React-lua hook for determining DPI scale.

useDpiScale.lua

local UserInputService = game:GetService("UserInputService")

local React = require(script.Parent.Parent.Packages.React)

local useState = React.useState
local useEffect = React.useEffect

local function calculateDpiScale()
	local BUTTON_CONTENTID = UserInputService:GetImageForKeyCode(Enum.KeyCode.ButtonA)
	local BUTTON_SCALE = BUTTON_CONTENTID:lower():match("@([%d%.]-)x%.%w+$")

	return tonumber(BUTTON_SCALE or 1)
end

local function connectCamera(camera: Camera, setDpiScale)
	return camera:GetPropertyChangedSignal("ViewportSize"):Connect(function()
		setDpiScale(calculateDpiScale())
	end)
end

local function useDpiScale()
	local dpiScale, setDpiScale = useState(calculateDpiScale())

	useEffect(function()
		local viewportConnection = connectCamera(workspace.CurrentCamera, setDpiScale)

		local changedConnection = workspace
			:GetPropertyChangedSignal("CurrentCamera")
			:Connect(function()
				viewportConnection:Disconnect()
				viewportConnection = connectCamera(workspace.CurrentCamera, setDpiScale)
			end)

		return function()
			changedConnection:Disconnect()
			viewportConnection:Disconnect()
		end
	end, {})

	return dpiScale
end

return useDpiScale