I've got a funny problem with an external monitor which is actually an eink android tablet that can double as an HDMI monitor. It's called the Dasung Not-eReader 103. I'm trying to use this to reduce strain on my eyes from staring at an LCD 15 hours a day. To answer the question of "why would you try to use an Android tablet as a monitor?".
Anyway, the device has a non-standard 4:3 resolution of 1872x1404. It renders fine when plugged into my Ubuntu 20.04 machine and using the 1872x1404 resolution. The problem is that everything is way too tiny on the 10 inch screen and I need to cut the resolution in half to be able to see anything.
So I tried selecting 800x600 which is the only other resolution selectable by default. But the resulting image is glitchy-looking and static-y and unrecognizable. Here is a photo:
So I figured maybe using 936x702 resolution would work better so it could just scale the image 200% to fill up the screen. This resolution wasn't available for selection but I tried using xrandr to add it. I did this and selected the resolution but the result was the same static that I saw with 800x600.
Note that keeping the large resolution and selecting 200% scaling in the display settings does work, but this isn't an option for me because I don't want to scale my primary display. If it were possible to select scaling per-screen (100% for screen 1, 200% for screen 2), that could also solve my problem.
Does this ring any bells for anyone? I'm totally new to xrandr so it's possible I don't understand the correct way to do this. I keep wondering if there's something special I need to do for the refresh rate because it's an eink display that doesn't update at 60 frames per second.
Here is the output I get from running xrandr to get the default available resolutions. Not sure if it will be helpful.
DP-3 connected primary 1872x1404+0+0 (normal left inverted right x axis y axis) 621mm x 341mm
1872x1404 45.25*+
800x600 75.04
