Public bug reported:

Dear community 
Recently I upgraded my old netbook from Linux from Linux Mint 18 to Linux Mint 
20 

Distribution: 
cat /etc/upstream-release/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu Focal Fossa"

Netbook is with small screen 
1024x600
To get bigger virtual screen I use xrandr like:

xrandr --fb 1024x768 --output LVDS1 --panning 1024x768

To return to normal screen I use

xrandr --fb 1024x600

What is expected:
when the mouse moves outside the 1024x600 screen - new "clean" virtual area 
appears.

What is in reality:

With fresh Ubuntu the first script results to wrong "background" image on the 
extended area:
When I move mouse down below the original 600 pixels,
first 768-600=168 strings are shown like a background image.
Or 
new virtual 601 string is the copy of the old 1
            602 string is the copy of the old 2
...
            768 string is the copy of the old 168
 
It looks like an index shift in the array:
The string which "disappears" from the top is moved to the bottom   

This "background" image can be overwritten by the real application window.
For example, if I move the terminal window it appears on the top of this 
"background"   
But after moving mouse back inside the 1024x600 screen and back outside the 
1024x600 screen,
the shifted copy of the top part of the screen appears at the bottom according 
the 
1->601 
2->602 etc logic.

After playing a lot with xrandr parameters I had found a workaround:
One has to specify the first parameter in --fb bigger than the first parameter 
in --panning

For example:
xrandr --fb 1025x768 --output LVDS1 --panning 1024x768    

Here 1025>1024

I had checked this bug  with two different laptops, so it is not related with 
the hardware.
More information:
xrandr -v
xrandr program version       1.5.0
Server reports RandR version 1.6

The working configuration:
xrandr
Screen 0: minimum 8 x 8, current 1025 x 768, maximum 32767 x 32767
LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 
220mm x 130mm panning 1024x768+0+0
   1024x600      60.19*+
   1024x576      59.90    59.82  
   960x540       59.63    59.82  
   800x600       60.32    56.25  
   864x486       59.92    59.57  
   640x480       59.94  
   720x405       59.51    58.99  
   640x360       59.84    59.32  
   512x300       60.00  
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis

Wrongly working configuration:
 
xrandr
Screen 0: minimum 8 x 8, current 1024 x 768, maximum 32767 x 32767
LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y axis) 
220mm x 130mm panning 1024x768+0+0
   1024x600      60.19*+
   1024x576      59.90    59.82  
   960x540       59.63    59.82  
   800x600       60.32    56.25  
   864x486       59.92    59.57  
   640x480       59.94  
   720x405       59.51    58.99  
   640x360       59.84    59.32  
   512x300       60.00  
VGA1 disconnected (normal left inverted right x axis y axis)
VIRTUAL1 disconnected (normal left inverted right x axis y axis)

Hope you can reproduce this bug.

Best regards, Dmitry

** Affects: xorg (Ubuntu)
     Importance: Undecided
         Status: New

-- 
You received this bug notification because you are a member of Ubuntu
Touch seeded packages, which is subscribed to xorg in Ubuntu.
https://bugs.launchpad.net/bugs/1923513

Title:
  xrandr --panning problem

Status in xorg package in Ubuntu:
  New

Bug description:
  Dear community 
  Recently I upgraded my old netbook from Linux from Linux Mint 18 to Linux 
Mint 20 

  Distribution: 
  cat /etc/upstream-release/lsb-release 
  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=20.04
  DISTRIB_CODENAME=focal
  DISTRIB_DESCRIPTION="Ubuntu Focal Fossa"

  Netbook is with small screen 
  1024x600
  To get bigger virtual screen I use xrandr like:

  xrandr --fb 1024x768 --output LVDS1 --panning 1024x768

  To return to normal screen I use

  xrandr --fb 1024x600

  What is expected:
  when the mouse moves outside the 1024x600 screen - new "clean" virtual area 
appears.

  What is in reality:

  With fresh Ubuntu the first script results to wrong "background" image on the 
extended area:
  When I move mouse down below the original 600 pixels,
  first 768-600=168 strings are shown like a background image.
  Or 
  new virtual 601 string is the copy of the old 1
              602 string is the copy of the old 2
  ...
              768 string is the copy of the old 168
   
  It looks like an index shift in the array:
  The string which "disappears" from the top is moved to the bottom   

  This "background" image can be overwritten by the real application window.
  For example, if I move the terminal window it appears on the top of this 
"background"   
  But after moving mouse back inside the 1024x600 screen and back outside the 
1024x600 screen,
  the shifted copy of the top part of the screen appears at the bottom 
according the 
  1->601 
  2->602 etc logic.

  After playing a lot with xrandr parameters I had found a workaround:
  One has to specify the first parameter in --fb bigger than the first 
parameter in --panning

  For example:
  xrandr --fb 1025x768 --output LVDS1 --panning 1024x768    

  Here 1025>1024

  I had checked this bug  with two different laptops, so it is not related with 
the hardware.
  More information:
  xrandr -v
  xrandr program version       1.5.0
  Server reports RandR version 1.6

  The working configuration:
  xrandr
  Screen 0: minimum 8 x 8, current 1025 x 768, maximum 32767 x 32767
  LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y 
axis) 220mm x 130mm panning 1024x768+0+0
     1024x600      60.19*+
     1024x576      59.90    59.82  
     960x540       59.63    59.82  
     800x600       60.32    56.25  
     864x486       59.92    59.57  
     640x480       59.94  
     720x405       59.51    58.99  
     640x360       59.84    59.32  
     512x300       60.00  
  VGA1 disconnected (normal left inverted right x axis y axis)
  VIRTUAL1 disconnected (normal left inverted right x axis y axis

  Wrongly working configuration:
   
  xrandr
  Screen 0: minimum 8 x 8, current 1024 x 768, maximum 32767 x 32767
  LVDS1 connected primary 1024x768+0+0 (normal left inverted right x axis y 
axis) 220mm x 130mm panning 1024x768+0+0
     1024x600      60.19*+
     1024x576      59.90    59.82  
     960x540       59.63    59.82  
     800x600       60.32    56.25  
     864x486       59.92    59.57  
     640x480       59.94  
     720x405       59.51    58.99  
     640x360       59.84    59.32  
     512x300       60.00  
  VGA1 disconnected (normal left inverted right x axis y axis)
  VIRTUAL1 disconnected (normal left inverted right x axis y axis)

  Hope you can reproduce this bug.

  Best regards, Dmitry

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