Empty space between monitors

English Hardware
1

This post I originally made at: https://np.reddit.com/r/linuxquestions/comments/4c2o4p/what_does_panning_and_fb_in_xrandr_stand_for/

I have a Macbook with Retina display (2560x1600) and an external monitor (1920x1080) connected with Thunderbolt to VGA adapter.

xrandr output initially:

Screen 0: minimum 8 x 8, current 4480 x 1600, maximum 32767 x 32767
eDP1 connected 2560x1600+0+0 (normal left inverted right x axis y axis) 286mm x 179mm
   2560x1600     59.97*+
   2048x1536     60.00
   1920x1440     60.00
   1856x1392     60.01
   1792x1344     60.01
   1600x1200     60.00
   1400x1050     59.98
   1280x1024     60.02
   1280x960      60.00
   1024x768      60.00
   800x600       60.32    56.25
   640x480       59.94
DP1 connected 1920x1080+2560+0 (normal left inverted right x axis y axis) 521mm x 293mm
   1920x1080     60.00*+
   1680x1050     59.95
   1600x900      60.00
   1280x1024     75.02    60.02
   1440x900      59.89
   1280x800      59.81
   1152x864      75.00
   1280x720      60.00
   1024x768      75.08    70.07    60.00
   832x624       74.55
   800x600       72.19    75.00    60.32    56.25
   640x480       75.00    72.81    66.67    60.00
   720x400       70.08
DP2 disconnected (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)        
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Some calculations and I arrive at solution, so that I scale the Retina display to 0.56x0.56, it matches with external monitor.

xrandr --output eDP1 --scale 0.56x0.56

Now output of xrandr (removing extraneous lines) is:

Screen 0: minimum 8 x 8, current 4480 x 1080, maximum 32767 x 32767
eDP1 connected 1434x896+0+0 (normal left inverted right x axis y axis) 286mm x 179mm
   2560x1600     59.97*+
  
DP1 connected 1920x1080+2560+0 (normal left inverted right x axis y axis) 521mm x 293mm
   1920x1080     60.00*+

Things scale up fine But now between the edges of monitors and space below there is a space which is not visible but cursor can go there and I have to drag mouse a lot to actually get it on other screen. I can move windows onto it. If I keep a window between monitors a big chunk is in that area, hence not visible. And similarly some vertical invisible space on Retina monitor.

I took up KRuler and measured whats the size of horizontal space missing from view. It is 1126 pixels, exact same difference between original and scaled resolutions!

Original

eDP1 connected **2560x1600+0+0** (normal left inverted right x axis y axis) 286mm x 179mm

** Scaled**

eDP1 connected **1434x896+0+0** (normal left inverted right x axis y axis) 286mm x 179mm

**Also to be noted
**You see the position of DP1 is actually at +2560+0 in line

DP1 connected 1920x1080+**2560+0** (normal left inverted right x axis y axis) 521mm x 293mm

which is same as before scaling.

To my surprise KDE’s plasma panel is located at the proper bottom edge of the scaled screen and not on the invisible space. But for desktop switching this edge doesn’t work! (KDE bug?)
**Reason: **Plasma scales with X.org, so that’s why panel fits in there.

By changing the position of screen DP1 I am able to solve the problem of “empty black hole” space between monitors. But vertical space is still a problem. I know this is a workaround and doesn’t actually solve the problem!

xrandr --output DP1 --pos 1434x0

KDE’s display settings show exactly what I am doing: http://i.imgur.com/7Sis7Q2.png

2

Here, on openSUSE 13.2 with Nvidia-Driver, it works without Problems for years:

xrandr
Screen 0: minimum 8 x 8, current 3520 x 1080, maximum 16384 x 16384
DVI-I-0 disconnected primary (normal left inverted right x axis y axis)
DVI-I-1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 442mm x 249mm
   1600x900      59.98*+
   1440x900      74.98    59.89  
   1280x1024     75.02    60.02  
   1280x960      60.00  
   1152x864      75.00  
   1024x768      75.03    70.07    60.00  
   800x600       75.00    72.19    60.32    56.25  
   640x480       75.00    72.81    59.94  
HDMI-0 disconnected (normal left inverted right x axis y axis)
DVI-D-0 connected 1920x1080+1600+0 (normal left inverted right x axis y axis) 477mm x 268mm
   1920x1080     60.00*+
   1680x1050     59.95  
   1600x900      60.00  
   1440x900      59.89  
   1400x1050     59.98  
   1280x1024     75.02    60.02  
   1280x800      59.81  
   1280x720      60.00  
   1152x864      75.00  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   640x480       75.00    59.94
3

You are not facing problem of high difference in DPI, so you are not scaling. So, you don’t face the problem mentioned in this post :good:

4

Not high difference, but 1600x900 to 1920x1080.

5

96DPI would work fine in your case. Try connecting a HiDPI display (e.g. Retina display or some 4K display) to your laptop. If it works, please let us know, we need to figure out what your graphic system is doing right.