Ubuntu – Scale application differently on different monitors – Ubuntu 16.04

I have nvidia driver 340.98 with GT218M [NVS 3100M], Xubuntu 16.04, any results below are from this environment if I don't mention otherwise. Here is my testing environment info, the output of:

sudo apt-get install pastebinit; \
sudo sh -c "lsb_release -sd; \
 dmidecode -s system-product-name; echo ==; \
 lshw -c display; echo ==; \
 xrandr --verbose; echo ==; \
 cat /etx/X11/xorg.conf" \
 | tee ~/Desktop/ubuntu-graphic-info.txt \
 | pastebinit

Weird and complex stack to debug specially using proprietary drivers. Most of the time, I get unexpected behaviors, may be due to lack of knowledge about the current Linux graphics stack setup.

• I wrote this answer before, that may introduce some debugging tools like xtrace
• Avoid running multiple/sequential xrandr commands, only after X server reset. Same command may have different result depending on previous commands. I have noticed that with --scale (see test case from my answer, linked above) --transform & --fb. Still don't know an easy way only by logout/login. So always logout/login before making another trial.
• Screenshots take only pixel size image from FB, so I will add camera photos to show the real results.

Method 1: xrandr --output .. --scale HCoefxVCoef or --scale-from WxH

Note, works fine for me. --scale is a shortcut for --transform, see method3

(VGA-0 below DP-3)

xrandr \
--output DP-3 --mode 1280x800 --scale 1x1 --pos 0x0 --fb 2880x2600 \
--output VGA-0 --mode 1440x900 --scale 2x2 --pos 0x800

or:

xrandr \
--output DP-3 --mode 1280x800 --pos 0x0 --fb 2880x2600 \
--output VGA-0 --mode 1440x900 --scale-from 2880x1800 --pos 0x800

FrameBuffer size calculation:

width = max(1280,1440*2) = 2880
height = 800+900*2 = 2600

Results:

• nvidia xrandr scale screenshot

  

• nvidia xrandr scale photo

  

Method 2: nvidia-settings View Port In/Out

Note, doesn't work well. nvidia-settings does not change frame-buffer to the required size as in xrandr command. It seems a bug (kind of, nvidia has its own FB), need more research.

Tried to replicate xrandr setup directly using nvidia-settings (I used xrandr from method1, marked down nvidia setting, reset settings, then used nvidia-settings directly):

1. gksu nvidia-settings → X Server Display Configuration
2. Select external monitor → advanced...
3. Make ViewPortIn & Panning double of ViewPortOut (which is the same as original resolution)
4. Leave internal monitor unchanged then Apply

Example:

• Internal monitor nvidia settings

  Position:    +0+0
  ViewPortIn:  1280x800
  ViewPortOut: 1280x800+0+0
  Panning:     1280x800
  

• External monitor nvidia settings

  Position:    +1280+0 (rightof) or +0+800 (below)
  ViewPortIn:  2880x1800
  ViewPortOut: 1440x900+0+0
  Panning:     2880x1800
  

Results: Notice the mouse pointer, it can reach all edges of the 2nd monitor even it only draws the top left quarter.

• nvidia-settings viewportin screenshot

  

• nvidia-settings viewportin photo

  

Update: Well, I could finally get a workaround trick. Add 1px to the width or height of panning (Panning)

    Panning:     2881x1800 or 2880x1801

New Results: I can't explain this, just the background is corrupted if i use below, otherwise every thing seems ok.

• nvidia-settings viewportin with panning trick screenshot

  ^{lowered the color quality of above picture to make less then 2MB imgur limit}

• nvidia -settings viewportin with panning trick photo

  

Method 3: xrandr --output .. --transform "H,0,0,0,V,0,0,0,1"

Note, works fine for me, same as method1

(VGA-0 right of DP-3)

xrandr \
--output DP-3  -primary --mode 1280x800 --pos 0x0 --transform "1,0,0,0,1,0,0,0,1" --fb 4160x1800 \
--output VGA-0 --mode 1440x900 --transform "2,0,0,0,2,0,0,0,1" --right-of DP-3

FrameBuffer size calculation:

width = 1280+1440*2 = 4160
height = max(800,900*2) = 1800

Results:

• nvidia xrandr transform screenshot

  

• nvidia xrandr transform photo