Wrong computation of the current screen size when using xrandr's scale option

Pierre Neyron pierre.neyron at imag.fr
Thu Oct 5 09:19:16 UTC 2017


Hello,

To complete my bug report, I have to tell that the problem seems to come 
from the fact I use multiple subsequent xrandr commands... However this 
was on purpose, because using a one-liner command failed (Xerror, failed 
not doing anything, or even machine crash).

I finally found a sequence of command that works...:

$ xrandr --output $INTDISPLAY --mode 3840x2160 --scale 1x1
(reset the internal screen)
$ xrandr --output $INTDISPLAY --mode 3840x2160 --scale 0.666x0.666 --pos 0x0
(configure scaling on internal display)
$ xrandr --output $INTDISPLAY --mode 3840x2160 --scale 0.666x0.666 --pos 
0x721 --output $EXTDISPLAY --mode 3840x2160 --scale 1x1 --pos 2558x0
(configure the dual screen in a single command)

 From the hardware point of view, I have a Dell Precision 5520 (Intel(R) 
Core(TM) i5-7440HQ CPU @ 2.80GHz with Intel® HD Graphics 630, but no 
additional Nvidia card), connected to a Dell UltraSharp 27 4K Monitor ( 
U2718Q) thanks to a Dell Thunderbolt Dock (TB16).

Thanks,
Pierre

On 10/04/2017 11:02 AM, Pierre Neyron wrote:
> Hello,
> 
> I'd like to report an issue with the computation of the Xorg current 
> screen size when using xrandr's --scale option.
> 
> I'm using a dual screen setup, with a 15" 4K laptop screen, and a 28" 4K 
> external screen which are positioned the first one left to the second 
> one. Since I don't use gnome or another window manager which can tweak 
> the DPI at a higher level (I use e16, the best WM ever :-) ), I rely in 
> my setup on xrandr's --scale and --pos options, e.g.:
> 
>               +--------------+
>               |              |
>    +----------+ EXTERNAL     |2
> 1 |LAPTOP    | DISPLAY      |1
> 4 |DISPLAY   | DP-1-2       |6
> 3 |eDP-1     |              |0
> 9 +----------+--------------+
>       2558          3840
> 
> $ xrandr --output eDP-1 --mode 3840x2160 --scale 0.666x0.666
> (scaled size = 2558x1439)
> $ xrandr --output eDP-1 --pos 0x721
> $ xrandr --output DP-1-2 --mode 3840x2160 --scale 1x1
> $ xrandr --output DP-1-2 --pos 2558x0
> 
> 
> This works quite well with the commands above (some other sequences of 
> commands may result in errors, though), but the computed current screen 
> size is wrong (xrandr output provided below): 7680 x 2160 instead of the 
> expected 6398 x 2160 (2558+3840). As a result, I have a black hole 
> between virtual screen areas of e16, from x=Xn+6398 to x=Xn+7680 for 
> each virtual area, which I did not expected. That's very annoying 
> because it breaks continuity between areas.
> 
> (One may notice that there are other black holes in my virtual screen 
> areas, above my laptop screen display, but those ones are somehow 
> "expected" from my viewpoint...)
> 
> ...........+--------------+....
> . expected |              |B  .
> +----------+ EXTERNAL     |L H. <- unexpected
> |LAPTOP    | DISPLAY      |A O.
> |DISPLAY   | DP-1-2       |C L.
> |eDP-1     |              |K E.
> +----------+--------------+....
> 
> Could this be handled by xrandr (I get Errors when trying commands with 
> --fb or --fbmm) ?
> Or could this be considered a bug in Xorg ?
> Or should this be handled by the WM (e16) ?
> 
> FYI:
> I'm running Debian Stretch, xorg deb pkg 1:7.7+19, e16 master git branch.
> 
> $ /usr/lib/xorg/Xorg -version
> 
> X.Org X Server 1.19.2
> Release Date: 2017-03-02
> X Protocol Version 11, Revision 0
> Build Operating System: Linux 4.9.0-3-amd64 x86_64 Debian
> Current Operating System: Linux caigang 4.13.0-trunk-amd64 #1 SMP Debian 
> 4.13.2-1~exp1 (2017-09-19) x86_64
> Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.13.0-trunk-amd64 
> root=/dev/mapper/caigang-stretch ro quiet
> Build Date: 07 July 2017  06:14:06AM
> xorg-server 2:1.19.2-1+deb9u1 (https://www.debian.org/support)
> Current version of pixman: 0.34.0
>      Before reporting problems, check http://wiki.x.org
>      to make sure that you have the latest version.
> 
> $ xrandr --version
> xrandr program version       1.5.0
> Server reports RandR version 1.5
> 
> $ xrandr --prop
> Screen 0: minimum 320 x 200, current 7680 x 2160, maximum 8192 x 8192
> eDP-1 connected primary 2558x1439+0+721 (normal left inverted right x 
> axis y axis) 346mm x 194mm
>      EDID:
>          00ffffffffffff004d10761400000000
>          311a0104a52313780eeff1a55534ba25
>          0a495200000001010101010101010101
>          0101010101014dd000a0f0703e803020
>          35005ac2100000180000000000000000
>          00000000000000000000000000fe0059
>          32584e44804c51313536443100000000
>          0002410328001200000b010a202000b1
>      scaling mode: Full aspect
>          supported: Full, Center, Full aspect
>      Broadcast RGB: Automatic
>          supported: Automatic, Full, Limited 16:235
>      audio: auto
>          supported: force-dvi, off, auto, on
>      link-status: Good
>          supported: Good, Bad
>     3840x2160     60.00*+
>     2048x1536     60.00
>     1920x1440     60.00
>     1856x1392     60.01
>     1792x1344     60.01
>     1920x1200     59.95
>     1920x1080     59.93
>     1600x1200     60.00
>     1680x1050     59.95    59.88
>     1600x1024     60.17
>     1400x1050     59.98
>     1280x1024     60.02
>     1440x900      59.89
>     1280x960      60.00
>     1360x768      59.80    59.96
>     1152x864      60.00
>     1024x768      60.04    60.00
>     960x720       60.00
>     928x696       60.05
>     896x672       60.01
>     960x600       60.00
>     960x540       59.99
>     800x600       60.00    60.32    56.25
>     840x525       60.01    59.88
>     800x512       60.17
>     700x525       59.98
>     640x512       60.02
>     720x450       59.89
>     640x480       60.00    59.94
>     680x384       59.80    59.96
>     576x432       60.06
>     512x384       60.00
>     400x300       60.32    56.34
>     320x240       60.05
> DP-1 disconnected (normal left inverted right x axis y axis)
>      Broadcast RGB: Automatic
>          supported: Automatic, Full, Limited 16:235
>      audio: auto
>          supported: force-dvi, off, auto, on
>      link-status: Good
>          supported: Good, Bad
> HDMI-1 disconnected (normal left inverted right x axis y axis)
>      aspect ratio: Automatic
>          supported: Automatic, 4:3, 16:9
>      Broadcast RGB: Automatic
>          supported: Automatic, Full, Limited 16:235
>      audio: auto
>          supported: force-dvi, off, auto, on
>      link-status: Good
>          supported: Good, Bad
> DP-2 disconnected (normal left inverted right x axis y axis)
>      Broadcast RGB: Automatic
>          supported: Automatic, Full, Limited 16:235
>      audio: auto
>          supported: force-dvi, off, auto, on
>      link-status: Good
>          supported: Good, Bad
> HDMI-2 disconnected (normal left inverted right x axis y axis)
>      aspect ratio: Automatic
>          supported: Automatic, 4:3, 16:9
>      Broadcast RGB: Automatic
>          supported: Automatic, Full, Limited 16:235
>      audio: auto
>          supported: force-dvi, off, auto, on
>      link-status: Good
>          supported: Good, Bad
> DP-1-1 disconnected (normal left inverted right x axis y axis)
> DP-1-2 connected 3840x2160+2558+0 (normal left inverted right x axis y 
> axis) 609mm x 349mm
>      EDID:
>          00ffffffffffff0010aceca04c355730
>          191b0104b53d23783eee95a3544c9926
>          0f5054a54b00714f8180a9c0a940d1c0
>          e100d10001014dd000a0f0703e803020
>          3500615d2100001a000000ff00464e38
>          344b37364b3057354c0a000000fc0044
>          454c4c205532373138510a20000000fd
>          0031560a8936000a20202020202001ce
>          02031df150101f200514041312110302
>          161507060123091f0783010000565e00
>          a0a0a0295030203500615d2100001aa3
>          6600a0f0701f8030203500615d210000
>          1a4dd000a0f0703e8030203500615d21
>          00001a023a801871382d40582c250061
>          5d2100001ebf1600a08038134030203a
>          00615d2100001a00000000000000004a
>     3840x2160     60.00*+  29.98
>     2560x1440     59.95
>     2048x1280     59.99
>     1920x1200     59.88
>     2048x1080     24.00
>     1920x1080     60.00    60.00    50.00    59.94    24.00    23.98
>     1600x1200     60.00
>     1600x900      60.00
>     1280x1024     75.02    60.02
>     1152x864      75.00
>     1280x720      60.00    50.00    59.94
>     1024x768      75.03    60.00
>     800x600       75.00    60.32
>     720x576       50.00
>     720x480       60.00    59.94
>     640x480       75.00    60.00    59.94
>     720x400       70.08
> DP-1-3 disconnected (normal left inverted right x axis y axis)
> 
> Best regards,



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