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Add X Resolution

similar solution:

https://forums.opensuse.org/showthread.php/507397-Adjusting-screen-resolution-on-a-system-with-no-monitor-connected

1.  Adding virtual device

This solution is for intel driver only, so install it if not yet done and remove proprietary (nvidia?) device.

Then add a file 20-intel to /etc/X11/xorg.conf.d/

 (true for openSUSE Leap), with:
Section "Device"
    Identifier "intelgpu0"
    Driver "intel"
    Option "VirtualHeads" "2"
EndSection

this creates two VIRTUAL devices (only one is really necessary right now). Then use the script below.

2.  Where one can set a config

Beware, it's easy to forget that you setup some file, there are a number!

 /etc/X11/xorg.conf.d/

Where 50-monitor.conf and 50-screen.conf are the place of choice for X. See man xorg.conf for syntax.

 Option "TransformationMatrix" "a b c d e f g h i"

seen on the web is only for input devices, not screen.

 /etc/X11/xinit/

and

 /etc/X11/xinit/xinitrc.d

(any file) - seen in logs at the very end of the file - but there the "panning" option of xrandr is not ack.

If you want to change all the system. The same file in ~/.xinitrc for user setup (a template file is available in openSUSE as example, with place for user change).

 /etc/bumblebee/xorg.conf.nouveau

Virtual x y have to be in Screen/Display

In ~/.config/Autostart one can set a bash file, made executable, activated in kde setup/"start and stop"

also ~/.xinitrc and ~/.bashrc

May also be in ~/.config/monitor.xml

etc/init.d/after.local

3.  ASUS 550

3.1  Best result on Nov 24, 2017 (and august 2019)

Inserted in a text file

xrandr --newmode "1920x1080"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync
xrandr  --addmode VIRTUAL1 1920x1080
xrandr --fb 1920x1080 --dpi 96 --output eDP1 --pos 0x0 --scale-from 1920x1080 --same-as VIRTUAL1

There are three useful lines. The first is the standard mode creation as 1920x1080. Using "hd" for name didn't show in the kde setup GUI. Second line creates the virtual screen. Third line create the frame buffer for virtual and place it in a good position.

4.  manual

On DEll 755 (vga Intel, TV), manually:

$ cvt 1920 1080 60
$ 1920x1080 59.96 Hz (CVT 2.07M9) hsync: 67.16 kHz; pclk: 173.00 MHz
Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

$xrandr --newmode "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

$xrandr --addmode VGA1 "1920x1080_60.00"

xrandr --output VGA1 --mode 1920x1080_60.00

To make it permanent, one need to edit files in /etc/X11/xorg.conf.d/50-*

Section "Monitor"
 Identifier "TV"

 VendorName "BELSON"
 HorizSync 31.0 - 84.0
 VertRefresh 56.0 - 77.0

Modeline "1920x1080_60.00"  173.00  1920 2048 2248 2576  1080 1083 1088 1120 -hsync +vsync

Option "PreferredMode" "1920x1080_60.00"
EndSection

Section "Screen"

  Identifier "VGA1"
  Device "VGA1"
  Monitor "TV"
  DefaultDepth 24
  SubSection "Display"
    Depth 24
    Modes "1920x1080_60.00"
  EndSubSection

EndSection 

take attention to the fact that xorg stores somewhere the used resolution and start with it, so you may need to issue "xrandr" to verify is the new resolution is recorded, then "xrandr --output VGA1 --mode 1920x1080_60.00" to use it the first time.