Hacky C0/C1 CFrameEditor Plugin

CFrameEditor.lua

local Selection = game:GetService("Selection")
local CoreGui = game:GetService("CoreGui")

local joints = {}
local attachments = {}
local conCFrame = {}
local conParent = {}

-- Event to deduplicate registered callbacks if plugins are reloaded.
local killmename = "CFrameEditor.Plugin.RefreshCleanupEvent"
local killme = CoreGui:FindFirstChild(killmename)
if killme and not killme:IsA("BindableEvent") then
	error(killmename .. " wasn't a BindableEvent. WHY.")
end
if not killme then
	killme = Instance.new("BindableEvent")
	killme.Name = killmename
	killme.Archivable = false
	killme.Parent = CoreGui
end
killme:Fire()

local function reset()
	-- Disconnect property changed before changing parent
	for attachment,v in pairs(attachments) do
		conCFrame[attachment]:Disconnect()
		conParent[attachment]:Disconnect()
	end
	conCFrame = {}
	conParent = {}

	for attachment,v in pairs(attachments) do
		attachment:Destroy()
	end
	attachments = {}
	joints = {}
end

local function createAttachment(joint, partProp, cframeProp)
	local a = Instance.new("Attachment")
	a.Archivable = false
	a.Name = joint.Name .. "." .. cframeProp
	a.CFrame = joint[cframeProp]
	a.Parent = joint[partProp]

	conCFrame[a] = a:GetPropertyChangedSignal("CFrame"):Connect(function()
		joint[cframeProp] = a.CFrame
	end)
	conParent[a] = a:GetPropertyChangedSignal("Parent"):Connect(function()
		joint[partProp] = a.Parent
	end)

	attachments[a] = true
end 

local valid = false

local selectionConnection = Selection.SelectionChanged:Connect(function()
	local selection = Selection:Get()
	
	valid = false
	for i,instance in ipairs(selection) do
		if instance and instance:IsA("JointInstance") then
			if not joints[instance] then
				createAttachment(instance, "Part0", "C0")
				createAttachment(instance, "Part1", "C1")
				joints[instance] = true
			end
			valid = true
		elseif attachments[instance] then
			valid = true
		end
	end
	
	if not valid then
		 -- Selecting an attachment in 3d view clears selection first. Check again next frame before resetting.
		wait()
		if not valid then
			reset()
		end
	end
end)

-- Register for cleanup on refresh
local rip
rip = killme.Event:Connect(function()
	reset()
	selectionConnection:Disconnect()
	
	rip:Disconnect()
end)