_buffer(mod_link)
+			if("Imprint")
+				mod_link.frequency = tool_frequency
+
+/obj/item/clothing/neck/link_scryer/worn_overlays(mutable_appearance/standing, isinhands)
+	. = ..()
+	if(!QDELETED(mod_link.link_call))
+		. += mutable_appearance('icons/mob/clothing/neck.dmi', "modlink_active")
+
+/obj/item/clothing/neck/link_scryer/ui_action_click(mob/user)
+	if(mod_link.link_call)
+		mod_link.end_call()
+	else
+		call_link(user, mod_link)
+
+/obj/item/clothing/neck/link_scryer/proc/get_user()
+	var/mob/living/carbon/user = loc
+	return istype(user) && user.wear_neck == src ? user : null
+
+/obj/item/clothing/neck/link_scryer/proc/can_call()
+	var/mob/living/user = loc
+	return istype(user) && cell.charge && user.stat < DEAD
+
+/obj/item/clothing/neck/link_scryer/proc/make_link_visual()
+	var/mob/living/user = mod_link.get_user_callback.Invoke()
+	user.update_worn_neck()
+	return make_link_visual_generic(mod_link, PROC_REF(on_overlay_change))
+
+/obj/item/clothing/neck/link_scryer/proc/get_link_visual(atom/movable/visuals)
+	return get_link_visual_generic(mod_link, visuals, PROC_REF(on_user_set_dir))
+
+/obj/item/clothing/neck/link_scryer/proc/delete_link_visual()
+	var/mob/living/user = mod_link.get_user_callback.Invoke()
+	if(!QDELETED(user))
+		user.update_worn_neck()
+	return delete_link_visual_generic(mod_link)
+
+/obj/item/clothing/neck/link_scryer/Hear(message, atom/movable/speaker, message_language, raw_message, radio_freq, list/spans, list/message_mods, message_range)
+	. = ..()
+	if(speaker != loc)
+		return
+	mod_link.visual.say(raw_message, sanitize = FALSE, message_range = 3)
+
+/obj/item/clothing/neck/link_scryer/proc/on_overlay_change(atom/source, cache_index, overlay)
+	SIGNAL_HANDLER
+	addtimer(CALLBACK(src, PROC_REF(update_link_visual)), 1 TICKS, TIMER_UNIQUE)
+
+/obj/item/clothing/neck/link_scryer/proc/update_link_visual()
+	if(QDELETED(mod_link.link_call))
+		return
+	var/mob/living/user = loc
+	mod_link.visual.cut_overlay(mod_link.visual_overlays)
+	mod_link.visual_overlays = user.overlays - user.active_thinking_indicator
+	mod_link.visual.add_overlay(mod_link.visual_overlays)
+
+/obj/item/clothing/neck/link_scryer/proc/on_user_set_dir(atom/source, dir, newdir)
+	SIGNAL_HANDLER
+	on_user_set_dir_generic(mod_link, newdir)
+
+/obj/item/clothing/neck/link_scryer/loaded/Initialize(mapload)
+	. = ..()
+	cell = new /obj/item/stock_parts/cell/high(src)
+
+/obj/item/clothing/neck/link_scryer/loaded/charlie
+	starting_frequency = MODLINK_FREQ_CHARLIE
+
+/// A MODlink datum, used to handle unique functions that will be used in the MODlink call.
+/datum/mod_link
+	/// The frequency of the MODlink. You can only call other MODlinks on the same frequency.
+	var/frequency
+	/// The unique ID of the MODlink.
+	var/id = ""
+	/// The atom that holds the MODlink.
+	var/atom/movable/holder
+	/// A reference to the visuals generated by the MODlink.
+	var/atom/movable/visual
+	/// A list of all overlays of the user, copied everytime they have an overlay change.
+	var/list/visual_overlays = list()
+	/// A reference to the call between two MODlinks.
+	var/datum/mod_link_call/link_call
+	/// A callback that returns the user of the MODlink.
+	var/datum/callback/get_user_callback
+	/// A callback that returns whether the MODlink can currently call.
+	var/datum/callback/can_call_callback
+	/// A callback that returns the visuals of the MODlink.
+	var/datum/callback/make_visual_callback
+	/// A callback that receives the visuals of the other MODlink.
+	var/datum/callback/get_visual_callback
+	/// A callback that deletes the visuals of the MODlink.
+	var/datum/callback/delete_visual_callback
+
+/datum/mod_link/New(
+	atom/holder,
+	frequency,
+	datum/callback/get_user_callback,
+	datum/callback/can_call_callback,
+	datum/callback/make_visual_callback,
+	datum/callback/get_visual_callback,
+	datum/callback/delete_visual_callback
+)
+	var/attempts = 0
+	var/digits_to_make = 3
+	do
+		if(attempts == 10)
+			attempts = 0
+			digits_to_make++
+		id = ""
+		for(var/i in 1 to digits_to_make)
+			id += num2text(rand(0,9))
+		attempts++
+	while(GLOB.mod_link_ids[id])
+	GLOB.mod_link_ids[id] = src
+	src.frequency = frequency
+	src.holder = holder
+	src.get_user_callback = get_user_callback
+	src.can_call_callback = can_call_callback
+	src.make_visual_callback = make_visual_callback
+	src.get_visual_callback = get_visual_callback
+	src.delete_visual_callback = delete_visual_callback
+	RegisterSignal(holder, COMSIG_QDELETING, PROC_REF(on_holder_delete))
+
+/datum/mod_link/Destroy()
+	GLOB.mod_link_ids -= id
+	if(link_call)
+		end_call()
+	return ..()
+
+/datum/mod_link/proc/get_other()
+	RETURN_TYPE(/datum/mod_link)
+	if(!link_call)
+		return
+	return link_call.caller == src ? link_call.receiver : link_call.caller
+
+/datum/mod_link/proc/call_link(datum/mod_link/called, mob/user)
+	if(!frequency)
+		return
+	if(!istype(called))
+		holder.balloon_alert(user, "invalid target!")
+		return
+	var/mob/living/link_user = get_user_callback.Invoke()
+	if(!link_user)
+		return
+	if(HAS_TRAIT(link_user, TRAIT_IN_CALL))
+		holder.balloon_alert(user, "user already in call!")
+		return
+	var/mob/living/link_target = called.get_user_callback.Invoke()
+	if(!link_target)
+		holder.balloon_alert(user, "invalid target!")
+		return
+	if(HAS_TRAIT(link_target, TRAIT_IN_CALL))
+		holder.balloon_alert(user, "target already in call!")
+		return
+	if(!can_call_callback.Invoke() || !called.can_call_callback.Invoke())
+		holder.balloon_alert(user, "can't call!")
+		return
+	link_target.playsound_local(get_turf(called.holder), 'sound/weapons/ring.ogg', 15, vary = TRUE)
+	var/atom/movable/screen/alert/modlink_call/alert = link_target.throw_alert("[REF(src)]_modlink", /atom/movable/screen/alert/modlink_call)
+	alert.desc = "[holder] ([id]) is calling you! Left-click this to accept the call. Right-click to deny it."
+	alert.caller_ref = WEAKREF(src)
+	alert.receiver_ref = WEAKREF(called)
+	alert.user_ref = WEAKREF(user)
+
+/datum/mod_link/proc/end_call()
+	QDEL_NULL(link_call)
+
+/datum/mod_link/proc/on_holder_delete(atom/source)
+	SIGNAL_HANDLER
+	qdel(src)
+
+/// A MODlink call datum, used to handle the call between two MODlinks.
+/datum/mod_link_call
+	/// The MODlink that is calling.
+	var/datum/mod_link/caller
+	/// The MODlink that is being called.
+	var/datum/mod_link/receiver
+
+/datum/mod_link_call/New(datum/mod_link/caller, datum/mod_link/receiver)
+	caller.link_call = src
+	receiver.link_call = src
+	src.caller = caller
+	src.receiver = receiver
+	var/mob/living/caller_mob = caller.get_user_callback.Invoke()
+	ADD_TRAIT(caller_mob, TRAIT_IN_CALL, REF(src))
+	var/mob/living/receiver_mob = receiver.get_user_callback.Invoke()
+	ADD_TRAIT(receiver_mob, TRAIT_IN_CALL, REF(src))
+	make_visuals()
+	START_PROCESSING(SSprocessing, src)
+
+/datum/mod_link_call/Destroy()
+	var/mob/living/caller_mob = caller.get_user_callback.Invoke()
+	if(!QDELETED(caller_mob))
+		REMOVE_TRAIT(caller_mob, TRAIT_IN_CALL, REF(src))
+	var/mob/living/receiver_mob = receiver.get_user_callback.Invoke()
+	if(!QDELETED(receiver_mob))
+		REMOVE_TRAIT(receiver_mob, TRAIT_IN_CALL, REF(src))
+	STOP_PROCESSING(SSprocessing, src)
+	clear_visuals()
+	caller.link_call = null
+	receiver.link_call = null
+	return ..()
+
+/datum/mod_link_call/process(seconds_per_tick)
+	if(can_continue_call())
+		return
+	qdel(src)
+
+/datum/mod_link_call/proc/can_continue_call()
+	return caller.frequency == receiver.frequency && caller.can_call_callback.Invoke() && receiver.can_call_callback.Invoke()
+
+/datum/mod_link_call/proc/make_visuals()
+	var/caller_visual = caller.make_visual_callback.Invoke()
+	var/receiver_visual = receiver.make_visual_callback.Invoke()
+	caller.get_visual_callback.Invoke(receiver_visual)
+	receiver.get_visual_callback.Invoke(caller_visual)
+
+/datum/mod_link_call/proc/clear_visuals()
+	caller.delete_visual_callback.Invoke()
+	receiver.delete_visual_callback.Invoke()
+
+/proc/call_link(mob/user, datum/mod_link/calling_link)
+	if(!calling_link.frequency)
+		return
+	var/list/callers = list()
+	for(var/id in GLOB.mod_link_ids)
+		var/datum/mod_link/link = GLOB.mod_link_ids[id]
+		if(link.frequency != calling_link.frequency)
+			continue
+		if(link == calling_link)
+			continue
+		if(!link.can_call_callback.Invoke())
+			continue
+		callers["[link.holder] ([id])"] = id
+	if(!length(callers))
+		calling_link.holder.balloon_alert(user, "no targets on freq [calling_link.frequency]!")
+		return
+	var/chosen_link = tgui_input_list(user, "Choose ID to call from [calling_link.frequency] frequency", "MODlink", callers)
+	if(!chosen_link)
+		return
+	calling_link.call_link(GLOB.mod_link_ids[callers[chosen_link]], user)
+
+/atom/movable/screen/alert/modlink_call
+	name = "MODlink Call Incoming"
+	desc = "Someone is calling you! Left-click this to accept the call. Right-click to deny it."
+	icon_state = "called"
+	timeout = 10 SECONDS
+	var/end_message = "call timed out!"
+	/// A weak reference to the MODlink that is calling.
+	var/datum/weakref/caller_ref
+	/// A weak reference to the MODlink that is being called.
+	var/datum/weakref/receiver_ref
+	/// A weak reference to the mob that is calling.
+	var/datum/weakref/user_ref
+
+/atom/movable/screen/alert/modlink_call/Click(location, control, params)
+	. = ..()
+	if(usr != owner)
+		return
+	var/datum/mod_link/caller = caller_ref.resolve()
+	var/datum/mod_link/receiver = receiver_ref.resolve()
+	if(!caller || !receiver)
+		return
+	if(caller.link_call || receiver.link_call)
+		return
+	var/list/modifiers = params2list(params)
+	if(LAZYACCESS(modifiers, RIGHT_CLICK))
+		end_message = "call denied!"
+		owner.clear_alert("[REF(caller)]_modlink")
+		return
+	end_message = "call accepted"
+	new /datum/mod_link_call(caller, receiver)
+	owner.clear_alert("[REF(caller)]_modlink")
+
+/atom/movable/screen/alert/modlink_call/Destroy()
+	var/mob/living/user = user_ref?.resolve()
+	var/datum/mod_link/caller = caller_ref?.resolve()
+	if(!user || !caller)
+		return ..()
+	caller.holder.balloon_alert(user, end_message)
+	return ..()

code/modules/mod/mod_theme.dm

@@ -306,7 +306,7 @@
 		the bare essentials, geared far more for environmental hazards than combat against fauna; however, \
 		this gives way to incredible protection against corrosives and thermal protection good enough for \
 		both casual backstroking through molten magma and romantic walks through arctic terrain. \
-		Instead, the suit is capable of using its' anomalous properties to attract and \
+		Instead, the suit is capable of using its anomalous properties to attract and \
 		carefully distribute layers of ash or ice across the surface; these layers are ablative, but incredibly strong. \
 		Lastly, the suit is capable of compressing and shrinking the mass of the wearer, as well as \
 		rearranging its own constitution, to allow them to fit upright in a sphere form that can \
@@ -1437,7 +1437,7 @@
 
 /datum/mod_theme/responsory
 	name = "responsory"
-	desc = "A high-speed rescue suit by Nanotrasen, intended for its' emergency response teams."
+	desc = "A high-speed rescue suit by Nanotrasen, intended for its emergency response teams."
 	extended_desc = "A streamlined suit of Nanotrasen design, these sleek black suits are only worn by \
 		elite emergency response personnel to help save the day. While the slim and nimble design of the suit \
 		cuts the ceramics and ablatives in it down, dropping the protection, \

code/modules/mod/mod_types.dm

@@ -1,4 +1,5 @@
 /obj/item/mod/control/pre_equipped
+	starting_frequency = MODLINK_FREQ_NANOTRASEN
 	/// The skin we apply to the suit, defaults to the default_skin of the theme.
 	var/applied_skin
 	/// The MOD core we apply to the suit.
@@ -196,6 +197,7 @@
 
 /obj/item/mod/control/pre_equipped/traitor
 	theme = /datum/mod_theme/syndicate
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/super
 	applied_modules = list(
 		/obj/item/mod/module/storage/syndicate,
@@ -213,6 +215,7 @@
 
 /obj/item/mod/control/pre_equipped/traitor_elite
 	theme = /datum/mod_theme/elite
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/bluespace
 	applied_modules = list(
 		/obj/item/mod/module/storage/syndicate,
@@ -229,6 +232,7 @@
 
 /obj/item/mod/control/pre_equipped/nuclear
 	theme = /datum/mod_theme/syndicate
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/hyper
 	req_access = list(ACCESS_SYNDICATE)
 	applied_modules = list(
@@ -248,6 +252,7 @@
 
 /obj/item/mod/control/pre_equipped/elite
 	theme = /datum/mod_theme/elite
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/bluespace
 	req_access = list(ACCESS_SYNDICATE)
 	applied_modules = list(
@@ -280,6 +285,7 @@
 
 /obj/item/mod/control/pre_equipped/infiltrator
 	theme = /datum/mod_theme/infiltrator
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/super
 	applied_modules = list(
 		/obj/item/mod/module/emp_shield,
@@ -291,6 +297,7 @@
 
 /obj/item/mod/control/pre_equipped/interdyne
 	theme = /datum/mod_theme/interdyne
+	starting_frequency = MODLINK_FREQ_SYNDICATE
 	applied_cell = /obj/item/stock_parts/cell/super
 	applied_modules = list(
 		/obj/item/mod/module/defibrillator/combat,
@@ -304,6 +311,7 @@
 
 /obj/item/mod/control/pre_equipped/enchanted
 	theme = /datum/mod_theme/enchanted
+	starting_frequency = null
 	applied_core = /obj/item/mod/core/infinite
 	applied_modules = list(
 		/obj/item/mod/module/storage/large_capacity,
@@ -313,6 +321,7 @@
 
 /obj/item/mod/control/pre_equipped/ninja
 	theme = /datum/mod_theme/ninja
+	starting_frequency = null
 	applied_cell = /obj/item/stock_parts/cell/ninja
 	applied_modules = list(
 		/obj/item/mod/module/storage,
@@ -334,6 +343,7 @@
 
 /obj/item/mod/control/pre_equipped/prototype
 	theme = /datum/mod_theme/prototype
+	starting_frequency = MODLINK_FREQ_CHARLIE
 	req_access = list(ACCESS_AWAY_GENERAL)
 	applied_modules = list(
 		/obj/item/mod/module/storage,
@@ -349,6 +359,7 @@
 
 /obj/item/mod/control/pre_equipped/responsory
 	theme = /datum/mod_theme/responsory
+	starting_frequency = MODLINK_FREQ_CENTCOM
 	applied_cell = /obj/item/stock_parts/cell/hyper
 	req_access = list(ACCESS_CENT_GENERAL)
 	applied_modules = list(
@@ -427,6 +438,7 @@
 
 /obj/item/mod/control/pre_equipped/apocryphal
 	theme = /datum/mod_theme/apocryphal
+	starting_frequency = MODLINK_FREQ_CENTCOM
 	applied_cell = /obj/item/stock_parts/cell/bluespace
 	req_access = list(ACCESS_CENT_SPECOPS)
 	applied_modules = list(
@@ -452,6 +464,7 @@
 
 /obj/item/mod/control/pre_equipped/corporate
 	theme = /datum/mod_theme/corporate
+	starting_frequency = MODLINK_FREQ_CENTCOM
 	applied_core = /obj/item/mod/core/infinite
 	req_access = list(ACCESS_CENT_SPECOPS)
 	applied_modules = list(
@@ -463,6 +476,7 @@
 
 /obj/item/mod/control/pre_equipped/chrono
 	theme = /datum/mod_theme/chrono
+	starting_frequency = null
 	applied_core = /obj/item/mod/core/infinite
 	applied_modules = list(
 		/obj/item/mod/module/eradication_lock,
@@ -483,6 +497,7 @@
 
 /obj/item/mod/control/pre_equipped/debug
 	theme = /datum/mod_theme/debug
+	starting_frequency = null
 	applied_core = /obj/item/mod/core/infinite
 	applied_modules = list( //one of every type of module, for testing if they all work correctly
 		/obj/item/mod/module/storage/bluespace,
@@ -496,6 +511,7 @@
 
 /obj/item/mod/control/pre_equipped/administrative
 	theme = /datum/mod_theme/administrative
+	starting_frequency = MODLINK_FREQ_CENTCOM
 	applied_core = /obj/item/mod/core/infinite
 	applied_modules = list(
 		/obj/item/mod/module/storage/bluespace,
@@ -516,6 +532,7 @@
 
 //these exist for the prefs menu
 /obj/item/mod/control/pre_equipped/empty
+	starting_frequency = null
 
 /obj/item/mod/control/pre_equipped/empty/syndicate
 	theme = /datum/mod_theme/syndicate

code/modules/mod/mod_ui.dm

@@ -15,6 +15,8 @@
 		"ai_name" = ai_assistant?.name,
 		"has_pai" = ispAI(ai_assistant),
 		"is_ai" = ai_assistant && ai_assistant == user,
+		"link_id" = mod_link.id,
+		"link_call" = mod_link.get_other()?.id,
 		// Wires
 		"open" = open,
 		"seconds_electrified" = seconds_electrified,
@@ -76,10 +78,6 @@
 	. = ..()
 	if(.)
 		return
-	if(locked && (!allowed(usr) || !ispAI(usr))) // pAIs automatically fail out of allowed()
-		balloon_alert(usr, "insufficient access!")
-		playsound(src, 'sound/machines/scanbuzz.ogg', 25, TRUE, SILENCED_SOUND_EXTRARANGE)
-		return
 	if(malfunctioning && prob(75))
 		balloon_alert(usr, "button malfunctions!")
 		return
@@ -87,6 +85,11 @@
 		if("lock")
 			locked = !locked
 			balloon_alert(usr, "[locked ? "locked" : "unlocked"]!")
+		if("call")
+			if(!mod_link.link_call)
+				call_link(usr, mod_link)
+			else
+				mod_link.end_call()
 		if("activate")
 			toggle_activate(usr)
 		if("select")

code/modules/paperwork/ticketmachine.dm

@@ -54,7 +54,7 @@ MAPPING_DIRECTIONAL_HELPERS(/obj/machinery/ticket_machine, 32)
 	if(!multitool_check_buffer(user, I)) //make sure it has a data buffer
 		return
 	var/obj/item/multitool/M = I
-	M.buffer = src
+	M.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [I]'s buffer."))
 	return TRUE
 

code/modules/plumbing/plumbers/teleporter.dm

@@ -72,7 +72,7 @@
 		return
 
 	var/obj/item/multitool/M = I
-	M.buffer = src
+	M.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [I]'s buffer."))
 	return TRUE
 

code/modules/power/turbine/turbine.dm

@@ -421,7 +421,7 @@
 	//log rotor to link later to computer
 	balloon_alert(user, "all parts linked")
 	var/obj/item/multitool/multitool = tool
-	multitool.buffer = src
+	multitool.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [tool]'s buffer."))
 
 	//success

code/modules/research/designs/mechfabricator_designs.dm

@@ -1513,6 +1513,18 @@
 		RND_CATEGORY_MODSUITS + RND_SUBCATEGORY_MODSUITS_MISC
 	)
 
+/datum/design/modlink_scryer
+	name = "MODlink Scryer"
+	desc = "A neck-worn piece of gear that can call with another MODlink-compatible device."
+	id = "modlink_scryer"
+	build_type = MECHFAB
+	materials = list(/datum/material/iron = HALF_SHEET_MATERIAL_AMOUNT, /datum/material/gold = SMALL_MATERIAL_AMOUNT * 3, /datum/material/glass = SMALL_MATERIAL_AMOUNT * 3)
+	construction_time = 5 SECONDS
+	build_path = /obj/item/clothing/neck/link_scryer
+	category = list(
+		RND_CATEGORY_MODSUITS + RND_SUBCATEGORY_MODSUITS_MISC
+	)
+
 //MODsuit modules
 
 /datum/design/module

code/modules/research/server.dm

@@ -102,7 +102,7 @@
 /obj/machinery/rnd/server/multitool_act(mob/living/user, obj/item/multitool/tool)
 	if(!stored_research)
 		return
-	tool.buffer = stored_research
+	tool.set_buffer(stored_research)
 	to_chat(user, span_notice("Stored [src]'s techweb information in [tool]."))
 	return TRUE
 

code/modules/research/techweb/all_nodes.dm

@@ -1650,6 +1650,7 @@
 		"mod_clamp",
 		"mod_drill",
 		"mod_orebag",
+		"modlink_scryer",
 	)
 	research_costs = list(TECHWEB_POINT_TYPE_GENERIC = 2500)
 

code/modules/station_goals/bsa.dm

@@ -54,7 +54,7 @@ GLOBAL_VAR_INIT(bsa_unlock, FALSE)
 	if(!multitool_check_buffer(user, I)) //make sure it has a data buffer
 		return
 	var/obj/item/multitool/M = I
-	M.buffer = src
+	M.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [I]'s buffer."))
 	return TRUE
 
@@ -71,7 +71,7 @@ GLOBAL_VAR_INIT(bsa_unlock, FALSE)
 	if(!multitool_check_buffer(user, I)) //make sure it has a data buffer
 		return
 	var/obj/item/multitool/M = I
-	M.buffer = src
+	M.set_buffer(src)
 	to_chat(user, span_notice("You store linkage information in [I]'s buffer."))
 	return TRUE
 
@@ -94,11 +94,11 @@ GLOBAL_VAR_INIT(bsa_unlock, FALSE)
 		if(istype(M.buffer, /obj/machinery/bsa/back))
 			back_ref = WEAKREF(M.buffer)
 			to_chat(user, span_notice("You link [src] with [M.buffer]."))
-			M.buffer = null
+			M.set_buffer(null)
 		else if(istype(M.buffer, /obj/machinery/bsa/front))
 			front_ref = WEAKREF(M.buffer)
 			to_chat(user, span_notice("You link [src] with [M.buffer]."))
-			M.buffer = null
+			M.set_buffer(null)
 	else
 		to_chat(user, span_warning("[I]'s data buffer is empty!"))
 	return TRUE

tgstation.dme

@@ -2591,6 +2591,7 @@
 #include "code\modules\admin\view_variables\mark_datum.dm"
 #include "code\modules\admin\view_variables\mass_edit_variables.dm"
 #include "code\modules\admin\view_variables\modify_variables.dm"
+#include "code\modules\admin\view_variables\nobody_wants_to_learn_matrix_math.dm"
 #include "code\modules\admin\view_variables\particle_editor.dm"
 #include "code\modules\admin\view_variables\reference_tracking.dm"
 #include "code\modules\admin\view_variables\tag_datum.dm"
@@ -4537,6 +4538,7 @@
 #include "code\modules\mod\mod_construction.dm"
 #include "code\modules\mod\mod_control.dm"
 #include "code\modules\mod\mod_core.dm"
+#include "code\modules\mod\mod_link.dm"
 #include "code\modules\mod\mod_paint.dm"
 #include "code\modules\mod\mod_theme.dm"
 #include "code\modules\mod\mod_types.dm"

tgui/packages/tgui/interfaces/MODsuit.tsx

@@ -35,6 +35,8 @@ type SuitStatus = {
   ai_name: string;
   has_pai: boolean;
   is_ai: boolean;
+  link_id: string;
+  link_call: string;
 };
 
 type UserStatus = {
@@ -317,6 +319,8 @@ const SuitStatusSection = (props, context) => {
     ai_name,
     has_pai,
     is_ai,
+    link_id,
+    link_call,
   } = data.suit_status;
   const { display_time, shift_time, shift_id } = data.module_custom_status;
   const status = malfunctioning
@@ -377,6 +381,19 @@ const SuitStatusSection = (props, context) => {
             onClick={() => act('lock')}
           />
         </LabeledList.Item>
+        <LabeledList.Item label="MODLink">
+          <Button
+            icon={'wifi'}
+            color={link_call ? 'good' : 'default'}
+            disabled={!link_id}
+            content={
+              link_call
+                ? 'Calling (' + link_call + ')'
+                : 'Call (' + link_id + ')'
+            }
+            onClick={() => act('call')}
+          />
+        </LabeledList.Item>
         {!!open && (
           <LabeledList.Item label="Cover">
             <Box color="red">Open</Box>

tgui/packages/tgui/interfaces/MatrixMathTester.tsx

@@ -0,0 +1,226 @@
+import { useBackend, useLocalState } from '../backend';
+import { Input, NumberInput, Section, Button, Table } from '../components';
+import { toFixed } from 'common/math';
+import { Window } from '../layouts';
+
+const MatrixMathTesterInput = (
+  props: { value: number; varName: string },
+  context
+) => {
+  const { act } = useBackend(context);
+  return (
+    <NumberInput
+      value={props.value}
+      step={0.005}
+      format={(value) => toFixed(value, 3)}
+      width={'100%'}
+      onChange={(e, value) =>
+        act('change_var', { var_name: props.varName, var_value: value })
+      }
+    />
+  );
+};
+
+type MatrixData = {
+  matrix_a: number;
+  matrix_b: number;
+  matrix_c: number;
+  matrix_d: number;
+  matrix_e: number;
+  matrix_f: number;
+  pixelated: boolean;
+};
+
+export const MatrixMathTester = (props, context) => {
+  const { act, data } = useBackend<MatrixData>(context);
+  const {
+    matrix_a,
+    matrix_b,
+    matrix_c,
+    matrix_d,
+    matrix_e,
+    matrix_f,
+    pixelated,
+  } = data;
+  const [scaleX, setScaleX] = useLocalState(context, 'scale_x', 1);
+  const [scaleY, setScaleY] = useLocalState(context, 'scale_y', 1);
+  const [translateX, setTranslateX] = useLocalState(context, 'translate_x', 0);
+  const [translateY, setTranslateY] = useLocalState(context, 'translate_y', 0);
+  const [shearX, setShearX] = useLocalState(context, 'shear_x', 0);
+  const [shearY, setShearY] = useLocalState(context, 'shear_y', 0);
+  const [angle, setAngle] = useLocalState(context, 'angle', 0);
+  return (
+    <Window title="Nobody Wants to Learn Matrix Math" width={290} height={270}>
+      <Window.Content>
+        <Section fill>
+          <Table>
+            <Table.Row header>
+              <Table.Cell width={'30%'}>X</Table.Cell>
+              <Table.Cell width={'30%'}>Y</Table.Cell>
+              <Table.Cell width={'40%'}>Z</Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_a} varName="a" />
+              </Table.Cell>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_d} varName="d" />
+              </Table.Cell>
+              <Table.Cell>
+                <Input disabled placeholder="0 (fixed value)" width={'100%'} />
+              </Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_b} varName="b" />
+              </Table.Cell>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_e} varName="e" />
+              </Table.Cell>
+              <Table.Cell>
+                <Input disabled placeholder="0 (fixed value)" width={'100%'} />
+              </Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_c} varName="c" />
+              </Table.Cell>
+              <Table.Cell>
+                <MatrixMathTesterInput value={matrix_f} varName="f" />
+              </Table.Cell>
+              <Table.Cell>
+                <Input disabled placeholder="1 (fixed value)" width={'100%'} />
+              </Table.Cell>
+            </Table.Row>
+          </Table>
+          <Table mt={3}>
+            <Table.Row header>
+              <Table.Cell>Action</Table.Cell>
+              <Table.Cell>X</Table.Cell>
+              <Table.Cell>Y</Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <Button
+                  icon={'up-right-and-down-left-from-center'}
+                  content={'Scale'}
+                  width={'100%'}
+                  onClick={() => act('scale', { x: scaleX, y: scaleY })}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={scaleX}
+                  step={0.05}
+                  format={(value) => toFixed(value, 2)}
+                  width={'100%'}
+                  onChange={(e, value) => setScaleX(value)}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={scaleY}
+                  step={0.05}
+                  format={(value) => toFixed(value, 2)}
+                  width={'100%'}
+                  onChange={(e, value) => setScaleY(value)}
+                />
+              </Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <Button
+                  icon={'arrow-right'}
+                  content={'Translate'}
+                  width={'100%'}
+                  onClick={() =>
+                    act('translate', { x: translateX, y: translateY })
+                  }
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={translateX}
+                  step={1}
+                  format={(value) => toFixed(value, 0)}
+                  width={'100%'}
+                  onChange={(e, value) => setTranslateX(value)}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={translateY}
+                  step={1}
+                  format={(value) => toFixed(value, 0)}
+                  width={'100%'}
+                  onChange={(e, value) => setTranslateY(value)}
+                />
+              </Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <Button
+                  icon={'maximize'}
+                  content={'Shear'}
+                  width={'100%'}
+                  onClick={() => act('shear', { x: shearX, y: shearY })}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={shearX}
+                  step={0.005}
+                  format={(value) => toFixed(value, 3)}
+                  width={'100%'}
+                  onChange={(e, value) => setShearX(value)}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={shearY}
+                  step={0.005}
+                  format={(value) => toFixed(value, 3)}
+                  width={'100%'}
+                  onChange={(e, value) => setShearY(value)}
+                />
+              </Table.Cell>
+            </Table.Row>
+            <Table.Row>
+              <Table.Cell>
+                <Button
+                  icon={'rotate-right'}
+                  content={'Rotate'}
+                  width={'100%'}
+                  onClick={() => act('turn', { angle: angle })}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <NumberInput
+                  value={angle}
+                  step={0.5}
+                  maxValue={360}
+                  minValue={-360}
+                  format={(value) => toFixed(value, 1)}
+                  width={'100%'}
+                  onChange={(e, value) => setAngle(value)}
+                />
+              </Table.Cell>
+              <Table.Cell>
+                <Button
+                  icon={'dog'}
+                  color={'bad'}
+                  selected={pixelated}
+                  content={'PET'}
+                  tooltip={'Pixel Enhanced Transforming'}
+                  tooltipPosition={'bottom'}
+                  width={'100%'}
+                  onClick={() => act('toggle_pixel')}
+                />
+              </Table.Cell>
+            </Table.Row>
+          </Table>
+        </Section>
+      </Window.Content>
+    </Window>
+  );
+};