External monitor on HiDPI Dell Inspiron 7559 - scaling? issue

[coen56]

I'm trying to use an external monitor with a Dell laptop. To my (temporary?) delight it came with a high DPI (HiDPI) monitor, at 3840x2160 for a 15" screen. This means that text comes up extremely small. So I've set Desktop Scaling (Preferences->General) to Auto. This scales everything by a factor of two. So my 3840x2160 laptop screen becomes 1920x1080 and I can read the text again. The same happens with Desktop Scaling set to "Double (Hi-DPI)"

When I connect an external monitor, this also gets scaled up. So my 24" 1920x1080 (HDMI-connected) becomes 960x540

My question is: How do I get LM output to the laptop screen to be scaled up, but without scaling up output to the external monitor. (So both screens are at 1920x1080)

I've tried using "xrandr --output HDMI-1 --scale 2x2" (based on advise found at the end of this page: https://wiki.archlinux.org/index.php/HiDPI
However, this gives me the following error message:
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 140 (RANDR)
Minor opcode of failed request: 26 (RRSetCrtcTransform)
Value in failed request: 0x40
Serial number of failed request: 33
Current serial number in output stream: 34

The laptop has a GeForcce GTX 960M graphics card. I'm using the nvidia-370 driver, having previously tried the nvidia-364 and nvidia-367 drivers. They all give the same error message

I could probably switch back to normal scaling for LM, but that would mean having to change the (font) settings for each individual package or buying a magnifying glass to read the extremely small (but perfectly sharp) text. I would prefer a more generic solution, if possible

I'm using LM 18 64 bit

Any suggestions or solutions? Many thanks

[coen56]

Update: I'm now on LM 18.1, NVIDIA driver 378. Still the same problem

But I've finally worked out a work-around: When I set the laptop's resolution to 1920x1080 (half of the laptop screen's maximum resolution), I no longer need the (Preferences -> General) user interface scaling. Now both screens (laptop and external monitor) have very similar resolutions, and I can use my external monitor again . Should have thought of that 5 months ago

Only downside: text, etc, now looks less crisp/sharp on the laptop (because of the lower resolution), but still looks quite good, so not too big an issue

If you know how to fix the original issue, let me know. Thanks

[Bradford_Le]

I'm in the same boat