xrandr-scale.hs

#!/usr/bin/env runhaskell

import System.Process (callCommand)

runcmd args =
    putStrLn ("+ " ++ cmd) >> callCommand cmd
    where cmd = unwords args

-- (Name of your laptop's internal display, x res, y res)
(internalOutput, intX, intY) = ("eDP1", 3840, 2160)

-- (Name of your external display, x res, y res)
(externalOutput, extX, extY) = ("DP2", 3840, 2160)

-- Coefficient to use when computing resolution for the virtual screen
-- to scale down for your external display:
scaleFactor = 1.75

(scaledExtX, scaledExtY) = (extX * scaleFactor, extY * scaleFactor)

extScaleFrom = show (round scaledExtX) ++ "x" ++ show (round scaledExtY)
internalPos = show (round scaledExtX) ++ "x" ++ show (round (scaledExtY - intY))

-- If your laptop has a touchscreen, put its xinput name here (from `xinput list`)
touchXinputId = "ELAN\\ Touchscreen"

main = do
    runcmd [ "xrandr", "--auto" ]
    runcmd [ "xrandr"
           , "--output", externalOutput
           , "--scale-from", extScaleFrom
           , "--pos", "0x0"
           , "--primary"
           , "--output", internalOutput
           , "--pos", internalPos
           ]
    runcmd [ "xinput", "map-to-output", touchXinputId, internalOutput ]
    -- Any other extra commands to run can go here, e.g.
    -- runcmd [ "feh", "~/.background-image", "--bg-scale" ]