I regularly use my notebook for teaching, with the full screen shown on the projector. With projectors getting better, I often find the projectors resolution to be higher or different than the ones offered by my LCD screen (in the past I just used 1024x768).

What I now would like to do is use the best resolution of the external display, while having the same content down-scaled on the notebook screen (without panning). Alternatively, if the resolution of the projector is smaller in one dimension, black bars would be ok on the LC display. I don't worry about aliasing artefacts on the LCD as long as the external projector uses the highest quality possible.

For example, I recently had:

LVDS1 connected 1280x800+0+0 
   1280x800       60.2*+   50.0  
VGA1 connected 1280x720+0+0 
   1280x720       60.0*+

I tried:

xrandr --output VGA1 --mode 1280x720 --output LVDS1 --mode 1280x800 

but then the bottom of a full screen presentation was clipped on the projector. In this case, I would like a black bar or vertical rescaling on the laptop screen. How can I achieve that?

I played with the scale option (can't reproduce this here without projector) but was unsuccessful.

How can I achieve this behaviour?


I figured out that the --scale-from option does what I need:

xrandr --output VGA1 --mode 1280x720 --output LVDS1 --primary --scale-from 1280x720 
  • I was not aware for the scale-from option! Thanks for the tip. In similar case at home, i am using something like --scale 0.8x0.8 to match the other monitor (and this method of fixed scale also works ok). – George Vasiliou Dec 9 '16 at 11:26

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