set different scaling on an extend screen, this script is expected to solve the scaling problem on HiDPI screens of Linux

extend_screen.sh

#!/bin/bash

#
# extend second screen with different scaling
#
# Copyright (C) 2015 http://www.shuyz.com  
# REF: 1. http://blog.jamiek.it/2015/04/manually-fixing-multiple-screens-with.html
#      2. https://bbs.archlinux.org/viewtopic.php?id=118999
#      3. http://unix.stackexchange.com/questions/101809/how-can-i-automatically-update-my-monitor-layout-in-xfce

has_dp2=$(xrandr -q | grep "DP2 connected")

if [ -z "$has_dp2" ]; then
	exit 0
fi

# scale:
# 1920/1440 = 1.33
# 1080/900 = 1.2


# mirror
#xrandr --output DP2 --scale 1.33x1.2 --mode 1440x900 --pos 0x0	
#xrandr --output eDP1 --scale 1x1 --pos 0x0		

# extend horizonly

#fb: 
# x:1920 + 1440x1.33 +1 = 3836
# y:1080 = 900x1.2		

#second screen on right
#bug: mouse is limitted by invisible border on second screen 
#xrandr --output DP2 --scale 1.33x1.2 --mode 1440x900 --fb 3836x1080 --pos 1920x0
#xrandr --output eDP1 --scale 1x1 --pos 0x0

#second screen on left
#xrandr --output DP2 --scale 1.33x1.2 --mode 1440x900 --fb 3836x1080 --pos 0x0
#xrandr --output eDP1 --scale 1x1 --pos 1915x0


#extend veritically

#fb:
# x: MAX(1920, 1440x1.33) = 1920
# y: 900x1.2+1080 = 2160

# second screen at top
#xrandr --output DP2 --scale 1.33x1.2 --mode 1440x900 --fb 1920x2160 --pos 0x0
#xrandr --output eDP1 --scale 1x1 --pos 0x1080

#second screen at bottom
#bug: mouse is limitted by invisible border on second screen
xrandr --output DP2 --scale 1.33x1.2 --mode 1440x900 --fb 1920x2160 --pos 0x1080
xrandr --output eDP1 --scale 1x1 --pos 0x0