Dell XPS 13 highDPI and external monitor

[Guest]

Hello,

I'm having a real headache trying to setup a descent configuration for my new Dell XPS 13 laptop with an external monitor. I have a USB 3.0 dongle from Dell called DA100 that offers extensions to HDMI and VGA outputs among others. It's a DisplayLink chipset which is supported by Ubuntu (http://www.displaylink.com/downloads/ubuntu). First of all, a few things on my setup:

jimakos@kubu:~$ uname -a
Linux kubu 4.4.0-59-generic #80-Ubuntu SMP Fri Jan 6 17:47:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

My laptop screen is set to 3200x1800 and my external monitor is a 1920x1080. I've setup correctly my dpi as well following the links in

http://askubuntu.com/questions/19782.../272172#272172.
For example
jimakos@kubu:~$ xdpyinfo |grep dots
resolution: 277x277 dots per inch which is the correct dpi for my resolution.

xrandr identifies both monitors correctly

jimakos@kubu:~$ xrandr | grep -w connected
eDP1 connected primary 3200x1800+0+0 (normal left inverted right x axis y axis) 294mm x 165mm
DVI-I-1-1 connected 1920x1080+3200+0 510mm x 287mm and I can enable the external one in System Settings -> Display and Monitor.



At this point my external monitor is activated with a black desktop and the desktop toolbox appears at the top left corner. I suppose they are in a side-by-side configuration. I want to keep my lid closed and only use the external monitor so I tried to unify the outputs and I got a 1920x1080 resolution for both. Now all my desktop appears on the external monitor but everything is huge. By the way, when I close the lid the monitor turns off, where can I set this behavior?

The problem is obviously because I use a scale factor of 2 for my highDPI laptop screen to get a nice output! Ideally, the solution would be to set 2 different scalings for the laptop and the external monitor, right?

I tried some xrandr commands shown here http://askubuntu.com/questions/39340...fferent-screen and here https://wiki.archlinux.org/index.php...tiple_displays but I was not able to scale down the external monitor. For example I tried to run (DVI-I-1-1 is my external monitor)

jimakos@kubu:~$ xrandr --output DVI-I-1-1 --scale 2x2
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 140 (RANDR)
Minor opcode of failed request: 26 (RRSetCrtcTransform)
Value in failed request: 0x129
Serial number of failed request: 48
Current serial number in output stream: 49


ps: in Windows 10 a was able to get a descent setup to work with on the very same monitor.

[Guest]

Updating own thread. I tried experimenting with the fonts dpi in Settings -> Fonts and set them to just 90. Rebooted and then my external desktop appears "fine" but some applications or parts of applications do not scale well. For example Firefox and Thunderbird scale fine, while kate appears like this

[img]https://s29.postimg.org/or5nqvvdv/kate.png[/img]

and VLC like this



I understand that I wasn't able to scale the complete screen with xrandr and setting just the font dpi would work for parts of the components. But I don't know how fonts, windows, etc scale together. Why for example Thunderbird scales perfect and kate not?