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#1 2016-05-13 10:25:44

Registered: 2011-06-17
Posts: 7

Multihead displays with HiDPI scaling problem

Hi guys,
I have an XPS 15 laptop, that comes with a built-in HiDPI display, and I would really like to get two external monitors, which are not HiDPI to be usable.
I've tried to follow every guide I could find on how to accomplish my task, and the solution with the best results that I could get, is the xrandr panning option, with scaling - from the wiki page on HiDPI.
There is still one problem though when I run this.

My setup is as follows:
List of monitors
Monitor order
Both external displays are configured to 1920x1080 resolution (which is their maximum)
HDMI1 ==> Physical HDMI port on my laptop, screen number 2
HDMI2 ==> Mini DisplayPort on laptop ==> HDMI adapter, screen number 3
eDP1 ==> Internal display

The xrandr command I am running, is:

--output HDMI1 --auto --panning [1920*2]x[1080*2]+[0]+0 --scale [2]x[2]
--output HDMI2 --auto --panning [1920*2]x[1080*2]+[1920*2]+0 --scale [2]x[2] --right-of HDMI1
--output eDP1 --auto --panning [3200]x[1800]+[1920*4]+0 --scale [1]x[1] --right-of HDMI2

Which is equivalent to:

--output HDMI1 --auto --panning 3840x2160+0+0 --scale 2x2
--output HDMI2 --auto --panning 3840x2160+3840+0 --scale 2x2 --right-of HDMI1
--output eDP1 --auto --panning 3200x1800+7680+0 --scale 1x1 --right-of HDMI2

Now after the command, the HiDPI display is fine, so is display number 2, but display number 3 behaves weirdly - it is enlarged (seems by the scaling factor I provided) and does not fit the screen, when I move the cursor to an edge, it "scrolls" the screen.
I tried different values, and also other options (xrandr without panning) but it only brought more problems.
I'd be really happy if somebody could help me figure this out.

My xrandr (after running the command):

Screen 0: minimum 8 x 8, current 10880 x 2160, maximum 32767 x 32767
eDP1 connected primary 3200x1800+7680+0 (normal left inverted right x axis y axis) 346mm x 194mm panning 3200x1800+7680+0
   3200x1800     59.98*+
   2880x1620     60.00  
   2560x1440     60.00  
   2048x1536     60.00  
   1920x1440     60.00  
   1856x1392     60.01  
   1792x1344     60.01  
   2048x1152     60.00  
   1920x1080     60.00  
   1600x1200     60.00  
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     60.02  
   1280x960      60.00  
   1368x768      60.00  
   1280x720      60.00  
   1024x768      60.00  
   1024x576      60.00  
   960x540       60.00  
   800x600       60.32    56.25  
   864x486       60.00  
   640x480       59.94  
   720x405       60.00  
   640x360       60.00  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected 3840x2160+0+0 (normal left inverted right x axis y axis) 477mm x 268mm panning 3840x2160+0+0
   1920x1080     60.00*+
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1024x768      75.08    60.00  
   800x600       75.00    60.32  
   640x480       75.00    60.00  
   720x400       70.08  
HDMI2 connected 3840x2160+3840+0 (normal left inverted right x axis y axis) 509mm x 286mm panning 3840x2160+3840+0
   1920x1080     60.00*+  50.00    59.94  
   1920x1080i    60.00    50.00    59.94  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x720      60.00    50.00    59.94  
   1024x768      75.08    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
VIRTUAL1 disconnected (normal left inverted right x axis y axis)


#2 2016-09-08 16:37:31

Registered: 2016-09-08
Posts: 1

Re: Multihead displays with HiDPI scaling problem

Were you able to get this to work?


#3 2016-11-12 00:14:40

Registered: 2012-03-10
Posts: 3

Re: Multihead displays with HiDPI scaling problem

The best I could do was to go the other way and just reduce my laptop HiDPI screen from 3200x1800 to 1600x900:

xrandr --output eDP1 --mode 1600x900 --output DP1 --auto --left-of eDP1

Granted I'm not making use of my high-res laptop display, however I can't tell the difference. If you do graphics-intensive work or have superhuman eyesight this may not be a good solution, or if only rarely then running

xrandr --output eDP1 --auto

at those times might work out. Personal preference, but I find that I do notice a negative difference when using scaling but not just using a lower (but still quite high) resolution. Anyway, if you come up with something better please post what you did. I've also searched all over the place and haven't found the golden answer.

Edit: I also created


<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
    <match target="pattern">
        <edit name="dpi" mode="assign">

and found my fonts look nicer, I just use smaller sizes in my applications. Just get the DPI right for your particular monitor; 276 may work fine if using 3200x1800 natively on a 13-13.3" display.

Last edited by nharward (2016-11-12 00:21:33)


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